We present the concept of a cost-effective broadband SWIR-MIR mJ-level femtosecond laser source for hazardous gas detection by LIDAR based on multi-stage nonlinear conversion in readily available media. Developed affordable laser based on Yb:YAG rods with >10 mJ, ~1.2 ps output pulses at 1030 nm pump 3-stage OPCPA based on BiBO and simultaneously excite a supercontinuum in YAG for its seed. Output pulses amplified to >2 mJ in the wavelength range 1800 – 2400 nm with a pump-to-signal OPCPA conversion efficiency of ~30% after compression to <100 fs are used to generate rotational SRS in compressed nitrogen, hydrogen, or their mixtures to expand the spectrum beyond 3400 nm, limited by the spectrometer used.
We are demonstrating a BiBO crystal based three-stage OPCPA operating in the SWIR wavelength range from ~1800 nm to ~2000 nm for signal and from ~2100 nm to ~2400 nm for idler. This OPCPA was seeded with supercontinuum pulses from a 130 mm YAG crystal. Both the OPCPA and supercontinuum were pumped by transform-limited ~1.2 ps pulses from a Yb:YAG chirped pulse amplifier. In the second stage, a signal energy of ~220 μJ was achieved with a conversion efficiency of 10%, and the signal energy in the third stage exceeded 1 mJ, which corresponds to a conversion efficiency of 19%. Subsequently, the signal-to-idler energy transfer with efficiency of 20% was achieved by Transient Stimulated Raman Chirped-Pulse Amplification in a KGW crystal 30 mm long. Preliminary results were obtained on the compression of the amplified pulse. The laser will be used for remote detection of hazardous gases.
We report efficient amplification of supercontinuum pulses in a stimulated Raman amplifier. The Yb:YAG pump laser produced 1.2 ps transform-limited pulses with an energy of 20 mJ at 100 Hz. Supercontinuum pulses in the wavelength range of 1050 – 2500 nm were obtained in a 15 mm YAG crystal. A larger portion of the laser energy was used to pump a two-stage stimulated Raman amplifier based on Np-cut KGW crystals with the main Stokes shifts of 768 and 901 cm-1 . Spectral broadening to ~16 nm of amplified pulses at 901 cm-1, conversion efficiency of 55%, and pulse width of ~145 fs after compression were demonstrated. Spectral synthesis of Stokes components at 768 and 901 cm-1 provides an even wider spectrum up to ~38 nm, which corresponds to ~50 fs transform-limited pulse. The differences between collinear and non-collinear TSRCPA configurations are investigated in terms of conversion efficiency and gain bandwidth.
We describe sub-TW class modular laser with multiple outputs in the visible and near-infrared wavelength range based on Optical Parametric Chirped Pulse Amplification (OPCPA) and Transient Stimulated Raman Chirped Pulse Amplification (TSRCPA). It provides 1.2 ps pulses with an energy of ~20 mJ at 1030 nm from two-stage double-pass Yb:YAG chirped pulse amplifier; ~20 fs pulses with an energy of <2 mJ at a central wavelength of 790 nm from OPCPA and 145 fs pulses with an energy of 0.6 mJ at a central wavelength of 1135 nm from TSRCPA. White light supercontinuum extending from 500 nm to 2300 nm in the YAG was used for seeding both a three-stage OPCPA based on BBO and a two-stage TSRCPA based on KGW crystals. The wide OPCPA bandwidth was maintained by the temporal shaping of pump pulses. We demonstrate the expansion of the spectrum of pulses amplified in the TSRCPA by ~10 times in comparison with the spectral bandwidth of the pump pulses. A maximum conversion efficiency of 55% was achieved in the second TSRCPA stage. The amplified pulses after compression were more than 8 times shorter than the pump pulses.
We demonstrate an alternative concept of laser wavelength conversion to the NIR – SWIR range with simultaneous multiple spectral broadening based on transient stimulated Raman chirped pulse amplification (TSRCPA) and pulse compression to fs pulsewidth for the sub-TW class lasers, with possible application in the next generation LIDARs. Transform limited pulses of a Yb:YAG laser with a duration of ~1.2 ps were used to pump a multistage TSRCPA based on KGW crystals seeded with 1100 – 2500 nm supercontinuum. A 16-times spectral broadening was shown after TSRCPA compared to pump pulses, conversion efficiency 55%, and compression to ~145 fs. This concept, extended for gases and diamond with larger Stokes shifts, allows further exploration of SWIR range, especially for the 2nd Stokes.
The ability to identify explosives by ultrasonic spectra up to 45 kHz has been investigated for forensic and anti-terror applications. To lower the threshold for laser initiation, nontrivial and well-known azides, CTAP, HMDT, ETN, HMX and other energetic materials have been synthesized. Upon initiation of copper azide by Nd:YAG laser with 11 ns pulsewidth, a threshold of only ~80 μJ was reached, and for 50 μs pulses of laser diode it was ~300 μJ, which is consistent with the thermal initiation nature. Significant differences were found in the spectrum of high-frequency acoustic and ultrasonic vibrations for various energetic materials and bilayer structures. The effective frequency range for the dissociation of copper azide, silver azide and HMTD is limited by ~27 kHz. The spectra of bilayer structures demonstrate suppression of the characteristic lines of copper azide and enrich the spectrum in the ~27 – 45 kHz range: ETN appears in relatively wide bands, while HMX modulates the spectrum with periodic ~3 kHz bands. If successful, the discovered patterns can be used in disaster forensics.
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