Jennifer E. Hastie

High power CW red VECSEL with linearly polarized TEM00 output beam

High-power, continuous-wave operation at red wavelengths has been achieved with a vertical external cavity surface emitting laser based on the GaInP/AlGaInP/GaAs material system. Output power of 0.4W was obtained in a linearly polarized, circularly symmetric, diffraction-limited beam. A birefringent filter inserted in the cavity allowed tuning of the laser output spectrum over a 10nm range around 674nm.

0.5-W single transverse-mode operation of an 850-nm diode-pumped surface-emitting semiconductor laser

We report the power scaling of a diode-pumped GaAs-based 850-nm vertical external-cavity surface-emitting laser, by use of an intracavity silicon carbide (SiC) heatspreader optically contacted to the semiconductor surface. To our knowledge, this is the first demonstration of bonding of SiC to a III-V semiconductor structure using the technique of liquid capillarity. High output power of >0.5 W in a circularly symmetric, TEM/sub 00/ output beam has been achieved with a spectral shift of only 0.6 nm/W of pump power. No thermal rollover was evident up to the highest pump power available, implying significant further output-power scaling potential using this approach.

Thermal management in vertical-external-cavity surface-emitting lasers: finite-element analysis of a heatspreader approach

The use of crystalline heatspreaders to improve thermal management in optically pumped vertical-external-cavity surface-emitting lasers is studied via finite-element analysis. The required properties of a heatspreader are examined and the effect on heat flow is discussed, as are thermal lensing effects. The advantages of diamond heatspreaders are highlighted. The power-scaling potential is compared to other approaches. Heatspreaders are found to be promising, particularly for use with low thermal conductivity semiconductors.

Tunable ultraviolet output from an intracavity frequency-doubled red vertical-external-cavity surface-emitting laser

An optically pumped red vertical-external-cavity surface-emitting laser with an AlInGaP gain region produced more than 1W of continuous-wave output power at a wavelength of 675nm. Frequency doubling in a beta-barium borate crystal placed at an intracavity beam waist generated 120mW of total output power at 338nm. Using an intracavity birefringent filter a second harmonic tuning range of ∼5nm was achieved.

Characterization of Single-Crystal Synthetic Diamond for Multi-Watt Continuous-Wave Raman Lasers

A continuous-wave diamond Raman laser is demonstrated with an output power of 5.1 W at 1217 nm. This Raman laser is intracavity pumped by a side-pumped Nd:YLF rod laser: a 43-fold brightness enhancement between the Nd:YLF and diamond Raman lasers is observed, with the M2 beam propagation factor of the diamond Raman laser measured to be <; 1.2. Although higher output powers are demonstrated in a similar configuration using KGd(WO4)2 (KGW) as the Raman laser material (6.1 W), the brightness enhancement is much lower (2.5 fold) due to the poorer beam quality of the KGW Raman laser (M2 <; 6). The Raman gain coefficient of single-crystal synthetic diamond at a pump wavelength of 1064-nm is also measured: a maximum value of 21±2 cm/GW is returned compared to 5.7±0.5 cm/GW for KGW at the same wavelength.

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.

Multiwatt, Continuous-Wave, Tunable Diamond Raman Laser With Intracavity Frequency-Doubling to the Visible Region

Multiwatt emission from a continuous-wave diamond Raman laser pumped within a diode-pumped InGaAs-based semiconductor disk laser (SDL) is reported. The Raman laser achieved a maximum output power of 4.4 W at 1228 nm with a beam quality factor (M2) of 1.4 and diode-to-Stokes conversion efficiency of 14.2%. Via tuning of the SDL oscillation wavelength, the diamond Raman laser was tuned from 1209 to 1256 nm, with output power exceeding 4 W over a 10-nm range. The evolution of the emission spectra and beam quality of both the SDL and the Raman laser have been investigated for different pump powers, revealing the onset of spectral broadening and beam “clean-up” effects with increasing power. The SDL spectral linewidth and beam overlap are then taken into account in calculations of the efficiency of the Raman laser. Using intracavity frequency-doubling in lithium triborate (LBO) within the Raman laser, up to 1.5-W output power at orange wavelengths was achieved with M2 <; 1.3 and linewidth ~0.1 nm full-width at half-maximum. Tuning of the visible emission was achieved via tuning of the SDL and temperature control of the LBO and covered the range 604.5-619.5 nm.

InP/AlGaInP quantum dot semiconductor disk lasers for CW TEM00 emission at 716-755nm

Multiple layers of InP QDs, self-assembled during epitaxial growth, were incorporated into the active region of an (Al(x)Ga(1-x))(0.51)In(0.49)P based semiconductor disk laser with monolithic Al(x)Ga(1-x)As distributed Bragg reflector. Three gain structure samples were selected from the epitaxial wafer, bonded to single-crystal diamond heatspreaders and optically pumped at 532 nm within a high finesse external laser cavity. Laser emission with peak wavelengths at 716, 729, and 739 nm, respectively, was achieved from the three samples; the latter demonstrating tuning from 729 to 755 nm. Maximum continuous wave output power of 52 mW at 739 nm was achieved with 0.2% output coupling; the threshold and slope efficiency were 220 mW and 5.7% respectively.

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.

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%.