ИСТИНА

Ultrafast optics in the mid-infrared (mid-IR) is a rapidly growing field of research, gaining a new momentum from the development of high-power sources of ultrashort mid-infrared pulses and novel methods of broadband field waveform characterization in the mid-infrared [1]. In this work we have extended existing strategies of pulse compression and coherent broadband waveform generation to the mid-IR range. We identified a physical scenario whereby freely propagating mid-infrared pulses can be compressed to pulse widths close to the field cycle. Generation of tunable few-cycle pulses has been demonstrated in the wavelength range from 4.2 to 6.8 μm through self-focusing-assisted spectral broadening in a GaAs plate, serving as a normally dispersive, highly nonlinear material, followed by pulse compression in the regime of anomalous dispersion, where the dispersion-induced phase shift is finely tuned by adjusting the overall thickness of anomalously dispersive components. This approach is shown to enable the generation of sub-two-cycle pulses with a peak power up to 60 MW in the range of central wavelengths tunable from 5.9 to 6.3 μm [2]. We identified a physical scenario whereby freely propagating mid-infrared pulses can be compressed to pulse widths close to the field cycle. Generation of tunable few-cycle pulses has been demonstrated in the wavelength range from 4.2 to 6.8 μm through self-focusing-assisted spectral broadening in a GaAs plate, serving as a normally dispersive, highly nonlinear material, followed by pulse compression in the regime of anomalous dispersion, where the dispersion-induced phase shift is finely tuned by adjusting the overall thickness of anomalously dispersive components. This approach is shown to enable the generation of sub-two-cycle pulses with a peak power up to 60 MW in the range of central wavelengths tunable from 5.9 to 6.3 μm [2]. Soliton-based self-compression of optical field waveforms in the regime of anomalous dispersion is an interesting alternative to a standard pulse compression technique. For instance, recent experiments with 80-fs pulses with a central wavelength of 3.9 μm have revealed self-compression to a pulse width of 40 fs [3]. We have moved further on into the mid-IR, toward longer driver wavelengths, and explored the potential of anomalously dispersive nonlinear materials for pulse self-compression and supercontinuum generation in the spectral region above 7 μm. We have shown that a strongly coupled nonlinear spatiotemporal dynamics of ultrashort mid-IR pulses undergoing self-focusing simultaneously with soliton self-compression in an anomalously dispersive, highly nonlinear solid semiconductor can provide a source of multioctave supercontinua with spectra spanning the entire mid-IR range and compressible to subcycle pulse widths. With 7.9-μm, 150-fs, 2-μJ, 1-kHz pulses used as a driver, mid-IR supercontinuum radiation spanning the range of wavelengths from 3 to 18 μm was generated in a 5-mm GaAs plate. With supercontinuum pulse widths as short as 45 fs achieved in these experiments through soliton self-compression in GaAs [4], a further pulse compression to subcycle pulse widths is possible through a straightforward compensation of the residual phase shift.