Andrea Caprara

High-power optically pumped semiconductor lasers

Optically pumped, external-cavity, surface emitting semiconductor lasers (also known as optically pumped semiconductor lasers, OPS lasers, and vertical external cavity surface emitting lasers, VECSELs) generate near-diffraction limited beams from low brightness diode-array pumps. We have demonstrated 30 W cw at 980 nm and 15 W cw at 488 nm in a single spatial mode from these emitters and believe they can be scaled to > 100 W. Potential applications we have explored for such devices include wavelength conversion, spectral and spatial brightness conversion.

Blue and green optically pumped semiconductor lasers for display

We discuss a compact RGB source with ouput power of several watts per color consisting of a red (638 nm) diode and OPS lasers with blue (460 nm) and green (530) nm output. Suitability for display applications is shown by replacing the lamp of a standard Rear Projection TV.

Power-scaling of optically pumped semiconductor lasers

Power-scaling of optically pumped semiconductor lasers (OPSLs) using a resonator with multiple OPS chips is demonstrated. With a 3-chip cavity and intra-cavity second harmonic generation, we obtain 55W of TEM00 mode output at 532 nm and 66 W in multi-transverse mode. In addition, we describe the design of a periodic dynamically stable resonator that allows scaling to more than 4 chips and demonstrate that the output power scales with the number of chips in the cavity.

Optically pumped semiconductor lasers: a new reliable technique for realizing highly efficient visible lasers

Optically pumped semiconductor material is a complimentary gain medium for rare earth or transition metal doped crystals. The design of several compositions based on GaAs allows the realization of a wavelength range between 710nm and 1180nm. This can be diode pumped and frequency doubled to cover the near UV up to the yellow spectral range. The power is scaleable and we have realized several Watts at 488nm and 460nm. Experimental results will be presented and discussed as well as reliability data to show that this technology has ripened for industrial applications.

Semi-analytical solution for the temperature profiles in solid-state laser disks mounted on heat spreaders

Temperature profiles in pumped solid-state laser disks are generally calculated numerically by using finite-element programs to solve the heat conduction equation in the disk and the heat spreader. Analytical expressions exist for the longitudinal temperature profile in the case of an infinitely thick heat spreader or in the limit of zero thickness of the disk. We are presenting a simplified, semi-analytical method to calculate the three-dimensional temperature profiles for any disk or heat spreader dimensions by solving the heat conduction equation using Hankel transforms. This method allows for straightforward optimization of the cooling properties of heat-sink-mounted solid-state and semiconductor disk lasers.

20 Watt CW TEM00 intracavity doubled optically pumped semiconductor laser at 532 nm

Optically-pumped semiconductor (OPS) lasers are power-scalable, wavelength-flexible, infrared brightness converters. Adding intra-cavity frequency doubling turns them into efficient, low noise, high power visible laser sources. We report on a laser combining an InGaAs gain medium with an LBO nonlinear crystal to produce more than 20 Watt CW in single transverse mode at 532 nm. Efficient cooling of the single gain chip using advanced mounting techniques is the key to making the laser reliable at high CW powers. A rugged and compact package withstands significant environmental excursions. The lasers low noise makes it suitable for demanding Ti:Sapphire pumping applications.

2 W cw OPO in mid-IR pumped by OPSL laser intra-cavity radiation

The design and experimental testing of an Optical Parametric Oscillator generating 2 Watts of continuous wave radiation at 3.5 micron is presented. The oscillator uses a KTA (Potassium Titanyl Arsenate) crystal as the nonlinear medium, pumped by the 1.06 mm intracavity radiation of an Optically Pumped Semiconductor Laser (OPSL). A review of the nonlinear characteristics of KTA is presented, and design criteria for the OPSL intra-cavity pumped OPO are given. The experimental results are presented and discussed.

Intracavity-tripled optically-pumped semiconductor laser at 355 nm

Optically-pumped semiconductor lasers provide efficient laser sources in the ultraviolet by intra-cavity nonlinear frequency tripling. A laser combining InGaAs gain media with LBO nonlinear crystals produces hundreds of mW CW at 355 nm. A compact package that combines thermal and opto-mechanical stability is the key to making this laser robust and manufacturable. A temperature controlled, monolithic aluminum base supports opto-mechanical mounts made from low expansion alloys and ceramics to create a resonator that can withstand substantial environmental excursions.

200-mW continuous-wave laser source at 198.5 nm for lithographic applications

We report on the development and testing of a laser system that delivers up to 200 mW of continuous-wave radiation at 198.54 nm in a near diffraction-limited beam, to be used as a source for photolithography mask writing and mask inspection. The source has been developed with the support of International SEMATECH. The laser output is obtained by intra-cavity sum frequency generation in a CLBO (Cesium Lithium Borate) non-linear crystal

Aberration Insensitive Resonators for OPS lasers

Phase aberrations play an important role in shaping the beam and in determining the losses of laser resonators. An efficient method is presented for modeling arbitrary phase aberrations in a resonator and for computing modes, modal losses and frequencies in the aberrated resonator. The method is then used to assess the effect of thermal phase aberrations in lasers where the active medium is a solid state rod, and in lasers where the active medium is an OPS (Optically Pumped semiconductor). The adverse effect of the thermal aberrations is found to be severe in the case of rod geometries and small and less significant in the case of OPS lasers. The analysis conducted allows one to identify simple design criteria that further minimize the effect of thermal aberrations in the case of OPS lasers.