Pulsed Multi-Color Laser Using Nonlinear Fiber Optics

We demonstrate how polarization and intensity of the pump laser impact the multi-color laser output from an optical fiber. The pulsed laser source is a Q-switched Nd:YAG microchip laser. The 1064 nm laser pulses are frequency doubled in a KTP crystal to produce 532 nm laser pulses. The 532 nm pulses pass through a half-wave plate before entering the tip of a single-mode, polarization-maintaining optical fiber. The multi- color output wavelengths are measured using a spectrometer. The angle of the waveplate is adjusted to explore the impact of polarization on the output. Additionally, the output is measured both when the pump laser is at full power and when it passes through an ND 03 filter before entering the optical fiber to explore the impact of pump laser intensity on the output. In Stimulated Raman Scattering (SRS), a sufficiently intense laser pulse will nonlinearly interact with the optical fiber's glass structure, causing internal vibrations and producing some downshifted optical frequencies (Stokes lines) and some upshifted optical frequencies (anti-Stokes lines). Additionally, four wave mixing (FWM) occurs in the optical fiber, where photons in phase-matched frequencies produce new frequencies, following conservation of energy and momentum. These two nonlinear processes - SRS and FWM - occur within the optical fiber and transform a single-frequency pump laser into a multi- color output laser.