High average power generation in barium nitrate Raman laser

Thermal aberrations and high power frequency conversion in a barium nitrate Raman laser

“…The same holds for higher-order Stokes generation where heat is dissipated at each stage during the cascaded process of the frequency conversion. For instance, thermally induced refractive index changes acting as a negative lens with focal lengths shorter than 15 cm were observed at the third-order Stokes generation in a barium nitrate (BN) Raman laser at a pump power of 40 W [13]. This effect was found to be responsible for a decrease of its output power by a factor of more than 20.…”

“…The output to the first order was about twice that as in Ref. [13]. Enhancing of the first Stokes output power was provided by decreasing the intracavity losses when the compensating lens inside the Raman cavity was replaced by a concave input mirror.…”

“…Inserting of additional positive lenses into the cavity was demonstrated in Ref. [13] where both an improvement of the beam quality and an increase of the output power of the generated beam were obtained.…”

“…The temperature growth causes deviation of the Raman shift, broadening of the Stokes generation band, and, in turn, a decrease of the Raman gain coefficient [12]. Moreover, the induced temperature gradient is responsible for optical distortions which are important to be taken into account when Stokes generation is developed in the cavity of a Raman laser [9,13] or in a laser system with intracavity Raman conversion [14]. Here, the thermooptical distortions affect the stability of the cavity, change the mode structure of the generated radiation, and can result in drastic decrease of the output pulse energy [9].…”

“…For conditions similar as in Ref. [13], we monitor the dynamics of the thermal distortions. Using the beam propagation and heat conduction numerical algorithms, we reconstruct the steady-state phase profile of the probe beam as well as the temperature profile inside the Raman crystal.…”