We demonstrate continuous-wave (cw) operation of a diamond Raman laser at 1240 nm in an external cavity configuration. The output power increased linearly with pump power with a 49.7% slope efficiency and reached 10.1 W at the maximum available pump power of 31 W. The combination of resonator design with diamond provides a novel approach to power-scalable cw wavelength and beam conversion.

We report high-power frequency conversion of a Yb-doped fiber laser using a double-pass pumped external-cavity diamond Raman oscillator. Pumping with circular polarization is shown to be efficient while facilitating high-power optical isolation between the pump and Raman laser. We achieved continuous-wave average power of 154W with a conversion efficiency of 50.5% limited by backward-amplified light in the fiber laser. In order to prove further scalability, we achieved a maximum steady-state Raman-shifted output of 381W with 61% conversion efficiency and excellent beam quality using 10ms pump pulses, approximately a thousand times longer than the transient thermal time-constant. No power saturation or degradation in beam quality is observed. The results challenge the present understanding of heat deposition in Raman crystals and foreshadow prospects for reduced thermal effects in diamond than originally anticipated. We also report the first experimental evidence for stimulated Brillouin scattering in diamond. Diamond is used for Raman beam conversion of a 700 W Yb fiber laser, achieving record conversion efficiency (>60%) and output power (380 W). High beam quality and efficient conversion at high powers-in stark contrast to predictions for the thermal lens and cavity stability-challenge the current understanding of heat deposition in diamond Raman lasers. Experimental evidence for stimulated Brillouin scattering in diamond is reported

Laser gain materials possessing high thermal conductivity and robust mechanical properties are key prerequisites for high power lasers. We show that diamond, when configured as a Raman laser, enables access to these and other extreme properties, providing an important new route to high power and high brightness beam generation. Recent achievements in pulsed and continuous wave oscillators, beam combining amplifiers, and single longitudinal mode oscillators are summarized, along with wavelength extension of these concepts through adaption to other pumps, use of Raman cascading, and intracavity harmonic generation. To date, diamond laser powers have attained 750 W with efficiency and beam quality so far unperturbed by nonlinear or thermally induced side-effects. Large factor brightness enhancement of low coherence inputs is demonstrated using multiple pump beams (via Raman beam combination) or highly multimode pumps for oscillator and amplifier configurations. Future directions for direct diode pumping, and for realizing extraordinary power and power density through reduced temperature operation and isotopically enriched diamond, are also discussed. Our results indicate that diamond is emerging as a generic high-power laser technology with advantages in terms of brightness (high average power and high beam quality) and wavelength range.

Quasi-cw pumping is used to investigate the high-power characteristics of cw beam conversion in diamond Raman lasers (DRLs). We show that thermal gradients establish in DRLs at approximately 50 μs for a 100 μm pump beam diameter, and thus that the steady state for cw operation can be reached within the 100-300 μs pulse duration of conventional quasi-cw pump laser technology. Using this approach, a steady-state on-time output power of 108 W was obtained from an external-cavity DRL during 250 μs pulses with 34% conversion efficiency. No thermal lens in the diamond was evident, showing excellent prospects for further power scaling.

Brightness enhancement in an external cavity diamond Raman laser designed for high power conversion of a neodymium (1064 nm) laser to the eye‐safe spectral region is reported. Using a multimode input beam pulsed at 36 kHz pulse repetition frequency, 16.2 W with 40% overall conversion efficiency was obtained at the second Stokes wavelength of 1485 nm. The output beam had a quality factor of M2=1.17±0.08 which is a factor of 2.7 times lower than that of the input beam, resulting in a higher overall brightness. The output power, brightness, and brightness enhancement obtained represent significant advances in performance for Raman lasers as well as other competing kHz‐pulsed eye‐safe technologies.