Benefits (e.g., for two-color Particle Imaging Velocimetry Application)
conversion has been an active research field since the invention of laser.
Harmonic generators only convert laser frequencies to their harmonics.
Optical parametric oscillators (OPO’s) provide continuous tunability over
a broad range (typically from 200 nm to 3 mm). OPO has recently been revitalized
through the development of new nonlinear crystals. Stimulated Raman
scattering (SRS) can either up-shift or down-shift a single frequency
line by multiples of the vibrational or rotational energy of the medium.
Stimulated Raman scattering is, in most cases, simpler than any other
frequency conversion approach because phase matching is not required.
The approach often leads to high conversion efficiency over a wide range
of wavelengths, from the IR to the UV. A Raman shift remains constant
independent of the pump laser frequency. A Raman cell will not be damaged
even if optical breakdown occurs in the medium. The recent report on obtaining
high conversion efficiencies from some low gain Raman media will have
its impact on the application of stimulated Raman scattering.
Taitech, Inc. offers Raman cells for the following gases:
H2, D2, CH4, N2, O2, and CO2* [* Contact Taitech
for applications of gases other than those listed above.]
A typical energy-conversion efficiency to the first Stokes ranges from
a few percent to higher than 70 percent depending upon the following factors:
Laser wavelength, repetition rate, pulse width, gas or gases used, cell
pressure, focusing f number, and number of passes.
1. R. Danielius,
A. Piskarskas, and A. Stabinis, "Traveling-wave parametric generation
of widely tunable, highly coherent femtosecond light pulses," J. Opt.
Soc. Am. B, 10, (11), 2222, (1993).
2. M. Noble, "Reaching those awkward wavelengths," Lasers & Optronics,
November, 17, (1991).
3. B. Zhang, W. R. Lempert, R. B. Miles, and G. Diskin, "Efficient vibrational
Raman conversion in O2 and N2 cells by use of super-fluorescence seeding,"
Opt. Lett., 18, (14), 1132, (1993).