Luis A. Spinelli

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.

UV Resonance Raman Spectroscopy Using a New cw Laser Source: Convenience and Experimental Simplicity

A new laser has been developed which generates hundreds of milliWatts of cw UV power below 260 nm. The laser consists of a small-frame Ar+-ion laser which is intracavity doubled with the use of BBO nonlinear optical crystals. More than 300 mW are available at 244 and 257 nm, while 180, 100, and 30 mW are available at 248, 238, and 228.9 nm, respectively. This laser is an ideal source for UV Raman spectroscopy since it avoids the nonlinear and saturation problems common with the typical pulsed laser excitation sources. It also minimizes thermal sample degradation. We demonstrate the increased spectral signal-to-noise ratios possible due to the ability to focus the cw laser into a small-volume element that can be efficiently imaged into the spectrometer. We demonstrate the ability of this laser to excite Raman spectra of solid samples such as coal-liquid residuals, and point out the utility of the 228.9-nm line for studying aromatic amino acids in proteins. We also demonstrate the ability to selectively study pyrene intercalated into calf thymus DNA.

Recent advances in optically pumped semiconductor lasers

Optically pumped semiconductor lasers offer significant advantages with respect to all traditional diode-pumped solid state lasers (including fiber lasers) in regards to wavelength flexibility, broad pump tolerance, efficient spectral and spatial brightness conversion and high power scaling. In this talk we will describe our recent progress in the lab and applying this technology to commercial systems. Results include diversified wavelengths from 460 to 570nm, power scaling to >60W of CW 532nm, and the launch of a low cost 5W CW visible source for forensic applications.

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.

Applications of a New 206.5-nm Continuous-Wave Laser Source: UV Raman Determination of Protein Secondary Structure and CVD Diamond Material Properties

We demonstrate the utility of a new 206.5-nm continuous-wave UV laser excitation source for spectroscopic studies of proteins and CVD diamond. Excitation at 206.5 nm is obtained by intracavity frequency doubling the 413-nm line of a krypton-ion laser. We use this excitation to excite resonance Raman spectra within the π → π amide transition of the protein peptide backbone. The 206.5-nm excitation resonance enhances the protein amide vibrational modes. We use these high signal-to-noise spectral data to determine protein secondary structure. We also demonstrate the utility of this source to excite CVD and gem-quality diamond within its electronic bandgap. The diamond Raman spectra have very high signal-to-noise ratios and show no interfering broad-band luminescence. Excitation within the diamond bandgap also gives rise to narrow photoluminescence peaks from diamond defects. These features have previously been observed only by cathodoluminescence measurements. This new continuous-wave UV source is superior to the previous pulsed sources, because it avoids nonlinear optical phenomena and thermal sample damage; Photoluminescence.

Sub-100 Femtosecond Pulse Generation by Kerr Lens Mode-locking in Ti:Al2O3

Ti:Al2O3 has the available bandwidth for directly generating very short tunable pulses at high average power. Passive modelocking techniques have been described in the literature [1], [2]. We report 800mW at sub-100fs (when pumped with 8W) and 2.1W output with 120fs pulsewidth (pumped with 14W).

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.

Al-glass kW fibre laser end-pumped by MCCP-cooled diode stacks

High power industrial fibre lasers are typically pumped by single emitter diodes, with pump power aggregation and the fibre laser cavity being achieved in a monolithic “all-bibre” architecture comprising fused fiber bundles, fiber Bragg grating reflectors and numerous splices. [1]. The gain fiber utilizes a low index polymer coating to provide the wave-guiding for the multimode pump as well as for compatibility with the NA increase (typically 0.22–0.45) which occurs in the fused taper combiners. While this all fibre approach has been shown to be viable, it is not trivial to implement at power levels in excess of several hundred watts Issues include polymer coating degradation, transverse mode-coupling induced instability at splices or FBGs, grating walk-off, and modal instability, [2]. The latter issue arises because these fiber laser designs are focused on single-transverse-mode operation, [3.4], even though the fibres themselves are multimode to avoid nonlinear impairments. This is despite the face that most cutting and welding applications actually utilize a multimode fibre for delivery to the cutting head. The BBP of such systems is typically 2.5mm.mRad at a wavelength around 1080nm. However, single mode operation allows power scaling by incoherently combining several lower power fiber lasers into a single beam with that BPP.

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