Near- to far-infrared tunable Raman laser

The importance of stimulated Raman scattering of tunable laser beams in molecular fluids for generating powerful infrared radiation tunable from the near to the far infrared (FIR) is demonstrated. Main criteria (frequency shift, transparency, and Raman gain) leading to the choice of the best Raman medium for a given tunable laser are discussed. For the high power (400-1000 MW), monochromatic (0.02 cm
^-1
), and broadly tunable (
0.72-1.09 \mu
m) ruby pumped dye laser described here, gaseous hydrogen is chosen for the
1-10 \mu
m wavelength region yielding powers ranging from 1 to 200 MW. For mid-infrared (IR) generation (
10-18 \mu
m), one more Raman shifting in liquid nitrogen permits one to obtain up to 1.7 mJ in the 16 μm region. For longer wavelengths the use of resonantly enhanced stimulated Raman scattering in hydrogen fluoride gives rise to the generation of powerful radiation (
2 \times 10^{17}
photons per pulse of 2.5 ns duration) tunable over half of the
40-250 \mu
m spectral range.