New mid IR (1.5–2.2 μm) Raman lasers based on barium tungstate and barium nitrate crystals

Abstract

Efficient mid IR (1.5-2.2 µm) Raman lasers based on novel BaWO 4 and known Ba(NO 3 ) 2 Raman crystals were developed and investigated. Different Stokes shifted components were obtained with longest wavelength about 2.2 µm with efficiency up to 10%. Main informationNowadays great attention is paid to the development of novel lasers oscillating in mid IR spectral range (2-5 µm) where the lack of laser sources (especially within 3-5 µm range) is quite noticeable. There are several approaches towards development of laser sources for mid IR spectral region: development of new solid state laser media, molecular gas lasers, OPO generators etc. One of the promising approaches is Raman shifting of the available laser sources towards mid IR range. The main problem here is that most of the Raman crystals' frequency shift is about 1000 cm −1 , so to obtain mid IR radiation one should start from as long wavelength as possible and obtain second or even third Stokes shifted components. At the same time it should be kept in mind that Raman gain drops rapidly with longer wavelength pump, so that stimulated Raman scattering threshold intensities become separated from the crystal optical damage threshold intensities by rather narrow interval making Raman lasing a sort of challenge. Another problem for mid IR Raman lasing is that a lot of well known efficient Raman crystals are opaque in this spectral range due to the matrix absorption.The newly developed barium tungstate crystals are proved to be efficient source for both picosecond and nanosecond time scale Raman lasing [1]. Our results on stimulated Raman scattering under nanosecond IR pumping in comparison with the well-known barium nitrate crystal showed rather close thresholds and conversion efficiency. Though BaWO 4 crystals are much further transparent and allows obtaining Raman shifted radiation up to 3 µm.As the initial pump source the 1.34 µm YAG:Nd 3+ laser and 1.53 µm Er:Glass laser were applied. These lasers were selected due to their longest lasing wavelengths where short Q-switched pulses can be rather reliably obtained. In our experiments accousto-optically Qswitching for Nd:YAG laser and passive Q-switching by Co 2+ :spinel crystal for Er:Glass laser were applied which allowed to obtain pulses with 40-50 ns duration in both cases. This lasers served as pump sources for 80 mm long BaWO 4 crystal or 50 mm long Ba(NO 3 ) 2 crystal based Raman lasers with the cavity formed by a rear plain HR mirror with 90-100% reflectivity within oscillating spectral range and about 80% transmittance at pumping wavelengths. To optimize first, second or third Stokes

Stimulated Raman scattering in mid IR spectral range 2.31–2.75–3.7 μm in BaWO4 crystal under 1.9 and 1.56 μm pumping

“…Using SRS lasers based on these crystals with single-stage (∆ν=925 cm −1 ), two-, and three-stage SRS conversion schemes, we have already demonstrated shifting of laser radiation from the spectral range 1-1.5 µm to the mid IR region 1.5-2.3 µm [2,10,11]. However, the optical transparency spectrum of these crystals lasts up to 5 µm, which promises the possibility of advancing further in the mid IR spectral region [6].…”

High-peak power multi-wavelength picosecond pulses generated from a BaWO4 Raman-seeded optical parametric amplifier

“…Chen et al reported an actively Q-switched Nd:YAG/BaWO 4 Raman laser with average output power and pulse duration of 1.56 W and 24 ns at the same wavelength [10]. Basiev et al reported a $50-ns, 1.34-lm acoustic-optically Q-switched Nd:YAG/ BaWO 4 Raman laser with output energy of 6 mJ for the first-Stokes [11]. The maximum peak power of the above-mentioned Raman laser pulses were at the level of kW.…”

“…Generally speaking, SRS in solid-state crystals has a possibility of designing all-solid-state lasers emitting radiation in specified spectral regions [5,6]. Recently, BaWO 4 crystal is known to have the characteristics of becoming a promising solidstate Raman crystal due to its advantages of thermal and mechanical properties, narrow line width of the vibrational modes, and especially high concentration of active Raman centers [5,[7][8][9][10][11][12][13][14]. Much attention has been paid on Q-switched BaWO 4 Raman laser output.…”

Widely tunable continuous wave mid-IR DFG source based on fiber lasers and amplifiers

“…Several laser sources, such as lead-salt diode laser, quantum cascade laser [3], colorcenter laser, Raman lasers [4,5] and optical parametric oscillator (OPO) [6,7], can emit CW laser radiations in the mid-infrared region. However, all these sources have their own issues when they are put into practical applications.…”