Average Laser Output Power Research Articles

Diode-pumped passively mode-locked femtosecond Yb:YLF laser at 1.1 GHz

We report femtosecond pulse generation at GHz repetition rates with the Yb:YLF gain medium for the first time. A simple, low-cost, and compact architecture is implemented for the potential usage of the system as a low-noise timing jitter source. The system is pumped by 250 mW, 960 nm single-mode diodes from both sides. The semiconductor saturable absorber mirror (SESAM) mode-locked laser is self-starting and generates transform-limited 210 fs long pulses near 1050 nm. The laser's average output power is 40 mW, corresponding to a pulse energy of 36 pJ at 1.1 GHz repetition rate. The measured laser relative intensity noise (RIN) from 1 Hz to 1 MHz is 0.42%. The performance obtained in this initial work is limited by the specifications of the available optics and could be improved significantly by employing custom-designed optical elements.

The Adoption of Chalcogenide Glass Fiber as Pulse Stretcher in an All-Fiber Structured 2 μm Chirped Pulse Amplification System

We present the development of an As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber-based reusable inline optical connector; and, for the first time to the best of our knowledge, integrated it into a 2 μm chirped pulse amplification system as the pulse stretcher. By this mechanism, a near 20 times pulse stretching ratio was achieved in 0.5 m-long this As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber and the introduction of insertion loss as low as 2.84 dB while it was connected with silica fiber. After the follow-up fiber amplification and self-compression mechanism, the laser average output power was boosted to 1.97 W and pulse duration was optimized to 2.53 ps. Moreover, to further inspect the laser pulse property, the pulses were then delivered into a 5.3 m-long ZrF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -BaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -LaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -AlF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -NaF (ZBLAN) fiber which was fusion spliced to SM1950 fiber. Thanks to the 0.4-dB low fusion splice loss between these fibers, a 1.56-W supercontinuum source with bandwidth of 1.93-3.50 μm is obtained. The measured two hours of root-mean-square value of power fluctuation of this laser source is 0.13%, indicating an ultra-high long-term power stability. This work will lay a solid foundation in the realization of the all-fiber structured high-power thulium-doped fiber amplifier with high compactness.

Passive Coherent Laser Beam Combining With Spatial Mode Selecting Feedback

A general ${N}$ -by- ${N}$ coupling matrix that provides lossless uniform feedback to all laser array elements is demonstrated in the analysis of a passive coherent beam combining resonator. The resonator contains a spatial filter that sends rejected optical power from the combining optic back into the cavity. This recycling of otherwise unused power yields an increase in the average laser output power that scales with array size ${N}$ , even in the absence of passive phase effects that depend on the gain, intensity, and wavelength of the laser mode. To achieve this improvement, tailored path lengths and mirror reflectivities are required in the feedback arms, where the phase may be fixed, whereas in the gain arms, the path lengths vary randomly.

Compression of femtosecond ytterbium fibre laser pulses using nonlinear processes in silica fibre

The temporal compression of 100-fs nanojoule laser pulses using nonlinear processes in silica fibre has been studied by numerical simulation and experimentally. The simulation results demonstrate that, in the case of spectral broadening in a normal dispersion fibre, followed by the temporal compression of the pulse in a compressor with a negative second-order dispersion, up to 90 % of the compressed pulse energy can be concentrated in the main peak, whose duration is a factor of 8 shorter than the initial laser pulse duration. In our experiments, 100-fs ytterbium fibre laser pulses have been compressed to pulses with an ∼13-fs main peak accounting for 87 % of the compressed pulse energy. At an average ytterbium laser output power of 4.2 W, the average power at the compressor output has been 3.1 W.

Copper vapor laser pumped by pulse-periodic high-frequency discharge

We present the results of numerical experiments considering the physical processes specific to the laser based on self-terminating atomic transitions of copper and study of the output characteristics of this laser numerically. The laser is pumped by trains of high-frequency (10−70 MHz) current oscillations with the repetition rate of 2−30 kHz. Inductive-type electrodeless discharge pumping is regarded. The calculations were carried out for a small set of the specified basic parameters providing a way to partially optimize the performance of the laser over its basic output characteristics and to reveal its features. The feasibility of efficient laser pumping by high-frequency discharge is demonstrated. In our numerical experiments the maximum value of the physical efficiency was about 6% and the maximum average laser output power was as high as 174 W. These values were obtained for a discharge chamber with a volume of 1.7 L.

Picosecond holmium fibre laser pumped at

We report a passively mode-locked, all-fibre holmium laser based on nonlinear polarisation rotation. As a pump source use is made of an ytterbium-doped fibre laser. The pulse repetition rate of the holmium laser is , and the pulse duration does not exceed at wavelengths of 2065 and . The average laser output power reaches .

Simulation model of a new solar laser system of Fresnel lens according to real observed solar radiation data in Helwan of Egypt

A new simulation model of a new solar pumped laser system was tested to be run in Helwan in Egypt (latitude φ=29°52′N, longitude λ=31°21′E and elevation=141m) as an example of an industrial polluted area. The system is based on concentrating the solar radiation using a Fresnel lens on a laser head fixed on a mount tracking the sun during the day and powered by a DC battery. Two cases of this model are tested; the first one is the model consisting of a Fresnel lens and a two-dimensional Compound Parabolic Concentrator (CPC), while the other is the model consisting of a Fresnel lens and a three-dimensional Compound Parabolic Concentrator (CPC). The model is fed by real actual solar radiation data taken in Helwan Solar Radiation Station at NRIAG in the various seasons in order to know the laser power got from such a system in those conditions. For the system of Fresnel lens and 2D-CPC, an average laser output power of 1.27W in Winter, 2W in Spring, 5W in Summer and 4.68W in Autumn respectively can be obtained. Accordingly, the annual average output power for this system is 3.24W. For the system of Fresnel lens and 3D-CPC, an average laser output power of 3.28W in Winter, 3.55W in Spring, 7.56W in Summer and 7.13W in Autumn respectively can be obtained. Accordingly, the annual average output power for this system is 5.38W.

Compact gain-switching linearly polarized high-power Yb pulse fiber laser

A compact gain-switching pumped linearly polarized high-power Yb pulse fiber laser is experimentally demonstrated. The laser was mainly composed of a piece of polarization-maintaining (PM) Yb-doped fiber and a pair of PM FBGs. Three fiber pig-tailed laser diodes (LDs) were applied as the pump source through a (6+1) × 1 fiber coupler and configured in a pulse-working scheme. Stable pulse operation was achieved with repetition rate up to 200 kHz, pulse duration of 120 ns and a spectral FWHM of 0.08 nm. A maximum average laser output power of 21 W was obtained at 200 kHz with respect to the pump power of 30.3 W. The polarization extinction ratio was as good as 15 dB.

A LD side-pumped deep ultraviolet laser at 266nm by using a Nd:YAG/Cr4+:YAG/YAG composite crystal

Abstract A stable and compact deep ultraviolet laser system operation at 266 nm with diode-side-pumped and passively Q-switched is reported. The Nd:YAG/Cr4+:YAG/YAG composite crystal is used in realizing fundamental laser output and passively Q-switched modulation and for achieving a high conversion efficiency from 532 nm to 266 nm; a multi-reflected cavity for 532 nm is used in the system. The performances of the average power, pulse width, and pulse repetition rate on pump power are measured. Under the green laser of 13.03 W, the deep ultraviolet laser average output power of 1.27 W is obtained, with a pulse width of 60 ns, the repetition rate of 12.5 kHz, and the corresponding conversion efficiency of 9.74%.

Solid-State System for Copper Vapor Laser Excitation

The present paper describes an all-solid-state high voltage nanosecond pulse generator for pumping a copper vapor laser. The main feature of this device is using a high voltage switch composed of a stack of insulated gate bipolar transistors (IGBT), what makes it compacter and more cost effective than traditional systems based on thyratrons and vacuum tubes. A fast transformer circuit provides highly synchronous on/off control of the IGBT stack. Two-stage magnetic pulse compressor is used to enhance the system efficiency.The developed laser pumping system generates current pulses with amplitude of 230 A and rise time of 30 ns at pulse repetition rate of 15 kHz. Average laser output power of 13 W was obtained under these pumping conditions.

Study on the purification of hydrogen bromide gas by fractional distillation technique and its effect on improvement of copper–hydrogen bromide laser performance

This paper presents a purification process of hydrogen bromide (HBr) gas by fractional distillation technique and its use for performance enhancement of copper-HBr laser (Cu-HBrL). The residual impurities in HBr were suppressed by a two-step distillation process at temperatures of −196°C and −20°C. The lowering of the impurities was confirmed by comparing the mass spectrograph of the HBr gas before and after distillation, using a quadrupole mass spectrometer. The effect of the purified HBr gas on the performance of Cu-HBrL average output power as well its electrical discharge characteristics were studied. More than 37% improvement in the laser average output power (40 to 55 W) was observed with the use of this distilled HBr gas compared to undistilled gas. The underlying mechanism of the enhancement was analyzed by comparing electrical discharge characteristics in the two cases. The improvement in Cu-HBrL performance with distilled HBr gas was attributed to lowering of bromine and hydrogen concentration, mainly manifested as increased average electrical energy coupling to the discharge. This resulted in increased laser gain as well as gain volume, which were reflected in increases in laser output power and beam diameter.

Spectroscopic analysis and efficient diode-pumped 19 μm Tm^3+-doped β′-Gd_2(MoO_4)_3 crystal laser

Tm3+-doped β'-Gd2(MoO4)3 single crystal was grown by the Czochralski method. Spectroscopic analysis was carried out along different polarizations. End-pumped by a quasi-cw diode laser at 795 nm in a plano-concave cavity, an average laser output power of 58 mW around 1.9 μm was achieved in a 0.93-mm-thick crystal when the output coupler transmission was 7.1%. The absorbed pump threshold was 8 mW and the slope efficiency of the laser was 57%. This crystal has smooth and broad gain curve around 1.9 μm, which shows that it is also a potential gain medium for tunable and short pulse lasers.

Passive Q-switching performance of intracavity frequency-doubled red laser with mixed Nd:GdxY1−xVO4 crystals

Passive Q-switching laser operation of Nd:GdxY1−xVO4 mixed crystals at 671nm has been compared in the same V-shape folded cavity. Based on our comparative analysis, the best laser characteristics – the highest pulse energy and peak power and the shortest pulse width – were demonstrated by Nd:Gd0.63Y0.37VO4 crystal. At the same time, this crystal possesses the lowest thermal conductivity in comparison with the other Nd:GdxY1−xVO4 crystals, which could result in decreasing the average laser output power. To verify this assumption we also measured the focal lengths of thermal lens induced in the crystals during the laser operation.

Minimizing Heat Generation in Solid-State Lasers

Novel high-power ytterbium YAG lasers are described. These lasers incorporate the principle of anti-Stokes fluorescence cooling to reduce or eliminate detrimental heating. Lasers with net heating and net cooling are demonstrated. By balancing the spontaneous and stimulated emission, we have reduced the net thermal loading to below 0.01% of the laser's average output power. Design, testing, and analysis are reported for lasers up to 500 W average power and pulsed operation up to 30 s. Issues and limitations of this approach are discussed.

Simultaneous all-solid-state multi-wavelength lasers—a promising pump source for generating highly coherent terahertz waves

A diode-end-pumped Nd:YAG dual-wavelength laser operating at 1319 and 1338 nm is demonstrated. The maximum average output power of the quasi-continuous wave linearly polarized dual-wavelength laser is obtained to be 2.1 W at a repetition rate of 50 kHz with an output power instability of less than 0.38% and beam quality factor M2 of 1.45. Using the two lines, the highly coherent and narrow linewidth terahertz radiation of 3.23 THz can be generated in an organic 4-N, N-dimethylamino–methyl-stilbazolium tosylate (DAST) crystal. Meanwhile, the multi-wavelength red laser at 659.5, 664 and 669 nm is generated by frequency doubling and sum frequency processes in a lithium triborate (LBO) crystal. The average red laser output power is enhanced up to 1.625 W at a repetition rate of 15 kHz with an output power instability of better than 0.53% and beam quality factor M2 of 6.05. Using the three lines, it is possible to generate the multi-wavelength THz radiation of 3.3, 3.43 and 6.73 THz in an appropriate difference frequency crystal.

A Diode-Pumped Nd:YAG Ceramic Laser with a 540-W Output Power

A diode-pumped, high power Nd:YAG ceramic laser was developed by using a diffusive ceramic reflector as an optical pump cavity. An average laser output power of 542 W was obtained with a corresponding optical-to-optical efficiency of 39.5 %. The design parameters and the laser properties of the ceramic laser module are described, and the thermal effects on the laser output power were measured and analyzed.

Intracavity-pumped Cr2+:ZnSe laser with ultrabroad tuning range between 1880 and 3100 nm

We obtained, what is to our knowledge, record tuning from an intracavity-pumped gain-switched Cr2+:ZnSe laser. In the experiments, a polycrystalline Cr2+:ZnSe sample with an absorption of about 43% at 1570 nm was used to minimize reabsorption losses at the lasing wavelengths below 2000 nm. By placing the gain medium inside the cavity of a pulsed KTP optical parametric oscillator (OPO) operating at 1570 nm, smooth, continuous tuning was achieved in the 1880-3100 nm range with four different sets of cavity optics. As high as 145 mW of average laser output power was obtained at 2365 nm with 1.2 W of intracavity OPO power.

Continuous high-repetition-rate operation of collisional soft-x-ray lasers with solid targets

We have generated a laser average output power of 2 microW at a wavelength of 13.9 nm by operating a tabletop laser-pumped Ni-like Ag laser at a 5 Hz repetition rate, using a solid helicoidal target that is continuously rotated and advanced to renew the target surface between shots. More than 2 x 10(4) soft-x-ray laser shots were obtained by using a single target. Similar results were obtained at 13.2 nm in Ni-like Cd with a Cd-coated target. This scheme will allow uninterrupted operation of laser-pumped tabletop collisional soft-x-ray lasers at a repetition rate of 10 Hz for a period of hours, enabling the generation of continuous high average soft-x-ray powers for applications.

Stable mode-locked operation of a low repetition rate diode-pumped Nd:GdVO4laser by combining quadratic polarisation switching and a semiconductor saturable absorber mirror

In this paper, we present the mode-locked operation of an ultra-robustly stabilised Nd:GdVO(4) laser with low repetition rate by combining quadratic polarisation switching and a semiconductor saturable absorber mirror (SESAM). In addition, similar experiment was also done with Nd:YVO(4). For Nd:GdVO(4), 16-ps pulses at 1063 nm with a repetition rate of 3.95 MHz have been obtained for a laser average output power of 1.4 W. For Nd:YVO(4), the performance was 2.5 W of average power for 15-ps pulses at 1064 nm. Moreover, we demonstrate experimentally the advantage of combining these two passive mode locking techniques in terms of stability ranges. We show how the dual mode-locking technique is crucial to obtain a stable and long-term mode-locked regime in our case of a diode-pumped Nd:GdVO(4) laser operating at low repetition rate and more generally how this dual mode-locking technique improves the stability range of the mode-locked operation giving more flexibility on different parameters.

Nd 3+:Y 3Al 5O 12 laser ceramics: Flashlamp pumped laser operation with a UV cut filter

A Nd 3+:Y 3Al 5O 12 ceramic laser under the hard-UV cutting condition of Xe flashlamp pumping was demonstrated for the first time. By using a 16.4 kW Xe flashlamp and a samarium-doped flow tube, an average laser output power of 386 W was obtained at 1064 nm with a 1.1 at.% Nd 3+:Y 3Al 5O 12 ceramic rod of Ø10 mm × 152 mm. The slope efficiency was measured to be 2.3%, which was the same as for a Nd 3+:Y 3Al 5O 12 single crystal rod of similar size. The degradation of output power by the solarization effect was found to be negligible when the UV radiation below 350 nm wavelength was cut by a Sm:glass flow tube.