G.J. Valentine

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.

Low-loss 1.3um GaInNAs saturable bragg reflector for high-power picosecond neodymium lasers

A novel low-loss, single-step-growth 1.3‐µm GaInNAs saturable Bragg reflector mode-locking element has been developed. Combined radial thickness and postgrowth annealing control have permitted a tuning range of 46 nm for passive mode locking to be demonstrated from one wafer. With this structure, stabilized mode locking was obtained from quasi-cw diode-pumped Nd:YLF and Nd:YALO lasers operating at 1314 and 1342 nm, respectively, with average on-time output powers of as much as 20 W and pulse durations as low as 22 ps.

Highly compact and efficient femtosecond Cr:LiSAF lasers

Methods for developing more compact femtosecond Cr:LiSAF laser sources are examined. By careful modeling of the low threshold performance and intracavity dispersion characteristics of these cavities, a highly asymmetric z-cavity design with a single prism for dispersion compensation is developed. Transform-limited pulses as short as 113 fs and modelocked output powers up to 20 mW are demonstrated for less than 110 mW of laser-diode pump power. The complete laser system (including the laser diode pump system and drivers) has a footprint of 21.5 /spl times/ 28 cm/sup 2/, about the size of a sheet of US letter or A4 paper.

Enhancement of laser performance using an intracavity deformable membrane mirror

An intracavity deformable membrane mirror has been successfully used to optimise the brightness of solid-state lasers--a side-pumped Nd(3+):YAlO laser where the oscillation of a low-order transverse mode was obtained, and a grazing incidence Nd(3+):GdVO(4) laser where a brightness increase by an order of magnitude with negligible drop in power was achieved. Several search algorithms were also implemented in the system and compared with respect to intracavity optimisation.

Search-based active optic systems for aberration correction in time-independent applications

We describe a protocol for the use of a control feedback loop incorporating an iterative optimization routine for a range of time-independent adaptive optics applications. These applications are characterized by the quasi steady state of the aberrative effects (>0.1 s) and contrast, for instance, to astronomical applications where the aberrations constantly vary at frequencies above 10 Hz. For optimal performance in such time-independent applications, the control systems typically require specialized tailoring. A typical example of two different types of time-independent adaptive optics applications--an adaptive optic microscope and an adaptive optic laser platform--are detailed and compared. It is shown that implementing a number of minor, but crucial, application-specific modifications to the control system results in an improved efficiency of an already extremely successful technique for aberration compensation. We present a description of the crucial parameters to consider in a search-based adaptive optics system.

Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes

We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370 nm UV light from a demonstrator 8 x 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8 W/cm2 per imaged pixel in circular spots of diameter approximately 8 microm. We show example structures written in positive as well as in negative photoresist.

Passive stabilization of a passively mode-locked laser by nonlinear absorption in indium phosphide

A diode-pumped Nd:KGd(WO4)2 laser mode locked by a saturable Bragg reflector (SBR) is passively stabilized to suppress Q-switched mode locking and to extend the parameter range of continuous-wave mode locking. An indium phosphide plate exhibiting two-photon absorption and free-carrier absorption is used for passive stabilization. The intracavity pulse energy for the onset of stable continuous-wave mode locking is reduced by a factor of 4 compared with the laser without stabilization. By increasing the modulation depth of the SBR, pulse shortening by 30% is achieved and bandwidth-limited 6.2-ps pulses are measured.

Development of high average power picosecond laser systems

The use of semiconductor saturable absorbers has emerged as an enabling technology in modern passively modelocked laser systems. Their application to high power picosecond lasers, most notably Nd-doped lasers, has produced systems with average power levels of a few tens of watts. In this paper, the development of these laser systems to the 100W level and above will be outlined.

Low-loss GaInNAs saturable Bragg reflector for mode-locking of a femtosecond Cr/sup 4+/ : forsterite-laser

A GaInNAs saturable Bragg reflector is used to mode-lock a Cr/sup 4+/ : forsterite solid-state laser. This low-loss saturable absorber mediates the generation of tunable femtosecond pulses having durations as short as 62 fs in the 1300-nm spectral region.

Nd:GdVO4 in Face-Cooled Geometries: Thin-Disk and High-Power Microchip Lasers

The potential of Nd:GdVO4 for face-cooled geometries is discussed. Particular emphasis is given to experimental and finite element studies of thin-disk and high-power, monolithic, microchip geometries. Efficient laser operation is reported.