A. Ginolas

20W continuous wave reliable operation of 980nm broad-area single emitter diode lasers with an aperture of 96μm

High power broad area diode lasers provide the optical energy for all high performance solid state and fiber laser systems. The maximum achievable power density from such systems is limited at source by the performance of the diode lasers. A crucial metric is the reliable continuous wave optical output power from a single broad area laser diode, typically for stripe widths in the 90-100 μm range, which is especially important for users relying on fibered multi-mode pumps. We present the results of a study investigating the reliable power limits of such 980nm sources. We find that 96μm stripe single emitters lasers at 20°C operate under continuous wave power of 20W per emitter for over 4000 hours (to date) without failure, with 60μm stripe devices operating reliably at 10W per stripe. Maximum power testing under 10Hz, 200μs QCW drive conditions shows that 96μm stripes reach 30W and 60μm stripes 21W per emitter, significantly above the reliable operation point. Results are also presented on step-stress-studies, where the current is step-wise increased until failure is observed, in order to clarify the remaining reliability limits. Finally, we detail the barriers to increased peak power and discuss how these can be overcome.

Root-Cause Analysis of Peak Power Saturation in Pulse-Pumped 1100 nm Broad Area Single Emitter Diode Lasers

Many physical effects can potentially limit the peak achievable output power of single emitter broad area diode lasers under high current, pulse-pumped operation conditions. Although previous studies have shown reliable operation to high pump levels (240 A, 300 ns, and 1 kHz), power was found to saturate. We present here results of a systematic study to unambiguously determine the sources of this power saturation. A combination of detailed measurements and finite element device simulation were used for the diagnosis. We find that the measured power saturation is dominated by electron leakage caused by band bending at high bias due to the low mobility of the p-type waveguide. However, the power saturation is only fully reproduced when longitudinal spatial hole-burning is included. Higher powers are expected to be achieved if higher energy barriers and lower confinement factors are used to mitigate leakage and longitudinal hole-burning, respectively.

High-Power 980-nm Broad-Area Lasers Spectrally Stabilized by Surface Bragg Gratings

We report on broad-area distributed Bragg reflector (DBR) lasers with a stripe width of 90 ¿m providing up to 14-W optical power and 50% maximum conversion efficiency. Ninety-five percent of the power is included within a wavelength range of less than 1 nm. The wavelength shift between threshold and the maximum output power is less than 3.5 nm. The wavelength stabilization is achieved with a 500-¿m -long DBR containing a sixth-order Bragg grating defined by i-line wafer stepper lithography and fabricated by reactive ion etching.

Ultrahigh-brightness 850 nm GaAs/AlGaAs photonic crystal laser diodes

One-dimensional photonic crystal lasers emitting in the 850 nm range show high internal quantum efficiencies of 93% and very narrow vertical beam divergence of 7.1° (full width at half maximum). 50u2002μm broad area lasers with unpassivated facets exhibit a high total output power of nearly 20 W in pulsed mode with a divergence of 9.5°×11.3° leading to a record brightness of 3×108u2002Wu2009cm−2u2009sr−1, being presently the best value ever reported for a single broad area laser diode. 100u2002μm broad devices with unpassivated facets show continuous wave operation with an output power of 1.9 W.

Dual-Wavelength Y-Branch Distributed Bragg Reflector Diode Laser at 785 Nanometers for Shifted Excitation Raman Difference Spectroscopy:

A dual-wavelength Y-branch distributed Bragg reflector (DBR) diode laser at 785 nm is presented as an excitation light source for shifted excitation Raman difference spectroscopy (SERDS). The monolithic device was realized with deeply etched surface DBR gratings using one-step epitaxy. An optical output power of 140 mW was obtained in continuous-wave (CW) operation for each laser cavity, with emission wavelengths of the device at 784.50 and 785.12 nm. A spectral width of the laser emission of 30 pm (0.5 cm−1), including 95% of optical power, was measured. The mean spectral distance of both excitation lines is 0.63 nm (10.2 cm−1) over the whole operating range. Raman experiments using polystyrene as the test sample and ambient light as the interference source were carried out and demonstrate the suitability of the dual-wavelength diode laser for SERDS.

Wavelength-Stabilized Compact Diode Laser System on a Microoptical Bench With 1.5-W Optical Output Power at 671 nm

A wavelength-stabilized compact diode laser system emitting at 671 nm mounted on a microoptical bench with the dimensions of 13 mmtimes4 mm is presented. A reflecting Bragg grating was aligned on the rear side of a broad-area gain medium for wavelength stabilization at 671 nm. A maximum output power of 1.5 W was obtained together with a spectral width of 40 pm (full-width at half-maximum). At 1.0 W, a center wavelength stability below 20 pm over 5 h was determined. With these features, the devices are well-suited for spectroscopic applications.

Y-branch coupled DFB-lasers based on high-order Bragg gratings for wavelength stabilization

Y-branch coupled distributed-feedback lasers with 40th- and 80th-order surface Bragg gratings have been fabricated using a process based on I-line wafer stepper lithography. The devices allow dual wavelength lasing at around 975xa0nm. Wavelength spacing of 0.5 and 4xa0nm have been achieved by using grating period differences of 2.9 and 47.6xa0nm for the 40th- and 80th-order gratings, respectively. The manufactured devices with internal wavelength stabilization work as master oscillator power amplifiers with two separate and one common amplifier sections. We present optical output characteristics of the devices under continuous wave operation.

High-power, spectrally stabilized, near-diffraction-limited 970 nm laser light source based on truncated-tapered semiconductor optical amplifiers with low confinement factors

High-power spectrally single-moded coherent emission with high beam quality is demonstrated using a master-oscillator (MO) power-amplifier (PA) system. The MO is a single-moded distributed Bragg reflector ridge-waveguide (DBR-RW) laser and the PA is a semiconductor amplifier with a truncated-tapered gain region. The spectrum of the DBR-RW is found to be preserved, with >40 dB of noise suppression. Peak output powers from the PA of >50 W (250 ?s, 100 Hz) are demonstrated for laser designs with conventional confinement factors in the active region, ? = 1%, but only with substantial degradation in the beam quality (M2 at 1/e2 level of >30). The use of alternative designs with low confinement (? = 0.4%) reduces the gain and hence peak power, but dramatically improves the beam quality (M2 at 1/e2 level of ~3), enabling ~11 W emission into a diffraction-limited central lobe, with temperature and current invariant central wavelength and a spectral width of ~40 pm.

High-Power Distributed Feedback Lasers With Surface Gratings

We present the results for high-power broad-area distributed feedback lasers with surface gratings of 80th, 135th, and 270th Bragg orders. A maximum output power of 11 W for a laser with 80th order grating, emitting around 976 nm with a spectral width <; 1 nm has been achieved. Similar narrow linewidth operation occurs for devices with 135th Bragg order from 7- to 11-W output power. The technological approach to fabricating these devices based on stepper lithography and reactive ion etching is described.

650-nm InGaP Broad Area Lasers With 5000-h Reliable Operation at 600 mW

Reliable operation of 650-nm broad area laser diodes with InGaP quantum-wells embedded in AlGaInP waveguide layers and n-AlInP and p-AlGaAs cladding layers is reported. Mounted on chemical vapor deposition (CVD)-diamond heat spreader and standard C-mounts, the 100-mum stripe width lasers showed reliable operation over 5000 h at 15 degC and 600 mW