Search

We introduce a toolbox for modelling laser diode operation over a large temperature range, as is encountered in long-pulse hair removal, and in mobile applications such as LiDAR. Power-to-current characteristics and lifetime estimations are sought for arbitrary pulse patterns in quasi-continuous-wave (QCW) operation. Our model is based on (1) the Zth-representation of the package thermal transient, (2) a temperature-dependent family of diode characteristics replacing the insufficient T0,T1-approach, and (3) the assumption that the device lifetime depends on the maximum junction temperature. The simulated evolution of output power and temperature is experimentally verified. Using our model, we assess the influence of the package geometry on the diode temperature and on the efficiency of diode-pumped solid state lasers. We also re-assess lifetime data, and derive safe operating parameters for an arbitrary pulse length.

Laser stacks emitting short light pulses are ideally suited for medical and cosmetic applications. Developing enhanced, stable and reliable assembly processes, Jenoptik is reaching for higher energy densities and lower manufacturing costs. In this paper an improved technology for actively cooled QCW stacks is presented. Based on simulations and experimental data, the impacts on the laser stack performance are described and shown as power-current and thermal impedance plots. We show that the bar-to-bar pitch can be reduced from 1.7 mm to 1.2 mm without detrimental thermal effects for pulse durations up to 100 ms.

High-energy class laser systems operating at high average power are destined to serve fundamental research and commercial applications. System cost is becoming decisive, and JENOPTIK supports future developments with the new range of 500 W quasi-continuous wave (QCW) laser diode bars. In response to different strategies in implementing high-energy class laser systems, pump wavelengths of 880 nm and 940 nm are available. The higher power output per chip increases array irradiance and reduces the size of the optical system, lowering system cost. Reliability testing of the 880 nm laser diode bar has shown 1 Gshots at 500 W and 300 μs pulse duration, with insignificant degradation. Parallel operation in eight-bar diode stacks permits 4 kW pulse power operation. A new high-density QCW package is under development at JENOPTIK. Cost and reliability being the design criteria, the diode stacks are made by simultaneous soldering of submounts and insulating ceramic. The new QCW stack assembly technology permits an array irradiance of 12.5 kW/cm². We present the current state of the development, including laboratory data from prototypes using the new 500 W laser diode in dense packaging.

A new high-power semiconductor laser diode module, emitting at 760 nm is introduced. This wavelength permits optimum treatment results for fair skin individuals, as demonstrated by the use of Alexandrite lasers in dermatology. Hair removal applications benefit from the industry-standard diode laser design utilizing highly efficient, portable and light-weight construction. We show the performance of a tap-water-cooled encapsulated laser diode stack with a window for use in dermatological hand-pieces. The stack design takes into account the pulse lengths required for selectivity in heating the hair follicle vs. the skin. Super-long pulse durations place the hair removal laser between industry-standard CW and QCW applications. The new 760 nm laser diode bars are 30% fill factor devices with 1.5 mm long resonator cavities. At CW operation, these units provide 40 W of optical power at 43 A with wall-plug-efficiency greater than 50%. The maximum output power before COMD is 90 W. Lifetime measurements starting at 40 W show an optical power loss of 20% after about 3000 h. The hair removal modules are available in 1x3, 1x8 and 2x8 bar configurations.

This paper discusses some of the advantages of nanowire structures for use in LEDs as well as the challenges that need to be overcome towards the realisation of real-world devices. Our experimental results pertain to group-III nitride nanowire structures grown by MBE. We present clear evidence that the catalyst-free growth approach on Si yields best results with respect to structural and optical material properties. We elucidate the mechanism of nanowire nucleation and the factors determining the initial nanowire diameter, discuss the issue of InGaN growth in small-diameter nitride nanowires and review the results reported for nanowire-based group-III nitride LEDs reported so far.