Selected Topics in Quantum Electronics, IEEE Journal of - new TOC

Frontcover

Jan.-Feb. 2012

IEEE Journal of Selected Topics in Quantum Electronics publication information

Jan.-Feb. 2012

Editorial

Jan.-Feb. 2012

Introduction to the Issue on Ultrafast Science and Technology

Jan.-Feb. 2012

Second-Harmonic Generation of Super Powerful Femtosecond Pulses Under Strong Influence of Cubic Nonlinearity

Jan.-Feb. 2012

A theoretical model of second-harmonic generation (SHG) under strong influence of cubic nonlinearity was verified in experiment. Effective energy conversion in thin potassium dihydrogen phosphate crystals at peak intensity up to 5 TW/cm$^2$ (B-integral equaled 6.4) was demonstrated and no crystal damage was observed. Comparative analysis of SHG of radiation at the fundamental wavelengths of 910 and 800 nm showed the major advantages of the first one. The double-pass geometry of SHG in an ultrathin crystal on a substrate is discussed in detail. Additional correction of parabolic spectral phase of the SH radiation allows pulse duration to be shortened from 20 to 9 fs for 910 nm fundamental wavelength and from 20 to 12 fs for 800 nm.

Differential Multiphoton Laser Scanning Microscopy

Jan.-Feb. 2012

Multifocal multiphoton laser scanning microscopy (mfMPLSM) in the biological and medical sciences has the potential to become a ubiquitous tool for obtaining high-resolution images at video rates. While current implementations of mfMPLSM achieve very high frame rates, they are limited in their applicability to essentially those biological samples that exhibit little or no scattering. In this paper, we report on a method for mfMPLSM in which whole-field detection with a single detector, rather than detection with a matrix of detectors, such as a charge-coupled device (CCD) camera, is implemented. This advance makes mfMPLSM fully compatible for use in imaging through scattering media. Further, we demonstrate that this method makes it possible to simultaneously obtain multiple images and view differences in excitation parameters in a single scan of the specimen.

SESAMs for High-Power Oscillators: Design Guidelines and Damage Thresholds

Jan.-Feb. 2012

We present for the first time to the best of our knowledge a systematic study of lifetime and damage of semiconductor saturable absorber mirrors (SESAMs) designed for operation in high-power oscillators. We characterize and compare nonlinear reflectivity and inverse saturable absorption (ISA) parameters as well as damage threshold and lifetime of different representative SESAMs under test using a nonlinear reflectivity measurement setup at unprecedented high fluence levels. We investigate the catastrophic damage that occurs at very high fluences by demonstrating a dependence of the damage threshold on the ISA parameter F $_2$ and the maximum reflectivity fluence F$_0$. We can clearly demonstrate that the damage fluence F$_d$ scales proportionally to $sqrt{F_2}$ for all SESAMs. In the case of SESAMs with the same absorber where the product F $_{rm sat}$·ΔR is constant, the damage fluence F$_d$ scales proportionally to F $_0$. Therefore, damage occurs due to heating of the lattice by the energy absorbed due to the ISA process and is not related to the quantum well (QW) absorbers. Furthermore, we present guidelines on how to design samples with high saturation fluences, reduced induced absorption, and high damage thresholds. Using multiple QWs and a suitable dielectric topsection, we achieved SESAMs with saturation fluences >200 μJ/cm$^2$, nonsaturable losses <0.1%, and reduced ISA. Our best sam- le could not be damaged at a maximum available fluence of 0.21 J/cm $^2$ and a peak intensity of 370 GW/cm $^2$. These SESAMs will be suitable for future high-power femtosecond oscillators in the kilowatt average output power regime, which is very interesting for attosecond science and industrial material processing applications.

Interference Stabilization Revisited

Jan.-Feb. 2012

Interference stabilization of Rydberg atoms in a sufficiently strong laser field is revisited. Its main features predicted theoretically and observed experimentally are described together with the newest experimental and theoretical results. The most important new results concern the found efficient population of atomic Rydberg levels in the process of multiphoton ionization and interference stabilization of population at Rydberg levels. Another important new topic is the interference stabilization at vibrational levels of dissociating molecules.

Generation and Optimization of Femtosecond Pulses by Four-Wave Mixing Process

Jan.-Feb. 2012

Four-wave mixing (FWM) was used to generate and optimize ultrashort pulses with wavelengths from ultraviolet (UV) to near-infrared in bulk media and gases. Wavelength-tunable multicolored pulses were simultaneously generated by cascaded FWM in glass plates. By using incident chirped pulses, 15-fs self-compressed multicolored pulses were obtained with excellent properties. Self-compression was also used to generate ultrashort deep-UV (DUV) pulses. The positive frequency chirp in a self-phase-modulated pulseissuitable for this objective. Sub-10-fs DUV pulses were generated without using any additional pulse compressors. Self-diffraction was used to clean the pulse, broaden the spectrum, and enhance the spatial beam quality. These multicolored pulses can be simultaneously amplified and compressed by a four-wave optical parametric amplifier. The generated multicolored pulses are useful for multicolored ultrafast spectroscopy, microscopy experiments, and as seeds for petawatt lasers with high temporal contrasts.

2-ps Hard X-Ray Streak Camera Measurements at Sector 7 Beamline of the Advanced Photon Source

Jan.-Feb. 2012

A hard X-ray streak camera capable of 2-ps time resolution is in operation at the Sector 7 beamline of the Advanced Photon Source. It is used for laser-pump, X-ray probe experiments using the Ti:Sapphire femtosecond laser system installed on the beamline. This streak camera, combined with standardized and prealigned experimental setups, can perform time-resolved liquid-phase absorption spectroscopy, reflectivity, and diffraction experiments.

Femtosecond Nd:Glass Lasers Pumped by Single-Mode Laser Diodes and Mode Locked With Carbon Nanotube or Semiconductor Saturable Absorber Mirrors

Jan.-Feb. 2012

In this paper, single-mode 200-mW laser diodes have been demonstrated to be very effective pump devices for low-power Nd:glass lasers, yielding the remarkable continuous wave (cw) slope efficiency of 46.5% for silicate and 58.2% for phosphate glasses, respectively. Femtosecond operation has been investigated with both semiconductor saturable absorber mirrors (SESAMs) and a single-walled carbon nanotube SAM (SWCNT-SAM). Furthermore, a detailed comparison of the mode-locking performance with Nd:phosphate and Nd:silicate, employing either one of the SA devices is presented. Although not fully optimized for this particular application yet, SWCNT-SAs yielded sub-100-fs pulses for the first time in Nd:glass. With SESAM mode locking and a single-prism resonator for dispersion compensation, pulse duration as short as 92 fs has been measured, whereas shorter pulses down to 80 fs have been obtained with a two-prism resonator. Tuning range as broad as 30 nm and output power up to 55 mW have also been achieved, confirming the effectiveness of the proposed laser architecture.

Advances in Ultrafast Control and Probing of Correlated-Electron Materials

Jan.-Feb. 2012

In this paper, we present recent results on ultrafast control and probing of strongly correlated-electron materials. We focus on magnetoresistive manganites, applying excitation and probing wavelengths that cover the mid-IR to the soft X-rays. In analogy with near-equilibrium “filling” and “bandwidth” control of phase transitions, our approach uses both visible and mid-IR pulses to stimulate the dynamics by exciting either charges across electronic bandgaps or specific vibrational resonances. X-rays are used to unambiguously measure the microscopic electronic, orbital, and structural dynamics. Our experiments dissect and separate the nonequilibrium physics of these compounds, revealing the complex interplay and evolution of spin, lattice, charge, and orbital degrees of freedoms in the time domain.

Femtosecond Carrier Dynamics and Nonlinear Effects in Quantum Cascade Lasers

Jan.-Feb. 2012

Quantum cascade lasers (QCLs) are complicated unipolar semiconductor devices based on intersubband transitions and resonant tunneling. In this study, femtosecond mid-infrared (Mid-IR) pulses are employed to investigate the nature of carrier transport through the active and injector regions of a room temperature, pulse biased ultrastrong coupling design QCL. Despite the low average power (<1 mW) of femtosecond Mid-IR pulses, the efficient coupling of these pulses into the QCL waveguide made the study of nonlinear effects in QCLs possible. Biased just below threshold, we observed ultrafast gain recovery within the first 200 f s mainly contributed by electrons resonant tunneling through a much thinner injector barrier than that of conventional designed QCLs, which overcomes the interface-roughness-induced detuning of resonant tunneling. Oscillation or overshooting within the first picosecond is caused by electron relaxation from continuum region excited by strong pump beam, as well as coherent electron tunneling transport from injector to active region. The former feature is supported by the observation of second harmonic generation (SHG) with emission of λ ≈ 2.2 μm pulses and measured positive photoconductivity. The transport of electrons through the injector region contributes to a slower gain recovery. A much longer recovery (hundreds of picoseconds) can be explained as electrons are depleted from upper stages down to lower stages in real space.

Molecular Dynamics in Strong Laser Fields

Jan.-Feb. 2012

One of the goals for strong field physics is imaging the dynamics of the quantum systems, and in case of molecules, there is strong interest in imaging of the electron rearrangement during chemical reactions. Strong field ionization of molecules has many attractive features that make this process a candidate tool for strong field imaging of transient states and chemical reactions. In this paper, we present analysis of ionization dependence on orientation of molecular axis with respect to polarization of the electric field of the laser. By considering several examples of molecules at their equilibrium internuclear distances and an example of the simplest chemical reaction, namely, the dissociation of diatomic molecule, we present how symmetries of the molecular orbitals influence the alignment-dependent ionization and how this dependence can be used to follow molecular dynamics using strong field multiphoton ionization.

Mode Locking in the Few-Femtosecond Regime Using Waveguide Arrays and the Coupled Short-Pulse Equations

Jan.-Feb. 2012

A new theoretical model is proposed for characterizing the ultrashort (few femtoseconds and below) propagation dynamics in a laser cavity that is mode locked with a waveguide array. The theory circumvents the standard and problematic center-frequency expansion methods that typically result in the nonlinear Schrödinger-based master mode-locking equation. The resulting short-pulse-equation framework, which is the equivalent of the nonlinear Schrödinger equation for ultrafast pulses, provides an asymptotically valid description of the electric-field amplitude, even if pulses are shortened below a single cycle of the electric field. Given the lack of theory in the ultrafast regime, the model provides the beginning theoretical framework for quantifying the pulse dynamics and stability, as pulsewidths approach the attosecond regime.

Electron Dynamics and Its Control in Molecules: From Diatomics to Larger Molecular Systems

Jan.-Feb. 2012

Electrons and their dynamics are involved in bond breaking and formation; thus, the idea to steer chemical reactions by localization of electronic wavepackets seems natural. The formation of a localized electronic wavepacket requires the superposition of two or more appropriate electronic states through, e.g., an external electric field. The guiding of such an electronic wavepacket is only possible within the coherence time of the system. In theoretical studies, we elucidate the role of electron wavepacket motion for the control of molecular processes. We analyze three examples of electron wavepacket-driven processes with direct connection to already performed or ongoing experiments. From these examples, we extract the system requirements defining the time window for intramolecular electronic coherence and efficient control. With this knowledge, we derived an appropriate molecular configuration in a photoreaction of a polyatomic molecule where a control by guiding electronic wavepackets is possible. For such a photoreaction, we designed a new control scheme with the carrier envelope phase as a control parameter that works at high efficiency.

Rapid Birefringent Delay Scanning for Coherent Multiphoton Impulsive Raman Pump–Probe Spectroscopy

Jan.-Feb. 2012

Ultrafast pump–probe spectroscopy experiments often measure weak nonlinear interactions, which produce very low signal levels. Averaging is usually required to increase the SNR to obtain the system response from the stochastic noise background. It has been recognized that averaging rapidly acquired pump–probe scans yields performance that is often superior to long averaging at each delay point, particularly in the presence of flicker ( $1/f$) noise. We have demonstrated a particularly simple method for high-speed pump–probe delay scanning that maintains interferometric stability between the two pulses. This technique nicknamed lighthouse scanning uses a spinning birefringent crystal to rapidly vary the time separation between a pump and probe pulse pair. This scanning technique will be valuable for most pump–probe spectroscopy techniques. We demonstrate the technique in a six-wave mixing process of coherence-modulated third-harmonic generation (CM-THG). CM-THG is a recently demonstrated method for separating bulk and interface contributions to vibrational coherences, but the high nonlinearity of the experiment leads to low signal levels. Rapid scan averaging with the lighthouse scanner improves signal to noise by at least an order of magnitude, greatly expanding the number of systems that can be studied with this technique.

Electron Pulse Compression With a Practical Reflectron Design for Ultrafast Electron Diffraction

Jan.-Feb. 2012

Ultrafast electron diffraction (UED) is a powerful method for studying time-resolved structural changes. Currently, space-charge-induced temporal broadening prevents obtaining high-brightness electron pulses with sub-100 fs durations limiting the range of phenomena that can be studied with this technique. We review the state of the art of UED in this respect and propose a practical design for reflectron-based pulse compression that utilizes only electrostatic optics and has a tunable temporal focal point. Our simulation shows that this scheme is capable of compressing an electron pulse containing 100 000 electrons with 60:1 temporal compression ratio.

Ultrarapid Optical Frequency-Domain Reflectometry Based Upon Dispersion-Induced Time Stretching: Principle and Applications

Jan.-Feb. 2012

This paper reviews recent progress on a new, simple, and powerful technique for ultrahigh-speed optical frequency-domain reflectometry (OFDR), namely, time-stretching (TS)-OFDR. This method is essentially based on the use of linear-dispersion-induced frequency-to-time mapping of the target broadband spectral interferogram so that this information can be captured in real time using a single photodetection stage and a fast analog-to-digital converter. The principle of operation, design tradeoffs, performance advantages, and limitations of TS-OFDR are discussed. Recent results on the application of TS-OFDR for fiber-optics device characterization and biomedical imaging are also presented.

Wavenumber-Domain Theory of Terahertz Single-Walled Carbon Nanotube Antenna

Jan.-Feb. 2012

A theoretical study is presented on the characteristics of terahertz antennas formed by metallic single-walled carbon nanotube (SWCNT) dipoles. The Boltzmann transport equation and Maxwell’s equations are combined with boundary conditions of the electron distribution function, in order to formulate a wavenumber-domain integral equation for the current, which considers the spatial dispersion and provides higher level of accuracy and generality than existing approaches. Through proper approximations of that equation, the same spatial integral equations from several other studies can be drawn. The radiation properties of the SWCNT antenna are derived from the wavenumber-domain current. Numerical results are given for short dipole antennas and those with length close to the half wavelength in free space. They are compared to the results calculated by other methods. We also investigate the frequency dependence of conductance under different values of relaxation frequency and find the increase of relaxation frequency leads to strong attenuation of surface-wave resonances.

Femtosecond Laser in Polymeric Materials: Microfabrication of Doped Structures and Micromachining

Jan.-Feb. 2012

The use of laser light to modify the material's surface or bulk as well as to induce changes in the volume through a chemical reaction has received great attention in the last few years, due to the possibility of tailoring the material's properties aiming at technological applications. Here, we report on recent progress of microstructuring and microfabrication in polymeric materials by using femtosecond lasers. In the first part, we describe how polymeric materials' micromachining, either on the surface or bulk, can be employed to change their optical and chemical properties promising for fabricating waveguides, resonators, and self-cleaning surfaces. In the second part, we discuss how two-photon absorption polymerization can be used to fabricate active microstructures by doping the basic resin with molecules presenting biological and optical properties of interest. Such microstructures can be used to fabricate devices with applications in optics, such as microLED, waveguides, and also in medicine, such as scaffolds for tissue growth.

Following Ultrafast Radiationless Relaxation Dynamics With Strong Field Dissociative Ionization: A Comparison Between Adenine, Uracil, and Cytosine

Jan.-Feb. 2012

We present the application of ultrafast time- and mass-resolved ion yield laser spectroscopy in conjunction with ab initio electronic structure calculations to track molecular excited-state dynamics. We discuss how molecular fragment ions can be associated with conformations the molecule assumes during its relaxation, and how various features of the pump-probe signal for those fragments can be used to infer details of the excited-state dynamics. We present results for radiationless relaxation in DNA and RNA bases adenine, cytosine, and uracil in the gas phase, pumped near a one-photon resonance transition to an excited state, and probed via strong-field near-IR dissociative ionization.

Low-Energy Photoelectron Angular Distributions of Above-Threshold Ionization of Atoms and Molecules in Strong Laser Fields

Jan.-Feb. 2012

We present high-resolution fully differential experimental data on low-energy photoelectron angular distributions (PADs) of above-threshold ionization of atoms (Xe), and diatomic (H$_2$ , O$_2$) and triatomic (CO $_2$) molecules at the same Keldysh parameter (∼1.4) in near-infrared strong laser fields (25 fs, 795 nm). We observe that the electron zero longitudinal momentum distributions (along laser-polarization direction) show a feature of pronounced “dip” or “peak” for those targets. However, the low-energy PADs are similar, even though the binding energy and electronic core structure are very different. The PADs show that the dominant angular momentum of zero-order above-threshold ionization (E < 0.5 eV) is L = 4 (ng Rydberg states). The experimental observations challenge the current qualitative models that are now only available for atoms. In the end, we discuss the role of Coulomb focusing and the effect of the electron longitudinal momentum on the transverse-momentum distribution.

Integrated Fourier-Domain Mode-Locked Lasers: Analysis of a Novel Coherent Comb Laser

Jan.-Feb. 2012

Fourier-domain (FD) mode locking of integrated laser diode structures is studied theoretically and their application for wavelength division multiplexing (WDM) comb generation for future terabits per second interconnects is discussed. Twenty-five-gigahertz FD mode-locked structures with ring and Mach–Zehnder-based bandpass filters show comb widths of 1.0–1.8 THz, i.e., 40–72 comb lines, but the mode comb is not flat, which increases the mode relative intensity noise (RIN). It is shown that by combining AM and FD mode-locking wide and flat combs (down to 7 dB) can be achieved, with mode RIN values of less than 0.3%, suitable for error-free transmission. These novel structures have been simulated using experimentally verified parameters and technologically feasible configurations.

Toward Broad Bandwidth 2-D Electronic Spectroscopy: Correction of Chirp From a Continuum Probe

Jan.-Feb. 2012

Recent implementations of 2-D spectroscopy in the pump–probe geometry using a pulse-shaper demonstrate the ease with which frequency-resolved pump–probe experiments can be readily adapted to 2-D methods. Many frequency-resolved pump–probe experiments employ continuum probes to observe a broad range of electronic transitions. These continuum probes are often chirped, leading to distortions that can be postcorrected by characterizing the chirp and appropriately adjusting the observed wavelength-dependent pump–probe time delay. We present an analogous chirp-correction scheme for 2-D spectroscopy, facilitating the use of continuum probing to expand the frequency information available in 2-D spectroscopy experiments. We demonstrate the method through experiments and simulations of a laser dye in solution.

Extending Femtosecond Metrology to Longer, More Complex Laser Pulses in Time and Space

Jan.-Feb. 2012

We review several recently developed simple, yet powerful, techniques for the measurement of the complete temporal (and spatiotemporal) intensity and phase of laser pulses up to nanoseconds in length. Spatially encoded arrangement for temporal analysis by dispersing a pair of light e-fields (SEA TADPOLE) is a simple and practical variation of spectral interferometry that can measure pulses as long as ∼50 ps with complexities, that is, time-bandwidth products (TBPs) as large as ∼100. SEA TADPOLE can also measure the complete spatiotemporal electric field of pulses with femtosecond temporal and submicrometer spatial resolution. Using a train of identical reference pulses, multiple delays for temporal analysis by dispersing a pair of light e-fields (MUD TADPOLE) extends SEA TADPOLE to pulses up to several nanoseconds long with TBPs of ∼100 000 or more. Finally, a simple variation of frequency-resolved optical gating (FROG) measures the complete intensity and phase of nanosecond-long laser pulses on a single shot without a reference pulse. It uses a novel approach in which the pulse to be measured is tilted by ∼89.9°, so that one side of it precedes the other by over a meter, yielding several nanoseconds of delay without appreciably distorting the pulse in time. This remarkably simple and compact FROG device has no sensitive alignment parameters.

Characterizing Fast Arbitrary CW Waveforms With 1500 THz/s Instantaneous Chirps

Jan.-Feb. 2012

The instantaneous frequency of a rapidly tuned continuous-wave (CW) laser is measured through linear optical sampling against dual-frequency combs. This dual-comb interferometer determines the instantaneous frequency of the CW laser during a quasi-sinewave frequency sweep of 3 THz amplitude with a 10 ms period. More complicated waveforms are also measured with instantaneous chirps exceeding 1500 THz/s (12 000 nm/s). The uncertainty is 1.5 MHz at 20 ns time resolution, averaging down to 5 kHz at 5 μs time resolution. The absolute frequency accuracy can be calibrated to within 2.5 kHz provided there is a brief period (<1 ms) of low laser chirp (<160 GHz/s) during the waveform measurement to allow for a dual-comb Vernier measurement of the absolute frequency, modulo 3 THz. This approach allows for the characterization of arbitrary CW waveforms with instantaneous frequencies that change rapidly and over wide optical bandwidth.

Isolated Attosecond Pulse Generation by Two-Mid-IR Laser Fields

Jan.-Feb. 2012

The availability of tunable mid-infrared laser systems capable to deliver high intensity few cycle pulses offers the perspective of generating ultrashort radiation in the extreme UV range through the high-order harmonic generation (HHG) of the fundamental. In particular, such systems make possible the superposition of multiple colors of incommensurable frequencies that gives rise to time gating of HHG, thereby realizing the necessary condition leading to isolated attosecond pulse (IAP) generation. In this paper, the HHG resulting from the superposition of two incommensurable frequencies is analyzed with the aim to find out the conditions that the relative intensity and frequency of the two fields have to fulfill in order to generate isolated attosecond pulses. It is observed that the two fields can be superimposed in parallel and perpendicular polarization, both giving rise to IAP under appropriate conditions.

Next-Generation X-Ray Free-Electron Lasers

Jan.-Feb. 2012

Research frontiers for future free-electron lasers are discussed. Attention is given to ideas for improving the temporal coherence and obtaining subfemtosecond X-ray pulses. Improving brightness of the electron bunches is considered to be a major step forward for an electron beam accelerator simultaneously supporting multiple free-electron laser lines.

Advanced Ultrafast Technologies Based on Optical Frequency Combs

Jan.-Feb. 2012

This paper presents recent results in the development of novel ultrafast technologies based on the generation and application of stabilized optical frequency combs. By using novel active resonant cavity injection locking techniques, filtering, modulation and detection can be performed directly on individual components of the frequency comb enabling new approaches to optical waveform synthesis, waveform detection and matched filtering, with effective signal processing bandwidths in excess of 1 THz.

Nano-Optical Control of Hot-Spot Field Superenhancement on a Corrugated Silver Surface

Jan.-Feb. 2012

Coherent control of ultrafast nano-optical excitations of a corrugated silver surface is demonstrated by means of predetermined few-parameter scans and adaptive polarization laser pulse shaping. “Hot spots” in the multiphoton photoemission signals are enhanced and manipulated with a high contrast. Switching between separated and closely spaced hot spots is shown. The latter allows controlling the shape of hot spots and yields improved nanofocusing and “purification” of the photoemission signals. Complex pulse shapes were obtained in adaptive optimizations whose features were reproducible in repeated runs. Predetermined few-parameter control scans provide insight into the interpretation of optimal pulse shapes. The results indicate the existence of long coherence lifetimes on a corrugated silver surface. This combination of collective strong nanoplasmonic near-field enhancement and long-lived coherence may be used to achieve an even stronger field enhancement (“superenhancement”) making these hot spots ideal candidates for future nanophotonic, spectroscopic, sensor and quantum information applications. In addition the observation of such long coherence lifetimes is relevant to the understanding of surface-enhanced spectroscopies such as single-molecule Raman spectroscopy.

Ultrafast Multidimensional Spectroscopy: Principles and Applications to Photosynthetic Systems

Jan.-Feb. 2012

We present the utility of 2-D electronic spectroscopy for the investigation of energy transfer dynamics in photosynthetic light-harvesting systems. Elucidating ultrafast energy transfer within photosynthetic systems is difficult due to the large number of molecules and complex environments involved in the process. In many spectroscopic methods, these systems appear as overlapping peaks with broad linewidths, obscuring the details of the dynamics. 2-D spectroscopy is a nonlinear, ultrafast method that yields a correlation map between excitation and emission energies, and can track incoherent and coherent energy transfer processes with femtosecond resolution. A 2-D spectrum can provide important insight into the structure and the mechanisms behind the excited state dynamics. We review the principles behind 2-D spectroscopy and describe the content of a 2-D electronic spectrum. Several recent applications of this technique to the major light-harvesting complex of Photosystem II are presented, including monitoring the time scales of energy transfer processes, investigation of the excited state energies, and determination of the relative orientations of the excited state transition dipole moments.

Ultrafast Optical Parametric Chirped-Pulse Amplification

Jan.-Feb. 2012

In recent years, optical parametric chirped-pulse amplification (OPCPA) has emerged as a powerful tool for the generation of ultrashort pulses with extreme peak intensity. It has enabled the generation of phase-controlled few-cycle pulses in widely different parts of the spectrum. For the near-infrared spectral range, OPCPA is becoming an interesting alternative to conventional Ti:Sapphire-based laser technology for various applications. In this paper, we discuss the physics behind OPCPA, as well as the practical design considerations for the development of high-intensity, phase-stable few-cycle OPCPA systems. Also, we review the experimental achievements in ultrafast OPCPA systems to date.

Femtosecond Extreme Ultraviolet Ion Imaging of Ultrafast Dynamics in Electronically Excited Helium Nanodroplets

Jan.-Feb. 2012

A novel femtosecond extreme ultraviolet (EUV) ion-imaging technique is applied to study ultrafast dynamics in electronically excited helium nanodroplets. Ion mass spectra recorded by single-photon EUV ionization and by transient EUV-pump/IR-probe two-photon ionization differ significantly for EUV photon energies below and above ∼24 eV, in agreement with recently performed synchrotron measurements. Pump–probe time-delay-dependent ion kinetic energy (KE) spectra exhibit two major contributions: a decaying high KE component and a rising low KE component, which are attributed to the different excitation regimes. A model is presented that describes the excitation energy dependence of the relaxation and ionization dynamics within the framework of bulk and surface states. The model is supported by recent ab initio calculations on electronically excited states of 25-atom clusters. An intraband relaxation mechanism is proposed that proceeds on a ∼10–20-ps time scale and that corresponds to the transfer of electronic excitation in the Rydberg n = 2 manifold from bulk to surface states.

Optical 2-D Fourier Transform Spectroscopy of Excitons in Semiconductor Nanostructures

Jan.-Feb. 2012

Optical 2-D Fourier transform spectroscopy is a powerful technique for studying resonant light-matter interactions, determining the transition structure and monitoring dynamics of optically created excitations. The ability to separate homogeneous and inhomogeneous broadening is one important capability. In this paper, we discuss the use of this technique to study excitonic transitions in semiconductor nanostructures. In quantum wells, the effects of structural disorder is observed as inhomogeneous broadening of the exciton resonances. In quantum dots, the temperature dependence of the homogeneous width gives insight into the nature of the dephasing processes.

Tracking Ultrafast Energy Flow in Molecules Using Broadly Tunable Few-Optical-Cycle Pulses

Jan.-Feb. 2012

Many (bio) molecules, following light absorption, undergo ultrafast nonradiative decay processes, taking place over timescales of tens to hundreds of femtoseconds. Ultrafast optical spectroscopy allows tracking in real time this energy flow using broadly tunable few-optical-cycle light pulses. Optical parametric amplifiers, thanks to their broad and tunable gain bandwidths, are powerful tools for the generation of such pulses. This paper first reviews our work on broadband optical parametric amplifiers, which led to the demonstration of few-optical-cycle sub-10-fs pulses continuously tunable from the visible (500 nm) to the near-IR (2 μm). We then present selected examples of applications to ultrafast spectroscopy of molecules, such as isomerization of rhodopsin, carotenoid–bacteriochlorophyll energy transfer in light-harvesting complexes, and polymer–fullerene electron transfer in blends for organic photovoltaics.

Relaxation of Photoinduced Quasi-Particles in Correlated Electron Metals

Jan.-Feb. 2012

We present our studies of photoinduced quasi-particle dynamics in correlated electron metals. At room temperature, these materials exhibit metallic behavior characterized by the presence of a Fermi surface. Electronic correlations lead to a modification of the low-energy electronic structure near the Fermi level resulting in the opening of gaps or partial gaps due to such phenomena as density waves or superconductivity. We describe the results of optical pump-probe studies of quasi-particle dynamics in the spin density wave metal UNiGa $_5$, the heavy-fermion superconductor PuCoGa $_5$, and the pnictide high-temperature superconductor (Ba,K)Fe $_2$As$_2$.

Femtosecond and Attosecond Spectroscopy in the XUV Regime

Jan.-Feb. 2012

Attosecond-duration, fully coherent, extreme-ultraviolet (XUV) photon bursts obtained through laser high-harmonic generation have opened up new possibilities in the study of atomic and molecular dynamics. We discuss experiments elucidating some of the interesting energy redistribution mechanisms that follow the interaction of a high-energy photon with a molecule. The crucial role of synchronized, strong-field, near-IR laser pulses in XUV pump–probe spectroscopy is highlighted. We demonstrate that near-IR pulses can in fact be used to modify the atomic structure and control the electronic dynamics on attosecond timescales. Our measurements show that the Gouy phase slip in the interaction region plays a significant role in these attosecond experiments. We perform precision measurement of interferences between strong field-induced Floquet channels to extract the intensity and phase dependence of photoionization dynamics. Applications of emerging table-top ultrafast XUV sources in the study of core electron dynamics are also discussed.

Ultrafast Coherent Optical Transmission

Jan.-Feb. 2012

This paper presents recent progress toward the realization of ultrahigh-speed coherent optical transmission with a single-channel bit rate of more than 1 Tbit/s using ultrashort pulse technology and an advanced modulation format. We first describe Tbit/s optical time-division multiplexing (OTDM) transmission employing differential binary or quadrature phase shift keying. We present our recent demonstrations of single-polarization 640-Gb/s differential phase-shift keying and 1.28-Tb/s differential quadrature phase-shift keying transmissions over 525 km, which employ an ultrafast optical Fourier transformation technique. We then focus on coherent optical transmission using quadrature amplitude modulation (QAM) with a multiplicity of 512 that enables us to achieve an ultrahigh spectral efficiency of more than 10 b/s/Hz. Finally, we demonstrate a novel ultrahigh-speed, spectrally efficient coherent pulse transmission combining OTDM and QAM. A 400 Gb/s, 32 RZ/QAM signal was successfully transmitted over 225 km on a single carrier at 10 Gsymbol/s × 4-OTDM.

Periodic Time-Domain Modulation for the Electrically Tunable Control of Optical Pulse Train Envelope and Repetition Rate Multiplication

Jan.-Feb. 2012

An electrically tunable system for the control of optical pulse sequences is proposed and demonstrated. It is based on the use of an electrooptic modulator for periodic phase modulation followed by a dispersive device to obtain the temporal Talbot effect. The proposed configuration allows for repetition rate multiplication with different multiplication factors and with the simultaneous control of the pulse train envelope by simply changing the electrical signal driving the modulator. Simulated and experimental results for an input optical pulse train of 10 GHz are shown for different multiplication factors and envelope shapes.

Mechanisms of Epi-Detected Stimulated Raman Scattering Microscopy

Jan.-Feb. 2012

Epi-detection is indispensible for stimulated Raman scattering (SRS) imaging of opaque samples. We present an analysis of the mechanisms underlying the generation of epi-detected SRS signals. By study of forward- and epi-detected SRS signals from pharmaceutical films of controlled thickness and scatterer density, we show that the epi-detected SRS signal arises from the backscattering of the forward-propagating probe photons. Furthermore, we show that both forward- and epi-detected SRS signal intensity linearly depends on the local oscillator power at the detector at the same slope. Under the same excitation conditions, stimulated Raman loss produces a larger epi-detected signal than stimulated Raman gain due to the larger scattering cross section of light with a shorter wavelength.

Pulse Shaping and Evolution in Normal-Dispersion Mode-Locked Fiber Lasers

Jan.-Feb. 2012

Fiber lasers mode locked with large normal group-velocity dispersion have recently achieved femtosecond pulse durations with energies and peak powers at least an order of magnitude greater than those of prior approaches. Several new mode-locking regimes have been demonstrated, including self-similar pulse propagation in passive and active fibers, dissipative solitons, and a pulse evolution that avoids wave breaking at high peak power but has not been reproduced by theoretical treatment. Here, we illustrate the main features of these new pulse-shaping mechanisms through the results of numerical simulations that agree with experimental results. We describe the features that distinguish each new mode-locking state and explain how the interplay of basic processes in the fiber produces the balance of amplitude and phase evolutions needed for stable high-energy pulses. Dissipative processes such as spectral filtering play a major role in normal-dispersion mode locking. Understanding the different mechanisms allows us to compare and contrast them, as well as to categorize them to some extent.

Coherent X-Ray Diffraction Imaging

Jan.-Feb. 2012

For centuries, lens-based microscopy, such as optical, phase-contrast, fluorescence, confocal, and electron microscopy, has played an important role in the evolution of modern science and technology. In 1999, a novel form of microscopy, i.e., coherent diffraction imaging (also termed coherent diffraction microscopy or lensless imaging), was developed and transformed our conventional view of microscopy, in which the diffraction pattern of a noncrystalline specimen or a nanocrystal was first measured and then directly phased to obtain a high-resolution image. The well-known phase problem was solved by combining the oversampling method with iterative algorithms. In this paper, we will briefly discuss the principle of coherent diffraction imaging, present various implementation schemes of this imaging modality, and illustrate its broad applications in materials science, nanoscience, and biology. As coherent X-ray sources such as high harmonic generation and X-ray free-electron lasers are presently under rapid development worldwide, coherent diffraction imaging can potentially be applied to perform high-resolution imaging of materials/nanoscience and biological specimens at the femtosecond time scale.

Timing Fluctuations Due to Beam Steering in Prism-Compensated Kerr-Lens Mode-Locked Lasers

Jan.-Feb. 2012

Variation in the round-trip group delay through an intracavity prism pair is studied as a function of index variation in the gain medium. The resulting sensitivity to index perturbation gives insight into the degree to which pump noise will transfer to timing instability through this mechanism. General expressions for group-delay time change and slope are derived. It is found that thermal and nonlinear index changes in the gain crystal result in group-delay time sensitivities of $4.34 times 10^{-17}$ s/K and $1.25times 10^{-26}$ s$cdot$ cm$^{2}$/W, respectively, for a conventional 100-MHz Kerr-lens mode-locked laser. For a nominal temperature fluctuation of 1 K and a peak intensity variation of $5times 10^8$ W/m$^{2}$ , this implies round-trip timing variation of $5times 10^{-17}$ s, which is very small, but not insignificant in today’s clock technology.

Scaling of High-Order Harmonic Generation in the Long Wavelength Limit of a Strong Laser Field

Jan.-Feb. 2012

The development of intense, ultrashort, table-top lasers operating in the mid-infrared spectral region, offers many new avenues for strong-field physics. Atoms submitted to such radiation allow photoelectrons to acquire huge quiver energies well over an order of magnitude larger than the binding energy of the neutral. Consequently, many interesting phenomena arise. First, wavelength offers a convenient experimental knob to tune the ionization regime by controlling the Keldysh parameter. Second, high harmonic generation depends directly on the quiver energy and can, therefore, be pushed to unprecedented limits. Third, wavelength controls the spectral phase of harmonics, and hence the possibility to improve the generation of pulses in the attosecond regime. The use of long wavelength lasers is critical to studying high-order harmonic generation in condensed phase systems, because they facilitate harmonic generation within the transmission window of the material and increase the damage threshold. We review some of the recent discoveries in long wavelength driven high-order harmonic generation in the case of isolated atoms, bulk crystals, and liquid.

Imaging at the Nanoscale With Practical Table-Top EUV Laser-Based Full-Field Microscopes

Jan.-Feb. 2012

The demonstration of table-top high average power extreme-ultraviolet (EUV) lasers combined with the engineering of specialized optics has enabled the demonstration of full-field microscopes that have achieved tens of nanometer spatial resolution. This paper describes the geometry of the EUV microscopes tailored to specific imaging applications. The microscope illumination characteristics are assessed and an analysis on the microscope's spatial resolution is presented. Examples of the capabilities of these table-top EUV aerial microscopes for imaging nanostructures and surfaces are presented.

Demonstration of Nanomachining With Focused Extreme Ultraviolet Laser Beams

Jan.-Feb. 2012

A major challenge in laser machining of microstructures is that of extending the spatial domain to the smaller dimensions of interest in nanotechnology. We demonstrate the feasibility of directly machining nanoscale structures with a focused extreme ultraviolet (EUV) laser beam. Clean sub-200–nm-wide trenches (130-nm full width at half maximum) were ablated on polymethyl methacrylate photoresist by focusing the 46.9–nm wavelength beam from a Ne-like Ar capillary discharge tabletop laser with a Fresnel zone plate lens. Considering that clean 82-nm holes were also ablated using the same laser, it can be expected that focused EUV laser light will enable the machining of significantly smaller features.

A Quantum Control Spectroscopy Approach by Direct UV Femtosecond Pulse Shaping

Jan.-Feb. 2012

A quantum control spectroscopy (QCS) approach using directly shaped UV excitation pulse is demonstrated. Ultrafast tailored pulses in the region of 310–335 nm are combined with transient absorption to investigate reactive pathways in the excited state of (2,2′-bipyridyl)-3,3′-diol BP(OH) $_2$. In particular, we apply QCS in the disentanglement of the competing excited-state intramolecular proton-transfer (ESIPT) channels of BP(OH)$_2$. Our results challenge parallel reactive pathways in the excited state and suggest a newer model based on an extremely fast sequential double ESIPT process.

Toward Single-Cycle Pulse Generation in Raman-Active Crystals

Jan.-Feb. 2012

We study broadband sideband generation in Raman-active crystals. The sidebands come out at different angles and cover infrared, visible, and ultraviolet spectral regions. We combine the sidebands into a collinear beam by using a prism. We use a pulse shaper to control the relative phases of the sidebands aiming to produce single-cycle pulses.

Ultrafast Grating Instruments in the Extreme Ultraviolet

Jan.-Feb. 2012

Optical grating instruments enjoy several advantages in the optimal conditioning of subpicosecond, or ultrafast, pulses in the extreme ultraviolet (XUV) spectral region. The main application of such instruments is the spectral selection of high-order laser harmonics and free-electron-laser pulses in the femtosecond time scale. Broadband XUV monochromators require the use of diffraction gratings at grazing incidence. We discuss here an innovative configuration, that is the off-plane geometry, to realize single-grating XUV monochromators with high efficiency and ultrafast time response. Furthermore, the off-plane design has been modified to realize a double-grating XUV monochromator with time-delay compensated (TDC) response. Two examples of realizations applied to the spectral selection of high-order laser harmonics are presented. In particular, XUV pulses as short as 8 fs have been measured at the output of the TDC monochromator. Finally, the problem of temporal compression of broadband XUV attosecond pulses by means of a double-grating compressor will be addressed. The TDC design has been modified to realize an XUV attosecond compressor that introduces a variable group-delay dispersion to compensate for the intrinsic chirp of the attosecond pulse.

Digital Light-in-Flight Recording by Holography by Use of a Femtosecond Pulsed Laser

Jan.-Feb. 2012

We succeeded in digital light-in-flight recording by holography by use of a femtosecond pulsed laser. We recorded and reconstructed a moving picture of femtosecond light pulse propagation on a diffuser plate on which a test chart pattern was printed. A mode-locked Ti:sapphire laser was used as a femtosecond pulsed laser. The center wavelength and the duration of the light pulse were 800 nm and 96 fs, respectively. We conducted a numerical simulation in order to validate the proposed technique. We confirmed that the technique was capable of recording the moving picture of femtosecond light pulse propagation. In addition, we experimentally demonstrated the technique and successfully observed femtosecond light pulse propagation for 576 fs. The experimental results agreed well with the simulation results.

Dynamic Temperature Distribution in Cylindrical Laser Rods With Time-Varying Pump Sources

Jan.-Feb. 2012

A rigorous analysis of the temperature distribution of a laser rod with a time-varying axial heat source is presented. Closed-form expressions for the space-time dependence of the temperature are obtained and can be used to predict dynamic optical and mechanical fluctuations. These in turn can degrade timing stability in mode-locked lasers used as precision clocks and oscillators through the noise transfer process.

Theory and Simulation of Ultrafast Intense Pulse Propagation in Extended Media

Jan.-Feb. 2012

The theory of femtosecond pulse propagation in dispersive nonlinear media is reviewed with emphasis on modeling light–matter interactions in femtosecond optical filaments. Discussion of the principles underlying the pulse propagation models is followed by the description of the “standard” light–medium interaction model utilized in the ultrafast nonlinear optics, and open problems are identified across the field.

Attosecond Technology and Science

Jan.-Feb. 2012

The generation of attosecond pulses has been the result of tremendous efforts and advances in the field of the interaction of ultrashort intense laser pulses with matter. Nowadays, the electric field waveform of femtosecond pulses can be precisely controlled and used to synthesize and measure the evolution in time of attosecond pulses. The quest for increasing photon fluxes in the extreme-ultraviolet region (XUV) and the requirement of a complete characterization of complex attosecond waveforms are stimulating the development of new technological approaches that should make feasible XUV sources combining attosecond pulse duration, high energy, and high repetition rate. The use of such sources with state-of-the-art techniques for the measurement of the momentum of charged particles will allow a detailed description of photoionization and photodissociation processes. Advances in selection of the initial quantum state and structure of molecules will open the way for the extension of attosecond spectroscopy to complex molecules. The first applications of attosecond pulses allowed the investigation of electron dynamics with a resolution close to the atomic unit of time. Simple systems such as helium and noble gases were investigated using trains and isolated pulses. These experiments represent benchmarks to elucidate the response of atoms on the typical electron timescale.

Attosecond Time-Resolved Electron Dynamics in the Hydrogen Molecule

Jan.-Feb. 2012

Recent advances in the generation and characterization of extreme-ultraviolet pulses, generated either by intense femtosecond lasers or by free electron lasers, are pushing the frontier of time-resolved investigations down to the attosecond domain, the relevant timescale for electron motion. The quantum nature of the intertwined electronic and nuclear motion requires theoretical models going beyond the Born–Oppenheimer approximation and taking into account electron correlation, representing a challenge for the computational power available nowadays. Understanding how the electron dynamics inside molecules can influence chemical reactions presents important implications in several fields and allows for the development of new technologies. In this paper, we report on experimental and theoretical results of an investigation in ${rm H_2/D_2}$ , where for the first time control of molecular dynamics with attosecond resolution was achieved. The data represent the first evidence of the control of the electron motion in a molecule undergoing a chemical reaction on the subfemtosecond scale.

New Mid-Infrared Light Sources

Jan.-Feb. 2012

We present a novel mid-infrared (mid-IR) source of ultrashort pulses applicable to a wide range of biological, spectroscopic, and strong-field physics investigations. The source produces 67 fs pulses at 3.2 microns, with energy of 3.8 $mu$J at 100 kHz repetition rate and a pulse-to-pulse RMS stability of 0.7%. The system is based on OPCPA, is scalable in energy and repetition rate, and provides a platform for a new generation of ultrashort mid-IR sources.

Using Quantum Coherence to Generate Gain in the XUV and X-Ray: Gain-Swept Superradiance and Lasing Without Inversion

Jan.-Feb. 2012

It was shown some time ago that when the excitation of an ensemble of two-level atoms is swept in the direction of lasing, so that atoms are prepared in the excited state just as the radiation from previously excited atoms reaches them, the resulting laser amplifier is “highly anomalous” and yields superradiant emission without population inversion. We here show that transient gain in a three-level system has common features with Dicke superradiance and can yield strong extreme ultraviolet lasing in, for example, He atoms (at 58 nm) or He-like ions such as $B^{3+}$ (at 6.1 nm).

Special issue on Optical Interconnects for Data Centers

Jan.-Feb. 2012

Special issue on current trends in terahertz photonics and applications

Jan.-Feb. 2012

IEEE Journal of Selected Topics in Quantum Electronics information for authors

Jan.-Feb. 2012

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Jan.-Feb. 2012

Selected Topics in Quantum Electronics, IEEE Journal of - new TOC

Frontcover

IEEE Journal of Selected Topics in Quantum Electronics publication information

Table of Contents

Editorial

Introduction to the Issue on Ultrafast Science and Technology

Second-Harmonic Generation of Super Powerful Femtosecond Pulses Under Strong Influence of Cubic Nonlinearity

Differential Multiphoton Laser Scanning Microscopy

SESAMs for High-Power Oscillators: Design Guidelines and Damage Thresholds

Interference Stabilization Revisited

Generation and Optimization of Femtosecond Pulses by Four-Wave Mixing Process

2-ps Hard X-Ray Streak Camera Measurements at Sector 7 Beamline of the Advanced Photon Source

Femtosecond Nd:Glass Lasers Pumped by Single-Mode Laser Diodes and Mode Locked With Carbon Nanotube or Semiconductor Saturable Absorber Mirrors

Advances in Ultrafast Control and Probing of Correlated-Electron Materials

Femtosecond Carrier Dynamics and Nonlinear Effects in Quantum Cascade Lasers

Molecular Dynamics in Strong Laser Fields

Mode Locking in the Few-Femtosecond Regime Using Waveguide Arrays and the Coupled Short-Pulse Equations

Electron Dynamics and Its Control in Molecules: From Diatomics to Larger Molecular Systems

Rapid Birefringent Delay Scanning for Coherent Multiphoton Impulsive Raman Pump–Probe Spectroscopy

Electron Pulse Compression With a Practical Reflectron Design for Ultrafast Electron Diffraction

Ultrarapid Optical Frequency-Domain Reflectometry Based Upon Dispersion-Induced Time Stretching: Principle and Applications

Wavenumber-Domain Theory of Terahertz Single-Walled Carbon Nanotube Antenna

Femtosecond Laser in Polymeric Materials: Microfabrication of Doped Structures and Micromachining

Following Ultrafast Radiationless Relaxation Dynamics With Strong Field Dissociative Ionization: A Comparison Between Adenine, Uracil, and Cytosine

Low-Energy Photoelectron Angular Distributions of Above-Threshold Ionization of Atoms and Molecules in Strong Laser Fields

Integrated Fourier-Domain Mode-Locked Lasers: Analysis of a Novel Coherent Comb Laser

Toward Broad Bandwidth 2-D Electronic Spectroscopy: Correction of Chirp From a Continuum Probe

Extending Femtosecond Metrology to Longer, More Complex Laser Pulses in Time and Space

Characterizing Fast Arbitrary CW Waveforms With 1500 THz/s Instantaneous Chirps

Isolated Attosecond Pulse Generation by Two-Mid-IR Laser Fields

Next-Generation X-Ray Free-Electron Lasers

Advanced Ultrafast Technologies Based on Optical Frequency Combs

Nano-Optical Control of Hot-Spot Field Superenhancement on a Corrugated Silver Surface

Ultrafast Multidimensional Spectroscopy: Principles and Applications to Photosynthetic Systems

Ultrafast Optical Parametric Chirped-Pulse Amplification

Femtosecond Extreme Ultraviolet Ion Imaging of Ultrafast Dynamics in Electronically Excited Helium Nanodroplets

Optical 2-D Fourier Transform Spectroscopy of Excitons in Semiconductor Nanostructures

Tracking Ultrafast Energy Flow in Molecules Using Broadly Tunable Few-Optical-Cycle Pulses

Relaxation of Photoinduced Quasi-Particles in Correlated Electron Metals

Femtosecond and Attosecond Spectroscopy in the XUV Regime

Ultrafast Coherent Optical Transmission

Periodic Time-Domain Modulation for the Electrically Tunable Control of Optical Pulse Train Envelope and Repetition Rate Multiplication

Mechanisms of Epi-Detected Stimulated Raman Scattering Microscopy

Pulse Shaping and Evolution in Normal-Dispersion Mode-Locked Fiber Lasers

Coherent X-Ray Diffraction Imaging

Timing Fluctuations Due to Beam Steering in Prism-Compensated Kerr-Lens Mode-Locked Lasers

Scaling of High-Order Harmonic Generation in the Long Wavelength Limit of a Strong Laser Field

Imaging at the Nanoscale With Practical Table-Top EUV Laser-Based Full-Field Microscopes

Demonstration of Nanomachining With Focused Extreme Ultraviolet Laser Beams

A Quantum Control Spectroscopy Approach by Direct UV Femtosecond Pulse Shaping

Toward Single-Cycle Pulse Generation in Raman-Active Crystals

Ultrafast Grating Instruments in the Extreme Ultraviolet

Digital Light-in-Flight Recording by Holography by Use of a Femtosecond Pulsed Laser

Dynamic Temperature Distribution in Cylindrical Laser Rods With Time-Varying Pump Sources

Theory and Simulation of Ultrafast Intense Pulse Propagation in Extended Media

Attosecond Technology and Science

Attosecond Time-Resolved Electron Dynamics in the Hydrogen Molecule

New Mid-Infrared Light Sources

Using Quantum Coherence to Generate Gain in the XUV and X-Ray: Gain-Swept Superradiance and Lasing Without Inversion

Special issue on Optical Interconnects for Data Centers

Special issue on current trends in terahertz photonics and applications

IEEE Journal of Selected Topics in Quantum Electronics information for authors

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