mJ Output Energy Research Articles

Single frequency pulsed Er,Yb co-doped fiber amplifier with 2 mJ of output energy

High-energy single-frequency pulsed light with low noise is generated from a master oscillator power amplifier (MOPA) system at 1.55 μm eye-safe wavelength using an ultra large mode area Er-Yb gain fiber. At a pulse repetition rate of 2 kHz, the maximum pulse energy without stimulated Brillouin scattering (SBS) reaches 2.07 mJ with 375 ns pulse duration for a pump power of 56.4 W. The pulse energy fluctuation is approximately 0.72 % within 21.5 min. The signal noise ratio (SNR) from the single-frequency fiber amplifier, at the highest pulse energy, centered at 1551.1 nm, is approximately 30 dB. The spectral half width of the signal light is calculated to be 1.28 MHz, which is close to the transform limit.

350 mJ electro-optically Q-switched 2.79 µm Cr:Er:YSGG MOPA.

We report on developing three flashlamp-pumped electro-optically Q-switched Cr:Er:YSGG lasers with the Q-switch based on a La3Ga5SiO14 crystal. The "short" laser cavity was optimized for high peak power applications. In this cavity, 300 mJ output energy in 15 ns pulses at a 3 Hz repetition rate was demonstrated with pump energy below 52 J. However, several applications, such as Fe:ZnSe pumping in a gain-switched regime, require longer (∼ 100 ns) pump pulse duration. We developed a 2.9 m long laser cavity that delivers 190 mJ of output energy in 85 ns pulses for these applications. We also demonstrated the Cr:Er:YSGG MOPA system producing 350 mJ output energy at 90 ns pulse duration and 47.5 J of pumping, corresponding to an amplification factor of 3.

130 mJ compact diode side-pumped Tm:Ho:YAG laser at 2.1 [formula omitted

A compact high energy co-doped Tm:Ho:YAG Q-switched laser side-pumped by the 785 nm quasi-continuous wave (QCW) laser diodes (LDs) at room temperature is demonstrated. Up to 130 mJ output energy at 2.1 μm has been generated, operating at 5 Hz repetition rate with a pulse duration of 73.7 ns. The average beam quality factor of M2 is measured to be ∼3.5. This laser has a simple design and compact structure, which is very suitable for many applications. To the best of our knowledge, this is the highest output energy for LDs pumped single rod Tm:Ho:YAG laser.

Life Cycle Assessment of Substitute Natural Gas production from biomass and electrolytic hydrogen

The synthesis of a Substitute Natural Gas (SNG) that is compatible with the gas grid composition requirements by using surplus electricity from renewable energy sources looks a favourable solution to store large quantities of electricity and to decarbonise the gas grid network while maintaining the same infrastructure. The most promising layouts for SNG production and the conditions under which SNG synthesis reduces the environmental impacts if compared to its fossil alternative is still largely untapped. In this work, six different layouts for the production of SNG and electricity from biomass and fluctuating electricity are compared from the environmental point of view by means of Life Cycle Assessment (LCA) methodology. Global Warming Potential (GWP), Cumulative Energy Demand (CED) and Acidification Potential (AP) are selected as impact indicators for this analysis. The influence of key LCA methodological aspects on the conclusions is also explored. In particular, two different functional units are chosen: 1 kg of SNG produced and 1 MJ of output energy (SNG and electricity). Furthermore, different approaches dealing with co-production of electricity are also applied. The results show that the layout based on hydrogasification has the lowest impacts on all the considered cases apart from the GWP and the CED with SNG mass as the functional unit and the avoided burden approach. Finally, the selection of the multifunctionality approach is found to have a significant influence on technology ranking.

High beam quality of nanosecond Nd:YAG slab laser system with SBS-PCM

All-solid-state nanosecond laser has a wide application prospect, but it remains an outstanding challenge to achieve high-power output with excellent beam quality. An optimized slab-amplifier-based laser system was demonstrated with 600 mJ output energy, 9.3 ns pulse duration and 200 Hz repetition rate. Most importantly, the beam quality M2 reached to approximately 2, which can be attributed to the improvement of spatial profile of near/far-field by the stimulated Brillouin scattering phase conjugation mirror (SBS-PCM). The comprehensive performance shows that the slab laser adopting SBS-PCM is a promising technical solution for high power laser system.

Efficient extraction of high pulse energy from partly quenched highly Er3+-doped fiber amplifiers.

We demonstrate efficient pulse-energy extraction from a partly quenched erbium-doped aluminosilicate fiber amplifier. This has a high erbium concentration that allows for short devices with reduced nonlinear distortions but also results in partial quenching and thus significant unsaturable absorption, even though the fiber is still able to amplify. Although the quenching degrades the average-power efficiency, the pulse energy remains high, and our results point to an increasingly promising outcome for short pulses. Furthermore, unlike unquenched fibers, the conversion efficiency improves at low repetition rates, which we attribute to smaller relative energy loss to quenched ions at higher pulse energy. A short (2.6 m) cladding-pumped partly quenched Er-doped fiber with 95-dB/m 1530-nm peak absorption and saturation energy estimated to 85 µJ reached 0.8 mJ of output energy when seeded by 0.2-µs, 23-µJ pulses. Thus, according to our results, pulses can be amplified to high energy in short highly Er-doped fibers designed to reduce nonlinear distortions at the expense of average-power efficiency.

High‐energy high‐power near‐diffraction‐limited 1064 and 532 nm picosecond Nd:YAG laser

The authors describe a diode-pumped Nd:YAG laser that produces 920 mJ output energy pulses with a pulse duration of 76 ps at 200 Hz pulse repetition rate. Second-harmonic generation with a pulse energy of 730 mJ and pulse duration of 63 ps was obtained by using LiB3O5 crystal with II-type phase matching. The output beam divergence was about 1.5 × DL (the diffraction limit) and 1.9 × DL for 1064 and 532 nm wavelengths, respectively.

2 mJ room temperature Fe:CdTe laser tunable from 5.1 to 6.3 μm.

We report a room temperature (RT) operation of a Fe:CdTe laser pumped by a Q-switched 2.94μm Er:Y3Al2(AlO4)3 laser. The Fe:CdTe laser produced 2mJ of output energy at λ=5.55 μm with slope efficiency of 16% with respect to absorbed pump energy. With the use of an intracavity prism, the spectral tuning was demonstrated in the 5.1-6.3μm range, being the longest wavelength tuning achieved for Fe2+:II-VI lasers. The lifetime of the upper laser level was measured to be 530ns at RT.

24 mJ Cr+4:forsterite four-stage master-oscillator power-amplifier laser system for high resolution mid-infrared spectroscopy.

We present the design of a Cr:forsterite based single-frequency master-oscillator power-amplifier laser system delivering much higher output energy compared to previous literature reports. The system has four amplifying stages with two-pass configuration each, thus enabling the generation of 24 mJ output energy in the spectral region around 1262 nm. It is demonstrated that the presented Cr:forsterite amplifier preserves high spectral and pulse quality, allowing a straightforward energy scaling. This laser system is a promising tool for tunable nonlinear down-conversion to the mid-infrared spectral range and will be a key building block in a system for high-resolution muonic hydrogen spectroscopy in the 6.8 μm range.

Novel unstable resonator configuration for highly efficient cryogenically cooled Yb:YAG Q-switched laser.

A novel method to shape the intensity distribution within an unstable laser cavity is demonstrated. This method is characterized by inscribing a tailored gain profile generated by a spatially tophat-shaped longitudinal pump beam into the gain medium. The mode shaping mechanism is still effective with zero output coupling. Therefore, this method enables to operate unstable laser cavities in cavity dump mode or as a regenerative amplifier. The theoretical background is described by means of geometrical optics, and operation of a prototype setup using cryogenically cooled Yb:YAG is demonstrated. The system produces 13ns pulses with 285 mJ at a repetition rate of 10 Hz, with an extraction efficiency of 35 %. Successful cavity dump operation is demonstrated with 110 mJ output energy.

Demonstration of a 100-mJ OPO/OPA for future lidar applications and laser-induced damage threshold testing of optical components for MERLIN

In the field of atmospheric research, lidar is a powerful technology that can measure gas or aerosol concentrations, wind speed, or temperature profiles remotely. To conduct such measurements globally, spaceborne systems are advantageous. Pulse energies in the 100-mJ range are required to achieve highly accurate, longitudinal resolved measurements. Measuring concentrations of specific gases, such as CH4 or CO2, requires output wavelengths in the IR-B, which can be addressed by optical-parametric frequency conversion. An OPO/OPA frequency conversion setup was designed and built as a demonstration module to address the 1.6-μm range. The pump laser is an Nd:YAG-MOPA system, consisting of a stable oscillator and two subsequent Innoslab-based amplifier stages that deliver up to 500 mJ of output pulse energy at 100 Hz repetition frequency. The OPO is inherited from the OPO design for the CH4 lidar instrument on the French–German climate satellite methane remote-sensing lidar mission (MERLIN). To address the 100-mJ regime, the OPO output beam is amplified in a subsequent multistage OPA. With potassium titanyl phosphate as nonlinear medium, the OPO/OPA delivered more than 100 mJ of output energy at 1645 nm from 450 mJ of the pump energy and a pump pulse duration of 30 ns. This corresponds to a quantum conversion efficiency of about 25%. In addition to demonstrating optical performance for future lidar systems, this laser will be part of a laser-induced damage thresholds test facility, which will be used to qualify optical components especially for the MERLIN.

Building and Characterization of Q-Switched Pulsed Nd:YAG Laser Range Finder Transmitter

A passive Q-switched pulsed Nd:YAG laser system was built for TOF (time-of-flight) laser range finder. The main goal is to build a TOF laser rangefinder transmitter operating at 1064 nm with 25 mJ output energy, 22 mm beam diameter, 15 ns pulse width, 0.5 mrad beam divergence. Construction and characterization of the laser cavity components including the function of the component for the laser transmitter and factor affect the performance are presented. In our design it is possible to use the transmitter in other applications using its compact dimension and power supply mobility by using batteries and also exploiting the narrow angle of the output transmitter with power reaches distance up to 15 km.

Fe2+-doped CdSe single crystal: growth, spectroscopic and laser properties, potential use as a 6 µm broadband amplifier

We report on the successful growth of single crystals of Fe2+:CdSe by seeded physical vapor transport (SPVT) technique with doping within the growing process and subsequent annealing in Se vapor. Luminescence lifetime measurements, spectroscopic studies of 5E–5T2 transition of Fe2+ in CdSe, and laser experiments were performed. The lifetime of the 5T2 energy level was measured to be 20 ± 5 ns at a room temperature (RT) of 290 K. At liquid nitrogen (LN) temperature, luminescence kinetics displayed a non-exponential decay, which can be fitted to a bi-exponential function with time constants τ1 = 6 µs and τ2 = 29 µs. As much as 3.2 mJ of output energy at 5.2 µm with 27% absorbed pump energy slope efficiency of an Fe2+:CdSe laser was achieved at RT under 2.94 µm nanosecond Er:YAG laser pumping. The Fe2+:CdSe laser was tuned from 4.63 to 6.10 µm. Obtained characteristics of Fe2+:CdSe indicate that the crystal can be considered a promising medium for amplification of femtosecond pulses in the middle infrared range up to 6 µm.

High-gain mid-infrared optical-parametric generation pumped by microchip laser.

High-gain mid-infrared optical-parametric generation was demonstrated by simple single-pass configuration using PPMgLN devices pumped by giant-pulse microchip laser. Effective mid-infrared wavelength conversion with 1 mJ output energy from 2.4 mJ pumping using conventional PPMgLN could be realized. Broadband optical-parametric generation from 1.7 to 2.6 µm could be also measured using chirped PPMgLN.

Modeling of coherent beam combining from multimillijoule chirped pulse tapered fiber amplifiers

The amplification of high energy chirped pulses in Large Mode Area tapered fiber amplifiers and their coherent combining have been investigated numerically. We have developed a three-dimensional model of strongly chirped nanosecond pulse amplification and compression back to femtosecond duration fully taking into account transverse and longitudinal variations of refractive index profile and distribution of active ions in the fiber, wavelength dependence of emission and absorption cross sections, gain saturation and Kerr nonlinearity. Modeling of Yb-doped fiber amplifier shows that up to 3 mJ of output energy can be extracted in 1 ns pulse with single-mode beam quality. Finally, we have investigated numerically the capabilities of compression and coherent combining of up to 36 perturbed amplifying channels in which high-order modes were excited and have obtained more than 70% combining efficiency and 380 fs compressed pulse duration.

Nd:YAG long Q-switched versus short free-running laser cleaning trials at Chartres cathedral, France

Laser cleaning trials using a Nd:YAG (1064 nm) device (El. En. Combo) were performed on outdoor sculptures at Chartres cathedral, France. Two laser regimes were compared: long Q-switched (LQS), which corresponds to a regime wherein the pulse length reaches 100 nanoseconds, and short free-running (SFR), with a pulse duration of 100 µseconds. Surfaces cleaned with the LQS mode appear clean and slightly yellow while the SFR mode leads to a darker but less yellow appearance. Colour measurements were performed on a low-porous stone from Berchères, used as the main construction material of the cathedral and commonly found on flat background architectural elements and pediments. Samples were collected from a range of laser cleaning windows, and a small sample from a limestone column was cleaned with both laser regimes, leaving a sharply delimited untreated band between the two regimes. Polished sections were prepared perpendicularly to the stone surface after having embedded the samples in epoxy resin. Samples were observed using an optical microscope (reflected light, dark field) and a scanning electron microscope (SEM) and analysed with energy-dispersive X-ray analysis. As far as mm to cm scale samples may be representative of the reality of hundreds of square meters of sculptures and background architectures, we could see that in the operating conditions selected, SFR mode at 300 mJ output energy with fluence 5.4 J/cm2 gave fairly good preservation of the oxalate layer lining the stone surface, and left in place some fragments of black crust, while LQS at 150 mJ with fluence 0.37 J/cm2 preserved the layer well and left no trace of black crust.

Three-dimensional modeling of CPA to the multimillijoule level in tapered Yb-doped fibers for coherent combining systems.

We developed a three-dimensional numerical model of Large-Mode-Area chirped pulse fiber amplifiers which includes nonlinear beam propagation in nonuniform multimode waveguides as well as gain spectrum dynamics in quasi-three-level active ions. We used our model in tapered Yb-doped fiber amplifiers and showed that single-mode propagation is maintained along the taper even in the presence of strong Kerr nonlinearity and saturated gain, allowing extraction of up to 3 mJ of output energy in 1 ns pulse. Energy scaling and its limitation as well as the influence of fiber taper bending and core irregularities on the amplifier performance were studied. We also investigated numerically the capabilities for compression and coherent combining of up to 36 perturbed amplifying channels and showed more than 70% combining efficiency, even with up to 11% of high-order modes in individual channels.

Short-pulsed gain-switched Cr2+:ZnSe laser

We report the first demonstration of gain-switched, ultra-low-threshold Cr2+:ZnSe laser generating pulses as short as 1.75 ns. A diode pumped Tm3+:YLF laser delivering up to 5 mJ energy in 11 ns pulses was utilized as a pump source. The laser operated at 20 Hz repetition rate with 0.1 duty factor allowing us to reduce thermal effects in an active crystal. In a short resonator (length, 70 mm) we obtained more than 0.5 mJ of output energy and 300 kW of corresponding peak power. The Cr2+:ZnSe laser was characterized by very low losses manifesting themselves by an extremely low generation threshold of less than 7 μJ and very high slope efficiency (reaching the quantum efficiency) determined with respect to absorbed pump power.

Efficient, high peak power Tm:YLF laser

We demonstrate efficient generation of diode pumped, passively cooled Tm:YLF laser end-pumped by 25-W fiber coupled laser diode. Over 5 W of output power was achieved for 25-W pumping laser and for elongated 120-mm cavity. For the free-running and Q-switching regimes the output spectrum was centered at 1908-nm with linewidth less than 7 nm. In the experiments on active Q-switching up to 5.5 mJ of output energy was demonstrated with pulse duration of 11 ns, corresponding to ~0.5 MW of peak power. Full Text: PDF References Jabczynski, J.K., Gorajek, L., "High repetition rate, high peak power, diode pumped Tm:YLF laser," Laser Phys. Lett. 6 (2), 109-112 (2009) CrossRef Sha, J.J., Shen, D.Y., Zhao, T., Yan, X.F., "High power and highly efficient operation of a Tm:YAG laser in-band pumped at 1617 nm", Laser Phys. Lett. 10, 075801 (2013) CrossRef Guillemet, S., "High pulse energy sub-nanosecond Tm-doped fiber laser". Proc. SPIE 8237, Fiber Lasers IX: Technology, Systems, and Applications, 82373V (2012) CrossRef Swiderski, J., Maciejewska, M., Kwiatkowski, J. and Mamajek, M., "An all-fiber, resonantly pumped, gain-switched, 2 ?m Tm-doped silica fiber laser", Laser Phys. Lett. 10, 015107 (2013). CrossRef Swiderski, J. and Michalska, M., "Generation of self-mode-locked resembling pulses in a fast gain-switched thulium-doped fiber laser," Opt. Lett. 38, 1624-1626 (2013) CrossRef Kwiatkowski, J., Jabczynski, J. K., Gorajek, L., Zendzian, W., Jelinkowa, H., Sulc, J., Nemec, M., Koranda, P., "Resonantly pumped tunable Ho:YAG laser", Laser Phys. Lett. 6 (7), 531-534 (2009) CrossRef Kwiatkowski, J., Jabczynski, J.K., Zendzian, W., Swiderski J., Gorajek, L. and Galecki, L., "Resonantly pumped acousto-optically Q-switched hybrid Ho:YAG laser", Laser Phys. Lett. 8 (4), 281-285 (2011) CrossRef Gallian, A., Fedorov, V. V., "Hotpressed ceramic Cr2+:ZnSe gain-switched laser", Opt. Express 14, 11694?11701 (2006) CrossRef Creeden, D., Ketteridge, P., "Mid-infrared ZnGeP2 parametric oscillator directly pumped by a pulsed 2 ?m Tm-doped fiber laser," Opt. Lett. 33, 315-317 (2008) CrossRef Swiderski, J. and Maciejewska, M., "Watt-level, all-fiber supercontinuum source based on telecom-grade fiber components", Appl. Phys. B 109, 177-181 (2012) CrossRef Swiderski, J. and Michalska, M., "Mid-infrared supercontinuum generation in a single-mode thulium-doped fiber amplifier", Laser Phys. Lett. 10, 035105 (2013) CrossRef Swiderski, J., Michalska, M. and Maze, G., "Mid-IR supercontinuum generation in a ZBLAN fiber pumped by a gain-switched mode-locked Tm-doped fiber laser and amplifier system," Opt. Express 21, 7851-7857 (2013) CrossRef

Resonantly pumped 1645 nm Q-switched Er:YAG laser with a ring cavity

This paper report an 1645 nm Er:YAG laser resonantly pumped by an Er-fiber laser operating at 1532 nm. 1.78W continous wave (CW) output power with a slope efficiency of 52% was obtained using a long ring cavity and an 1 at.% doped Er:YAG crystal. In Q-switched mode, the obtained pulse energy was 1.6 mJ at a repetition rate of 500 Hz; for 1 kHz repetition rate, 1.2 mJ output energy was obtained.