Optically-pumped Semiconductor Disk Laser Research Articles

Repetition-rate-tunable second harmonic generation in mode-locked optically pumped semiconductor disk laser

We demonstrated a repetition-rate-tunable second harmonic mode-locked optically pumped semiconductor disk laser (OP-SDL), and the tuning range was from 1.168 GHz to 1.25 GHz. The entire tuning process was continuous, and OP-SDL was always in a mode-locked working state. To the best of our knowledge, this is the first work to obtain intracavity repetition rate tunable second harmonic laser in an OP-SDL. At same time, the repetition rate of fundamental wave can be continuously adjusted from 1.16 GHz to 1.66 GHz. The central wavelengths of the pulse trains were around 971 nm, and the highest repetition rate signal-to-noise ratio was more than 60 dB, indicating that the mode-locked pulses were stable.

Hybrid membrane-external-cavity surface-emitting laser.

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.

Growth and characterization of ZnCdMgSe-based green light emitters and distributed Bragg reflectors towards II-VI based semiconductor disk lasers

We report the structural and optical properties of molecular beam epitaxy grown II–VI semiconductor multiple quantum well (MQW) structures and distributed Bragg reflector (DBR) on InP substrates for application in developing optically-pumped semiconductor disk lasers (SDLs) operating in the green spectral range. One sample was grown directly on an InP substrate with an InGaAs buffer layer, while another had a 5-period ZnCdMgSe-based DBR grown on the InGaAs/InP substrate. X-ray diffraction and scanning electron microscopy measurements revealed sharp superlattice peaks and abrupt layer interfaces, while steady-state photoluminescence measurements demonstrated surface emission between 540–570 nm. Under pulsed excitation both samples exhibited features of amplified spontaneous emission (ASE) or stimulated emission, accompanied by luminescence lifetime shortening. The sample with the DBR showed higher surface luminescence and the onset of ASE at lower pump power. To further explore the design and performance of a ZnCdMgSe-based DBR, a 20-period DBR was grown and a reflectivity of 83% was obtained at ∼560 nm. We estimate that a DBR with ∼40 periods would be needed for optimal performance in a SDL using these materials. These results show the potential of II–VI MQW structures on InP substrates for the development of SDLs operational in the green–yellow wavelength range.

Carbon nanotube mode-locked optically-pumped semiconductor disk laser

An optically pumped semiconductor disk laser was mode-locked for the first time by employing a single-walled carbon nanotube saturable absorber. Stable passive fundamental mode-locking was obtained at a repetition rate of 613 MHz with a pulse length of 1.23 ps. The mode-locked semiconductor disk laser in a compact geometry delivered a maximum average output power of 136 mW at 1074 nm.

High-power InP quantum dot based semiconductor disk laser exceeding 1.3 W

We demonstrate an optically pumped semiconductor disk laser (OP-SDL) using InP quantum dots (QDs) as active material fabricated by metal-organic vapor-phase epitaxy. The QDs are grown within [(Al0.1Ga0.9)0.52In0.48]0.5P0.5 (abbr. Al0.1GaInP) barriers in order to achieve an emission wavelength around 655 nm. We present optical investigations of the active region showing typical QD behavior like blue shift with increasing excitation power and single emission lines, which show anti-bunching in an intensity auto-correlation measurement. We report maximum output powers of the OP-SDL of 1.39 W at low emission wavelength of ∼654 nm with a slope efficiency of ηdiff=25.4 %.

106 W continuous-wave output power from vertical-external-cavity surface-emitting laser

A report is presented on an optically-pumped semiconductor disk laser providing a continuous-wave output power of 106 W at a heatsink temperature of 3°C. The laser, which operates in the transversal multimode regime, emits at a wavelength of 1028 nm. This high output power is achieved by carefully optimising the chip design, the growth process, and the bonding layer.

Direct measurement of the spectral reflectance of OP-SDL gain elements under optical pumping

We report on a direct measurement method for acquiring highly precise reflectance spectra of gain elements for semiconductor disk lasers under optical pumping. The gain element acts as an active mirror, and the active mirror reflectance (AMR) was measured with a weak and tunable probe beam coincident on the gain element with a high-power pump beam. In particular, we measured the spectral AMR of a gain element designed to have a broad and flat AMR spectrum by being anti-resonant at the center wavelength and employing a parametrically optimized anti-reflection structure. We were able to confirm that this sophisticated gain element performs according to design, with an almost constant AMR of ∼103% over a wavelength range of nearly 35 nm, very well matching the simulated behavior. Such gain characteristics are useful for optically pumped semiconductor disk lasers (OP-SDLs) designed for broadband tuning and short-pulse generation through mode-locking. The measurement technique was also applied to a conventional resonant periodic gain element designed for fixed wavelength OP-SDL operation; its AMR spectrum is markedly different with a narrow peak, again in good agreement with the simulations.

Semiconductor disk laser pumped Cr^2+:Znse lasers

A new flexible pump source, the optically-pumped semiconductor disk laser (SDL), for the Cr(2+):ZnSe laser is reported. The SDL provides up to 6W output power at a free running central wavelength of 1.98 microm. The Cr(2+):ZnSe laser operated at an output power of 1.8W and a slope efficiency of approximately 50% with respect to absorbed pump power whilst maintaining a low output intensity noise figure of <0.14% RMS. The system required no optical isolation even under the situation of significant optical feedback.

13-µm optically-pumped semiconductor disk laser by wafer fusion

We report a wafer-fused high power optically-pumped semiconductor disk laser operating at 1.3 microm. An InP-based active medium was fused with a GaAs/AlGaAs distributed Bragg reflector, resulting in an integrated monolithic gain mirror. Over 2.7 W of output power, obtained at temperature of 15 degrees C, represents the best achievement reported to date for this type of lasers. The results reveal an essential advantage of the wafer fusing technique over both monolithically grown AlGaInAs/GaInAsP- and GaInNAs-based structures.

Power scalable semiconductor disk lasers for frequency conversion and mode-locking

The semiconductor disk laser, a relatively novel type of light oscillators, is now under intensive development. These lasers produce an excellent beam quality in conjunction with a scalable output power. This paper presents recent achievements in power scalability, mode-locking and frequency conversion with optically-pumped semiconductor disk lasers. A novel concept for power scaling described here allows the thermal load of the gain material to be reduced, increasing the threshold of rollover and extending the capability for boosting the output power without degradation in the beam quality. The proposed technique is based on the multiple gain scheme. The total power of over 8 W was achieved in dual-gain configuration, while one-gain lasers could produce separately up to 4 W, limited by the thermal rollover of the output characteristics. The results show that the reduced thermal load to a gain element in a dual-gain cavity allows extending the range of usable pump powers boosting the laser output. Orange—red radiation required for a number of challenging applications can be produced through frequency-doubling using a GaInNAs/GaAs laser. Using such a disk laser operating at a fundamental wavelength of 1224 nm, we demonstrate an output power of 2.68 W in the visible region with an optical-to-optical conversion efficiency of 7.4%. The frequency-converted signal could be launched into a single-mode optical fibre with 70%—78% coupling efficiency, demonstrating good beam quality for the visible radiation. Using a Fabry—Perot glass etalon, the emission wavelength could be tuned over an 8-nm spectral range. We report on optically-pumped disk lasers passively mode-locked with a semiconductor saturable-absorber mirror. The potential of harmonic mode-locking in producing pulse trains at multigigahertz repetition rates has been explored. The mode-locked disk laser is investigated for different designs of the gain medium that allow bistable mode-locking to be controlled. An explanation for hysteresis of mode-locking is given based on a laser model including saturable absorption and unsaturated gain in a semiconductor oscillator operating in pulsed regime.

26 W optically-pumped semiconductor disk laser operating at 157-μm using wafer fusion

We report a wafer fused high power optically pumped semiconductor disk laser incorporating InP-based active medium fused to a GaAs/AlGaAs distributed Bragg reflector. A record value of over 2.6 W of output power in a spectral range around 1.57 microm was demonstrated, revealing the essential advantage of the wafer fusing technique over monolithically-grown all-InP-based structures. The presented approach allows for integration of lattice-mismatched compounds, quantum-well and quantum-dot based media. This would provide convenient means for extending the wavelength range of semiconductor disk lasers.

Passively mode-locked GaInNAs disk laser operating at 1220 nm

We report an optically-pumped semiconductor disk laser passively mode-locked with a semiconductor saturable-absorber mirror. Both the absorber and the gain media were made of dilute nitride compound semiconductor, GaInNAs, which enables operation around 1.2 microm wavelengths. The laser generated 5 ps optical pulses with an average output power up to 275 mW. Our demonstration provides an attractive approach for efficiently generating red-wavelengths through external cavity frequency doubling.

High‐brightness long‐wavelength semiconductor disk lasers

AbstractA review on the recent developments in the field of long‐wavelength (λ &gt;1.2μm) high‐brightness optically‐pumped semiconductor disk lasers (OPSDLs) is presented. As thermal effects have such a crucial impact on the laser performance particular emphasis is given to modelling the thermal behaviour and optimisation of the heat‐sinking. Selected OPSDL devices, realized in different III‐V and IV‐VI semiconductor material systems, with corresponding emission wavelengths between 1.2 μm and 5.3 μm are presented. Specific applications in this broad spectral range are addressed and methods to obtain high output power are discussed in terms of the underlying material properties and device operating principles.

Dilute nitrides tailor the wavelength of semiconductor disk lasers

Interest is growing rapidly in efficient and compact optically pumped semiconductor disk lasers (OP-SDLs) since they provide a practical solution for generating high-power radiation at visible wavelengths. In particular, red-green-blue SDLs are thought to satisfy the demanding requirements of laser displays and projectors. Other applications, such as spectroscopy and biomedicine, are also expected to benefit greatly from the wavelength versatility and excellent beam quality offered by OPSDLs. Also known as vertical external cavity surface-emitting lasers,1, 2 OP-SDLs combine many of the advantages of traditional solid-state lasers with the versatility offered by semiconductor gain materials. Such laser sources can deliver Watt-level diffraction-limited output beams in a broad spectral range determined by the gain material. The key element of an OP-SDL is the semiconductor gain mirror, which is placed in an external laser cavity configuration, as shown in Figure 1. This arrangement allows a nonlinear crystal to be placed into the cavity for frequency conversion. The most notable results demonstrated with visible SDLs have been obtained in the blue-green region by frequency doubling 940nm and 1060nm laser radiation.3 However, the development of frequency-doubled OP-SDLs at red-orange wavelengths has been hindered by the lack of suitable semiconductor materials for fabricating high-quality gain mirrors operating at around 1200–1250nm. To tackle this problem, we have developed gallium indium nitride arsenide / gallium arsenide (GaInNAs/GaAs) gain regions that can be integrated with highquality gallium arsenide / aluminum arsenide (GaAs/AlAs) distributed Bragg reflectors (DBRs). DBRs act as mirrors for a specific wavelength range related to the optical thickness of Figure 1. Schematic of an OP-SDL with an intra-cavity heat-spreader.

1 W at 617 nm generation by intracavity frequency conversion in semiconductor disk laser

A 1234 nm GalnNAs/GaAs optically-pumped semiconductor disk laser utilising an intracavity BBO (beta barium borate) crystal for nonlinear frequency conversion is reported. 1 W of power at 617 nm has been achieved.

Power scalable semiconductor disk laser using multiple gain cavity

We report on power scaling of optically-pumped semiconductor disk lasers using multiple gain scheme. The method allows for significant power improvement while preserving good beam quality. Total power of over 8 W was achieved in dual-gain configuration, while one-gain lasers could produce separately about 4 W, limited by the thermal rollover of the output characteristics. The results show that reduced thermal load to a gain element in a dual-gain cavity allows extending the range of usable pump powers boosting the laser output.