Multifrequency parametric infrared Raman generation in KGd(WO(4))(2) crystal with biharmonic ultrashort-pulse pumping

Highly transient stimulated Raman scattering in SrMoO4 under ultrafast laser pumping with a controllable chirp

For the first time, to the best of our knowledge, we demonstrate highly transient, multiwavelength, single-pass Raman generation with combined frequency shifts on two Raman modes of an SrMoO4 crystal with high total Raman conversion efficiency of up to 48% in conditions of competition with self-phase modulation (SPM). A 58-mm-long SrMoO4 crystal was used as the active medium under pumping by the 1030-nm, 40-µJ laser pulses with controllable dispersive stretching in a range of 0.25-6 ps at negative and positive chirping. The pump pulse chirping was optimized for both high- and low-frequency Raman shifts on the primary (888 cm-1) and secondary (327 cm-1) Raman modes of the crystal. At the optimal conditions, four Stokes components of stimulated Raman scattering (SRS) radiation with high- and low-frequency Raman shifts at the wavelengths of 1066, 1134, 1177, and 1261 nm were efficiently generated.

Two-stage transient stimulated Raman chirped-pulse amplification in KGd(WO4)2 with compression to 145 fs

We report efficient amplification of chirped supercontinuum pulses in a two-stage stimulated Raman amplifier based on double tungstate [KGd(WO₄)₂] crystals, pumped with 1.2 ps transform-limited pulses at a 1030 nm wavelength. The second stage demonstrates a conversion efficiency of 55% with an output pulse energy of 0.6 mJ at a 1135 nm wavelength. The amplified Stokes bandwidth is 10 times the pump bandwidth, providing 145 fs pulses after compression.

Femtosecond Raman frequency shifter-pulse compressor

The conversion to the first Stokes component at a wavelength of 1.8 μm of ytterbium laser radiation with a pulse duration of 270 fs by stimulated Raman scattering (SRS) in hydrogen was carried out by using double-pulse pumping scheme. Simultaneously with SRS the process of nonlinear phase modulation of laser and Stokes waves was observed. The spectrally broadened chirped Stokes pulse was compressed to 35 fs in fused silica optical elements at the output of a Raman cell.

Diamond Raman laser with continuously tunable output from 3.38 to 3.80 μm

We report a pulsed mid-infrared diamond Raman laser with output tuned from 3.38 to 3.80 μm through varying the optical parametric oscillator (OPO) pump wavelength. To our knowledge this is the longest reported wavelength from a solid-state Raman laser. We generated up to 80 μJ with good beam quality and 22% quantum conversion efficiency. Whilst the conversion process itself is efficient, approximately 40% of the generated Stokes light is lost to multiphonon absorption. By introducing a secondary pump beam at the anti-Stokes wavelength to initiate a seed at the Stokes wavelength through Raman resonant four-wave mixing, the laser threshold was reduced by approximately half, and the maximum output increased by 44% to 115 μJ.

Efficient Raman shifting of high-energy picosecond pulses into the eye-safe 1.5-microm spectral region by use of a KGd(WO4)2 crystal

We report an efficient transient stimulated Raman conversion of high-energy picosecond pulses at 1350 nm into the eye-safe 1500-nm wavelength range by use of a KGd(WO4)2 crystal. The conversion efficiency into either 1503- or 1537-nm radiation (767- or 901-cm(-1) Raman modes, respectively) is measured to be approximately 10% in a single-pass configuration. The transient Raman gain coefficient is found to be approximately 0.8 cm/GW. Simultaneous generation of multiple Raman lines is also observed.

Coherent two-photon absorption spectroscopy of the Raman-active KGd(WO4)2 crystal

We report on the systematic open-aperture Z-scan characterization of the two-photon absorption properties in one of the most efficient solid-state Raman frequency shifters, the crystal potassium gadolinium tungstate [KGd(WO4)2]. The two-photon absorption coefficient was determined in the 370-600-nm wavelength range, with the highest value found to be approximately 1.9 cm/GW at 370 nm. Nonlinear losses are crucial in determining the conversion efficiency of the stimulated Raman scattering process when it is excited with ultrashort laser pulses with photon energy exceeding half of the bandgap. In addition, the results were analyzed within the context of a simple two-parabolic-band theoretical model to yield an effective bandgap energy value for the crystal.