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The polarisation properties of a quantum well spin – vertical cavity surface emitting laser (spin – VCSEL), both without injection and with variable polarisation optical injection, are investigated experimentally and compared with the spin flip model (SFM). Without injection, we demonstrate two distinct types of VCSEL-pump response depending on the signs of the linewidth enhancement factor, birefringence and dichroism: firstly where the pump and VCSEL have the same sign of the ellipticity, and secondly where the VCSEL ellipticity, accompanied by the linear polarisation, switches sign. We show that by controlling the injected power, ellipticity or linear angle, near circular polarisation can be obtained. These responses bothgive insight into the electro-optical injected spin-VCSEL system, and have practical implications for the use of spin VCSELs in unique applications exploiting the ellipticity degree of freedom.

We report narrow-linewidth 1180-nm GaInNAs/GaAs distributed Bragg reflector lasers reaching up to ~500-mW continuous-wave output power at room temperature. The lasers employ surface gratings, which avoided the problematic regrowth and enabled a high side-mode suppression ratio over a relatively large mode-hop-free tuning range. The wavelength tuning rates of 0.1 nm/°C and 1 pm/mA were obtained by changing the mount temperature and the drive current, respectively. The lasers exhibit a narrow emission linewidth (

Using continuous-wave optical pumping of a spin-VCSEL at room temperature, we find high spin amplification of the pump close to threshold within the communications wavelength window, here at 1300 nm. This facilitates a strong switch from left to right circularly polarised light emission, which has potential applications in polarisation encoding for data communications. We use a simple spin flip model to fit the experimental results and discuss the VCSEL parameters that affect this amplification. publishedVersion

The first monolithic GaAs-based vertical-external-cavity surface-emitting laser (VECSEL) operating at 1550 nm is reported. The VECSEL operation is based on a gain mirror which was grown in a single growth run by plasma-assisted molecular beam epitaxy. The gain mirror comprised eight GaInNAsSb/GaAs quantum wells with a photoluminescence peak at 1505 nm and an AlAs/GaAs distributed Bragg reflector ensuring high reflectivity. The VECSEL chip was pumped with an 808-nm diode laser that had a large quantum defect in respect to the lasing wavelength. An output power of 80 mW in continuous wave mode and 210 mW in pulsed pump mode are demonstrated close to room temperature.

Atomic-scale understanding and processing of the oxidation of III-V compound-semiconductor surfaces are essential for developing materials for various devices (e.g., transistors, solar cells, and light emitting diodes). The oxidation-induced defect-rich phases at the interfaces of oxide/III-V junctions significantly affect the electrical performance of devices. In this study, a method to control the GaAs oxidation and interfacial defect density at the prototypical Al2O3/GaAs junction grown via atomic layer deposition (ALD) is demonstrated. Namely, pre-oxidation of GaAs(100) with an In-induced c(8 × 2) surface reconstruction, leading to a crystalline c(4 × 2)-O interface oxide before ALD of Al2O3, decreases band-gap defect density at the Al2O3/GaAs interface. Concomitantly, X-ray photoelectron spectroscopy (XPS) from these Al2O3/GaAs interfaces shows that the high oxidation state of Ga (Ga2O3 type) decreases, and the corresponding In2O3 type phase forms when employing the c(4 × 2)-O interface layer. Detailed synchrotron-radiation XPS of the counterpart c(4 × 2)-O oxide of InAs(100) has been utilized to elucidate the atomic structure of the useful c(4 × 2)-O interface layer and its oxidation process. The spectral analysis reveals that three different oxygen sites, five oxidation-induced group-III atomic sites with core-level shifts between -0.2 eV and +1.0 eV, and hardly any oxygen-induced changes at the As sites form during the oxidation. These results, discussed within the current atomic model of the c(4 × 2)-O interface, provide insight into the atomic structures of oxide/III-V interfaces and a way to control the semiconductor oxidation.

We report high-power 1180-nm GaInNAs distributed Bragg reflector laser diodes with and without a tapered amplifying section. The untapered and tapered components reached room temperature output powers of 655 mW and 4.04 W, respectively. The diodes exhibited narrow linewidth emission with side-mode suppression ratios in the range of 50 dB for a broad range of operating current, extending up to 2 A for the untapered component and 10 A for the tapered component. The high output power is rendered possible by the use of a high quality GaInNAs-based quantum well gain region, which allows for lower strain and better carrier confinement compared with traditional GaInAs quantum wells. The development opens new opportunities for the power scaling of frequency-doubled lasers with emission at yellow–orange wavelengths. publishedVersion

We review the recent advances in the development of semiconductor disk lasers (SDLs) producing yellow-orange and mid-IR radiation. In particular, we focus on presenting the fabrication challenges and characteristics of high-power GaInNAs- and GaSb-based gain mirrors. These two material systems have recently sparked a new wave of interest in developing SDLs for high-impact applications in medicine, spectroscopy, or astronomy. The dilute nitride (GaInNAs) gain mirrors enable emission of more than 11 W of output power at a wavelength range of 1180–1200 nm and subsequent intracavity frequency doubling to generate yellow-orange radiation with power exceeding 7 W. The GaSb gain mirrors have been used to leverage the advantages offered by SDLs to the 2–3 μm wavelength range. Most recently, GaSb-based SDLs incorporating semiconductor saturable absorber mirrors were used to generate optical pulses as short as 384 fs at 2 μm, the shortest pulses obtained from a semiconductor laser at this wavelength range.

We report the fabrication and characterization of high-quality GaInNAs/GaAs gain mirror as an active media for semiconductor disk lasers emitting at the 12XX nm spectral range. The structure was fabricated by molecular beam epitaxy using a radio frequency plasma source for incorporating the nitrogen. The growth parameters have been optimized to reduce detrimental effects of nitrogen on the emission efficiency. Using the gain mirror, which comprised 10 GaInNAs quantum wells with a relatively low content of nitrogen, we demonstrated semiconductor disk laser with an output power of ∼5 W and a differential efficiency of ∼20%.

We report a single-mode 1180 nm distributed Bragg reflector (DBR) laser diode with a high output power of 340 mW. For the fabrication, we employed novel nanoimprint lithography that ensures cost-effective, large-area, conformal patterning and does not require regrowth. The output characteristics exhibited outstanding temperature insensitivity with a power drop of only 30% for an increase of the mount temperature from 20°C to 80°C. The high temperature stability was achieved by using GaInNAs/GaAs quantum wells (QWs), which exhibit improved carrier confinement compared to standard InGaAs/GaAs QWs. The corresponding characteristic temperatures were Tsub0/sub=110 K and Tsub1/sub=160 K. Moreover, we used a large detuning between the peak wavelength of the material gain at room temperature and the lasing wavelength determined by the DBR. In addition to good temperature characteristics, GaInNAs/GaAs QWs exhibit relatively low lattice strain with direct impact on improving the lifetime of laser diodes at this challenging wavelength range. The single-mode laser emission could be tuned by changing the mount temperature (0.1 nm/°C) or the drive current (0.5 pm/mA). The laser showed no degradation in a room-temperature lifetime test at 900 mA drive current. These compact and efficient 1180 nm laser diodes are instrumental for the development of compact frequency-doubled yellow-orange lasers, which have important applications in medicine and spectroscopy.

A high-power optically-pumped vertical-external-cavity surface-emitting laser (VECSEL) generating 10.5 W of cw output power at 615 nm is reported. The gain mirror incorporated 10 GaInNAs quantum wells and was designed to have an emission peak in the 1230 nm range. The fundamental emission was frequency doubled to the red spectral range by using an intra-cavity nonlinear LBO crystal. The maximum optical-to-optical conversion efficiency was 17.5%. The VECSEL was also operated in pulsed mode by directly modulating the pump laser to produce light pulses with duration of ~1.5 µs. The maximum peak power for pulsed operation (pump limited) was 13.8 W. This corresponded to an optical-to-optical conversion efficiency of 20.4%.

We report a high-power VECSEL emitting

We report the first monolithic GaAs-based vertical external-cavity surface-emitting laser (VECSEL) operating at 1550 nm. The VECSEL is based on a gain mirror which was grown by plasma-assisted molecular beam epitaxy and comprises 8 GaInNAsSb/GaAs quantum wells and an AlAs/GaAs distributed Bragg reflector. When pumped by an 808 nm diode laser, the laser exhibited an output power of 80 mW for a mount temperature of 16 °C.

We demonstrate a 1240-nm GaInNAs multi-quantum well laser diode with an integrated saturable electro-absorber whose wavelength is converted to 620 nm. For conversion, we used a MgO:LN nonlinear waveguide crystal with an integrated Bragg grating in direct coupling configuration. Broadened visible spectral width and reduced speckle as well as a high extinction ratio between the below and above threshold powers were observed in passively triggered pulsed operation with smooth direct current modulation characteristics. The demonstration opens a new avenue for developing 620-nm semiconductor lasers required for emerging projection applications.

Sodium guide star lasers operating at 589 nm are commonly deployed in earth based telescopes. Next generation guide star lasers require sources with output power of more than 20 W, stable operation with narrow linewidth (< 5MHz), and high beam quality [1]. Frequency doubled semiconductor disk lasers (SDLs) are anticipated to fulfil the specifications owing to their high power, efficient intracavity frequency conversion [2], and possibility to directly modulate the output beam. In order to achieve fundamental emission at 1178 nm we have developed high quality GaInNAs/GaAs quantum well based gain mirrors [3]. Here we report on the development of a multiple gain element disk laser for generating narrow band radiation at 1178 nm.

We report recent developments of GaInNAs-based semiconductor disk lasers (SDLs) emitting at around 590 nm. GaInNAs/GaAs (dilute nitride) quantum-wells enable lasing at a wavelength of ∼1180 nm with reduced indium content and hence reduced lattice strain as compared to InGaAs quantum wells [1], leading to SDL operation with output powers of more than 11W using a single gain chip [2]. The importance of dilute nitride material system for generating high power yellow-orange radiation via frequency doubling of ∼1180 nm SDLs has been recently recognized [3]. In the current experiments we use a single gain mirror cavity (shown in Fig. 1) and investigate the conversion efficiency, power stability, and polarization of the frequency converted output beam. The SDL gain mirror had 10 GaInNAs QWs and was grown by molecular beam epitaxy (MBE). The gain chips were capillary-bonded to a wedged diamond heat spreader. An antireflective coating was deposited on top of the heat spreader to alleviate parasitic reflection from the surface of the wedged diamond. The component was attached to a water-cooled copper mount. For frequency doubling, a 4 mm long type-I critically phase-matched beta barium borate (BBO) crystal was placed inside the laser cavity (between folding mirror and the plane mirror).

Dilute nitride semiconductor disk lasers offer a convenient way of producing 570-650 nm radiation required in medicine and life science. These lasers can produce multi-watt powers with narrow spectra and compact footprints similar to solid state lasers. The advantage of using semiconductor gain materials is their ability to reach wavelengths that are not attainable by traditional solid state lasers. Other advantages include a wide tuning range and the possibility for electrical modulation. Here we demonstrate a narrow band (

We demonstrate a dilute nitride (GaInAsN) based gain mirror capable of meeting the wavelength and linewidth requirements for laser guide stars. The mirror was grown by molecular beam epitaxy on a GaAs(100) substrate. The heat generated during laser operation was extracted from the active region with a wedged intracavity CVD diamond. An intracavity birefringent filter was employed for wavelength selection and a YAG etalon for linewidth narrowing. The laser radiation was intra-cavity frequency doubled to achieve emission at 589 nm. The frequency-doubled semiconductor disk laser emitted a narrow linewidth beam (~20 MHz) at 589 nm. In a free-running mode, the laser emitted more than 6W of yellow-orange light with a maximum conversion efficiency of 15.5%.

The effect of in‐situ N‐ion irradiation on the recombination dynamics of GaInNAs/GaAs semiconductor saturable absorber mirrors has been studied. The samples were fabricated by molecular beam epitaxy using a radio frequency plasma source for nitrogen incorporation in the absorber layers as well as for the irradiation. The recombination dynamics of irradiated samples were studied by pump‐probe measurements. The recombination time of the absorbers could be reduced by increasing the irradiation time. The effect of the reduced recombination time on the pulse dynamics of a mode‐locked laser setup was studied with a Bi‐doped fibre laser. The pulse quality was found to improve with increased irradiation time and reduced recombination time, demonstrating the potential of the in‐situ irradiation method for device applications.

We report two GaInNAs/GaAs semiconductor disk lasers emitting at the wavelengths of 1180 nm and 1220 nm. The lasers generated 5 W and 7 W output powers, respectively, at a mount temperature of 15° C. Both the gain mirrors were grown by molecular beam epitaxy and consisted of a GaAs/AlAs distributed Bragg reflector and an active region with 10 GaInNAs/GaNAs/GaAs QWs.

We demonstrate > 2 W of 589 nm output from an intra cavity frequency doubled optically pumped GaInNAs/GaAs laser. Single longitudinal mode operation with linewidths < 50 MHz are shown. Output powers are currently limited by available pump power and spot size.

There has been an increasing interest in compact coherent sources at 600 nm for a number of applications, e.g. orange-red components for laser projection displays [1], and excitation sources in photodynamic therapy [2]. The need for these sources become more apparent if one recalls that the amber-orange-red spectral region remains unreachable for conventional surface emitting diode lasers due to a lack of suitable direct bandgap materials providing sufficient carrier confinement in the quantum wells. One way forward is the frequency doubling of infrared light. Recently, a second-harmonic generation (SHG) at 610 nm with an output power of 2.7 W has been demonstrated from an optically-pumped semiconductor disk laser with a BBO crystal [3]. While nonlinear crystals such as BBO and LBO are highly resistant to optical damage inflicted by visible light, their effective non-linear coefficient, d eff is low (1–3 pm/V). Periodically poled lithium tantalate (LT) and lithium niobate crystals on the other hand offer d eff values above 10 pm/V. They are highly transparent from the UV to mid-IR spectral region. However, being photorefractive, these materials have traditionally been considered to be not suitable for intracavity generation of visible light. Recent advances in double-crucible Czochralski (DCZ) method made it possible to produce nearly stoichiometric LT materials (Mg:SLT) with increased resistance to optical damage [4].

Semiconductor disk lasers (SDLs) operating around 1.55 µm have been the subject of increasing interest. The performance of monolithically grown SDLs in this wavelength range suffers, however, from the poor quality of the InP-based distributed Bragg reflector (DBR). Recently, wafer fusion technique was applied to a long-wavelength SDL to avoid this obstacle [1]. An active region grown on InP substrate was wafer fused to a GaAs/AlGaAs-based DBR resulting in a device operating at 1.57 µm with 2.6 W average output power and a near diffraction limited beam. Here we present the first mode-locked SDL using a wafer-fused gain reflector.

We report the first use of a Semiconductor Disk Laser (SDL) as a pump source for ~2μm-emitting Tm3+ (,Ho3+)-doped dielectric lasers. The ~1213nm GaInNAs/GaAs SDL produces >1W of CW output power, a maximum power transfer net slope efficiency of 18.5%, and a full width half maximum wavelength tuning range of ~24nm. Free-running operation of a Tm3+-doped tellurite glass laser under 1213nm SDL pumping generated up to 60mW output power with 22.4% slope efficiency. Wavelength tunable output is also obtained from 1845 to 2043nm. Improved performance with output powers of ~200mW and a slope efficiency of ~35% are achieved by replacing the Tm3+-doped glass with a Tm3+-doped KYW active medium. Emission of a Tm3+,Ho3+-codoped tellurite glass laser is also reported with maximum output power of ~12mW and a ~7% slope efficiency. Finally, preliminary investigations of 1213nm-pumping of a Tm3+,Ho3+-codoped silica fibre laser lead to 36mW output power with ~19.3% slope efficiency.

We report a passively mode-locked optically pumped semiconductor disk laser with emission at 1220 nm. Both the gain and the semiconductor saturable absorber mirrors used to build the laser are based on InGaAsN/GaAs quantum wells fabricated by molecular beam epitaxy. The growth parameters have been optimized to reduce the detrimental effects of nitrogen on the emission efficiency. Using a gain mirror comprising ten GaInNAs quantum wells with a relatively low nitrogen content and a saturable absorber mirror incorporating two GaInNAs quantum wells, we demonstrate generation of pulses with durations of ∼5ps and average powers up to 275mW. We describe the fabrication procedure of the semiconductor structures and the results of laser characterization.

We report an essential progress towards the development of efficient GaInNAs-based semiconductor disk lasers operating at 1220 nm spectral range. The gain mirrors were fabricated by molecular beam epitaxy using a radio frequency plasma source for incorporating the nitrogen. The typical structure consisted of a 30-pair GaAs/AlAs distributed Bragg reflector and 10 GaInNAs quantum wells with relatively low content of nitrogen. The growth parameters and the composition of the structures have been optimized to reduce the detrimental effect of nitrogen on the emission efficiency. We have achieved a maximum output power of 3.5 W and a differential efficiency of 20%.

Photodynamic therapy (PDT) with porphyrins and red light (610–630nm) is finding increasing clinical application for both the eradication of relatively small tumors and the palliation of inoperable or obstructive tumors. PDT also shows some promise for the sterilization of the tumor bed after surgical removal of neoplastic masses.Opticallypumpedvertical external-cavity surface-emitting lasers (VECSELs) appear to be a very innovative and efficient technology in this specificwavelength range. Furthermore, VECSELs are power scalable and wavelength tunable, and are an appealing light source for PDT.We report a VECSEL emittingmore than 8Wof output power at around 615nm. The VECSEL was designed to emit at a fundamental wavelength of 1230nm by using GaInNAs/GaAs quantum wells. The cavity had a V-shaped geometry and incorporated a LBO-crystal for frequencydoubling to the red spectral range. The cavity also included an etalon and a birefringent filter forwavelength control. Thewavelengthwas tunableover a rangeof∼20nm. Additional developments including, wavelength extension, pulsed operation and construction of compact prototypes will also be presented.

We report the first room temperature optical spin-injection of a dilute nitride 1300 nm vertical-cavity surface-emitting laser (VCSEL) under continuous-wave optical pumping. We also present a novel experimental protocol for the investigation of optical spin-injection with a fiber setup. The experimental results indicate that the VCSEL polarization can be controlled by the pump polarization, and the measured behavior is in excellent agreement with theoretical predictions using the spin flip model. The ability to control the polarization of a long-wavelength VCSEL at room temperature emitting at the wavelength of 1.3 µm opens up a new exciting research avenue for novel uses in disparate fields of technology ranging from spintronics to optical telecommunication networks.

We report power scaling experiments of a GaInNAs/GaAs-based semiconductor disk laser operating at ~1180 nm. Using a single gain chip cooled to mount temperature of ~10 °C we obtained 11 W of output power. For efficient thermal management we used a water-cooled microchannel mount and an intracavity diamond heat spreader. Laser performance was studied using different spot sizes of the pump beam on the gain chip and different output couplers. Intracavity frequency-doubling experiments led to generation of ~6.2 W of laser radiation at ~590 nm, a wavelength relevant for the development of sodium laser guide stars.

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.

We demonstrate the use of Q-switched microchip [1] MOPA (master-oscillator power-amplifier) systems for generation of sub-100 ps pulses at 532 nm and sub-250 ps pulses at 671 nm. Such short pulses at the visible spectrum could be used for example in fluorescence lifetime measurements, 2-photon microscopy, etc. If compared with mode-locked lasers, Q-switched microchip lasers have intrinsically low repetition rate (here ∼30–500 kHz), which allows amplification to high pulse energies without need of a pulse picker or regenerative amplifier. Other advantages of the concept include compact footprint and monolithic design of the master oscillator.

We report the first room temperature optical spin-injection of a dilute nitride 1300 nm vertical-cavity surface-emitting laser under continuous wave pumping. Very good agreement is found with theoretical predictions obtained with the spin flip model.

We report on the intracavity frequency-doubling of a GaInNAs/GaAs disk laser. The laser operated at 1220 nm and delivered 4.6 W of power at ∼610 nm. The red emission was further frequency-doubled to 305 nm.