Helen M. Pask

The design and operation of solid-state Raman lasers

Solid-state Raman lasers are a practical and efficient class of laser systems which can substantially increase the spectral coverage of solid-state lasers. In this review, the theory of stimulated Raman scattering is presented in the context of understanding the design and operation of solid-state Raman lasers. The key design issues are discussed in relation to achieving efficient frequency conversion for various types of experimental configurations. Particular emphasis is placed on the effects of the thermal loading which occurs in Raman-active crystals. An overview is given of the performance characteristics of many of the devices reported to date, while selected experimental systems are reviewed in greater depth.

Crystalline Raman Lasers

In this paper, we review the developments of crystalline Raman lasers over the past five years. Average powers exceeding 5 W and pulse energies above 1 J in the near infrared have been demonstrated for larger scale devices. There has been a rapid development of all-solid-state sources based on the standard diode-pumped lasers, especially intracavity crystalline Raman lasers, which offer wavelength versatility at high conversion efficiencies (overall diode Stokes optical conversion efficiencies up to 17%) in the near infrared, including the 1.5- mum eye-safe band. Passively Q-switched intracavity Raman lasers based on self-Raman laser materials offer many advantages for miniaturization of short-pulse (1 ns) sources. Intracavity frequency-doubled crystalline Raman lasers have also emerged as practical and versatile sources in the yellow orange region at 1-W power levels with diode-visible efficiencies near 10%. Recent developments of all-solid-state continuous-wave (CW) intracavity crystalline Raman lasers offer many possibilities for the future: intracavity frequency doubling has already resulted in the demonstration of CW visible sources with powers approaching 1 W at 5% diode-visible efficiency.

Continuous-wave, intracavity doubled, self-Raman laser operation in Nd:GdVO(4) at 586.5 nm.

We report a continuous-wave self-Raman laser based on diode-pumped Nd:GdVO(4) giving first-Stokes output at 1173 nm and intracavity frequency-doubled output at 586.5 nm. A maximum cw output power at 1173 nm of 2 W was obtained for diode pump powers of 22 W and a maximum cw power at 586 nm of 678 mW with 16.3 W pump power. Infrared and yellow powers were limited by thermal lensing in the gain medium and parasitic oscillations of weak Nd(3+) transitions. Quasi-cw operation at 50% duty-cycle reduced the thermal load in the laser/Raman crystal, allowing cavity stability to be obtained near maximum available pump power (25.7 W) for which the maximum quasi-cw yellow output power was 1.88 W.

High efficiency, multi-Watt CW yellow emission from an intracavity-doubled self-Raman laser using Nd:GdVO4

Efficient multi-Watt continuous-wave (CW) yellow emission at 586.5 nm is demonstrated through intracavity frequency-doubling of a Nd:GdVO(4) self-Raman laser pumped at 880 nm. 2.51 W of CW yellow emission with an overall diode-to-yellow conversion efficiency of 12.2% is achieved through the use of a 20 mm long Nd:GdVO(4) self-Raman crystal and an intracavity mirror which facilitates collection of yellow emission generated within the resonator, and reduces thermal loading of the laser crystal.

Continuous-wave, all-solid-state, intracavity Raman laser

Continuous-wave operation of a diode-pumped solid-state Raman laser at 1176 nm is reported. The intracavity Raman laser, based on a Nd:YAG laser crystal and a KGd(WO4)2 Raman crystal, reached threshold for 4 W of diode input power and gave up to 800 mW of output power at an overall conversion efficiency of 4%.

Efficient, all-solid-state, Raman laser in the yellow, orange and red

We report efficient operation of a KGd(WO(4))(2) Raman laser pumped by a small, 1 W, 532 nm laser module. By changing the output coupler and Raman crystal orientation, more than 8 wavelengths in the yellow-to-red spectral region were generated including 555 nm, 559 nm, 579 nm, 589 nm, 606 nm, 622 nm, 636 nm and 658 nm, ie., the first 4 Stokes orders on the two orthogonal high-gain Raman shifts of KGd(WO(4))(2). We have also demonstrated spectrally pure output (typically >90% pure) for selected Stokes order with output power up to 400 mW. High slope efficiency (up to 68%) and high beam quality (M(2)~1.5) of Stokes output are obtained even at the highest pump power.

Heat generation in Nd:YVO 4 with and without laser action

We present quantitative interferometric measurements of thermal lensing in a diode-pumped Nd:YVO/sub 4/ crystal with and without laser action. The thermal loading increased by two times when laser action was inhibited. The thermal loading was strongly dependent on upper laser-level loss mechanisms (e.g. nonradiative decay, quenching, and Auger recombination).

Efficient all-solid-state yellow laser source producing 1.2-W average power

We report a practical and efficient all-solid-state laser source operating at 578 nm. The source comprises a diode-pumped Nd:YAG laser gain medium producing fundamental output at 1064 nm, an intracavity LiIO (3) Raman-active crystal that generates first-Stokes output at 1155 nm, and an intracavity LiB(3)O(5) frequency-doubling crystal, which frequency doubles the first-Stokes output to 578 nm. Q -switched output with as much as 1.2-W average power has been obtained; conversion efficiencies from the fundamental to the yellow as high as 33% have been obtained.

An intracavity, frequency-doubled BaWO 4 Raman laser generating multi-watt continuous-wave, yellow emission

We report the generation of multi-watt continuous-wave (CW) yellow laser emission from an intracavity diode-pumped Nd:GdVO(4) /BaWO(4) Raman laser utilising a high-Q resonator (for fundamental and first-Stokes wavelengths) and intracavity frequency-doubling in LBO. CW output power of 2.9 W is achieved with a high overall diode-to-yellow conversion efficiency of 11% and with good beam quality (M(2) approximately 2.5).

Efficient 5.3 W cw laser at 559 nm by intracavity frequency summation of fundamental and first-Stokes wavelengths in a self-Raman Nd:GdVO4 laser.

We report the generation of 5.3 W cw laser emission at 559 nm by sum-frequency mixing of the fundamental and first-Stokes fields generated within an Nd:GdVO(4) self-Raman laser. A high overall diode-to-visible conversion efficiency of 21% is demonstrated. We discuss the balance that must be maintained between the two nonlinear processes of Raman generation and sum-frequency mixing in order to obtain maximum emission at 559 nm.