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Average output power versus pulse duration. Square dots represent our experimental data from changing only the OC. The other points show a non-exhaustive but representative set of results for several Nd : Y V O 4 oscillators found in the literature (the number attached to the data is the reference). From the analysis of each article, + represent oscillators with SHB and − without SHB.
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We report on a high-power passively mode-locked TEM 00 Nd : Y V O 4 oscillator, 888 nm diode-pumped, with pulse durations adjustable between 46 ps and 12 ps . The duration tunability was obtained by varying the output coupler (OC) transmission while avoiding resorting to spatial hole burning (SHB) for pulse shortening. At a repetition rate of 91 MH...
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Citations
... Nd:YVO 4 enjoys large absorption and stimulated emission cross sections that may easily lead to high gain but weak thermal property due to the low thermal conductivity and high energy transfer upconversion (ETU) coefficient. In addition, an 888 nm pumping scheme is an effective way to compensate thermal effect for output properties upgrading in Nd:YVO 4 laser, which has been widely used in Q-switched [3], mode-locked [4,5] oscillators, pulse amplifiers [6,7] and optical parametric technology [8]. In particular, high-power Q-switched neodymium pulse lasers are widely used in laser machining manufacture [9] and the thermal effect is a key factor. ...
A theoretical analysis upon the four-dimensional (4D) spatio-temporal temperature dependent dynamics of 888 nm pumped Nd:YVO 4 dual-rod laser is established, which is valid in both continuous-wave (CW) and acousto-optic (AO) Q-switched pulse lasers conditions. Our model can accurately solve the 4D thermal generation and temperature evolution not only in the steady Q-switched state, but also in the first few unstable giant or dwarf pulses region. Factors including ground state depletion (GSD), energy transfer upconversion (ETU), fluorescence branching ratios, temperature-dependent cross sections and nonradiative relaxations processes are comprehensively considered for precisely estimating thermal effects, valid in both the steady pulse region and the unstable region at the beginning. Moreover, temporal and spatial temperature profiles and their coupling effect on output properties at different repetition-rates are discussed. Experiments of high-power high-repetition-rate 888 nm end-pumped Nd:YVO 4 dual-rod CW and AO Q-switched lasers are also firstly presented and the experimental results enjoy good consistency with our theory.
... Nd:YVO 4 is the most widely explored one among vanadate crystals in the past decades [11][12][13]. Its absorption coefficient along c axes is almost 4 times higher than that of a axes at 808 nm. ...
We report on a high power passively mode-locked picosecond oscillator based on Nd:GdVO4 crystal with σ polarized in-band pumping. Thermal gradient and thermal aberration was greatly decreased with proposed configuration. Maximum output power of 37 W at 81 MHz repetition rate with 19.3 ps pulse duration was achieved directly from Nd:GdVO4 oscillator, corresponding to 51% optical efficiency. The oscillator maintained diffraction limited beam quality of M² < 1.05 at different output coupling with pulse duration between 11.2 ps to 19.3 ps.
... 808 nm pumping and 914 nm pumping will be considered. We added calculations for 888 nm pumping to complete the study, as this pumping gives very interesting results [4,[23][24][25]. Upconversion and fluorescence quenching are nonradiative effects that are intrinsically related to additional sources of heating, and the heat loads can, therefore, be higher than the one brought by the quantum defect (defined by η Q ¼ ðν p − ν l Þ=ν l , where ν p is the the pump frequency and ν l is the laser frequency). ...
A comparative study between 808 and 914 nm pumping of Nd : YVO 4 crystals for laser operation at 1064 nm has been carried out. Using similar setups, performances of both configurations were first studied in the continuous wave, small-signal gain, and Q-switched regimes. Thanks to a numerical model, it is shown that fluorescence quenching and upconversion processes limit the possible uses for the 914 nm pumping scheme to regimes with low population inversions.
In this paper, a diode-pumped CW Kerr lens mode-locked Nd:YVO4 laser is demonstrated in the megahertz (MHz) oscillations mode-locked regime for the first time. Considered the beam mode size in the laser crystal and the Kerr lens sensitivity, an effective laser system with a symmetrical z-shaped cavity is strictly designed by the ABCD matrix and experimentally researched. The laser system can be self-starting without the need of any additional components. When an incident pump power is of 8 W, the maximum output power is 1.65 W, with a slope efficiency of 23.8%. The mode-locked repetition rate and pulse width are 530 MHz and 15.1 ps, respectively.
We report on a high-pulse-energy 888 nm diode-pumped passively mode-locked TEM00 Nd:YVO4 oscillator without spatial hole burning (SHB) effect in active medium. At a pump power of 40 W, the oscillator produced pulse energy up to 270 nJ at a repetition rate of 50 MHz, corresponding to average power of 13.5W with 34% optical-to-optical efficiency. To the best of our knowledge, it is the highest pulse energy obtained at the same pump power. The pulse duration produced varied from 16 to 59 ps. By varying the pump power, we observed a pulse duration ranging from 52 to 59 ps while the time-bandwidth product remained 0.88, and the factors that affect the pulse duration were also discussed. Meanwhile, a novel method of adjusting output coupling (OC) was introduced, which can simplify the structure of laser.
In this work we have investigated diode pumped passively mode-locked Yb:YAG laser operation in quasi-continuous mode. The laser was end-pumped by 25W laser diode operating in pulse mode, with 2ms long pulse and repetition rate of 10Hz. The laser system was designed with X-shaped resonator. Several semiconductor saturable absorber mirrors (SESAMs) were tested. Temporal development of a pulse train in a transient regime before the stabilization of the pulse amplitude and duration was investigated. After the transient period at the beginning of generation of about 25μs, the amplitude and also duration of mode-locked pulses is stabilized. Without intracavity dispersion compensation pulses with duration of 1,37ps (assuming sech2 shaped pulse) were generated with the spectral width of 1,61nm on the wavelength of 1,03μm and pulse energy of 4,5nJ. Autocorrelator trace and oscillogram confirm good reproducibility and stability of the laser operation.
We demonstrate a 10.5 W passively mode-locked Nd:YVO4 oscillator end-pumped by 808 nm laser diode. A novel resonator structure with large mode field space is introduced to solve thermal lens effect and semiconductor saturable absorber mirror’s (SESAM) damage, and then we achieve a single-beam-output picosecond pulse laser without inserting any other laser output elements in laser resonator. The repetition rate of mode-locked pulse is 63.4 MHz with 12.9 ps pulse width, corresponding to maximum pulse energy of 166 nJ and peak power of 12.9 kW. In addition, we discover a complete evolution process of pulses from Q-switched mode-locking to continuous wave (CW) mode-locking for the first time.
Report on a semiconductor saturable absorber mirror (SESAM) passively mode-locked picosecond Nd:YVO4 laser, with adjustable durations between 8.7 and 70 ps. The pulse duration was adjustable by varying the length of type II phase matching KTiOPO4 (KTP) crystal. Type II phase matched second harmonic interaction in combination with the anisotropic emission characteristic of Nd:YVO4 introduced additional bandwidth limiting through birefringent filtering.
We report on an experimental investigation of the noise properties of an free-running, high-power, picosecond Nd:YVO4 oscillator pumped by a 100 W laser diode. The amplitude noise has been measured with a photodiode and an electronic spectrum analyser, and then compared with other mode-locked oscillator's noise spectrum. We show that in terms of noise properties, our powerful oscillator is comparable with low-power oscillators such like low-noise Ti:Sapphire oscillators. We also show that the frequency doubling does not affect the amplitude noise of the oscillator. High power diode pumping is then not an issue to get low-noise high-power oscillators.
Self-starting cw mode locking of a 888 nm pumped high-power Nd : YVO 4 laser using the χ 2 ∶ χ 2 cascaded Kerr lens in lithium triborate without exploiting the “nonlinear mirror” technique is presented. The nonlinear loss modulations are mainly provided by a soft aperture mechanism in the gain medium. A high average output power up to 15.4 W at 10.8 ps pulse duration and short pulses down to 5.7 ps at 11.4 W have been achieved.
