We report a high-energy, high-average power burst-mode picosecond laser system, which is designed for space debris laser ranging. Pulses from a Nd : YVO4 mode-locked oscillator are first stretched by a piece of volume Bragg gratings (VBG) and then pass through an improved Michelson interferometer splitting system to obtain burst-mode pulses, which the relative amplitude and time-delay interval of each 4-pulse in bursts can be adjusted and controlled. A regenerative amplifier (RA), as a pre-amplifier, is adopted to decrease the repetition frequency of the seed beam from 80MHz to 1 KHz and raises the energy to millijoule-level. In order to reduce the performance requirement of the damage threshold of subsequent optical components and maximize the extraction of pulse energy, the Gaussian output beam of the RA is converted into a ring shaped pattern beam using an aspheric lenses reshaping system with the conversion efficiency of 93%. After a two-stage master oscillator power amplifier with 4f imaging systems, the pulse envelope energy is up to 100 mJ with the pulse duration of ~100 ps. To obtain high power green light, we compared the conversion efficiency of three crystals. When the fundamental frequency power is 80W, the second harmonic conversion efficiency of the first crystal (LBO, 6×6×10, Θ=90°, Φ=11.4°) is only about 50%, as well as the second (GTR-KTP, 7×7×7, θ=90°, Φ=23.5‡). But the conversion efficiency of the last crystal (LBO, 6×6×15, θ=90°, Φ=0°), reaches 68% and the output power of 532 nm as high as 50 W is obtained.
A single pulse energy 6.77mJ, repetition rate of 1kHz, pulse width of 11ps at 532nm wavelength with the near top-hat intensity profile in the near filed picosecond laser amplification system is realized using a semiconductor laser side pumped Nd:YAG crystal. The seed pulse is generated in a home-built Nd:YVO4 oscillator, pumped with a 808 nm CW diode laser. The oscillator provides 2.8nJ, 11ps pulse width, 86 MHz repetition rate at 1064 nm wavelength. Pulse from the Nd:YVO4 oscillator is first amplified to 1.5mJ by a diode side-pump Nd:YAG regenerative amplifier. Then the pulse, increased in size by a negative lens, sequentially passed through a circular aperture and a spatial filter-image relaying system to produce a top-hat intensity profile in the modules, and an 8th order super-Gaussian beam is obtained, and total transmission of beam shaping set-up is about 30%. The beam, passed through a double-pass preamplifier of single rod and a double-pass main amplifier of single rod, is amplified up to 17.3mJ, corresponding peak power is 1.57 GW. A 4F relay-imaging system is used in the amplification stages to preserve the top-hat intensity profile and compensate the thermally induced birefringence of Nd:YAG rod. The amplified output beam leaving the double-pass Nd:YAG module is decreased in size and imaged on a 5×5×13 m^3 second-harmonic generation (SHG) crystal-LBO by a 4F relay-imaging system, finally a 532nm approximate top-hat intensity profile in the near filed, which single pulse energy is 6.77mJ, is obtained after doublefrequency. The second-harmonic generation efficiency is over 51%.
Azimuthal polarization beam amplification up to an average power of 11.08 W using the Nd:YAG amplifier structure was obtained with the relative purity of 93% at 1 kHz.The beam quality factor M2 is 3.29 and the beam wavelength is 1064 nm. The amplification factor of the amplified picosecond azimuthally polarized beam is 207.9%.
A four-pulses sequence picosecond 1064nm regenerative amplifier system with repetition rate of 1 kHz are obtained, which with the average power of 9.2 W and beam quality M2 factor of 1.2. The Nd: YAG crystal with wedge angle of 2° and size of Φ 4×63 mm is adopted in the regenerative amplifier and around by three VCSEL pumping arrays with an angle of 120°. A laser diode (LD) pumped Nd: YVO4 crystal SESAM mode-locked seed laser is broadened from 20 to 260 ps by double-pass Volume Bragg Gratings and divided into equal amplitudes four-pulse sequence with the pulse spacing of 1ns by beam splitter mirrors. The four-pulse sequence enters the regenerative amplifier in order and the power is amplified from 0.68 to 9.5 W.
The effect of the gain medium planar shear stress, induced by non-radially symmetrical pumping during power amplification process, on the depolarization of radially polarized beam was analyzed in detail. For radially polarized beam, theoretical simulation had showed that the non-radial distribution of planar shear stress led to the different depolarization in different polarization directions, that the depolarization of the direction of 45° and 135° is five times more serious than that of 0° and 90°. In the following experiment, the radially polarized seed beam with a repetition rate of 1 kHz, an average power of 5 W and a pulse width of 100 ps was single-propagating double-rod Nd:YAG laser amplifier. Each rod was surrounded by three diode-pumped arrays with an angle of 120°. During the amplification process, the depolarization degree of radially polarized beam was 6.73%, which was obtained by measuring the difference between the power of the two beams transmitted and reflected by the analyzer TFP. The power of amplified radially polarized beam was 15.17 W with the purity of 89.3% and M2 of 3.95.
An average power of 58 W, pulse width of 40 ps at 1 KHz repetition rate of Nd:YAG picosecond laser is reported. It used an etalon to directly get pulse width of 135 ps from Nd:YVO4 mode locked laser in 1064 nm, which repetition rate was 88 MHz. When the seed pulses were injected into the double length of regenerative LD side-pump Nd:YAG cavity at 1 KHz repetition rate, the single pulse energy was amplified to 3 mJ, the pulse width was compressed to 99 ps, beam quality of M^2 factor was 1.3. The single pulse energy was amplified up to 58 mJ, the pulse width was self compressed to 40 ps, beam quality of M^2 factor was approximately 3.5 after single passing three stages of double high gain LD side-pump Nd:YAG module. Beam pointing was about 40 urad. The stability for pulse to pulse RMS was less than 3%. A thin-film polarizer and a quarter-wave plate was inserted into the regenerative amplification cavity to let pulses double travel the same geometric path basis on pulse polarization. Serrated aperture were used in the amplification. That's beneficial to decrease the nonlinear effect for the high power in the crystal. High gain LD side-pump Nd:YAG module could lead the pulse energy amplify more and self compress the pulse width. Double length of regenerative cavity was used to enhance the optical cavity length, it greatly decreased the laser's volume and improved stability of picosecond laser. It's a nice way for high power picosecond laser and the laser system would be more simple and smaller.
We report on a high-pulse-energy solid-state picosecond Nd:YVO4 oscillator with cavity-dumping. The laser is end-pumped by an 808 nm laser diode and passively mode-locked with a semiconductor saturable absorption mirror (SESAM). In pure cw-mode-locking, this laser produced 2.5 W of average power at a pulse repetition rate of 40 MHz and pulse duration around 12 ps. A cavity dumping technique using an intra-cavity BBO electro-optic crystal to which bidirectional voltage was applied was adopted, effectively improving the cavity-dumping rate. Tunable high repetition rate from 100 kHz to 1 MHz was achieved. With electro-optic cavity dumper working at 1 MHz repetition rate, we achieved average power 594 mW. The laser includes a 5 mm long, a-cut, 0.5% doped Nd:YVO4 crystal with a 5-degree angle at one end face. Laser radiation is coupled out from the crystal end face with a 5-degree angle, without requiring insertion of a thin-film polarizer (TFP), thus simplifying the laser structure. This picosecond laser system has the advantages of compact structure and high stability, providing a good oscillator for regenerative amplifiers.
A third-harmonic-generation picosecond pulse with several millijoules per pulse at 355 nm has been achieved by nonlinear optical materials LiB 3 O 5 (LBO). The single pulse energy of third harmonic was up to 2 mJ at the repetition rate of 1 kHz. The conversion efficiency was up to 33.3% from 1064 to 355 nm with the M 2 factor of 2.4. The system is based on a Nd:YAG regenerative amplifier with a simple double-pass post-amplifier.
We present a high compact structure laser diode (LD) side-pumped all-solid-state Q-switched master oscillator power amplifier (MOPA) laser system with high beam quality. Bidirectional voltage-supplied Q-switched and MOPA technologies were introduced in the design. An in-center wavelength of 1064 nm with pulse width adjustability from 5 to 18 ns was obtained at the repetition rate of 500 Hz. Through multistage Nd∶YAG amplifiers at the pulse width of 6 ns, the oscillator was scaled up to 145 W and the corresponding peak power reached 48.3 MW with single pulse energy fluctuation less than 0.45% in 1 h operation.
We present an optically pumped vertical external cavity surface emitting lasers using the semiconductor gain chip composed of quantum wells. The dependence of the spectrum of the output on the temperature of the gain chip was measured. The maximum output power reached 40mW at the wavelength of 1015.5nm with the pump power of 1.5W. The optical conversion efficiency reached 2.7%.
In this paper, the Ti:sapphire laser has been demonstrated with astigmatic compensated fold cavity of 3-mirror and 4- mirror standing wave cavities pumping by an internal frequency-doubled AO Q-switched Nd:YAG laser. The basic properties of 4-mirror cavity are analyzed theoretically by G-parameter. Up to 0.95 W output with 13.6% of efficiency in 4-mirror cavity and 0.77 W output with 11% of efficiency in 3-mirror cavity are obtained when pump power is 7 W, the tuning range from 720 nm to 820 nm with peak power wavelength at 800 nm is achieved. The experimental results are compared and discussed.
A new way of generating negative group-velocity dispersion in a Ti:sapphire laser is demonstrated. The
mathematical formulae of the optical path length and the negative group-velocity dispersion in a singleprism
system are given. Both of the theoretical analyses and the experimental results show that the
group-velocity dispersion is directly proportional to the distance between the prism and the Ti:sapphire
crystal, and the amount of the negative group-velocity dispersion generated by a single-prism system
may approach that generated by a pair of prisms.
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