Chuanshun Cao

High differential efficiency (>16%) quantum dot microcavity light emitting diode

Data are presented on high differential efficiency quantum dot microcavity light emitting diodes. The data show that differential efficiencies >16% can be achieved by the use of quantum dots to reduce carrier diffusion in small oxide-apertured microcavities. The measured efficiencies are sensitive to both microcavity tuning of the resonance peak to the quantum dot light emitters, and nonradiative recombination effects brought on by temperature, bias current, and edge effects. The peak efficiencies are obtained at a resonance temperature of ∼160 K.

Reliable high-power long-pulse 8XX-nm diode laser bars and arrays operating at high temperature

We report on the high-power high-temperature long-pulse performance of the 8XX-nm diode laser bars and arrays, which were recently developed at Lasertel Inc. for diode laser pumping within high-temperature (130 °C) environment without any cooling. Since certain energy in each pulse is required, the diode laser bars have to provide both high peak power and a nice pulse shape at 130 °C. Optimizing the epi-structure of the diode laser, the laser cavity and the distribution of waste heat, we demonstrate over 40-millisecond long-pulse operation of the 8XX-nm CS bars at 130 °C and 100 A. Pumping the bar with 5-Hz frequency 15-millisecond rectangular current pulses, we generate over 60 W peak power at 100 A and 130 °C. During the pulse duration, the pulse shape of the CS bars is well-maintained and the power almost linearly decays with a rate of 1.9% peak power per millisecond at 130 °C and 100 A. Regardless of the pulse shape, this laser bar can lase at very high temperature and output pulse can last for 8 ms/2ms at 170 °C/180 °C (both driven by 60 A current pulses with 5-Hz frequency, 10 millisecond pulse width), respectively. To the best of our knowledge, this is the highest operating temperature for a long-pulse 8XX-nm laser bar. Under the condition of 130 °C and 100 A, the laser bars do not show any degradation after 310,000 10-millisecond current pulse shots. The performance of stack arrays at 130 °C and 100 A are also presented. The development of reliable high-temperature diode laser bar paves the way for diode laser long-pulse pumping within a high-temperature environment without any cooling.

Recent Development of High-Power-Efficiency 50-W CW TE/TM Polarized 808-nm Diode Laser Bar at Lasertel

This paper gives an overview of recent development of high-efficiency 50-W CW TE/TM polarized 808-nm diode laser bar at Lasertel. Focused development of device design and MBE growth processes has yielded significant improvement in power conversion efficiency (PCE) of 50-W CW TE/TM polarized 808-nm laser bars. We have achieved CW PCEs of 67 % to 64 % at heat-sink temperature of 5 °C and 25 °C, respectively. Ongoing life-testing indicates that the reliable powers of devices based on the new developments exceed those of established, highly reliable, production designs.

Record low thermal resistance of mode-confined VCSELs using AlAs/AlGaAs DBRs

The influence of AlAs placed at various locations in oxide and non-oxide mode-confined VCSELs is studied. Experimental results show that removing oxide and introducing AlAs in various locations of the VCSEL DBRs can dramatically reduce the thermal resistance.

Record High-Temperature Long-Pulse Operation of 8xx-nm Diode Laser Bar with Aluminum-Free Active Region

We report on the first demonstration of long-pulse (milliseconds) operation of aluminum-free active-region 8xx-nm diode laser bar at heat-sink temperature of 180 °C. This is, to the best of our knowledge, the highest published operating temperature for a long-pulse 8xx-nm laser bar with Al-free active region. The laser bars have very robust performance at 130 °C without any active cooling. At this high temperature, the laser bars provide both high peak power (60 W at 100 A) and good pulse shape for tens of milliseconds pulse width, maintaining high energy per pulse. The dependence of laser output pulse shape on the pulse width and pump current is experimentally investigated at 130 °C. We find that the transient output power of the laser bar follows P(t) = A exp(-t /t0) + Bt + C, where A, B, C, and t 0 are fitting parameters that are pulse width and current dependent. We have also investigated the transient thermal behavior of the laser bar at high temperature and high pump current.

Thermally insensitive laser diode arrays

In this paper we present the use of high power diode arrays, spectrally stabilised using chirped Volume Bragg Gratings as a pump source for a Nd:YAG based laser. The temperature dependant performance of a series of different stabilised diodes, and the side pumped Nd:YAG slab resonator was measured over a 55°C temperature range. The best performing stabilised LDAs exhibited Q-switched output energy consistent over 80% of the temperature range, and drop off by 40% at the higher temperature extremes. Beam parameters of the laser such as divergence were found to drop in combination with input energy. Factors such as spectral drifting of the diodes are also considered and the effect on the resonator is characterised.

Impact of spin blocking on the energy relaxation of electrons in quantum-dot lasers

The impact of the electron spin relaxation time on the electron distribution in quantum-dot lasers is analyzed. The results show that a relatively long spin relaxation time (∼300 ps) can create a nonequilibrium carrier distribution in quantum-dot lasers. It is shown that a mechanism we call “spin blocking” increases emission from the quantum-dot excited states and can lead to excited state lasing in quantum-dot lasers.

CCD-based thermoreflectance imaging of high-power diode lasers with back-irradiance

The two-dimensional (2D) temperature profile of a high-power junction-down broad-area diode laser facet subject to back-irradiance (BI) is studied via CCD-based thermoreflectance (TR) imaging and finite element modeling. The temperature rise in the active region (ΔΤAR) is determined at different diode laser optical powers, back-irradiance reflectance levels, and back-irradiance spot locations. Interestingly, our study shows that ΔΤAR rises sharpest not when the back-irradiance is boresight-aligned with the active region but rather when it is centered in the absorbing substrate approximately 5 μm away from the active region, a distance roughly equal to half of the back-irradiance spot FWHM (9 μm). At this critical location, ΔΤAR is found to increase by nearly a factor of three compared to its increase without back-irradiance. This provides insight on an important location for back-irradiance that may be correlated with catastrophic optical damage (COD) for diode lasers fabricated on absorbing substrates, and also suggests a thermal basis for truncated lifetime and deegraded performance for diode lasers experiencing backirradiance.

Thermal imaging of high power diode lasers subject to back-irradiance

CCD-based thermoreflectance imaging and finite element modeling are used to study the two-dimensional (2D) temperature profile of a junction-down broad-area diode laser facet subject to back-irradiance. By determining the temperature rise in the active region (ΔΤAR) at different diode laser optical powers, back-irradiance reflectance levels, and back-irradiance spot locations, we find that ΔΤAR increases by nearly a factor of three when the back-irradiance spot is centered in the absorbing substrate approximately 5 μm away from the active region, a distance roughly equal to half of the back-irradiance spot FWHM (9 μm). This corroborates prior work studying the relationship between the back-irradiance spot location and catastrophic optical damage, suggesting a strong thermal basis for reduced laser lifetime in the presence of back-irradiance for diode lasers fabricated on absorbing substrates.