Advances in wide-tuning and narrow-linewidth external-cavity diode lasers

We develop, analyze, and demonstrate an optically-pumped semiconductor disk laser using an active mirror architecture formed by sandwiching the semiconductor gain membrane between two heatspreaders, one of which is coated with a high-reflectivity multilayer. Thermal modeling indicates that this structure outperforms traditional VECSELs. Employing an InGaAs/GaAs MQW gain structure, we demonstrate output powers of approximately 30 W at a center wavelength of λ ≈ 1178 nm in a TEM00 mode using an in-well pumped geometry.

Hybrid membrane-external-cavity surface-emitting laser.

Membrane external-cavity surface-emitting lasers (MECSELs) are vertically emitting semiconductor lasers that combine all the benefits of VECSELs (vertical-external-cavity surface-emitting lasers) with the new degree of freedom in creating gain structures without monolithically integrated distributed Bragg reflectors (DBRs). The absence of the DBR and the substrate, and the use of a very thin gain membrane (typically some hundreds of nanometers), which can be sandwiched between two transparent heat spreaders, represents the best solution for heat removal. The membrane configuration also allows the option of double side pumping, which in turn makes it possible to utilize an extensive amount of quantum well (QW) groups as well as multiple kinds of QWs in a periodic laser gain structure. Here we report on design strategy and results of different kinds of approaches on broadband, relatively high power MECSEL gain structures. Especially efficient pump absorption, sufficient gain on several different wavelengths and carrier mobility during laser operation, are discussed. We also present the characteristics of the laser systems created. Results show ∼ 83 nm (∼ 25 THz) tuning range with more than 100 mW of power at all wavelengths at room temperature operation. Strategies for further development are discussed as well.

Design and characterization of MECSELs for widely tunable (>25 THz) continuous wave operation

Sodium laser guide stars (LGS) play an essential role in ground-based telescope adaptive optics. Optically-pumped vertical-external-cavity semiconductor lasers (VECSELs) have long been investigated as possible next-generation LGS sources due to their high optical power, good beam quality, and ability to tune the emission wavelength. Here, we present the design and characterization of an emerging platform that shows potential in a high-power semiconductor laser, specifically in LSG applications. Using membrane external-cavity surface-emitting lasers (MECSELs), we demonstrated a record output power of 28.5 W adopting the in-well pumping technique. This allowed the reduction of the quantum defect, which typically hinders high power operation in standard barrier-pumped semiconductor lasers. Comparing the barrier-pumping and in-well pumping schemes showed slope efficiencies of 21.6% and 39.5%, respectively. A multi-pass scheme was designed for recirculating the in-well pump beam. Moreover, a tuning range of 71 nm from 1124 nm to 1195 nm was achieved with a 2 mm birefringent filter which led to a 1.7 nm linewidth at 1178 nm for future frequency conversion to 589 nm.

High-power in-well pumped MECSEL emitting at 1178 nm for sodium guide star applications

The external-cavity diode laser is advantageous in terms of low noise, high side-mode suppression ratio, high temperature stability, simple structure, and low cost, which has been the preferred scheme to realize wide-tuning and narrow-linewidth characteristics. Thus, it has been widely used in optical communication, lidar, environmental monitoring, spectral analysis, optical coherence tomography, and other frontier fields. Herein, we introduce the technical scheme and review the development status of wide-tuning and narrow-linewidth external-cavity diode lasers in detail. Primarily, the structure, working principles, and performance characteristics of external-cavity diode lasers are deeply analyzed according to different structures. The structural characteristics, key technologies, optical performance and application fields of state-of-the-art studies in recent years are discussed. Finally, the challenges and potential development prospects of wide-tuning and narrow-linewidth external-cavity diode lasers are analyzed and discussed. 

宽调谐窄线宽外腔半导体激光器研究进展

We present a detailed characterization and comparative study of a membrane external-cavity surface-emitting laser (MECSEL) operating in the λ = 1125-1190 nm wavelength range under in-well pumping (at 1070 nm) and barrier-pumping (at 808 nm). The slope efficiency of the laser is significantly improved from 21% with barrier-pumping to 39% when pumping only the quantum wells at 1070 nm at a heat-sink temperature of 10 °C. To address the low pump absorbance with in-well pumping, we design and implement a low-aberration multi-pass pumping scheme. An optical output power of 28.5 W and slope efficiency of ∼28% is achieved with 8 circulating passes. This represents the highest output power demonstrated in any MECSEL, as well as the highest output power in-well pumped vertical external-cavity surface-emitting laser (VECSEL). It is noted that our reported output power is only limited by the available laser input power and no thermal roll-over is observed.

Roman Bek

Papers

In-Well Pumping of a Membrane External-Cavity Surface-Emitting Laser