Ultra-compact diode-pumped single-frequency Ti:sapphire laser.

In this Letter, we report on the development of an ultra-compact single-frequency Ti:sapphire laser under direct diode pumping. Single-longitudinal-mode operation is realized from a miniature plane-parallel resonator using a volume Bragg grating as an output coupler. InGaN laser diodes operating at around 470 nm and 490 nm with a combined power of 6.7 W are used as an optical pump. A maximum output power of 700 mW is generated during single-frequency operation at 813.4 nm. A laser linewidth of 2.4 MHz is measured during free-running operation, which is reduced to about 180 kHz when the laser is locked to an external reference cavity.

Widely-tunable mid-infrared ring cavity pump-enhanced OPO and application in photo-thermal interferometric trace ethane detection.

The development of a broadly and accurately tunable single-frequency mid-infrared laser source and its application to a sensitive laser absorption detection method are described. Photo-thermal interferometric spectroscopy is employed as a phase-sensitive method to detect the minute refractive index change caused by the heating of a gas under laser radiation. A separate probe beam allows for the spectrally-interesting mid-infrared region to be examined whilst utilizing low cost, high detectivity photodetectors in the visible/near-infrared region. We also describe the implementation of a Sagnac interferometer to minimize the effects of environmental perturbation and provide inherent passive stability. A continuous-wave ring-cavity pump-enhanced OPO has been developed to provide excitation light from 3-4 µm at 140 mW with the ability to mode-hop tune continuously over 90 cm-1 in 0.07 cm-1 steps. Complementary use of both detection apparatus and excitation source has allowed for presence of ethane to be detected down to 200 parts per billion.

Spectral broadening in continuous-wave intracavity Raman lasers.

Spectral broadening of the fundamental field in intracavity Raman lasers is investigated. The mechanism for the spectral broadening is discussed and the effect is compared in two lasers using Raman crystals with different Raman linewidths. The impact of the spectral broadening on the effective Raman gain is analyzed, and the use of etalons to limit the fundamental spectral width is explored. It was found that an improvement in output power could be obtained by using etalons to limit the fundamental spectrum to a single narrow peak.

Measurement of thermal lensing in a CW BaWO4 intracavity Raman laser.

The thermal lens induced in an a-cut BaWO(4) crystal by stimulated Raman scattering is measured using lateral shearing interferometry. The strength of the lens is proportional to the Stokes output power. For light polarized parallel to the a-axis, and a Stokes mode radius of 120 µm, the lens is negative and highly astigmatic: -0.8 D W(-1) in the plane parallel to the a-axis and -7.7 D W(-1) in the plane parallel to the c-axis. The implications of this thermal lens for Raman laser design are discussed.

1.6 W continuous-wave Raman laser using low-loss synthetic diamond.

Low-birefringence (Δn<2x10(-6)), low-loss (absorption coefficient <0.006 cm(-1) at 1064 nm), single-crystal, synthetic diamond has been exploited in a CW Raman laser. The diamond Raman laser was intracavity pumped within a Nd:YVO4 laser. At the Raman laser wavelength of 1240 nm, CW output powers of 1.6 W and a slope efficiency with respect to the absorbed diode-laser pump power (at 808 nm) of ~18% were measured. In quasi-CW operation, maximum on-time output powers of 2.8 W (slope efficiency ~24%) were observed, resulting in an absorbed diode-laser pump power to the Raman laser output power conversion efficiency of 13%.

An intra-cavity Raman laser using synthetic single-crystal diamond.

Low birefringence synthetic single-crystal diamond was used as a Raman laser medium inside a Q-switched Nd:YVO(4) laser. A maximum average output power of 375 mW was achieved at a wavelength of 1240 nm and a repetition rate of 6.3 kHz. This equates to a conversion efficiency of 4% from the diode laser to the first Stokes component at 1240 nm. Optical losses within the diamond (approximately 1% per single pass) limited the performance and are currently the main barrier to the demonstration of an efficient CW diamond Raman laser.

Continuous-wave diamond Raman laser.

Continuous-wave operation of a diamond Raman laser is demonstrated. Low-birefringence synthetic single-crystal diamond is used and is intracavity pumped by a Nd:YVO(4) laser. A cw output power of 200 mW is achieved at the Raman wavelength (1240 nm), and 1.6 W of on-time output power is obtained in quasi-cw mode. Losses in the diamond (approximately 1% per pass) and thermal effects in the Nd:YVO(4) limit the efficiency.