Collisionally excited extreme ultra-violet lasers created by laser irradiation of plasmas

Short wavelength extreme ultra-violet (EUV) lasers pumped by electron collisional excitation in plasmas irradiated by infra-red lasers have achieved saturated output down to wavelengths as short as 5.9 nm [1] and are now used for applications [2, 3]. These lasers operate without mirrors with output due to amplified spontaneous emission (ASE). The beam profiles consist typically of a large number of individual coherent beamlets [4] with a total near-field profile that is typically crescent shaped [5]. Gain profiles are spectrally narrow dependent on thermal Doppler broadening of ions of temperature ∼ 100 – 200 eV. With gain narrowing, this result in pulses of spectral width v/Δv ≫ 10⁴. The shortest pulse durations of the output EUV lasers have consequently been close to Fourier transform limited at ≈ 3 ps [6, 7].