100 kW peak power external cavity diamond Raman laser at 2.52 µm.

We report an external cavity diamond Raman laser operating at 2.52 µm, pumped by a 1.89 µm Tm:LiYF4 (YLF) laser. The maximum pulse energy at 2.52 µm is 1.67 mJ for 4.4 mJ of pump, yielding a conversion efficiency of 38%. The best slope efficiency is ~60% and the Raman pulse duration is between 11 and 15 ns for ~33 ns pump pulse duration. The peak power at 2.52 µm is >100 kW. This demonstration of a Thulium laser pumped diamond Raman laser paves the way for accessing the industrially important wavelength region of ~2.5 µm.

Ultrafast diode-pumped Ti:sapphire laser with broad tunability.

We report a broadly wavelength-tunable femtosecond diode-pumped Ti:sapphire laser, passively mode-locked using both semiconductor saturable absorber mirror (SESAM) and Kerr-lens mode-locking (KLM) techniques. Using two pump laser diodes (operating at 450 nm), an average output power as high as 433 mW is generated during mode-locking with the SESAM. A tunability range of 37 nm (788-825 nm) was achieved with the shortest pulse duration of 62 fs at 812 nm. In the KLM regime, an average output power as high as 382 mW, pulses as short as 54 fs, and a tunability of 120 nm (755-875 nm) are demonstrated.

1.4 µm continuous-wave diamond Raman laser.

The longest wavelength (~1.4 µm) emitted by a diamond Raman laser pumped by a semiconductor disk laser (SDL) is reported. The output power of the intracavity-pumped Raman laser reached a maximum of 2.3 W with an optical conversion efficiency of 3.4% with respect to the absorbed diode pump power. Narrow Stokes emission (FWHM <0.1 nm) was attained using etalons to limit the fundamental spectrum to a single etalon peak. Tuning of the Raman laser over >40 nm was achieved via rotation of an intracavity birefringent filter that tuned the SDL oscillation wavelength.

Intracavity Raman conversion of a red semiconductor disk laser using diamond.

We demonstrate a diamond Raman laser intracavity-pumped by a red semiconductor disk laser (~675 nm) for laser emission at around 740 nm. Output power up to 82 mW of the Stokes-shifted field was achieved, limited by the available pump power, with an output coupling of 1.5%. We also report wavelength tuning of the diamond Raman laser over 736 - 750 nm.

Monolithic diamond Raman laser.

A monolithic diamond Raman laser is reported. It utilizes a 13-mm radius of curvature lens etched onto the diamond surface and dielectric mirror coatings to form a stable resonator. The performance is compared to that of a monolithic diamond Raman laser operating in a plane-plane cavity. On pumping with a compact Q-switched laser at 532 nm (16 µJ pulse energy; 1.5 ns pulse duration; 10 kHz repetition-rate; M2<1.5), laser action was observed at the first, second, and third Stokes wavelengths (573 nm, 620 nm and 676 nm, respectively) in both cases. For the microlens cavity, a conversion efficiency of 84% was achieved from the pump to the total Raman output power, with a slope efficiency of 88%. This compares to a conversion efficiency of 59% and a slope efficiency of 74% for the plane-plane case. Total Raman output powers of 134 and 96 mW were achieved for the microlens and plane-plane cavities, respectively.

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.

Power scaling of a directly diode-laser-pumped Ti:sapphire laser.

Improvements in the output power of a directly GaN diode-laser-pumped Ti:Al2O3 laser are achieved by using double-sided pumping. In continuous wave operation, an output power of 159 mW is reported. A tuning range of over 125 nm with output powers in excess of 100 mW is achieved. Pulses of 111 fs duration and an average power of 101 mW are demonstrated by mode locking the laser with a saturable Bragg reflector. Pumping with GaN diode lasers at wavelengths around 450 nm induces an additional parasitic crystal loss of about 1% per resonator roundtrip that is not observed at the conventional green pump wavelengths.

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.

Tunable continuous-wave diamond Raman laser.

Continuous-wave operation of a diamond Raman laser, intracavity-pumped by a diode-pumped InGaAs semiconductor disk laser (SDL), is reported. The Raman laser, which utilized a 6.5-mm-long synthetic single-crystal diamond, reached threshold for 5.3 W of diode laser pump power absorbed by the SDL. Output power up to 1.3 W at the first Stokes wavelength of 1227 nm was demonstrated with excellent beam quality and optical conversion efficiency of 14.4% with respect to absorbed diode laser pump power. Broad tuning of the Raman laser output between 1217 and 1244 nm was achieved via intracavity tuning of the SDL oscillation wavelength.

Continuous-wave Raman laser pumped within a semiconductor disk laser cavity.

A KGd(WO4)2 Raman laser was pumped within the cavity of a cw diode-pumped InGaAs semiconductor disk laser (SDL). The Raman laser threshold was reached for 5.6 W of absorbed diode pump power, and output power up to 0.8 W at 1143 nm, with optical conversion efficiency of 7.5% with respect to the absorbed diode pump power, was demonstrated. Tuning the SDL resulted in tuning of the Raman laser output between 1133 and 1157 nm.

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%.

Direct diode-laser pumping of a mode-locked Ti:sapphire laser.

Direct diode-laser pumping of a mode-locked Ti:Al(2)O(3) laser is reported. A single 1 W GaN-based diode laser operating at 452 nm is used as the pump laser. Pulse durations as short as 114 fs and average output powers of up to 13 mW are obtained.

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.

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.

Directly diode-laser-pumped Ti:sapphire laser.

A directly diode-laser-pumped Ti:Al(2)O(3) laser is demonstrated. Using a 1 W, 452 nm GaN diode laser, 19 mW of cw output power is achieved in a potentially portable format. Pumping at this short wavelength induces a loss at the laser wavelength that is not seen for the more typical green pump wavelengths. This effect is characterized and discussed.

Pulsed pumping of semiconductor disk lasers.

Efficient operation of semiconductor disk lasers is demonstrated using uncooled and inexpensive 905nm high-power pulsed semiconductor pump lasers. Laser emission, with a peak power of 1.7W, is obtained from a 2.3mum semiconductor disk laser. This is seven times the power achieved under continuous pumping. Analysis of the time-dependent spectral characteristics of the laser demonstrate that significant device heating occurs over the 100-200ns duration of the pumping pulse - finite element modelling of the thermal processes is undertaken in support of these data. Spectral narrowing to below 0.8nm is obtained by using an intra-cavity birefringent filter.

Intracavity diamond heatspreaders in lasers: the effects of birefringence.

The birefringence of a number of commercially-available diamond platelets is assessed in the context of their use for intracavity thermal management in lasers. Although diamond is normally thought of as isotropic, significant birefringence is found to be present in some samples, with considerable variation from batch to batch, and in some cases across an individual sample. Nonetheless, low-loss operation is achieved in a laser cavity containing a Brewster element, either by rotating the sample or by using a diamond platelet with low birefringence.