Impact of atmospheric molecular absorption on the temporal and spatial evolution of ultra-short optical pulses

Abstract

We present a rigorous study on the impact of atmospheric molecular absorption on the linear propagation of ultrashort pulses in the mid-infrared wavelength region. An ultrafast thulium-based fiber laser was employed to experimentally investigate ultrashort-pulse propagation through the atmosphere in a spectral region containing several strong molecular absorption lines. The atmospheric absorption profile causes a significant degradation of the pulse quality in the time domain as well as a distortion of the transverse beam profile in the spatial domain. Numerical simulations carried out in the small signal limit accurately reproduce the experimental observations in the time domain and reveal that the relative loss in peak power after propagation can be more than twice as high as the relative amount of absorbed average power. Although their nature is purely linear (i.e. the intensities considered are sufficiently low) the discussed effects represent significant challenges to performance-scaling of mid-infrared ultrafast lasers operating in spectral regions with molecular absorption bands. Guidelines for an efficient mitigation of the pulse quality degradation and the beam profile distortion are discussed.

Multi-octave spanning, Watt-level ultrafast mid-infrared source

“…The main amplifier fiber is a 3 m long large pitch photonic crystal fiber (LPF) [45], providing a maximum output power of 100 W. Both thulium-doped amplifier fibers are diode-pumped at a wavelength of 793 nm. The output of the main amplifier is sent to a free-space Treacy-type grating compressor housed in a vacuum chamber to avoid unwanted absorption by atmospheric water vapor and subsequent thermal air fluctuations [46].…”

Self-compression to 24 MW peak power in a fused silica solid-core fiber using a high-repetition rate thulium-based fiber laser system

“…For the experiments described herein, the laser was operated such that it delivered compressed pulse energies up to 1.3 µJ, corresponding to an average power of 29 W. The compressed laser output, which was circularly polarized at that point, was coupled into a solid-core fiber used for the subsequent nonlinear pulse compression. All high-power free-space sections of this setup were purged with dry nitrogen in order to prevent distortions of the temporal pulse shape or the spatial beam profile as described elsewhere 15 . After the nonlinear pulse compression stage the power and the characteristics of the output beam profile, the spectrum as well as the intensity autocorrelation were monitored.…”

Spectral and coherent properties of partially polarized pulsed electromagnetic beams upon turbulent atmosphere propagation for different source conditions

“…In the past decades, with the rapid development of femtosecond pulse laser technology, ultrashort pulse beam has aroused great interests of scholars at home and abroad [1][2][3][4][5][6]. For an optical pulse, it is commonly assumed that both its spatial and spectral components are completely coherent.…”