Advances in high brightness semiconductor lasers

Abstract

We review recent advances in high power semiconductor lasers including increased spectral brightness, increased spatial brightness, and reduced cost architectures at wavelengths from the near infrared to the eye-safe regime. Data are presented which demonstrate both edge emitter devices and high power surface emitting 2-dimensional arrays with internal gratings to narrow and stabilize the spectrum. Diodes with multimode high spatial brightness and high power single mode performance in the 808 and 976nm regime are described, and advances in high power bars at eye-safe wavelengths are presented. These devices have the potential to dramatically improve diode pumped systems and enable new direct diode applications.Keywords: Diode, laser, semiconductor, bar, stack, array IntroductionConventional edge emitting high power diode lasers have been used in printing, defense, medical, and materials processing because of their compactness, low cost per Watt-hour, and excellent electrical to optical efficiency. While these high power diode lasers are broadly accepted for low brightness applications, their use has been limited due to the low spatial and spectral brightness performance, costly power scaling, and limited range of emission wavelengths. In particular, the spatial beam quality from high power diode lasers is a factor of 10-20 times lower than non-diode lasers such as gas, solid state, or fiber laser counterparts. Moreover, the spectral output of conventional diode lasers is typically an order of magnitude wider than these non-diode systems and is inadequate for efficient wavelength conversion or other pumping applications requiring narrow linewidth. Power scaling is achieved by combining the output of individually mounted bars, the cost of which scales linearly or superlinearly with power. Finally, the range of wavelengths available commercially from high power conventional diode lasers has mainly been limited to broadband emission in the near infrared regime of 800 nm to 980 nm.

Q-switched lasing on a weak transition: new approach

“…(1) The diode-pump module is the main source of heat. Maximum plug-in efficiency for pumping Nd-doped medium at 808 nm is ≥ 50% [10,11]. Thus, less than 50% of the pump power is transformed into heat and the pump laser diodes need cooling to dissipate this thermal energy.…”

High-power broad-area buried-mesa lasers

“…Among the possible degradation mechanisms, catastrophic optical damage (COD) initiated at facets is probably the most critical one [9][10][11][12][13]. To reduce the optical absorption (and consequently the heating due to non-radiative recombination) at and near facets, non-absorbing mirrors (NAM) can be introduced, extending tens of microns from the facet inwards [8,9,15,[17][18][19][20][21][22][23]. For quantum well lasers, it is possible to create NAM using quantum well intermixing techniques, which produce a local increase in the bandgap energy [9,[20][21][22].…”

CW Fiber Laser for Second Harmonic Generation

“…1) [8] and [27] as well as master oscillator power amplifier (MOPA) configurations ( Fig. 2) [7], [28] and [29] can be used for power scaling of fiber lasers. Whereas the laser configuration offers simplicity and compactness, the MOPA approach allows for a more refined control of both temporal and spectral characteristics at high powers.…”

“…However, multiple-stage amplifiers have had to be used to achieve even a medium power level output (~10W), with each stage requiring a separate pump and thermal management system and a high-power inter-stage optical isolator, rendering such an approach to be rather complex. Recent advances in semiconductor laser diode technology [28] and [29] and the introduction of advanced photonic crystal fiber (PCF) design with an increased pump absorption have opened up a possibility to reduce the complexity of the MOPA architecture.…”