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We experimentally demonstrate a stable and compact high pulse energy mid-infrared (MIR) 6.45 μm laser, which is produced by an optical parametric oscillator (OPO) based on the non-oxide BaGa4Se7 (BGSe) nonlinear crystal pumped by 1064 nm Nd:YAG laser oscillator. With optimizing the parameters of the OPO system, a record high idler energy of 6.76 mJ at 6.45 μm was obtained with 18.85 ns of pulse duration (FWHM) at the repetition rate of 10 Hz under 93.5 mJ of pump energy, corresponding to an optical-to-optical conversion efficiency up to 7.23% from 1064 nm to 6.45 μm. The experimental results were in close approximation with the theoretical calculations. To date, it is both the highest MIR pulse energy and the highest conversion efficiency at 6.45 μm for any 1 μm pumped OPOs. Further, excellent output energy stability is demonstrated, with an energy fluctuation of less than ±0.5% over 165 min. Such a laser is interesting for both scientific and medical applications, including, for instance, for trace gas analysis and tissue ablation. [ABSTRACT FROM AUTHOR]

We report a Yb-doped all-fiber laser system generating burst-mode pulses with high energy and high peak power at a GHz intra-burst repetition rate. To acquire the uniform burst envelope, a double-pre-compensation structure with an arbitrary waveform laser diode driver and an acoustic optical modulator is utilized for the first time. The synchronous pumping is utilized for the system to reduce the burst repetition rate to 100 Hz and suppress the amplified spontaneous emission effect. By adjusting the gain of every stage, uniform envelopes with different output energies can be easily obtained. The intra-burst repetition rate can be tuned from 0.5 to 10 GHz actively modulated by an electro-optic modulator. Optimized by timing control of eight channels of analog signal and amplified by seven stages of Yb-doped fiber amplifier, the pulse energy achieves 13.3 mJ at 0.5 ns intra-burst pulse duration, and the maximum peak power reaches approximately 3.6 MW at 48 ps intra-burst pulse duration. To the best of our knowledge, for reported burst-mode all-fiber lasers, this is a record for output energy and peak power with nanosecond-level burst duration, and the widest tuning range of the intra-burst repetition rate. In particular, this flexibly tunable burst-mode laser system can be directly applied to generate high-power frequency-tunable microwaves. [ABSTRACT FROM AUTHOR]

We propose a 2.1 µm high-energy dissipative soliton resonant (DSR) fiber laser system based on a mode-locked seed laser and dual-stage amplifiers. In the seed laser, the nonlinear amplifying loop mirror technique is employed to realize mode-locking. The utilization of an in-band pump scheme and long gain fiber enables effectively exciting 2.1 µm pulses. A section of ultra-high numerical aperture fiber (UHNAF) with normal dispersion and high nonlinearity and an output coupler with a large coupling ratio are used to achieve a high-energy DSR system. By optimizing the UHNAF length to 55 m, a 2103.7 nm, 88.1 nJ DSR laser with a 3-dB spectral bandwidth of 0.48 nm and a pulse width of 17.1 ns is obtained under a proper intracavity polarization state and pump power. The output power and conversion efficiency are 0.233 W and 4.57%, respectively, both an order of magnitude higher than those of previously reported holmium-doped DSR seed lasers. Thanks to the high output power and nanosecond pulse width of the seed laser, the average power of the DSR laser is linearly scaled up to 50.4 W via a dual-stage master oscillator power amplifier system. The 3-dB spectral bandwidth broadens slightly to 0.52 nm, and no distortion occurs in the amplified pulse waveform. The corresponding pulse energy reaches 19.1 µJ, which is the highest pulse energy in a holmium-doped mode-locked fiber laser system to the best of our knowledge. Such a 2.1 µm, high-energy DSR laser with relatively wide pulse width has prospective applications in mid-infrared nonlinear frequency conversion. [ABSTRACT FROM AUTHOR]

The possibility to scale-up output pulse energy in diffraction-limited Er-doped fiber amplifier has been studied. It is shown that the utilization of tapered fiber design allows one to increase the pulse energy up to 2 mJ, while keeping the diffraction-limited beam quality (M2~1.4). Factors limiting the further increase in pulse energy are revealed. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a stable and compact high pulse energy mid-infrared (MIR) 6.45 μm laser, which is produced by an optical parametric oscillator (OPO) based on the non-oxide BaGa4Se7 (BGSe) nonlinear crystal pumped by 1064 nm Nd:YAG laser oscillator. With optimizing the parameters of the OPO system, a record high idler energy of 6.76 mJ at 6.45 μm was obtained with 18.85 ns of pulse duration (FWHM) at the repetition rate of 10 Hz under 93.5 mJ of pump energy, corresponding to an optical-to-optical conversion efficiency up to 7.23% from 1064 nm to 6.45 μm. The experimental results were in close approximation with the theoretical calculations. To date, it is both the highest MIR pulse energy and the highest conversion efficiency at 6.45 μm for any 1 μm pumped OPOs. Further, excellent output energy stability is demonstrated, with an energy fluctuation of less than ±0.5% over 165 min. Such a laser is interesting for both scientific and medical applications, including, for instance, for trace gas analysis and tissue ablation.

The possibility to scale-up output pulse energy in diffraction-limited Er-doped fiber amplifier has been studied. It is shown that the utilization of tapered fiber design allows one to increase the pulse energy up to 2 mJ, while keeping the diffraction-limited beam quality (M2~1.4). Factors limiting the further increase in pulse energy are revealed.

In this brief, a fully digitized pulse generator with programmable pulse number and width is used as an ultrawideband (UWB) pulse transmitter with 17.7-dBm output power for see-through-wall (STW) radar. A fully differential operation broadband CMOS power amplifier (PA) with a power-switchable mode and fast settling time for pulse radar is presented, achieving excellent power consumption, considerable output power, and a −3-dB bandwidth from 3.6 to 6.6 GHz. The on-chip transformer is used for impedance transformation in the output and converting signals from the differential to single ended. Fabricated in a 65-nm standard CMOS process, the operating carrier frequency range of the transmitter covers 3.2–5.8 GHz and the pulsewidth can be adjusted from 0.75 to 1.2 ns. The number of pulses varies from 4 to 1. At 10-MHz pulse repetition frequency (PRF), the maximum peak-to-peak voltage of the transmitter output pulse reaches 3.8 V with 50- $\Omega $ load, and the corresponding pulsewidth is 0.75 ns. The equivalent power is 17.7-dBm after calibration, and the average power consumption is only 22.5 mW. [ABSTRACT FROM AUTHOR]

A mode-locked high pulse energy fiber laser with a linear cavity by using an all-fiber structured graded index multimode fiber (GIMF) based saturable absorber (SA) is presented. The saturable absorption effect of the SA is based on the nonlinear multimode interference (NL-MMI). This is the first time the GIMF-based SA has been used in a mode-locked all-fiber laser with a linear cavity. The stable fundamental mode-locking operation can still be maintained at the maximum pump power. The output solitons have the center wavelength, spectral width, pulse duration, and repetition rate of 1571 nm, 4 nm, 675 fs, and 11.69 MHz, respectively. The maximum average output power reached is 61.4 mW, corresponding to the pulse energy up to 4.72 nJ and the pulse peak power of 7.79 kW. The proposed GIMF-based SA opens a promising way for a practical fiber-integrated mode-locker for large pulse energy fiber laser technology. [ABSTRACT FROM AUTHOR]

We report on mode-locked thulium-doped fiber lasers with high-energy nanosecond pulses, relying on the transmission in a semiconductor saturable absorber (SESA) and a carbon nanotube (CNTs-PVA) film separately. A section of an SMF–MMF–SMF structure multimode interferometer with a transmission peak wavelength of ∼2003 nm was used as a wavelength selector to fix the laser wavelength. When the SESA acted as a saturable absorber (SA), the mode-locked fiber laser had a maximum output power of ∼461 mW with a pulse energy of ∼0.14 μJ and a pulse duration of ∼9.14 ns. In a CNT-film-based mode-locked fiber laser, stable mode-locked pulses with the maximum output power of ∼46 mW, pulse energy of ∼26.8 nJ and pulse duration of ∼9.3 ns were obtained. To the best of our knowledge, our experiments demonstrated the first 2 μm region 'real' SA-based dissipative soliton resonance with the highest mode-locked pulse energy from a 'real' SA-based all-fiberized resonator. [ABSTRACT FROM AUTHOR]

We demonstrate a diode-pumped passively Q-switched Nd:GdYAG mixed garnet laser at 1,123 nm. A Cr4+:YAG crystal with an initial transmission of 97% is used as the saturable absorber. The maximum average output power is 1.05 W at an absorbed pumping power of 8.12 W. A single-pulse energy can reach up to 78.9 μJ, with a corresponding pulse repetition rate of 13.3 kHz. [ABSTRACT FROM AUTHOR]

We report efficient high-average-power, high-energy passively Q-switched operation of an Er3+-doped fluoride fiber laser at room temperature with wavelength-tunable resonator configuration utilizing a plane ruled grating for wavelength selection. The fiber laser produced stable Q-switched pulses with a maximum average output power of 5.16 W at 2811.7 nm and a maximum pulse energy of 27.7~\mu \textJ at 2834.6 nm for 30.5-W launched pump power and could be tuned over a wavelength range of 90 nm from 2762.5 to 2852.5 nm, with > 4-W average power over the range of 76.1 nm. Our results present fivefold increase in output power over previously published values directly attained from ~3- \mu \textm passively Q-switched fiber lasers and firmly establish a fiber laser as a compact, wavelength-tunable, multiwatt, tens of microjoules mid-infrared pulse source with large scope of both industrial and scientific applications. [ABSTRACT FROM PUBLISHER]

A high energy 532 nm hundred picoseconds laser based on stimulated Brillouin scattering (SBS) pulse compression and second-harmonic generation (SHG) is demonstrated. The seed is single frequency laser with pulse width 7 ns at 1064 nm delivered from a Cr 4+ :YAG passively Q-switched oscillator with Fabry-Perot etalon (FPE) as a frequency selector. Master oscillator power amplifier (MOPA) and compact single-cell FC–770 pulse compressor are combined to generate high energy output with hundred picosecond pulse width. Without any breakdown of optical devices, single frequency pulses are generated with compressed pulse width less than 450 ps and maximum energy up to 400 mJ. Type-II phase matching nonlinear crystal KDP is adopted for SHG of the fundamental laser. The optical-to-optical frequency conversion efficiency reaches up to 55%. The beam quality factor M 2 is measured to be 2.45 and the output power stability is better than 3.5%. [ABSTRACT FROM AUTHOR]

A high-efficiency picosecond (ps) 532-nm green laser with high pulse energy and high peak power at 5-kHz repetition rate was demonstrated by second-harmonic generation (SHG) from a 1064-nm master oscillator power amplifier (MOPA). The MOPA was based on the Innoslab structure under diode directly pumping, producing 4.8-mJ, 25-ps fundamental laser at the repetition rate of 5 kHz after a three-stage Innoslab amplification system. With a pulse energy of 2.93 mJ in the fundamental and using a type I noncritically phase matched lithium triborate crystal, the pulse energy of SHG was up to 1.96 mJ per pulse with a pulse width of 18.9 ps, which corresponds to a peak power of 104 MW in the green and SH conversion efficiency as high as 67%. The SHG green beam quality factor was measured to be M^2 = 1.75 . [ABSTRACT FROM PUBLISHER]

Abstract: We experimentally demonstrate pulse energy enhancement in an all-fiber passively mode-locked laser operating in the large normal dispersion regime. By increasing the laser cavity length as well as its net cavity dispersion, the proposed laser, which is mode-locked by nonlinear polarization rotation, generates highly chirped dissipative solitons with pulse energies up to 9.4nJ. The fundamental repetition rate is 2.3MHz, and the pulse duration is 35ps. Such low repetition rate as well as wide pulse width makes this mode-locked all-fiber laser a suitable oscillator to directly seed a fiber amplifier, which can be used as compact sources for high-power applications. [Copyright &y& Elsevier]

Abstract: We report on a scheme for efficient acousto-optical Q-switching. A flash lamp pumped Nd:YAG oscillator with an acousto-optic modulator (AOM) fourfold pass configuration is presented. The setup combines two important advantages: enhancement of the diffraction efficiency by additional AOM passes and a compact oscillator design in spite of an extension of the optical path length. A flash lamp pumped oscillator with an average output power of 7W and a beam quality of M 2 =1.2 is developed. The system operates with a 100Hz repetition rate for the flash lamps. In each pumping pulse a pulse train of 1 up to 40 Q-switched laser pulses is generated. The pulse duration is from 15 to 120ns. In comparison to a former setup (AOM double pass) the AOM fourfold pass configuration allows single pulses with energy above 20mJ and a pulse peak power of more than 1MW. In addition, the beam profile is improved due to a better separation of the incident and diffracted beam caused by the AOM. The laser is dedicated as master oscillator in a master oscillator power amplifier (MOPA) system where pulse peak powers in the MW range should be achieved. [Copyright &y& Elsevier]

• A picosecond master oscillator power amplifier system was proposed. • A single-pass traveling-wave amplifier with the optic-optic efficiency 19.39% was demonstrated. • A maximum output power 35.7 W was generated through the system. We have demonstrated a high pulse energy single-pass picosecond (ps) master oscillator power amplifier (MOPA) system of 1064 nm at a pulse repetition rate of 500 kHz. A 500 kHz, 32.38 μJ picosecond laser was used as the signal laser. Through a single-pass traveling-wave amplifier, a maximum output power of 35.7 W at a pump power of 100.6 W was generated with the optic-optic efficiency of 19.39%. The output pulse duration was 16.9 ps, corresponding to the pulse energy of 71.4 μJ, while simultaneously the beam quality factor M 2 was measured to be 1.36 and 1.32 along the x, y axis direction, respectively. [ABSTRACT FROM AUTHOR]

The development of an Yb 3+ -fiber-based chirped-pulse amplification system and the performance in the generation of extreme ultraviolet (EUV) radiation by high-harmonic generation is reported. The fiber laser produced 100 μJ, 350 fs output pulses with diffraction-limited beam quality at a repetition rate of 16.7 kHz. The system used commercial single-mode, polarization maintaining fiber technology. This included a 40 μm core, easily packaged, bendable final amplifier fiber in order to enable a compact system, to reduce cost, and provide reliable and environmentally stable long-term performance. The system enabled the generation of 0.4 μW of EUV at wavelengths between 27 and 80 nm with a peak at ~45 nm using xenon gas. The EUV flux of ~10 11  photons per second for a driving field power of 1.67 W represents state-of-the-art generation efficiency for single-fiber amplifier CPA systems, corresponding to a maximum calculated energy conversion efficiency of 2.4 × 10 -7 from the infrared to the EUV. The potential for high average power operation at increased repetition rates and further suggested technical improvements are discussed. Future applications could include coherent diffractive imaging in the EUV, and high-harmonic spectroscopy., (© The Author(s) 2017.)