TEM00 Output Research Articles

Investigation of a 100 W Solar-Pumped Disk Laser with TEM00 Output

Investigation of a 100 W Solar-Pumped Disk Laser with TEM00 Output

Continuous Tb-doped fiber laser emitting at ∼5.25 µm

The paper describes a chalcogenide glass fiber laser operating at the wavelength inaccessible to oxide and fluoride rare-earth doped fibers. The lasing fiber had 19 μm diam. selenide core doped with 2 × 1019 cm−3 of Tb3+ ions and 270 μm diam. undoped sulfide cladding. The pump source was a CW 1.98 µm Tm3+ fiber laser. Up to 36 mW TEM00 output was obtained in the 5.20–5.28 µm spectral band.

Dynamically stable single frequency ring resonator from diode pumped Nd:YAG modules with 55.6 W of output power

A Nd:YAG rod single-frequency ring laser based on side-pumped commercial modules is presented. Thermally induced birefringence compensation was applied in a dynamically stable resonator providing 55.6 W of continuous, linearly polarized, TEM00 output. The particular case of a symmetric ring resonator containing one or two focusing rods and a pair of curved mirrors was analyzed and a design technique is presented, allowing for easy, continuous shaping of the stability limits by changing only the distances in the resonator.

Single-frequency fiber amplifier at 1.5 µm with 100 W in the linearly-polarized TEM00 mode for next-generation gravitational wave detectors.

Next-generation gravitational wave detectors require single-frequency and high power lasers at a wavelength of 1.5 µm addressing a set of demanding requirements such as linearly-polarized TEM00 radiation with low noise to run for long periods. In this context, fiber amplifiers in MOPA configuration are promising candidates to fulfill these requirements. We present a single-frequency monolithic Er:Yb co-doped fiber amplifier (EYDFA) at 1.5 µm with a linearly-polarized TEM00 output power of 100 W. The EYDFA is pumped off-resonant at 940 nm to enhance the Yb-to-Er energy transfer efficiency and enable higher ASE threshold. We also performed numerical simulations to investigate the off-resonant pumping scheme and confirm the corresponding experimental results.

End-pumped Nd:YVO4 laser with reduced thermal lensing via the use of a ring-shaped pump beam.

A simple approach for alleviating thermal lensing in end-pumped solid-state lasers using a pump beam with a ring-shaped intensity distribution to decrease the radial temperature gradient is described. This scheme has been implemented in a diode-end-pumped Nd:YVO4 laser yielding 14W of TEM00 output at 1.064μm with a corresponding slope efficiency of 53% and a beam propagation factor (M2) of 1.08 limited by available pump power. By comparison, the same laser design with a conventional quasi-top-hat pump beam profile of approximately equal radial extent yielded only 9W of output before the power rolled over due to thermal lensing. Further investigation with the aid of a probe beam revealed that the thermal lens power was ∼30% smaller for the ring-shaped pump beam compared to the quasi-top-hat beam. The implications for further power scaling in end-pumped laser configurations are considered.

Passive Q-switching of an Er, Yb:glass laser with Co:Mg(Al,Ga)2O4-based glass-ceramics.

Transparent glass-ceramics (GCs) containing Co:Mg(Al,Ga)2O4 nanocrystals (mean diameter of 7-9nm) are synthesized by heat treatments at 850-950°C from magnesium aluminosilicate glass nucleated by TiO2 and doped with Ga2O3 and CoO. The GCs exhibit a broadband A24(F4)→T14(F4) absorption due to the Co2+ ions, low saturation fluence (∼0.5 J/cm2), fast recovery time of initial absorption (∼300 ns), and high laser damage threshold (∼20 J/cm2). They are used for passive Q-switching of a diode side-pumped Er,Yb:glass laser generating 3.1mJ/20ns pulses (peak power, 155kW) at 1535nm with a TEM00 output mode. The Q-switching performance of the Co:Mg(Al,Ga)2O4-based GCs is compared with that for various Co2+-doped GCs and Co:MgAl2O4 single crystal. The prepared GCs are promising for further applications in passively Q-switched Er:YAG and other Er crystalline (or ceramic) lasers.

High-power passively Q-switched Nd:KGW laser pumped at 877 nm

In this work, we demonstrate, for the first time, a high-power passively Q-switched Ng-cut Nd3+:KGd(WO4)2/Cr4+:YAG laser pumped at 877 nm. The maximum average output power of ~1.6 W is obtained at the pump power of 5.22 W, when a saturable absorber with 98 % of initial transmission is used. The corresponding pulse energy is up to 16 µJ. The maximum pulse energy of 25.3 µJ is achieved at a repetition rate of 59 kHz, by employing a saturable absorber with 95 % of initial transmission. The corresponding pulse width and average output power are 89.0 ns and 1.5 W, respectively. A careful cavity design and a good thermal management ensure nearly TEM00 output with M2 ≤ 1.22 within the whole range of operation in both Np and Nm directions at 877 nm pump.

Power scaling of a side-pumped Nd:YLF laser based on DBMC technology

This work demonstrates the power scalability of double-beam-mode controlling, a technique that has generated the highest optical efficiency reported so far for Nd:YLF lasers. We analyze two types of power scaling possibilities by numerical simulations: multiplication of intracavity pump modules and MOPA configuration. About 44 W of TEM00 output power at 1053 nm was experimentally demonstrated with a beam-parameter product of 1.07 × 1.15. The results show great ease of power scaling without sacrificing beam quality.

15 W Single Frequency Optically Pumped Semiconductor Laser With Sub-Megahertz Linewidth

We report on a single frequency optically pumped semiconductor laser exhibiting an output power of 15 W in continuous wave operation. The GaAs-based structure presents an emission wavelength of 1020 nm and a tuning range , with a continuous tunability of 9 GHz. The TEM00 output beam exhibits very low transverse phase fluctuations across the entire mode, leading to a beam quality . A free-running laser linewidth of 21 kHz has been deduced from frequency noise measurements for a sampling time of 1 ms and increases to 995 kHz for a sampling time of 1 s.

External-cavity diode laser in second-order Littrow configuration

In this Letter, we propose and demonstrate an external-cavity diode laser in second-order Littrow configuration. This topology utilizes a low-efficiency diffraction grating to establish a high-finesse external cavity, strong optical feedback, a high polarization discrimination, and a circular TEM00 output mode. In our proof-of-concept experiment, we realized a cavity with a finesse of 1855, being, to the best of our knowledge, the highest value ever reported for a three-port-grating-coupled cavity. With optical feedback, the laser threshold of the laser diode employed was reduced by a factor of 4.

A 10 W Diode-Pumped Solid-State Green Laser

This paper reports a 10W solid state green laser TEM00 mode output operation, pumped by 3 x 40W LD arrays. The theoretical analysis of the cavity stability and operation mode selection are presented. To make the system more compact, a Brewster plate is specially designed to function both as a polariser as well as a green output coupler.In the experiment, we obtain maximum 10W green laser TEM00 output at 10kHz by establishing a concave-flat stable resonator. Angle mismatch in the frequency doubling is corrected by optimising the crystal temperature to maximise the laser output. The system is completely enclosed in a customised chassis, enabling further integration of scanner head for application testings as well as inhibiting environmental factors that will affect the performance of the laser.

2 MHz AO $Q$-switched ${\rm TEM}_{00}$ Grazing Incidence Laser With 3 at.% Neodymium Doped Nd:YVO$_{4}$

We present a detailed experimental and theoretical study of the ultrahigh repetition rate AO Q -switched TEM00 grazing incidence laser. Up to 2.1 MHz Q-switching with TEM00 output of 8.6 W and 2.2 MHz Q -switching with multimode output of 10 W were achieved by using an acousto-optics Q -switched grazing-incidence laser with optimum grazing-incidence angle and cavity configuration. The crystal was 3 at.% neodymium doped Nd:YVO4 slab. The pulse duration at 2 MHz repetition rate was about 31 ns. The instabilities of pulse energy at 2 MHz repetition rate were less than plusmn6.7% with TEM00 operation and plusmn3.3% with multimode operation respectively. The modeling of high repetition rate Q-switched operation is presented based on the rate equation, and with the solution of the modeling, higher pump power, smaller section area of laser mode, and larger stimulated emission cross section of the gain medium are beneficial to the Q-switched operation with ultrahigh repetition rate, which is in consistent with the experimental results.

Compact TEM00 Nd:YVO4 slab laser end pumped by an LD bar

In this paper, we present a laser-diode (LD) bar end-pumped Nd:YVO4 slab laser, which uses a simple coupling system and a compact quasi-concentric resonator (QCR). A TEM00 output was obtained with a pump width varied from 2.57 to 9.44 mm and the slope efficiency is kept at about 48%. Under 40-W pumping, a maximum TEM00 output of 15.84 W was achieved and the optical-to-optical efficiency was 39.6% correspondingly.

High performance 2.2 μm optically-pumped vertical external-cavity surface-emitting laser

We report the operation of an optically-pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) oscillating at wavelengths up to 2.2 µm and at output powers greater than 200 mW. This versatile platform provides a broad gain bandwidth, and may be tuned and/or controlled by the addition of elements into the external cavity. Moreover, the nature of the semiconductor structure permits precise engineering of the operating wavelength---not possible with traditional solid state crystalline lasers---and the thin (few microns) pump absorption region, coupled with the external cavity control, permits the mode conversion of a low brightness pump into a high quality TEM00 output.

Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm

A high-power Er:YAG laser that is in-band pumped by a high-power cladding-pumped erbium-ytterbium codoped fiber laser operating at 1532 nm is reported. The Er:YAG laser produced 60.3 W of continuous-wave output at 1645.3 nm in a beam with M2 approximately equal to 3 for 82 W of incident pump power and 20 W of TEM00 output with M2 < 1.2 for 32.4 W of incident pump power. The slope efficiency with respect to incident pump power at pump powers of >20 W was approximately 81%. In the Q-switched mode of operation, a slightly modified resonator configuration incorporating an electro-optic Q switch produced pulses of approximately 4 mJ energy and approximately 100 ns (FWHM) duration, corresponding to a peak power of approximately 42 kW at a repetition rate of 1 kHz for an incident pump power of 16.8 W. The prospects for further improvement in continuous-wave and Q-switched performance are discussed.

Tunable high-power high-brightness linearly polarized vertical-external-cavity surface-emitting lasers

We report on the development and the demonstration of tunable high-power high-brightness linearly polarized vertical-external-cavity surface-emitting lasers (VECSELs). A V-shaped cavity, in which the antireflection-coated VECSEL chip (active mirror) is located at the fold, and a birefringent filter are employed to achieve a large wavelength tuning range. Multiwatt cw linearly polarized TEM00 output with a 20nm tuning range and narrow linewidth is demonstrated at room temperature.

Recent ITER-Relevant Gyrotron Tests

Recent tests of two different megawatt-class gyrotrons at CPI provide a design baseline for the 120 GHz, 1 MW CW gyrotrons required by ITER for plasma start-up. The two gyrotron designs include a 140 GHz, 900 kW CW device that was delivered to the Max Planck Institute for Plasma Physics in Greifswald, Germany, and a 110 GHz, 1.3 MW CW gyrotron that was recently tested at CPI. Both gyrotrons utilize many of the same features that are foreseen for the ITER 120 GHz gyrotrons. These features include: single-anode magnetron injection electron guns, high-efficiency internal converters that produce a pure TEM00 output mode, 88-mm-diameter diamond output windows and single-stage depressed collectors. In tests at CPI, the 140 GHz gyrotron achieved 500 kW power levels for 700-s pulses and 930 kW for short pulses. Long-pulse tests of the gyrotron, at beam currents above the 25-A test-set limit at CPI, were performed in Greifswald and resulted in output power levels of up to 900 kW for 30-minute pulses. In short-pulse operation at CPI, the 110 GHz gyrotron has achieved power levels of 1.28 MW. In long-pulse tests of the gyrotron, power levels of 500 kW were obtained for 10-s pulses.

High-power TEM00 grazing-incidence Nd:YVO4 oscillators in single and multiple bounce configurations

We describe single and multiple grazing incidence bounce laser configurations and present results of scaling a diode-pumped Nd:YVO4 amplifier to higher powers than previously demonstrated using these schemes. In a Nd:YVO4 slab amplifier laser employing a single total internal reflection bounce configuration 50.3 W of multimode and 46.2 W of TEM00 output power is demonstrated. This is the highest power demonstration to our knowledge of the grazing incidence Nd:YVO4 laser geometry. We further describe the design of novel multiple bounce geometries, in which the laser mode can take more than one total internal reflection path through the amplifier, and show it can offer advantages especially in terms of spatial quality. A demonstration of a double bounce laser oscillator configuration shows high power 41 W of TEM00 output power with high conversion efficiency but superior spatial beam quality compared to the TEM00 single bounce laser oscillator.

1.3-μm GaInNAs surface-normal devices

The compatibility of GaInNAs/GaAs active regions with AlGaAs Bragg mirror technology opens up a range of surface-normal device formats for the spectral region around 1.3 μm. The authors report recent progress on the development of diode-pumped vertical external-cavity surface emitting lasers (VECSELs) and vertical cavity semiconductor optical amplifiers (VCSOAs) based on this technology. Pertinent performance characteristics are reported for GaInNAs 1.3-μm VECSELs capillary-bonded to diamond heatspreader platelets. In a conventional three-mirror air-spaced laser cavity up to 0.6 W of TEM00 output power was obtained. With the outer surface of the diamond platelet coated to form a dielectric output coupler mirror, it was possible to obtain the first monolithic microchip operation of a GaInNAs VECSEL, where a Gaussian beam with output power up to 120 mW was obtained. The influence of temperature on the performance of a six-quantum-well VCSOA with on-chip gain values of up to 16 dB was also reported. It reveals that on-chip gain of 9 dB can be achieved over a range of 85°C, allowing the amplifier characteristics to be tuned over more than 9.5 nm. Further investigations of the influence of optical feedback on the performance of these vertical amplifiers demonstrate that a three-mirror analysis explains the observed phenomena.

Continuous-Wave Green Laser of 9.9 W by Intracavity FrequencyDoubling in Laser-Diode Single-End-Pumped Nd:YVO4/LBO

A maximum of 9.9 W cw TEM00 output at 532 nm laser has beenobtained by intracavity frequency doubling with LBO in laser-diodesingle-end-pumped Nd:YVO4. The Nd:YVO4/LBO green laserhas a simple three-mirror V-fold cavity structure. The optical-opticalconversion efficiency was 34.8%. Based on the equation of thermalconduction, a general solution for the laser-crystal interiortemperature distribution is obtained by the semi-analytical thermalanalysis method. Using the software system, the cavity parameters havebeen optimized according to the stability condition and the astigmaticcompensation principle. The astigmatism in the cavity has beeneffectively controlled and the resonator was insensitive to the thermallens in the Nd:YVO4 crystal.