Single longitudinal mode (SLM) operation of a 620 nm diamond Raman laser is demonstrated in a standing-wave cavity that includes a second-harmonic generation element. Mode competition provided by the harmonic mixing is shown to greatly increase mode stability, in addition to the benefits of the spatial-hole-burning-free gain medium. Using a multi-longitudinal mode 1064 nm Nd:YAG pump laser of power 321 W and linewidth 3.3 GHz, SLM powers of 38 W at 620 nm and 11.8 W at 1240 nm were obtained. The results indicate that simple standing-wave oscillators pumped by multimode Yb or Nd pumps compose a promising practical route towards the generation of high-power SLM beams in the yellow–red part of the spectrum.

Laser guide stars based on the mesospheric sodium layer are becoming increasingly important for applications that require correction of atmospheric scintillation effects. Despite several laser approaches being investigated to date, there remains great interest in developing lasers with the necessary power and spectral characteristics needed for brighter single or multiple guide stars. Here we propose and demonstrate a novel, to the best of our knowledge, approach based on a diamond Raman laser with intracavity Type I second-harmonic generation pumped using a 1018.4 nm fiber laser. A first demonstration with output power of 22 W at 589 nm was obtained at 18.6% efficiency from the laser diode. The laser operates in a single longitudinal mode (SLM) with a measured linewidth of less than 8.5 MHz. The SLM operation is a result of the strong mode competition arising from the combination of a spatial-hole-burning-free gain mechanism in the diamond and the role of sum frequency mixing in the harmonic crystal. Continuous tuning through the Na D line resonance is achieved by cavity length control, and broader tuning is obtained via the tuning of the pump wavelength. We show that the concept is well suited to achieve much higher power and for temporal formats of interest for advanced concepts such as time-gating and Larmor frequency enhancement.

We report a diamond Raman laser that is continuously-tunable across the range from 590 nm to 625 nm producing continuous wave output with up to 8 W. The system is based on an all-fiber and tunable (1020–1072 nm) Yb-doped pump laser with a spectral linewidth of 25 GHz that is Raman-shifted and frequency doubled in a cavity containing diamond and a lithium triborate second harmonic crystal. Despite the broad pump spectrum, single frequency output is obtained across the tuning range 590–615 nm. The results reveal a practical approach to obtain tunable high-power single-frequency laser in a wavelength region not well served by other laser technologies.

589 nm lasers pulsed at Larmor frequency, several hundreds of kilohertz, can increase the brightness of a sodium guide star and are required in remote magnetometry with mesospheric sodium. By amplification of a continuous-wave single-frequency 1178 nm laser in a pulse-pumped Raman fiber amplifier and frequency doubling in an external cavity, high-power pulsed 589 nm laser at Larmor frequency is obtained for the first time, to the best of our knowledge. The pulse format is mainly determined by the 1120 nm Raman pump laser, whose pulse repetition rate and duty cycle are adjustable. Active pulse shaping is applied to minimize the relaxation spike at the leading edge of the pulses. A reduction in pulse width and conversion efficiency from 1120 to 1178 nm is observed in the backwardly pumped Raman fiber amplifier due to the pump pulse transition effect. A 589 nm laser pulsed at a 350 kHz repetition rate and 20% duty cycle with average power up to 17 W is demonstrated as an operation example intended for a geomagnetic field of 0.5 G.

We report on the design and operation of a laser, which outputs wavelengths in the 1.2 and 1.5 μm ranges by leveraging two non-linear processes of stimulated Raman scattering and stimulated Brillouin scattering in diamond. By precisely controlling characteristics of the laser resonator formed around the diamond crystal, we are able to selectively control the onset of each non-linear process so as to tailor laser output characteristics both in way of wavelength and output power. This work demonstrates the high degree of flexibility and power-handling capacity of diamond for wavelength conversion of common laser wavelengths (such as 1064 nm as used in this work) and the generation of a span of discrete wavelengths (with up to eight cascaded orders being demonstrated in this work).

Despite their extremely high thermal conductivity and low thermal expansion coefficients, thermal effects in diamond are still observed in high-power diamond Raman lasers, which proposes a challenge to their power scaling. Here, the dynamics of temperature gradient and stress distribution in the diamond are numerically simulated under different pump conditions. With a pump radius of 100 μm and an absorption power of up to 200 W (corresponding to the output power in kilowatt level), the establishment period of thermal steady-state in a millimeter diamond is only 50 μs, with the overall thermal-induced deformation of the diamond being less than 2.5 μm. The relationship between the deformation of diamond and the stability of the Raman cavity is also studied. These results provide a method to better optimize the diamond Raman laser performance at output powers up to kilowatt-level.