Observation of visible light flashes in high power, near infrared, narrow-linewidth fiber lasers and its potential use as a visual monitor for stimulated Brillouin scattering

Vishal Choudhury; Santosh Aparanji; Roopa Prakash; V. Balaswamy; V. R. Supradeepa

doi:10.1117/12.2510276

4 March 2019 Observation of visible light flashes in high power, near infrared, narrow-linewidth fiber lasers and its potential use as a visual monitor for stimulated Brillouin scattering

Vishal Choudhury, Santosh Aparanji, Roopa Prakash, V. Balaswamy, V. R. Supradeepa

Author Affiliations +

Proceedings Volume 10903, Real-time Measurements, Rogue Phenomena, and Single-Shot Applications IV; 109030K (2019) https://doi.org/10.1117/12.2510276
Event: SPIE LASE, 2019, San Francisco, California, United States

Abstract

We report the surprising observation of yellow to red visible light flashes in the splice point connecting the seed stage to the power amplifier in a high power, narrow-linewidth, polarisation-maintaining Ytterbium doped fiber laser. The multistage laser delivers upto 500W of power with a tuneable linewidth between 2.88 GHz to 9.88 GHz at 1064 nm. For different linewidths, the visible flashes were observed at different power levels of the laser. We observed a strong correlation between these flashes to the appearance of backward pulses with the onset of Stimulated Brillouin Scattering (SBS). We identify the cause for the flashes to be a two part phenomena. Beyond a threshold level, SBS results in the formation of high peak power pulses. These pulses undergo cascaded Raman scattering into higher order stoke wavelengths. These higher order pulses are unaffected by the isolator separating the amplifier stages and moves back into the seed stage with lower effective area, higher NA fibers. We recently demonstrated that 2nd and 3rd harmonic generation can occur in high NA, low effective area fibers assisted by Cherenkov-type phase matching between core light in the NIR and cladding light in the visible. Through processing of the images of the flash acquired with high resolution, we identified the wavelengths to be a mixture of the second harmonic components of the 2nd and 3rd order Raman Stokes of the 1064 nm laser wavelength (1175nm/588nm and 1240nm/620nm). We anticipate the use of these flashes as a potential monitor for the onset of SBS.

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Vishal Choudhury, Santosh Aparanji, Roopa Prakash, V. Balaswamy, and V. R. Supradeepa "Observation of visible light flashes in high power, near infrared, narrow-linewidth fiber lasers and its potential use as a visual monitor for stimulated Brillouin scattering", Proc. SPIE 10903, Real-time Measurements, Rogue Phenomena, and Single-Shot Applications IV, 109030K (4 March 2019); https://doi.org/10.1117/12.2510276

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