Richard H. Abram

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.

Narrow linewidth operation of a tunable optically pumped semiconductor laser

We report on the single-frequency operation of an optically pumped external cavity semiconductor laser. An output power of up to 400 mW is obtained in a single spatial and longitudinal mode and with a tuning range exceeding 10 nm. The laser has been stabilized electronically to a reference cavity with a relative linewidth of less than 5 kHz.

Optical in-well pumping of a vertical-external-cavity surface-emitting laser

A scheme is demonstrated for optical pumping of a vertical-external-cavity surface-emitting laser. The scheme is based on absorption of the pump light within the wells of the multiple-quantum-well gain structure rather than the conventional approach of absorption of a shorter wavelength in the barrier regions. The operation of a laser around 850 nm pumped by an 808 nm source demonstrates the potential of this technique for allowing operation at a significantly shorter range of wavelengths for these devices in general and specific application of high-brightness pump lasers for devices in this spectral region. A further advantage is the smaller quantum defect which results in reduced heating of the gain medium. These advantages are achieved while maintaining a slope efficiency of up to 18%, which is comparable to results obtained with a traditional pumping scheme with a similar gain medium.

Novel Gain Medium Design for Short-Wavelength Vertical-External-Cavity Surface-Emitting Laser

We report on a novel material developed as the gain medium for a vertical-external-cavity surface-emitting laser (VECSEL) operating around 850 nm. The new material departs from the conventional approach of using GaAs as the quantum-well (QW) material and expands the previously reported concept of using InAlGaAs QWs. The inclusion of indium pins dislocation propagation into the active region of the VECSEL. Crucial for the success of this design is also the development of indium and phosphorous containing quinternary strain-compensating layers. These surround the QWs and provide a more substantial resistance to defect propagation. Results are presented for stable high-power single spatial mode operation of a laser based on this material together with measurements of the unsaturated gain of the device and the characteristic temperature for the threshold power

A birefringent etalon as single-mode selector in a laser cavity.

A novel technique is demonstrated for stabilizing an intra-cavity etalon used for single-mode selection in a laser cavity. By appropriate polarization analysis of the reflection from an etalon designed as a quarterwave plate an electronic signal can be derived, that enables the implementation of an electronic stabilization scheme. This scheme obviates the need for any modulation of the etalon in order to ensure stable single mode operation of a cw tunable laser.

Efficient coupling of several broad area laser diodes into an optical fiber

A high brightness, fiber coupled optical pumping system is described based on readily available optical components. Operating at a wavelength of 670nm we have achieved an output of 1.25W from a 50μm core diameter fiber (0.22 NA) and 3.5W from a 100μm core diameter fiber (0.22 NA). This represents a six- to eightfold increase over commercially available systems at that wavelength. The design is generic and can immediately be implemented at other wavelengths, where high brightness pumping systems are not commercially available. The design and implementation are detailed.

Optically pumped vecsels for high resolution spectroscopy: the new Ti : sapphire?

We report the CW performance of two broadly tuneable, optically pumped VECSEL gain structures operating around 850 nm and 960 nm. We have achieved 0.75W at 852 nm in diffraction limited TEM00 mode. A tuning range in excess of 30 nm has been demonstrated with the use of an intra-cavity birefiringent filter. At 960 nm we have achieved a power of 1.75 W and a tuning range in excess of 35 nm. Stabilised single frequency operation with a line width stabilised to 85 kHz r.m.s. at the 0.5 W output power level is reported.

Characteristics of high power VECSELs with silicon carbide heatspreaders

In this paper, we demonstrate that highly advantageous thermal management properties of the SiC heatspreader are wholly compatible with direct diode pumping. We investigate the transverse and longitudinal mode behaviour of the high-power vertical external-cavity surface-emitting semiconductor laser with the intra-cavity heatspreader.

A 0.5W 850nm Al(x)Ga(1-x)As VECSEL with intracavity silicon carbide heatspreader

High thermal conductivity intra-cavity crystalline heatspreaders are used to control the pump-induced temperature increase limiting the power scaling of vertical external-cavity surface-emitting lasers (VECSELs). Pump-power-limited output of greater than 0.4 W was achieved from a GaAs-based VECSEL at room temperature with the use of a silicon carbide heatspreader bonded to the surface of the gain element and 0.5 W by water-cooling the system to 7.5°C.

A fiber-based vertically emitting semiconductor laser at 850 nm

The possibility of wavelength tuning and insertion of intra-cavity control elements makes vertical external cavity surface emitting lasers (VECSEL) a useful tool for telecommunication and spectroscopic applications. Very small cavity lengths are desirable for achieving continuous single mode tuning and the fiber-based VECSEL is a simple device which avoids the complicated post-growth processing involved in the fabrication of a membrane-type laser. We report here on the successful operation of an optically-pumped fiber-based VECSEL in the 850 nm wavelength region. The device comprises a half cavity periodic gain structure made of 15 Al/sub 0.2/Ga/sub 0.8/As/GaAs quantum wells designed to be at the anti-nodes of the electric field standing wave, with a 30 pairs Al/sub 0.2/Ga/sub 0.8/As/AlAs distributed Bragg reflector (DBR) as the bottom mirror. The structure is similar to one previously described, used in a macroscopic external cavity geometry. The top mirror of our cavity is a dielectric DBR deposited onto the cleaved end of a single mode fiber whose distance from the semiconductor can be controlled via a piezoelectric actuator to allow for wavelength tuning. The aim of this work is to contribute to the understanding of the operation of this optically pumped fiber-based laser. By comparing the laser performance with the f finesseinesse of an empty cavity with otherwise identical geometry, we are able to conclude that the dominant photon loss mechanism is due to fundamental diffraction limits.