I have performed an experiment to frequency mix 974 nm LD laser and a C-band ASE laser source in a single period (10.2 um) MgO:PPLN. I however noticed five peaks at 487, 536, 598, 756, and 816 nm wavelengths detected with a fiber spectrometer. Whilst the 487 and 598 nm outputs could be second-order SHG of 974 nm and SFG (974 nm+~1550 nm), respectively, I can't account for the remaining outputs (536, 756, and 816 nm). Can someone kindly shed some light on what processes are likely involved here?. Please see the attached file for the experimental set up and output spectra at two different temperatures.
Hi!
I'm not sure but it looks like the stimulated Raman scattering I happened to observe a few years back in MgO:PPSLT. I attach the corresponding paper. You can also check the references 6, 7 and 8 cited in this paper that report similar observations in PPLN, with thich you can compare the frequency shifts you observed.
What peaks do you observe if only ASE source or only 974nm LD is coupled to PPLN?
Dear Dismas,
LN is Raman as well as infrared active. You are getting such additional peaks as a result of polariton scattering. Please check its dispersion relation and match the shifts between peaks with the Raman modes with the help of following paper
A. Barker and R. Loudon, “Dielectric Properties and Optical Phonons in LiNbO3,” Physical Review, vol. 158, no. 2, pp. 433–445, 1967.
@ Alexey Gladyshev , with only ASE source, no peaks are observed. 974nm LD gives the other peaks except 598 nm which appears when both sources are on.
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