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Optically pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55 μm wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors fixed on a diamond heat-sink substrate in a flip-chip geometry, incorporated in a V-cavity configuration. A maximum output power of 3.65 W was achieved for a heatsink temperature of 11°C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. This demonstration represents more than five-fold increase of the output power compared to the state-of-the-art flip-chip VECSELs previously reported at the 1.55 μm wavelength range. It opens new perspectives for developing practical VECSEL-based laser systems operating at a wavelength range widely used in many applications.

High power semiconductor disk lasers (SDLs) with near-diffraction limited beam quality were demonstrated. The influence of the incident angle, operation temperature, cavity length and curvature radius of the output coupler mirror on the beam quality were investigated. The condition for near-diffraction limited beam quality was analyzed. Choosing the pump spot size 10%–20% smaller than the fundamental mode size is the roughly optimized condition for achieving near-diffraction limited beam quality in SDLs. Finally, the SDL with an output power of 12.9 W and M2

A high-power 200-GHz extended interaction oscillator (EIO) is designed by large-signal analysis. Analyzing different resonant modes, we calculated the mode called, here, as ${L}_{{1}} $ to be the most efficient one for our structure. From eigenmode analysis, it was predicted that the resonator-slow wave structure (SWS) coupling region has a considerable effect on resonant RF mode due to a ${L}_{{1}} \rightarrow {L}_{-{1}} $ mode transformation, where ${L}_{-{1}} $ is a parasitic low-output power resonant mode of the resonator. Using the eigenmode outcomes in addition to large-signal results, we found the optimum dimensions for the coupling region. The designed oscillator was then simulated by Particle-in-Cell (PIC) solver, leading to approximately the same results as those predicted by the mentioned procedure. The observed mode competition of different modes of the oscillator is analyzed and then removed by inserting a lossy layer at a proper location. By properly introducing a stub mode tuner near the output coupler, we could selectively excite the ${L}_{{1}} $ mode and maximize the RF output power to values even higher than those observed in the absence of mode tuner. Stable RF powers up to 2 kW are predicted to be obtainable by the sheet electron beams with beam densities lower than the state of the art.

The diode-end-pumped continuous-wave (CW) properties of Nd:Gd0.69Y0.3NbO4 laser were investigated and optimized. By optimizing the parameters of the laser, the output power had been improved. With the 320 μm waist radius of pump beam, 40 mm length of the laser resonator, 5% transmission of output coupler and 6.13 W absorbed pump power, the maximum value of the laser output power was 2.76 W and the slope efficiency was 51.2%. The optical quality images of laser beam were also shot and presented, when the parameters of the laser were in the best condition.

We demonstrate that it is possible for a few-layer WSe2/Sapphire to act in specific high-gain solid-state lasers as both saturable absorber for passive Q-switching and as etalon mirror for output coupling. A passively Q-switched Yb:LuPO4 microchip laser formed in this manner is realized. With 11.5 W of pump power absorbed, a maximum output power of 1.8 W is produced at a pulse repetition rate of 1.2 MHz with a slope efficiency of 25%; the resulting pulse energy, duration, and peak power are, respectively, 1.5 μJ, 30 ns, and 50 W. Our work provides a simple way of making compact, reliable, high-repetition-rate pulsed microchip or miniature solid-state lasers based on 2D saturable absorbers.

Broadband sum frequency conversion of a slab RF discharge Q-switched CO laser system was performed with two BaGa2GeSe6 crystals resulting in its spectrum lying within 1.7–6.0 μm spectral range. The first BaGa2GeSe6 crystal was located in the CO laser cavity and operated as both CO laser sum frequency (second harmonic) generator and laser output coupler. Another BaGa2GeSe6 crystal was applied for external third harmonic generation, i.e. as sum frequency generator for fundamental CO laser radiation and its sum frequencies obtained within the cavity. Peak powers of fundamental CO laser radiation, its second and third harmonics were up to 4.7 kW, 100 W and 0.5 W, respectively.

A Nd3+ doped Gd0.1Y0.9AlO3 crystal was successfully grown using the Czochralski method. The segregation coefficient of Nd3+ ions was found to be as large as 0.76 in Gd0.1Y0.9AlO3 host. Based on the Judd-Ofelt theory, the three intensity parameters Ω2,4,6, radiative lifetimes, branching ratios were calculated to analyze the absorption and emission properties of the as-grown crystal. It is found that the width of the absorption band at around 880 nm is 29 nm, indicating that the Nd:Gd0.1Y0.9AlO3 crystal can be pumped efficiently by laser diodes. Furthermore, the large full width at half maximum at 1083 nm and long fluorescence lifetime (189.53 μs) were obtained, which means that the Nd:Gd0.1Y0.9AlO3 crystal may be an attractive host for ultrashort pulse and tunable broadband lasers. Being pumped by an 880 nm laser diode, the laser operation of Nd:Gd0.1Y0.9AlO3 crystal at 1.0 μm was obtained for the first time. A maximum output power of 677 mW was obtained with the 10% output coupler, corresponding to an optical-to-optical conversion efficiency of 22.16% and a slope efficiency of 27.80%. All these results show that Nd:Gd0.1Y0.9AlO3 crystal is a new mixed laser host which is suitable for 880 nm laser diode pump.

In this paper, we demonstrate the self-Q-switched (SQS) operation of a Nd:GdTaO4 laser with different output couplers. The SQS pulse trains are obtained by slightly adjusting the output coupler (OC) under stable continuous wave (CW) operation. In the SQS operation, we observe an output laser with the laser line at 1,066 nm. Under a pump power of 3.8 W, the laser designed shows the following results: (1) with an OC of 5%, the average output power is 0.249 W, the pulse width is 2.83 μs, and the repetition rate is 48.9 kHz, (2) with an OC of 10%, the average output power is 0.299 W, the pulse width is 3.62 μs, and the repetition rate is 53.0 kHz. In a word, the laser system designed is quite stable and suitable for generation of subnanosecond pulses.

A diode-pumped MoS2 passively Q-switched Nd:Gd0.69Y0.3NbO4 laser at 1066 nm was demonstrated for the first time. The maximum continuous (CW) wave output power of 1.77 W was obtained when the absorbed pump power was 7.28 W and the transmission of flat output coupler was 25%. The maximum slope efficiency reached 33.3%. The pulsed laser with high repetition rate was obtained when the two-dimensional (2D) MoS2 material was used as the saturable absorber. The highest repetition rate and the narrowest pulse width were reached 112 kHz and 532 ns, respectively.

Being different from the laser diode-pumped laser, the solar-pumped laser could not be analyzed directly by the model of the laser diode-pumped laser. A model about side-pumped four-level Nd3+:YAG solar laser is proposed, where the solar spectrum as well as Nd3+:YAG absorption spectrum is taken into account. The model is verified by the comparison between the calculated and experimental result. Then based on the proposed model, the effect of the beam waist radius, the rod radius, and the transmission of the output coupler on the output laser power is demonstrated, respectively. It is clear that, in order to obtain the maximum output laser power, we should optimize these parameters. Finally, for the given Nd3+:YAG rod, the simultaneous optimization about the beam waist radius and the transmission of the output coupler to maximize the output power is performed. The work may be of help for the choosing of the optimum value of the experimental parameters.

We report a high-beam-quality long pulse 532 nm laser, which can operate in wide range of temperature. By using a master-oscillator power amplifier (MOPA) system and LBO extracavity-frequency-doubling, we achieved 532 nm laser with the maximum output power of 32 W, the pulse frequency of 12 kHz, and the pulse width 90.2 ns. In addition, the beam quality factors reached M2 x = 1 . 31 , M2 y = 1 . 36 , respectively. In order to get long pulse, apart from choosing suitable transmissivity of output coupler, we also spreaded the cavity length with a 4f imaging system. The laser was proved to be stable when the ambient temperature changed from −19 °C to 27 °C. Compared to other green lasers, this laser can be applied in Rayleigh beaconing because of its long pulse and wide range of working temperature.

A diode-pumped passively Q-switched Nd:GSAG laser at 1060 nm with a novel two-dimensional tungsten disulfide (WS2) saturable absorber was demonstrated for the first time. In the continuous-wave operation, the maximum output power of 4.68 W was obtained with the output coupler transmission of 10%, at absorbed pump power of 9.95 W. The corresponding slope efficiency benefiting from high doping concentration (3%) of Nd:GSAG was up to 56.9%, which reached the highest value for Nd:GASG laser at 1060 nm, as far as we know. In the passively Q-switched operation, when the absorbed pump power was 3.96 W, pulse width and repetition rate were 1.5 μs and 146.9 kHz, respectively.

10 at.% Yb:Y3Sc1.5Al3.5O12 (Yb:YSAG) transparent ceramics were fabricated by the solid state reactive of high-purity Y2O3, α-Al2O3, Yb2O3 and Sc2O3 powders, utilizing MgO and tetraethoxysilane (TEOS) as the sintering aids. The Yb:YSAG ceramic sample sintered at 1820 °C for 10 h has a dense and homogenous microstructure with average grain size of 26.9 μm, whose in-line transmittance reaches 83.2% at 1100 nm (2 mm thick). The absorption and emission cross sections are calculated to be 5.09 × 10−21 cm2 at 941 nm and 12.33 × 10−21 cm2 at 1031 nm, respectively. The full width at half maximum (FWHM) of the main emission peak centered at 1031 nm is 12.4 nm, which is about 1.3 times larger than that of the 10 at.% Yb:YAG ceramics. By using the three-mirror resonator, the Yb:YSAG ceramic laser output power of 1.67 W at 1031 nm and slope efficiency of 13.1% were obtained with an output coupler (OC) of T = 5%.

Advances in vortex lasers with simplified robust designs that provide high purity vortex light with high power and efficiency, will help drive progress in material processing, communication and quantum technologies. We demonstrated in our earlier work [1] , [2] that a conventional laser, lasing on the fundamental Gaussian mode, can be converted to have a vortex output using a modified Sagnac ring, or vortex output coupler (VOC). This VOC provides handedness switchable LG 0±1 output, with variable output coupling. Here we report the highest average power vortex laser, to the best of our knowledge, operating in CW and Q-switched modes.

Here we compare the efficiency and beam parameters of different single-bounce Nd:YLF 4 resonators. A total of five cavities were made by changing both, the curved mirror and the output coupler of the resonator. The best configuration resulted in a cavity that generated a record optical-to-optical efficiency of 63.3% and 66.4% of slope efficiency, with a peak output power of 64.5 W for a pumping power of 101.8 W at 797 nm.

A compact Q-switched laser head emitting radiation at wavelength 1318 nm was designed and constructed. This laser was based on a separate Nd:YAG gain part and V:YAG saturable absorber. The dielectric mirrors of the laser resonator were directly deposited on the Nd:YAG crystal (pumping mirror highly reflecting at 1318 nm radiation; highly transparent for 808 nm and 1064 nm) and on the V:YAG crystal (output coupler with reflection 90 % at 1318 nm; highly transparent at 1064 nm). To decrease the influence of thermal effects and to reduce the residual unabsorbed pumping radiation, a 16 mm long low doped (0.85 at.% Nd/Y) Nd:YAG crystal was used. Similarly, the saturable absorber was based on V:YAG with low absorption coefficient (∼ 0.2 cm−1), corresponding to an 8 mm long V:YAG crystal (initial transmission 85% at 1.3 μm). For longitudinal Nd:YAG pumping, a fibre coupled (core diameter 400 µm; NA = 0.22; wavelength 808 nm, Pmax = 16W) laser diode was used. The pumping diode was operated in a pulsed regime with a repetition rate from 10 to 1000 Hz. The pumping pulse length was set to generate just one generated Q-switched pulse (420 μs for 10 Hz, 220 μs for 1 kHz). In the whole range of tested frequencies, the laser generated stable ∼ 15 ns long (FWHM) pulses with energy up to 160 µJ and peak power ∼ 10 kW. The output beam with TEM00 cross-section was linearly polarized (degree of polarization < 99%). The relative deviation of pulse duration, pulse energy, and pulse peak power at a fixed pumping repetition rate was lower than 1 %. The change of these parameters for the maximum change of pumping repetition rate was not greater than 20%.

Two different mid-infrared (mid-IR) crystalline laser active media of Zn1-xMnxSe and Zn1-xMgxSe with similar manganese or magnesium ions amount of x ≈ 0.3 co-doped by divalent chromium (Cr2+) and iron (Fe2+) ions were investigated at cryogenic temperatures and compared for different excitation wavelengths used. Both single crystals were synthesized by high pressure Bridgman method and their thickness were 2.6 mm and 5 mm, respectively. Crystals were investigated under three excitation wavelengths of the Q-switched Er3+:YLF laser at ~1.73 μm, Q-switched Er3+:YAG laser at ~2.94 μm, and the gain-switched Fe2+:ZnSe laser operated at liquid nitrogen temperature of 78 K at a wavelength of ~4.05 μm. Spectroscopic and laser output characteristics were measured: absorption and fluorescence spectra, laser output pulse duration, mean output energy, and laser oscillation spectra. Both laser systems were able to generate radiation by Cr2+ or by Fe2+ ions under direct excitation, or by Fe2+ ions via the Cr2+ → Fe2+ energy transfer depending on the excitation wavelength and the output coupler conditions. Fe2+ ions in Cr2+,Fe2+:Zn1-xMnxSe and Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.3) laser systems at 78 K pumped by Er3+:YLF laser radiation at ~1.73 μm via the energy transfer mechanism generated laser radiation at the wavelengths of ~4.4 μm and ~4.8 μm at 78 K, respectively. Obtained results have shown a possibility of developing novel coherent laser systems in mid-IR region (~2.3 – 2.5 μm and ~4.4 – 4.9 μm) based on AIIBVI matrices. Thus, possibility to excite the Fe2+ active ions in both samples directly by ~2.94 μm as well as ~4.05 μm radiation or eventually in a compact way through the Cr2+ → Fe2+ ions energy transfer-based mechanism by ~1.73 μm radiation was demonstrated.

We investigated high energy, near and mid-infrared optical vortex lasers formed by a 1 μm optical vortex-pumped KTiOAsO4 (KTA) optical parametric oscillator. The orbital angular momentum (OAM) of the pump beam can be selectively transferred to the signal or idler output by changing the reflectivity of the output coupler. With this system, 1.535 µm vortex signal output with an energy of 2.04 mJ and 3.468 µm vortex idler output with an energy of 1.75 mJ were obtained with a maximum pump energy of 21 mJ, corresponding to slope efficiencies of 14% and 10%, respectively. The spectral bandwidth (full width at half maximum, FWHM) of the signal and idler vortex outputs were measured to be Δλs ~ 1.3 nm (~ 5.5 cm−1) and Δλi ~ 1.7 nm (~ 1.4 cm−1), respectively.

This paper presents a novel high-efficiency surface-emitting laser emitting at 1550nm (long-wavelength). This laser is based on the grating structure, and it retains the advantages of edge-emitting lasers while realizing the surface-emitting through a high contrast grating which can be fabricated by ordinary photolithography and etching. This novel surfaceemitting laser has two resonant cavities. One laser resonator is formed by the first-order grating which can provide feedback in the longitudinal direction and fulfill the longitudinal oscillation build-up; the other one is formed by the sixth-order grating in the vertical direction and acts as a light output coupler. The surface-emitting efficiencies of the novel proposed laser increased a lot by forming a laser resonator in the vertical direction. Besides, the grating period of sixth-order grating is longer than traditional first-order grating. A grating period over 1000nm as well as no regrowth is a key prerequisite for simple fabrication. The laser mode properties were analyzed by the traveling-wave model and the Finite-Difference TimeDomain (FDTD) solution. The surface-emitting properties were analyzed by the famous Green’s Function analysis. Simulation results show that a single-mode operation with a linear output power of 20 mW and a high external surfaceemitting efficiency of 45% can be achieved using this novel design.

We report mechanically Q-switched 2.94 µm Er:YAG laser based on spinning mirror with 805 mJ output energy in a single 61 ns pulse at 1 Hz repetition rate and 670 Hz rotational rate of the spinning mirror. This record output energy was achieved with the use of 300 mm long MQS Er:YAG laser cavity consisted of 70% output coupler, 7x120 mm AR coated Er(50%):YAG crystal and spinning HR mirror. The maximum output energy was limited by the optical damage of the Er:YAG AR coatings.

A 1908 nm Tm:YLF laser, passively Q-switched (PQS) using a Cr:ZnS saturable absorber, is shown to generate significantly higher pulse energy and peak power than previously reported. Using a compact 13 cm-long, plano-concave resonator cavity, the end-pumped Tm:YLF laser generated 15.6 mJ, 26ns FWHM pulses, corresponding to a peak power of 600 kW, with a 0.5kHz PRF, and 7.8W average power. A 10 cm-long laser generated 10 mJ, 20 ns long pulses, with a 1 kHz PRF and 10 W average power. A laser utilizing the shortest, 4.5 cm-long cavity, generated 7 ns pulses with a pulse energy of 3.7mJ. All of the laser configurations incorporated a Volume Bragg Grating (VBG) high reflectivity cavity mirror to lock the laser wavelength and polarization. To minimize the energy fluence at Cr:ZnS saturable absorbers (To=88.6% and To=91.6%), they were placed near the concave output coupler where that laser mode field area of the plano-concave laser resonator was at its maximum.

This paper aims to characterise, both experimentally and theoretically, the dynamics which occur during the turn on transient of a long cavity semiconductor laser. The laser comprised of a semiconductor optical amplifier (SOA), centered around 1300nm, a tuneable narrow bandwidth filter, for wavelength selectivity, a polarisation controller, an output coupler and multiple single mode fibre isolators to ensure the unidirectional propagation of light within the ring cavity. The bias current driven to the SOA was periodically switched on and off in order to examine the laser dynamics within each cavity round trip. It is observed that the laser intensity builds up in a step-wise manner, with each step corresponding to one cavity round trip. By examining the space-time diagrams of the lasers intensity during the turn on, it is seen that the laser will initially randomly oscillate before transitioning into a semi-stationary state. After a certain amount of round trips the laser may develop one or more localised structures, characterised by their short and fast drops of intensity. In this paper we also aim to not only explain the formation of these localised structures but also expand on their development by examining the phase evolution of their electric field.

We describe a compact mid-IR source utilizing an intracavity, non-critically phase matched potassium titanyle arsenate (KTA) optical parametric oscillator (OPO) placed inside a passively Q-switched (PQS), 1.064 µm Nd:YAG laser resonator. A 45-degree dichroic beam splitter was employed to split the 1.064 µm resonator leg from the 1.5 μm/3.5 μm KTA OPO cavity that was singly resonant for the 1.5 μm signal. The 20 mm long KTA crystal was placed in the shared-path section of both cavities, with the KTA OPO output coupler partially reflective at 1.5 μm, and highly transmitting at 3.5 μm. With the Nd:YAG pumped by a 3-λ 12-bar diode stack at 5 Hz PRF, the KTA OPO generated 23.1 mJ signal pulses at 1.5 μm and 9.8 mJ idler pulses at 3.5 μm. To further increase the 3.5 μm energy, a cadmium silicon phosphide (CSP) optical parametric amplifier (OPA), phase matched for 1.5 μm-pumped amplification of 3.5 μm radiation, was placed immediately after the KTA OPO output coupler. A maximum 3.5 μm pulse energy of 13.2 mJ was measured after the OPA, with an additional 4.2 mJ generated at 2.8 μm. The 3.5 μm pulses had a measured temporal duration (FWHM) of 27 ns, corresponding to a peak-power of approximately 490 kW. This paper will detail the Nd:YAG pumped intracavity KTA OPO / CSP OPA and optimization of its performance as a pulsed midIR source.

A new, to the best of our knowledge, output coupler (OC) with enhancement of the cavity reflectivity is proposed to remarkably elevate the output powers and efficiencies of diode-pumped N d : G d V O 4 / K G W Raman yellow-orange lasers. The cavity reflectivity is effectively increased by using the double-sided dichroic coating on the OC. In comparison with the conventional single-sided coating, the conversion efficiency can be boosted from 15% to 26.3% in the experiment of a yellow laser at 578.8 nm, and the maximum output power can be increased from 5.7 to 10.5 W in the quasi-continuous-wave mode with 50% duty cycle and frequency of 500 Hz. Furthermore, in the operation of an orange laser at 588 nm, the maximum output power can be improved from 5.6 to 7.0 W by replacing the conventional OC with the new one.

We demonstrate operation of a mid-infrared dysprosium-doped fiber laser with emission at 3388 nm, representing the longest wavelength yet achieved from this class of laser, to the best of our knowledge. Oscillation far removed from the D y 3 + gain peak around 3 µm is achieved through the design of a high feedback optical cavity employing a directly inscribed fiber Bragg grating as the output coupler. Laser performance is characterized by a slope efficiency with respect to injected pump power of 38% and maximum output power of 134 mW, an improvement of at least three orders of magnitude over prior attempts at long wavelength D y 3 + fiber laser operation. This wavelength coincides with a maximum in the absorption coefficient of PMMA, which we exploit for preliminary demonstration of the utility of this source in polymer processing.

We report a flashlamp pumped mechanically Q-switched (MQS) 2.94 μm Er:YAG laser based on a spinning mirror with a highest output energy of 805 mJ at a pulse duration of 61 ns and 13 MW of peak power at 1 Hz repetition rate. This record output energy was achieved with the use of 300 mm long MQS Er:YAG laser cavity consisting of a 70% output coupler, 7 × 120 mm AR coated Er(50%):YAG crystal, and 4200 rad/s angular speed of the spinning mirror. The pulse jitter was also measured by using optical triggering and was smaller than 10 ns for 150 ns Q-switched pulses, which could be applicable to many laser applications where precise synchronization of pulses is required.

We present an operational characterization of a vertical-external-cavity surface-emitting laser emitting around 739 nm with over 150 mW in a single fundamental spatial mode. Results show that the laser is capable of oscillating on a single cavity axial mode at 740 nm for up to 22 mW. Tuning of the optical emission is shown to reach 737.3 nm. Furthermore, at best performance, the laser exhibits a slope efficiency of 8.3% and a threshold power of 1.27 W for an output coupler reflectivity of 98%.

We demonstrated a 202 W Tm:YLF slab laser using a reflecting volume Bragg grating (VBG) as an output coupler at room temperature. Two kinds of active heat dissipation methods were used for the VBG to suppress the shift of wavelength caused by its increasing temperature. The maximum continuous wave (CW) output power of 202 W using the microchannel cooling was obtained under the total incident pump power of 553 W, the corresponding slope efficiency and optical-to-optical conversion efficiency were 39.7% and 36.5%, respectively. The central wavelength was 1908.5 nm with the linewidth (full width at half maximum) of 0.57 nm. Meanwhile, with the laser output increasing from 30 to 202 W, the total shift was about 1.0 nm, and the wavelength was limited to two water absorption lines near 1908 nm. The beam quality factors M2 were measured to be 2.3 and 4.0 in x and y directions at 202 W.

We experimentally demonstrate, for the first time to our knowledge, that upconversion pumping can be employed with a 1064-nm fiber laser to achieve tunable laser operation with 8 at. % T m 3 + : K Y 3 F 10 crystal near 1.9 µm, in addition to the previously explored upconversion pumping of the 2.3-µm laser transition. Two different sets of cavity optics were used to investigate lasing at 1.9 and 2.3 µm, corresponding to the laser transitions 3 F 4 − 3 H 6 and 3 H 4 − 3 H 5 , respectively. In the case of the 3 F 4 − 3 H 6 laser transition, an x-cavity laser oscillator was constructed with a 2.3% output coupler and as high as 142 mW of output power was obtained at an incident pump power of 1.9 W at 1064 nm. Tunable laser operation could be obtained between 1849 and 1994 nm by using C a F 2 and suprasil prisms. The highest slope efficiency of 29% with respect to average absorbed pump power was obtained with a 5.5% output coupler. For the case of 1.9 µm lasing, it was further demonstrated that the nonlinear absorption of the crystal at 1064 nm depends on the intracavity laser intensity as well as the pump intensity. The 3 H 4 − 3 H 5 laser transition was also investigated with the same crystal in a z-cavity configuration under upconversion pumping, giving as high as 130 mW of output power at the central wavelength of 2344 nm with 1.6 W of incident pump power.

We experimentally demonstrate a diode-pumped passively Q-switched Yb:Lu3Al5O12 ceramic laser operating at 1031 nm or 1047 nm based on a semiconductor saturable absorber mirror (SESAM) and an output coupler (OC) of different transmission (T). For an OC of T=7.5% and an absorbed power of 9.25 W, the laser operates at 1031 nm with a maximum average output power of 1.47 W, the corresponding optical-to-optical efficiency of 15.85%, and the slope efficiency of 19.04%, respectively. The pulse width and the pulse repetition frequency (PRF) are about 1.23 μs and 245.04 kHz, respectively. For an OC of T=1.6% and an absorbed power of 9.25 W, the laser operates at 1047 nm with a maximum average output power of 0.85 W, the corresponding optical-to-optical efficiency of 9.21%, and the slope efficiency of 8.43%, respectively. The pulse width and the PRF are 1.49 μs and 112.63 kHz, respectively.

Spectral beam combining (SBC) is a regular approach of utilizing semiconductor laser arrays, as it can greatly improve output power and maintain the beam quality. External cavity spectral beam combining based on the six elements quantum cascade laser (QCL) array, with a 10μm ridge width and a pitch of 60μm, was realized. The divergence of the light from output coupler is 0.6mrad and 3.8mrad, for fast axis (perpendicular to the array) and slow axis (parallel to the array), respectively. Under a condition of 10kHz repetition frequency and 1μ s pulse width, the array’s peak power is 2.9W without SBC system. The peak power of 0.9W and 1.34W is achieved when utilizing a output coupler based on Ge without anti-reflection (AR) coating or with AR coating, respectively. Corresponding the beam combining efficiency is 31.0% and 46.2%, respectively. We recorded the cross-locking phenomenon when tuning array by rotating the external cavity output coupler angle, as a relatively close element spacing results in mutual locking of adjacent elements. The system could tuning over 99cm-1 (1904cm-1--2003cm-1).

We measured complex refractive indices of materials that transmitted well in the terahertz (THz) range using a tunable, monochromatic pulsed THz wave source and a high-sensitivity semiconductor detector. This approach is based on simple monochromatic transmission power measurements. Contrast enhancement by refractive index cladding was employed to measure the complex refractive indices. The experimental results were in good agreement with previously reported values. These results suggested that our approach could be used to quickly analyze material properties, such as surface roughness, and to determine the complex refractive indices of liquids or gases. In addition, as an application of the findings obtained here, we applied an anti-reflection polymer film to the silicon prism that served as an output coupler of the THz wave source. The film reduced surface reflection by 25%.

Various forms of light therapy have been practiced around the world for many years. Among them the laser therapy has experienced a prosperous development in recent years. More and more laser equipment has been used in this field. In this study, we present an optical pumped vertical external cavity surface emitting laser (OP-VECSEL) system using semiconductor gain chip as the lasering material. Through carefully design of the semiconductor gain chip structure, the fundamental and frequency doubled laser emitting wavelength can be set to the range of 1040-1160nm and 520nm-580nm which is the mainly laser-tissue interact wavelength range for laser therapy. In a flat concave short cavity laser assembly test, the maximum fundamental frequency output power of the system is 1.6W using a 2% output coupler. Through a frequency doubling crystal, the continuous output power of the yellow green light can achieve 24mW.

We report a new method for electronic control of lasing regimes in lasers with compact all-fiber cavities. The method relies on incorporation of a waveguide electro-optic switch which plays the dual role as a variable output coupler and an intracavity intensity modulator. We explored this method in a laser comprised of a semiconductor optical amplifier and an all-fiber cavity. Nanosecond pulse lasing at 1540 nm was achieved in mode-locked, harmonically mode-locked, and cavity-dumping regimes at different repetition rates on kHz and MHz scales. This method is suitable for different fiber lasers and will allow even picosecond pulse lasing with an appropriately fast switch.

A compact X-band power booster TWT was designed and developed for space applications that provides minimum of 350W of peak RF output power with 25% duty over a bandwidth of 800MHz with RF efficiency of 22% and minimum gain of 27 dB. This TWT uses an electron gun operating at a cathode voltage of 6 kV and current of 275 mA with beam filling factor of 0.5. The electron beam is focused using PPM structure with peak field of 2600G generated using Sm2Co17 magnets. The SWS comprises tungsten tape helix supported by three azimuthally, symmetrically placed T-shaped APBN support-rods inside a metallic envelope. The dimensions of SWS were derived using the in-house parametric codes and optimized using Eigen-mode solver of CST Studio to achieve the required dispersion characteristics. The beam-wave interaction analysis was carried out using the in-house 1D-codes and was optimized using 3D PIC simulations. The SWS employs positive velocity taper near the output coupler in order to enhance RF interaction efficiency and to reduce the second harmonic content. The length of the SWS is around 93 mm. A 3-stage depressed collector is used to enhance the overall efficiency of the TWT. A prototype TWT is developed and tested for performance and has achieved overall efficiency of 45% with TWT length of 250 mm and weight of 980 grams. This TWT is subjected for operational temperature cycling at +70°C and -20°C and also random vibration to verify the structural integrity and has met the requirements.

A low-voltage backward wave oscillator based on staggered double vane structure is designed in this paper and a novel straight-waveguide input/output coupler is also proposed. The high-frequency characteristics and transmission characteristics of the structure are calculated and the results of the circuit show that the reflection coefficient is below -10dB in the frequency range of 250-300GHz. The beam-wave interaction is also carried out and the output power is greater than 20mW within the frequency range of 290GHz to 300GHz, which the corresponding operating voltage is 3800V to 4500V. And a maximum output power of 2W is reached at 300GHz.

Reported is an experimental study of a new approach to laser synthesis of arbitrary optical waveforms with nanosecond resolution. This approach relies on combination of a fast-recovery active medium (semiconductor optical amplifier, SOA) and a waveguide electro-optic switch which plays the role of a variable output coupler in a SOA-fibre laser. Programmable electronical control of output coupling allowed production of periodic and aperiodic arbitrary optical waveforms profiled with a nanosecond resolution at arbitrary repetition rates ranging from single shot to tens of MHz. The proposed method is distinguished by its simplicity, high efficiency, and relatively narrow output radiation spectrum.

In this study, the output power and wavelength tuning performance of ring type erbium doped fiber laser (EDFL) were examined theoretically and experimentally. In order to investigate the effects of parameters such as erbium doped fiber (EDF) length, output coupler ratio, erbium ion density, pump power on the performance of ring-type EDFL, two-level model of EDFL was numerically analyzed and experimental characterization measurements were performed using an EDFL setup. Numerical results, which are in good agreement with the experimental measurements, showed that optimization of the parameters is extremely important for ring type EDFL performance. With the obtained optimum parameters, a moderate output power level (~+4.5 dBm) and a wide wavelength tuning range (~80 nm) covering C+L bands have been achieved.

Coaxial fiber lasers, consisting of a Ho-doped core surrounded by a Tm-doped ring, are studied via experiments and numerical simulations. Previous simulations indicated that coaxial fiber lasers have the potential to reach power conversion efficiencies of up to 54%, but experiments have yielded much lower efficiencies. To understand this difference, a wavelength dimension is added to the previous model. The new simulations explain the discrepancies with the experiments via spectral gain competition and lead to a path to optimize experimental efficiencies. Specifically, an output coupler is spectrally designed to optimize the efficiency of coaxial fiber systems, and a path towards realizing the predicted 54% efficiency is presented. The results indicate that the Tm/Ho coaxial fiber laser has the potential to be a compact and efficient means of producing 2100 nm radiation.

This work presents the design of a high power, two-stage, wideband, balanced power amplifier (PA) implemented in a 90 nm SiGe BiCMOS technology. Asymmetric coupled-line couplers were employed at the input and output of the circuit for impedance transformation and quadrature signal splitting and combining. The design achieves 17.3 dB small-signal gain with 41.8 GHz 3-dB bandwidth from 28.1 GHz to 69.9 GHz. To obtain high output power, two novel Wilkinson baluns were included, together with the output coupler, to achieve an overall 4-way differential power combining. A 24.4 dBm saturated output power (P SAT ) is achieved with a 22.0 GHz 1-dB P SAT bandwidth covering from 45.0 GHz to 67.0 GHz. The circuit shows a peak power added efficiency (PAE) of 14.2% at 60 GHz and the peak PAE is above 11.50% across the 1-dB P SAT bandwidth. The two stages adopt common-emitter power cells with the first stage biased at 2.0 V and second stage at 1.8 V. The chip size is 1.22 mm2 including bondpads.

In this paper, the input and output couplers are designed and simulated for a frequency range of 14.9 to 15.4 GHz Ku-band over 1 kW power. The input coaxial coupler section comprises of an impedance transition with the coaxial ceramic window of 99.5% alumina to handle the maximal input power less than 1 watt. In the output coupler, coaxial to waveguide (WR-62) progression is used to handle the maximal power from the TWT. Initially, the couplers are designed theoretically. Further, the designs are optimized by commercially available 3-D electromagnetic simulation software, micro-wave studio (MWS), computer simulation technology (CST). The Eigen mode simulations for both the couplers give the voltage standing wave ratio (VSWR) value of less than 1.20.

We demonstrate a distributed Bragg reflector fiber laser that is capable of long-term operation at ultra-high temperatures. To form the laser cavity, a piece of Er-doped fiber is fusion spliced to a pair of type II-IR gratings, which are written using a femtosecond laser with a phase mask. Saturated gratings with different reflectivities are fabricated by varying the position of the grating region relative to the fiber core center. An eccentric grating with a relatively low reflectivity is chosen as the laser output coupler, while a regular grating with a higher reflectivity is used as the laser’s high-reflection reflector. After an annealing process, the laser performance is tested at high temperatures. The results show that the laser can operate with a stable output wavelength and no output power degradation at high temperatures up to 1000°C.

A high power gas terahertz laser based on L-shaped cavity was demonstrated. We, for the first time, investigated the output performances of D2O gas 385 μm THz laser by optimizing the output coupler transmittance of the L-shaped cavity both in theory and experiment. Under the pump energy of 1.6 J, the optimum output coupler transmittance was about 0.78 and the optimum gas pressure was about 500 Pa. Up to 8.4 mJ pulse energy at 385 μm was achieved at output coupler transmittance of 0.8, corresponding to a photon conversion efficiency of 43.7%. Pulse width of 120 ns, and beam quality factor M2 of 1.58 were obtained at the highest output energy. In addition, the experimental results are in agreement with the theoretical simulation results.

A short pulse self-starting mode-lock fiber laser with femtosecond pulse width and high repetition rates is demonstrated. The oscillator features linearly cavity employing WDM system with a piece of Yb doped fiber. Semiconductor saturable absorber mirror (SESAM), with modulation depth of 30% and relaxation time of 4 ps, is employed. Two chirped fiber Bragg gratings are adopted. One FBG is placed in the cavity, with wide reflection near 1053nm. It compensates for the residual dispersion of the oscillator cavity elements and serves as an output coupler for the oscillator. The other FBG is placed out of the cavity to compress the pulse width further more. The length of laser cavity is around 10m. This modelock laser can self-start. Pulses as short as 225 fs pulse widths at repetition rates of 20 MHz are generated, with average output power is about 5mW. As all of the optical fiber components are small or bendable, the size of this laser is as tiny as Φ60mm×15mm.This femtosecond mode-lock all fiber laser affords a compact, novel and high-efficiency approach as seed source in the FrontEnd in inertial confinement fusion (ICF) laser illumination schemes.

In this paper, we demonstrated an all fiber laser passively Q-switched by black phosphorus saturable absorber with cylindrical vector beam output. A piece of few-mode fiber Bragg grating was used as the mode-selective output coupler. The repetition rate of the pulse trains increased from 16kHz to 24.9kHz when the pump power tuned from 364mW to 460mW. The maximum pulse energy was 305.2nJ with the shortest pulse duration of 7.5μs under the pump power of 460mW.Both radial polarized and azimuthal polarized pulse output could be achieved by adjusting the polarization controllers. The purity of the cylindrical vector beam output was estimated to be over 95%.

A passively Q-switched mode-locked (QML) operation in Tm, Ho: CaYAlO4 bulk laser was demonstrated experimentally by employing double wall carbon nanotube (DWCNTs) as a saturable absorber. The laser is pumped by a self-made wavelength tunable Ti: sapphire laser, and the pump threshold of Tm, Ho: CaYAlO4 laser was measured as 677 mW by using transmittance of 1.5% output coupler. A stable Q-switched mode-locked operation state was achieved when the absorption pumping power reached 1958 mW. And when the pumping power reached 2.6 W, a maximum output power was 64 mw with central wavelength of 2085 nm, the corresponding repetition frequency of mode-locked pulse was 98.04 MHz, and the modulation depth in Q-switching envelopes is close to 100%.

In this study, we use a hybrid mode-locked external cavity diode laser with subsequent amplification and pulse compression. The system provides laser pulses of 440 fs width (assuming a sech² pulse shape) and 160 mW average output power at a repetition rate of 383.1 MHz. The laser oscillator consists of a double quantum well laser diode with a gain segment of 1080 μm length and an absorber element of 80 μm lengths. The chip’s back facet is covered with a high reflective coating, the front facet with an anti-reflective coating. The resonator itself is operated in a collimated geometry and folded by two dielectric mirrors. The used output coupler provides a transmission of 20 percent, which is coupled into a tapered amplifier. Two Faraday isolators are used to decouple the laser and the amplifier from any back reflections. Subsequently, the pulses are compressed using a single pass Martinez type pulse compressor. Experiments on Two-Photon Polymerization were conducted on a conventional setup consisting of a 2D galvo-scanner system with an attached microscope objective. The oil immersion objective (NA =1.4) focusses the light pulses through a cover glass into a droplet of the photosensitive material. Process monitoring can be achieved by observing the image on a camera placed behind a semi-transparent mirror in front of the galvo-scanner. Using this experimental setup, test structures that consist of free-hanging lines supported by cuboids were produced. In addition, a procedure for automated linewidth measurements is outlined and used for analyzation of the generated structures. This work shows that mode-locked diode lasers can be used for the fabrication of microstructures by Two-Photon Polymerization. Typically used Ti:Sapphire or fiber lasers can be replaced by mode-locked diode lasers for Two-Photon- Polymerization. This allows for much cheaper Two-Photon-Polymerization systems and therefore, may open this field for more application-based research groups.

We demonstrate a wavelength tunable continuous wave single-frequency Cr:ZnSe laser based on a self-seeded ring cavity configuration in this paper. The laser system is based on anti-coated Cr:ZnSe crystal which has a length of 6 mm and a low signal transmission of 15% (at 1908nm). Unidirectional operation of Cr:ZnSe laser is obtained by using a retro-reflecting device which can retro reflect a self-seed laser back into the ring cavity. The transmission of the output coupler is also optimized to get unidirectional operation. With three different birefringent filters inserting in the cavity, single-frequency operation with narrow linewidth is obtained. By rotating the angle of the birefringent filters, the laser’s wavelength under single-frequency operation could be continuously tuned from 2338 nm to 2572 nm. The tuning range is over 200 nm. The maximum single-frequency output power is 0.92 W at wavelength of 2357 nm.