Pump Pulse Width Research Articles

A novel miniaturized passively Q-switched pulse-burst laser for engine ignition.

A novel miniaturized Cr⁴⁺:YAG passively Q-switched Nd:YAG pulse-burst laser under 808 nm diode-laser pulse-pumping was demonstrated for the purpose of laser-induced plasma ignition, in which pulse-burst mode can realize both high repetition rate and high pulse energy simultaneously in a short period. Side-pumping configuration and two different types of laser cavities were employed. The pumping pulse width was constant at 250 μs. For the plane-plane cavity, the output beam profile was flat-top Gaussian and the measured M² value was 4.1 at the maximum incident pump energy of 600 mJ. The pulse-burst laser contained a maximum of 8 pulses, 7 pulses and 6 pulses for pulse-burst repetition rate of 10 Hz, 50 Hz and 100 Hz, respectively. The energy obtained was 15.5 mJ, 14.9 mJ and 13.9 mJ per pulse for pulse-burst repetition rate of 10 Hz, 50 Hz and 100 Hz, respectively. The maximum repetition rate of laser pulses in pulse-burst was 34.6 kHz for 8 pulses at the incident pump energy of 600 mJ and the single pulse width was 13.3 ns. The thermal lensing effect of Nd:YAG rod was investigated, and an plane-convex cavity was adopted to compensate the thermal lensing effect of Nd:YAG rod and improve the mode matching. For the plane-convex cavity, the output beam profile was quasi-Gaussian and the measured M2 value was 2.2 at the incident pump energy of 600 mJ. The output energy was 10.6 mJ per pulse for pulse-burst repetition rate of 100 Hz. The maximum repetition rate of laser pulses in pulse-burst was 27.4 kHz for 6 pulses at the incident pump energy of 600 mJ and the single pulse width was 14.2 ns. The experimental results showed that this pulse-burst laser can produce high repetition rate (>20 kHz) and high pulse energy (>10 mJ) simultaneously in a short period for both two different cavities.

微型化LD泵浦Er 3+ ,Yb 3+ 共掺磷酸盐玻璃被动调Q激光器

A miniature diode pumped passively Q-switched Er3+ and Yb3+ co-doped phosphate glass laser is reported. The center wavelength of pump source is 940 nm. A Co2+: MgAl2O4 crystal is used as a saturable absorber. When the pump energy is 14 mJ, stable Q-switched pulses are obtained at repetition frequency of 10 Hz and pump pulse width of 5 ms. The output pulse energy of laser is 480 J and pulse width is 5 ns . The wavelength of laser is 1535 nm. The peak power is higher than 20 kW and beam quality is 1.2.

Optimized flat supercontinuum generation in high nonlinear fibers pumped by a nanosecond Er/Yb Co-doped fiber amplifier

Flat supercontinuum generation has been demonstrated in high nonlinear fibers with zero dispersion wavelengths at 1480 and 1500 nm, which were pumped by a MOPA structured Er/Yb co-doped fiber amplifier based on a modulated nanosecond seed laser with the wavelength of 1552 nm. The spectra and output powers affected by the zero dispersion wavelengths, fiber lengths and pump pulse widths were investigated experimentally. A flat spectrum with 5 dB bandwidth from 1220 nm to beyond 1700 nm (assuming the pump peak was filtered) in the optical spectrum analyzer detectable range was finally obtained by optimizing the fiber length and pump pulse width. The maximum output power was 1.02 W, including the peaks near 1550 nm.

Mismatch characteristics of optical parametric chirped pulse amplification

The stability of an optical parametric chirped pulse amplifier (OPCPA) is influenced by time and the angular matching of the input beams. We derived the Gaussian dependence of the monochromatic signal gain on the small mismatch between the signal and pump beams. Gain characteristics were also calculated for polychromatic amplification and the impact of different beam mismatches and interaction geometries was explained. The asymmetry of the energy gain, and the square root dependence of the phase matched wavelength on beam angles were found. The predicted dependences were verified in a noncollinear OPCPA system with LBO and KDP crystal amplifying pulses of a Ti:sapphire laser around a central wavelength of 800 nm, pumped by the third harmonic frequency of an iodine gas laser at a wavelength of 438 nm. The widths of the gain curves in the dependence on both the pump–signal or the phase matching angles varied from several tenths to a few milliradians. The gain curve widths dependent on the pump–signal pulse delay were about two thirds of the pump pulse width for moderate pumping and about a half of the pump pulse width for pumping on the order of GW cm−2. A stable gain output is achieved if angular and temporal fluctuations are fractions of the measured gain curve widths, and when the signal direction is between the pump and the crystal principal axis (i.e. in the psz geometry).

Temporal characteristics of in-band-pumped gain-switched thulium-doped fiber lasers

We numerically investigated temporal characteristics of in-band-pumped gain-switched thulim-doped fiber lasers (GSTDFL). Our theoretical model was based on rate equations and optical power propagation equations including both temporal and spatial variations. This model was validated by comparing the numerical results with results from previous experimental work. Due to the lack of a clear definition of the numerical threshold of gain-switched fiber lasers in the literature, we first defined it in our calculations as the status obtained when the variation of the widths of the generated pulses became nonlinear. Then, we used the model to explore the temporal characteristics of such lasers at and above the laser threshold. We found that the threshold pump energy would increase when the pump pulse width was longer than 500 ns and the pulse widths of the laser pulses at the threshold were kept the same at different pump widths. Above the threshold, by calculating the temporal shapes of the laser pulses under different pump conditions, we studied the origin of the trailing spike phenomenon in the in-band-pumped GSTDFLs and determined the parameter space of the pump conditions that could generate the pulses having a Gaussian-like temporal shape and free from the trailing spikes. We further investigated the variation of the laser pulse widths at different laser configurations and discussed their implications. We believe these numerical results can be referenced qualitatively by the design and optimization of the in-band-pumped GSTDFLs and other in-band-pumped gain-switched fiber lasers, such as those with Yb3+ and Ho3+ dopants.

Pump pulse width and temperature effects in lithium niobate for efficient THz generation

We present a study on THz generation in lithium niobate pumped by a powerful and versatile Yb:CaF(2) laser. The unique laser system delivers transform-limited pulses of variable duration (0.38-0.65 ps) with pulse energies up to 15 mJ and center wavelength of 1030 nm. From previous theoretical investigations, it is expected that such laser parameters are ideally suited for efficient THz generation. Here, we present experimental results on both the conversion efficiency and the THz spectral shape for variable pump pulse durations and for different crystal temperatures, down to 25 K. We experimentally verify the optimum pump parameters for the most efficient and broadband THz generation.

Generation of high-energy and broadband terahertz radiation via coherent synthesis

A new method for the generation of high-energy and broadband terahertz (THz) radiation via coherent synthesis from multiple optical rectifications has been proposed. It is found that the intensities of the synthesized THz pulse are proportional to the square of the number of optical rectification processes when the same nonlinear crystals are used, which provides a simple method for the scaling up of THz energies with a powerful femtosecond laser. This method presents the possibility for THz strong-field physics with this table-top THz source. Moreover, in order to ensure that all the spectral components of the THz pulses are coherently synthesized, the relative time delay among the pump pulses should be less than 0.22 T0 (T0 is the pump pulse width).

High Efficient, Intense and Compact Pulsed D2O Terahertz Laser Pumped With a TEA CO2 Laser

A high efficient, intense and compact pulsed D2O terahertz laser is presented, which is pumped by a multi-transverse mode TEA CO2 laser. For D2O gas as the active medium, with the cavity length of 120 cm, pulse energy of the THz laser has been investigated as the variation of pump energy and gas pressure. When the pump energy was 1.41 J, the maximum single pulse energy of 6.2 mJ was achieved at the wavelength of 385 μm. Photon conversion efficiency as high as 36.5% was obtained when laser operated at the maximum output energy. As the pump energy was raised from 0.57 to 1.41 J, the optimum pressure was slightly changed from 400 to 700 Pa. The THz pulse consisted of a spike pulse with pulse width of 120 ns and a tail pulse with pulse width of about 170 ns. The peak power of the spike pulse is about 44.3 kW. Comparing with the occurring time and pulse width of pump pulse, 70 ns delay and 10ns broadening were observed in the THz spike pulse.

Coherent Mid-IR Supercontinuum Generation in Bismuth-Based Glass Photonic Crystal Fibers

This paper points out the properties of bismuth-based glass and the related design of photonic crystal fibers with flatted and normal group velocity dispersion profile. Supercontinuum generation in fiber is studied by a split-step Fourier numerical stimulation method. The results are shown for highly coherent mid-IR supercontinuum generation with 1.6 octaves bandwidth when pumping pulse width of 150fs and peak power of 40kW at 2.0μm. Analysis illustrates that supercontinuum generation dynamics are dominated by self-phase modulation and optical wave breaking.

Dual-Wavelength Single-Mode Optical Fiber Raman Laser

In order to realize the dual-wave length lasing based on stimulated Raman scattering principle, the dual-wavelength single-mode optical fiber Raman laser is established. Firstly, 80m long G652b single-model quartz fiber is pumped by Nd3+:YAG solid pulse laser, and its output spectra when without grating which are measured and studied. Then, a linear external-cavity fiber laser is designed with fiber Bragg grating as mirrors to gain 1062nm and 1066.5nm laser output. To change pump energy (65.2uJ~100.4uJ), the mean-variances of energy percentages are all about 7.58%,and dual-wavelength energy ratio is close to 1:1. Pump pulse widths are close to 32.14ns. Finally, the main parameters of laser are analyzed too. The dual-wavelength single-mode optical fiber Raman laser can be applied to Raman amplifier filed.

Characterization of one-dimensional lasing in semiconductor disordered nanopowders

In this paper, we present characteristics of one-dimensional ZnO-based random lasers by using a time-domain traveling-wave model. The results reveal that by increasing pump intensity, at first the number of laser modes is increased, and then it gets saturated. Also, output intensity shows that by increasing pump pulse width at a fixed pump intensity, laser modes are made to appear; at first, by raising pump pulse width, more laser modes appear, and then the intensity of the output spectrum is increased. Additionally, we show that by nonuniform pumping, a single-mode laser can be achieved. Through investigation of the nanopowder's average size, we show that the output spectrum has its highest intensity and the sharpest laser modes for average nanopowder sizes less than 100 nm. Moreover, the results show that by decreasing pump area, lasing threshold is inclined.

Optoelectronic Logic Gates Based on Photovoltaic Response of Bacteriorhodopsin Polymer Composite Thin Films

We present designs of optoelectronic OR, AND, NOR, and NAND logic gates with multiple pulsed pump laser beams based on the photovoltaic response of bacteriorhodopsin (BR) molecules embedded in a polyvinyl matrix coated on ITO. A detailed experimental study of the photovoltaic response reveals that continuous pulsed exposure to 532 nm and 405 nm laser light results in a large photocurrent/photovoltage, due to rapid reprotonation and chromophore reisomerization, taking BR to the ground state in hundreds of nanoseconds. It also helps in sustaining the photovoltage at higher frequencies and in maintaining the shape of the photovoltage. It is shown experimentally that for a pulsed laser beam at 532 nm with peak pump intensity of 1.19 W/cm (2), a photovoltage of 50 mV is generated. A detailed numerical simulation of the photovoltaic response of BR has been carried out taking into account all the six states (B, K, L, M, N, and O) in the BR photocycle to ascertain the effect of various parameters such as lifetime of the M-state, the pump pulse-width, pump intensity, lifetime of excited protons, and rate constant of excited protons. Experimental results are in good agreement with theoretical simulations. The present study opens up new prospects for protein-based optoelectronic computing.

Theoretical and experimental study of the pump pulse width optimization of the Yb-doped fiber amplifier

In order to suppress the amplified spontaneous emission (ASE) in the low repetition rate high energy fiber master oscillator power amplifier (MOPA) system and achieve the best amplification results, it is necessary to optimize the pump pulse width. Based on solving a set of time-dependent rate and power transfer equations, the optimum pump pulse width is obtained by studying the transient response of the upper level population distribution, stored energy and ASE of the Yb-doped fiber amplifier under pulsed pump. The ASE built-up time is measured and the optimum value is found by tuning the width of pump pulse in the experiment, and the results show the validity of the numerical simulation.

Performance of large aperture tapered fiber phase conjugate mirror with high pulse energy and 1-kHz repetition rate

A large aperture fused silica tapered fiber phase conjugate mirror is presented with a maximum 70% stimulated Brillouin scattering (SBS) reflectivity, which is obtained with 1 kHz repetition rate, 15 ns pulse width and 38 mJ input pulse energy. To the best of our knowledge, this is the highest SBS reflectivity ever reported by using optical fiber as a phase conjugate mirror for such high pulse repetition rate (1 kHz) and several tens of millijoule (mJ) input pulse energy. The influences of fiber end surface quality and pump pulse widths on SBS reflectivity are investigated experimentally. The results show that finer fiber end surface quality and longer input pulse widths are preferred for obtaining higher SBS reflectivity with higher input pulse energy. Double passing amplification experiments are also performed. 52 mJ pulse energy is achieved at 1 kHz repetition rate, with a reflected SBS pulse width of 1.5 ns and a M(2) factor of 2.3. The corresponding peak power reaches 34.6 MW. Obvious beam quality improvement is observed.

掺镱光纤放大器泵浦脉宽优化

In order to suppress the amplified spontaneous emission (ASE) in the low-repetition rate high-energy fiber master-oscillator-power-amplifier (MOPA) system and achieve the best amplification results, it is necessary to optimize the pump pulse width. Based on solving a set of time-dependent rate and power transfer equations, the transient response of the upper level population distribution, stored energy and ASE of the Yb-doped fiber amplifier under pulsed pump are numerically studied. And the numerical optimum pump pulse width is 793 s under specific parameters given in the paper, including the pump power, fiber length, core area, Yb-doped concentration, etc. In the experiment the ASE built-up time is measured, and the optimum value is 800 s which is found by tuning the width of the pump pulse and measuring the amplification results of the fiber amplifier. The experiment shows the validity of the numerical simulation. 

Theoretical and experimental study of transient response of the Yb-doped fiber amplifier

Some analysis of the transient response of the Yb-doped fiber amplifier are performed by solving a set of time-dependent rate and power transfer equations based on finite-difference method. Meanwhile, the variation of time to reach the steady state for upper level population distribution, the forward and backward amplified spontaneous emissions (ASEs) and stored energy on the system parameters including pump power, fiber length, Yb-doped concentration, and core area are numerically simulated, respectively. The results show that, by optimizing pump pulse width, stored energy can reach or even exceed the steady state value of continuous wave (CW) pump. By increasing Yb-doped concentration and core area, stored energy is increased, the ASE is suppressed and the ASE built-up time is postponed. In addition, the experimental results show the validity of the theoretical ASE built-up time. The obtained results can provide important guiding for the optimization of pump pulse width and fiber parameters.

Influence of spectral broadening on femtosecond wavelength conversion based on four-wave mixing in silicon waveguides

Femtosecond wavelength conversion in the telecommunication bands via four-wave mixing in a 1.5 mm long silicon rib waveguide is theoretically investigated. Compared with picosecond pulses, the spectra are greatly broadened for the femtosecond pulses due to self-phase modulation and cross-phase modulation in the four-wave mixing process, and it is difficult to achieve a wavelength converter when the pump and signal pulse widths are close to or less than 100 fs in the telecommunication bands because of the spectral overlap. The influence of the spectral broadening on the conversion efficiency is also investigated. The conversion bandwidth of 220 nm and peak conversion efficiency of -8 dB are demonstrated by using 500 fs pulses with higher efficiency than the picosecond pulse-pumped efficiency when the repetition rate is 100 GHz.

AlGaInAs multiple-quantum-well 1.2-μm semiconductor laser in-well pumped by an Yb-doped pulsed fiber amplifier

An AlGaInAs multiple quantum well structure is reported as an effective gain medium of the in-well pumped high-peak-power semiconductor disk laser at 1.2 μm. We use an Yb-doped pulsed fiber amplifier as the pump source to effectively optimize the output characteristics. The maximum average output power of 1.28 W and peak output power of 0.76 kW is obtained at 1225 nm lasing wavelength under 60 kHz pump repetition rate and 28 ns pump pulse width.

Development of Optical Parametric Oscillator Tunable in the Range 970-1460 nm

Optical parametric oscillator (OPO) tunable in the range 970-1460 nm has been developed using bet barium borate (BBO) crystal as the gain medium and second harmonic of Nd:YAG laser as pump source. Two sets of resonators were used to cover the range; first was nearly degenerate (970-1180 nm) and the second was nondegenerate (1240-1460 nm). The measured threshold pump pulse energy was nearly 8 mJ. Maximum signal pulse energy of about 14 mJ was obtained for pump pulse energy of nearly 31 mJ. Power scaling efficiency was about 70 per cent. The signal pulse width was ~5 ns corresponding to the pump pulse width of ~ 9 ns. OPO signal beam quality was Gaussian although the pump beam was top-hat multimode. Defence Science Journal, 2011, 61(4), pp.377-382 , DOI:http://dx.doi.org/10.14429/dsj.61.562

Non-invasive estimation and control of inlet pressure in an implantable rotary blood pump for heart failure patients

We propose a dynamical model for mean inlet pressure estimation in an implantable rotary blood pump during the diastolic period. Non-invasive measurements of pump impeller rotational speed (ω), motor power (P), and pulse width modulation signal acquired from the pump controller were used as inputs to the model. The model was validated over a wide range of speed ramp studies, including (i) healthy (C1), variations in (ii) heart contractility (C2); (iii) afterload (C2, C3, C4), and (iv) preload (C5, C6, C7). Linear regression analysis between estimated and extracted mean inlet pressure obtained from in vivo animal data (greyhound dogs, N = 3) resulted in a highly significant correlation coefficients (R2 = 0.957, 0.961, 0.958, 0.963, 0.940, 0.946, and 0.959) and mean absolute errors of (e = 1.604, 2.688, 3.667, 3.990, 2.791, 3.215, and 3.225 mmHg) during C1, C2, C3, C4, C5, C6, and C7, respectively. The proposed model was also used to design a controller to regulate mean diastolic pump inlet pressure using non-invasively measured ω and P. In the presence of model uncertainty, the controller was able to track and settle to the desired input within a finite number of sampling periods and minimal error (0.92 mmHg). The model developed herein will play a crucial role in developing a robust control system of the pump that detects and thus avoids undesired pumping states by regulating the inlet pressure within a predefined physiologically realistic limit.