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Selected Topics in Quantum Electronics, IEEE Journal of

Issue 2 • Date March-April 1998

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Displaying Results 1 - 25 of 39
  • Introduction To The Issue On Ultrafast Optics

    Page(s): 157 - 158
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    Freely Available from IEEE
  • Real-time 3-D holographic imaging using photorefractive media including multiple-quantum-well devices

    Page(s): 360 - 369
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    We discuss a real-time coherence gated three-dimensional (3-D) imaging system, based on photorefractive holography with ultrashort pulses, which has been applied to imaging through turbid media with a view to developing biomedical instrumentation. Sub-100-μm depth-resolved images of 3-D objects embedded in a scattering medium have been obtained. Using a long integration time in rhodium-doped barium titanate (Rh:BaTiO4), an image of a test chart has been obtained through 16 mean-free paths of scattering medium. Real-time depth-resolved imaging through 13 mean free paths of scattering medium has been demonstrated using a fast response time (<0.4 ms) photorefractive multiple quantum well device. This latter system can acquire depth-resolved images direct to video with no requirement for frame grabbing or signal processing. We discuss the tradeoffs and limitations of these photorefractive media for this application View full abstract»

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  • Self-starting 6.5-fs pulses from a Ti:sapphire laser using a semiconductor saturable absorber and double chirped mirrors

    Page(s): 169 - 178
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    We demonstrate self-starting 6.5-fs pulses from a Kerr-lens-mode-locked Ti:sapphire laser with an average output power of 200 mW at a pulse repetition rate of 86 MHz. We have achieved a mode-locking buildup time of only 60 μs, using a broad-band semiconductor saturable absorber mirror to initiate the pulse formation. The dispersion has been compensated with a prism pair in combination with improved double-chirped mirrors. The prism pair allows for the flexible adjustment of both the duration and the center wavelength of the pulse. The double-chirped mirrors show a high reflectivity better than 99.8% over the full bandwidth of 300 nm and a controlled group delay over more than 250 nm. The choice of a proper output coupler turns out to be critical for ultrashort pulse generation directly from the laser View full abstract»

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  • High-power mode-locked external cavity semiconductor laser using inverse bow-tie semiconductor optical amplifiers

    Page(s): 209 - 215
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    This paper presents experimental results of using an inverse bow-tie gain guided semiconductor optical amplifier (SOA) as the optical gain element in a high-power external cavity semiconductor laser. An average output power of 700 mW is demonstrated in continuous-wave (CW) operation while 400 mW of average power is obtained in both passive and hybrid mode-locked operation, with subsequent optical amplification in an identical SOA. The mode-locked laser operates at a repetition rate of 1.062 GHz, owing to the interplay between the gain and saturable absorber dynamics. Optical pulses are generated with a temporal duration of 5 ps, which implies a pulse energy of 376 pJ, and a peak power of 60 W. Further reduction of the optical pulsewidth to 1.3 ps is also achieved by using dispersion compensation techniques. These results show the promise of novel SOA devices for use as gain elements in external cavity semiconductor lasers. The generated output pulse characteristics from mode-locked operation is sufficient for use in novel three-dimensional data storage applications, and in large-scale commercial printing and marking applications View full abstract»

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  • Theory of double-chirped mirrors

    Page(s): 197 - 208
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    A theory of double-chirped mirrors (DCMs) for dispersion compensation in ultrashort pulse laser sources is presented. We describe the multilayer interference coating by exact coupled-mode equations. They show that the analysis and synthesis of a coating with a slowly varying chirp in the layer thicknesses can be mapped onto a weakly inhomogeneous transmission line problem. Solutions of the transmission line equations are given using the WKB-method. Analytic expressions for reflectivity and group delay are derived. The solutions show that the main problem in chirped mirror design is the avoidance of spurious reflections, that lead to Gires-Tournois-like interference effects responsible for the oscillations in the group delay. These oscillations are due to an impedance matching problem of the equivalent transmission line. The impedance matching can be achieved by simultaneously chirping the strength of the coupling coefficient and the Bragg wavenumber of the mirror. An adiabatic increase in the coupling coefficient removes the typical oscillations in the group delay and results in broad-band mirrors with a controlled dispersion. Finally, the mirror is matched to air with a broadband antireflection coating. We discuss a complete design of a laser mirror with a reflectivity larger than 99.8% and a controlled dispersion over 300-nm bandwidth. Using such mirrors in a Ti:sapphire laser, we have demonstrated ≈30-fs pulses, tunable over 300 nm, as well as 8-fs pulses from the same setup. A different design resulted in 6.5-fs pulses View full abstract»

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  • Broad-bandwidth parametric amplification in the visible: femtosecond experiments and simulations

    Page(s): 224 - 229
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    A general geometric condition, involving group velocities, for large bandwidth parametric amplification with all types of phase-matching and in certain wavelength ranges is derived. This condition has been exploited to produce visible widely tunable sub-20-fs pulses from an optical parametric oscillator and an optical parametric amplifier based on β-barium borate (BaB2O4) pumped in the blue. These results are interpreted in terms of a modified soliton model for the optical parametric oscillator (OPO) and detailed numerical simulations for both devices View full abstract»

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  • Theoretical modeling of gain-guiding effects in experimental all-solid-state KLM lasers

    Page(s): 185 - 192
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    All-solid-state four-mirror Kerr lens mode locked (KLM) Cr:LiScGaAlF6 and three-mirror Cr:YAG femtosecond lasers have been experimentally developed and theoretically analyzed, using a numerical model that takes into account astigmatism, nonlinear xy coupling, and gain-guiding. For the soft-aperture three-mirror KLM system, the model is extended to include gain saturation and soft-aperturing and a new optimization parameter is proposed View full abstract»

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  • Mode-locking with slow and fast saturable absorbers-what's the difference?

    Page(s): 159 - 168
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    We investigate the differences in the dynamics of lasers mode-locked by fast and slow saturable absorbers. Slow saturable absorbers can already generate almost transform limited pulses much shorter than the recovery time of the absorber. If soliton-like pulse shaping is present in addition the pulses can be further compressed below the resulting net gain window until either the continuum breaks through or the pulses break up into multiple pulses, which sets a limit to the shortest pulsewidth achievable. Given a certain amount of saturable absorption, a comparison is made that results in an estimate for the shortest pulse achievable for a solitary laser stabilized by a fast or a slow saturable absorber. The theoretical results are compared with experiments View full abstract»

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  • Toward a terawatt-scale sub-10-fs laser technology

    Page(s): 414 - 420
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    Powerful techniques for spectral broadening and ultrabroad-band dispersion control, which allow compression of high-energy femtosecond pulses to a duration of a few optical cycles, are analyzed. Spectral broadening in a gas-filled hollow fiber and compression by chirped mirrors with high-energy 20-fs input pulses are presented. Using 1-mJ seed pulses we have demonstrated the generation of 0.5-mJ 5-fs pulses at 0.8-μm and 1-kHz repetition rate. General design criteria to scale the compression technique toward the terawatt level are presented View full abstract»

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  • Ensuring compactness, reliability, and scalability for the next generation of high-field lasers

    Page(s): 376 - 384
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    If further developments in high-field lasers are to be accessible to universities and institutes, new laser materials and phase control techniques, which will result in compact, reliable systems with higher peak power, must be adopted. The choice of high-saturation-fluence gain material and the measurement and active control of temporal and spatial phase distortions for compact chirped-pulse amplification (CPA) systems of the future are discussed. Using the proper material and phase control a focused intensity of 1025 W/cm2 is theoretically possible View full abstract»

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  • Widely tunable, near- to mid-infrared femtosecond and picosecond optical parametric oscillators using periodically poled LiNbO3 and RbTiOAsO4

    Page(s): 238 - 248
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    We describe the operation and characterization of Ti:sapphire laser-pumped femtosecond and picosecond optical parametric oscillators based the new quasi-phase-matched nonlinear materials of periodically poled LiNbO3 and RbTiOAsO4 with broad tunability in the near- to mid-infrared. We discuss the merits of the two materials for use in ultrafast optical parametric oscillators (OPOs) and compare and contrast their properties to the birefringent materials. We demonstrate an extended spectral coverage from <1 μm to >5 μm, pump power thresholds as low as 45 mW, average mid-infrared output powers in excess of 100 mW, and pulse durations of 100-200 fs and 1-2 ps at ~80 MHz repetition rate. We also report the efficient operation of Ti:sapphire-pumped femtosecond OPOs in all-solid-state configurations by utilizing diode-laser-based input pump sources View full abstract»

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  • Intracavity spectral shaping in external cavity mode-locked semiconductor diode lasers

    Page(s): 216 - 223
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    Intracavity spectral shaping techniques have been employed to artificially shape and broaden the optical spectrum of external cavity mode-locked semiconductor lasers. Using an intracavity spectrometer and intensity Fourier-plane filtering, active mode-locked output spectra with a multiplicity of independently tunable wavelengths have been generated, while an adjustable intracavity etalon has been employed to generate an 18-nm spectral width. Furthermore, hybrid mode-locking with a multiple-quantum-well (MQW) saturable absorber combined with the intracavity etalon, followed by dispersion compensation has led to the generation of optical pulses of 330 fs in duration View full abstract»

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  • Femtosecond pulse shaping for synthesis, processing, and time-to-space conversion of ultrafast optical waveforms

    Page(s): 317 - 331
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    Shaping, signal processing, and time-space conversion of femtosecond pulses can be achieved by linear and nonlinear manipulation of the spatially dispersed optical frequency spectrum within a grating and lens pulse shaper. In this paper, we first review our work on femtosecond pulse shaping and processing, with an emphasis on applications to high-speed communications and information processing. We then present a new concept for generalized time-space processing based on cascaded time-to-space and space-to-time conversions in conjunction with smart pixel optoelectronic arrays and provide a detailed discussion of our recent studies of time-to-space conversion based on second-harmonic generation (SHG) within a femtosecond pulse shaper View full abstract»

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  • Real-time measurement of ultrashort laser pulses using principal component generalized projections

    Page(s): 278 - 284
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    Frequency-resolved optical gating (FROG) is a technique to measure ultrashort laser pulses that optically constructs a spectrogram of a laser pulse. A two-dimensional (2-D) phase retrieval algorithm is used to extract the intensity and phase of a pulse from its spectrogram. We have improved a recently presented principal component generalized projections algorithm (PCGPA) making it easier to implement and fast enough to allow real-time inversion of FROG spectrograms. A femtosecond oscilloscope, based on second-harmonic generation (SHG) FROG, that displays the intensity and phase of ultrashort laser pulses in real time utilizing the improved PCGP phase retrieval algorithm is presented View full abstract»

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  • Dispersion considerations in ultrafast CPA systems

    Page(s): 430 - 440
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    A basic assumption underlies many designs for chirped-pulse amplification (CPA) of ultrashort pulses. This assumption is that a Taylor's series expansion of the dispersive delay is well behaved in the sense that each phase order in the expansion produces an effect on the pulse that is significantly smaller than the effect of the previous order. This work investigates this assumption both qualitatively and quantitatively. We show quantitatively that the requirements for achieving sub-20-fs pulses are much more stringent than for 100-fs pulses. We find that when the basic assumption holds, a chirped pulse amplification (CPA) system may be designed by zeroing each order in succession, but that zeroing may not work well for some systems that are not well behaved. For these cases minimizing the overall dispersion becomes necessary. We discuss some common optical components including bulk materials, expanders, and compressors and show that they generally satisfy the basic assumption. Finally, we discuss the problem of optimizing a CPA system in the laboratory, and describe a new polarization-gate (PC) frequency-resolved optical gating (FROG) arrangement that is based on thin-film polarizers and that allows accurate measurements of the phase as well as the intensity with minimal dispersive effects View full abstract»

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  • Design and implementation of a TW-class high-average power laser system

    Page(s): 395 - 406
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    We describe the design, modeling and characterization of a titanium-doped sapphire multipass, kilohertz amplifier system with output pulses of energy 4.4 mJ and duration 17 fs, giving a peak power of 0.26 TW. The thermal lensing in the second amplifier stage is virtually eliminated by cryogenic cooling of the laser crystal. Gain-narrowing and shifting of the amplified spectrum are reduced by tailoring the output spectrum of the oscillator and by using a low-loss multipass amplifier chain. Fourth-order spectral dispersion was completely eliminated by using a prism pair in addition to adjusting the stretcher and compressor grating separation and angle. We also numerically modeled the evolution of the pulse energy and spectral phase and amplitude through the amplifier system. The results of the model are in excellent agreement with measurements made using the technique of transient-grating frequency-resolved optical gating View full abstract»

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  • Temporal contrast in Ti:sapphire lasers, characterization and control

    Page(s): 449 - 458
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    As ultrafast lasers achieve ever higher focused intensities on target, the problem of ensuring a clean laser-solid interaction becomes more pressing. In this paper, we give concrete examples of the deleterious effects of low-contrast interactions, and address the problem of subpicosecond laser intensity contrast ratio on both characterization and control fronts. We present the new technique of high-dynamic-range plasma-shuttered streak camera contrast measurement, as well as two efficient and relatively inexpensive ways of improving the contrast of short pulse lasers without sacrificing on the output energy: a double-pass Pockels cell (PC), and clean high-energy-pulse seeding of the regenerative amplifier View full abstract»

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  • Reconstruction of the time profile of femtosecond laser pulses through cross-phase modulation

    Page(s): 295 - 300
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    Experimental results concerning the determination of the time profile of femtosecond laser pulses are presented. The method is based on the analysis of the changes of the laser spectrum induced at different delays by cross-phase modulation. Pulses from a 30-fs Ti:sapphire laser at 800 nm are characterized over a high dynamic range. Second-harmonic pulses at 400 nm from the same laser are also characterized, exhibiting the expected improvement in contrast ratio View full abstract»

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  • Frequency-resolved optical gating using cascaded second-order nonlinearities

    Page(s): 271 - 277
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    We demonstrate frequency-resolved optical gating (FROG) using cascaded second-order nonlinearities (up-conversion followed by down-conversion). We describe two different cascaded second-order beam geometries-self-diffraction and polarization-gate-which are identical to their third-order nonlinear-optical cousins, except that they use second-harmonic-generation crystals instead of (weaker) third-order materials. Like the corresponding third-order processes, these new versions of FROG yield the same intuitive traces, uniquely determine the pulse intensity and phase (without direction-of-time ambiguity), and yield signal light at the input-pulse wavelength (which simplifies the required spectral measurements). Most importantly, however, we show that these techniques are significantly more sensitive than the corresponding third-order FROG methods, conveniently allowing, for the first time, the unambiguous measurement of ultrashort ~1-nJ pulses, that is, unamplified Ti:sapphire oscillator pulses View full abstract»

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  • Phase amplitude coupling in spectral phase modulation

    Page(s): 342 - 345
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    We report the experimental study of spatio-temporal coupling in spectral phase modulation. Spectral phase modulation relies on the creation of a Fourier plane where spectral components are dispersed and independently focused on a modulator, which allows to locally change the optical path. Spatio-temporal coupling arising from the principle of spectral phase modulation in itself has been experimentally studied for various typical phase modulations and compared to simulations View full abstract»

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  • Cancellation of B-integral accumulation for CPA lasers

    Page(s): 459 - 469
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    The B-integral accumulated in a chirped-pulse-amplification (CPA) laser can be canceled using a semiconductor with a negative nonlinear index of refraction. We demonstrate this experimentally using GaAs at 1.053 μm. The compressed-pulse duration was broadened due to self-phase modulation (SPM) of the chirped pulse. It was reduced to its unmodulated value with substantial wing reduction after passing through a semiconductor wafer before compression. Optimum semiconductor sample parameters for minimizing the B-integral such as gap energy, nonlinear and linear absorption, nonlinear refraction, and thickness for different pulse durations and intensities are discussed View full abstract»

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  • Measurement of femtosecond pulse shapes via ionization of air

    Page(s): 301 - 305
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    In summary, we have demonstrated a new method for the characterization of ultrashort pulses which can be easily implemented and which is particularly well suited to high intensity lasers. It is shown that it is possible to simply determine the temporal shape of femtosecond pulses using plasma-induced cross-phase modulation in ionized air View full abstract»

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  • Generation of coherent, femtosecond, X-ray pulses in the “water window”

    Page(s): 266 - 270
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    We report experimental and theoretical results on high-harmonic generation with 25-fs laser excitation pulses. The shortest wavelength we observe, at 2.7 nm, is well within the “water window” region of X-ray transmission. In the case of all the noble gases, we obtain excellent agreement between theoretical predictions for the highest harmonic photon energy generated and our experimental observations. We also obtain excellent agreement between theory and experiment for the highest photon energy generated as a function of laser pulsewidth between 25 and 100 fs. Finally, we observe that the individual harmonic peaks near the cutoff are well resolved for positively chirped pump pulses, but are unresolved in the case of negatively chirped excitation pulses View full abstract»

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  • Evaluation of femtosecond pulse shaping with low-loss phase-only masks

    Page(s): 346 - 352
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    We numerically and experimentally evaluate the performance of programmable femtosecond pulse shaping with specified time-dependent amplitude and phase profiles using phase-only masks. With the masks that have discrete phase levels of ⩾4 designed by simulated annealing optimization algorithm, various pulses with arbitrarily specified amplitudes, pulsewidths, and pulse intervals are obtained with high accuracy. However, when specifying temporal phase profiles together with the amplitude, the range of shaped output pulses that can be produced with phase-only masks is somewhat limited even with a phase level of 64. The efficiency of transmitted optical power in the experiments is ~60%, mainly due to the diffraction loss at a grating pair, which is much higher than that using an amplitude-and-phase mask View full abstract»

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  • Optical pump-terahertz probe spectroscopy utilizing a cavity-dumped oscillator-driven terahertz spectrometer

    Page(s): 353 - 359
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    A terahertz spectrometer capable of steady-state and time-resolved measurements over the 0.1-3.5-THz spectral region has been built. This spectrometer routinely produces and detects terahertz pulses that exhibit signal-to-noise ratios (SNRs) greater than 6000 in the time domain and a spectral noise door of magnitude 2.7×10-4. Hence, the spectrometer achieves nearly four decades of dynamic range in the frequency domain. Two pulse generation processes are observed to give rise to the measured terahertz pulse. High-quality optical pump-terahertz probe data on ⟨111⟩ GaAs samples are presented, demonstrating the applicability of this spectrometer to the study of optically induced dynamical processes. Non-Drude relaxation behavior is observed in the transient terahertz spectra View full abstract»

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Aims & Scope

Papers published in the IEEE Journal of Selected Topics in Quantum Electronics fall within the broad field of science and technology of quantum electronics of a device, subsystem, or system-oriented nature.

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Meet Our Editors

Editor-in-Chief
John Cartledge
Queen's University