Investigation of the pulse characteristics of an injection seeded diamond Raman amplifier

Raman amplification is a highly efficient means by which amplification of laser radiation and beam clean-up can be achieved. Although this process has been described in the literature, little attention has been given to the investigation of pulse characteristics of the laser fields involved in the process. In this work, we analyze the evolution of the fundamental and Stokes fields involved in the Raman amplification process, with a focus on Stokes extraction efficiency within a diamond Raman amplifier. This work offers insight into the means by which the Raman amplification process can be optimized/maximized for a given set of laser fields. Experimental observations show that depletion of the fundamental field occurs during the amplification process, causing an initially Gaussian pulse shape to become increasingly concave. The rate at which the pulse peak diminishes and the overall shape becomes concave is correlated with the rate of amplification of the Stokes field pulse intensity. This experimental observation is supported by theoretical modeling using rate equations wherein Raman amplification under different initial conditions is numerically simulated, and the energy extraction efficiency and pulse shapes under different intensities are analyzed. Experimentally, the amplified laser output of the Stokes field from this system is 4.2 mJ (equivalent to a peak power of up to 37.5 kW), and an amplification efficiency of 18% is achieved.