Output Pulse Peak Power Research Articles

Highly efficient diode-pumped passively Q-switched Nd:YVO4/KGW Raman lasers at yellow and orange wavelengths.

Efficient diode-pumped passively Q-switched Nd:YVO4 yellow and orange lasers are developed with the pulse pumping scheme and the intracavity stimulated Raman scattering (SRS) and second harmonic generation (SHG). A Np-cut KGW is exploited in the SRS process to generate the yellow 579 nm laser or the orange 589 nm laser in a selectable way. The high efficiency is achieved by designing a compact resonator to include a coupled cavity for intracavity SRS and SHG and to provide a focused beam waist on the saturable absorber for reaching an excellent passive Q-switching. The output pulse energy and peak power can reach 0.08 mJ and 50 kW for the orange laser at 589 nm. On the other hand, the output pulse energy and peak power can be up to 0.10 mJ and 80 kW for the yellow laser at 579 nm.

Pedagogically fast model to evaluate and optimize passively Q-switched Nd-doped solid-state lasers.

The coupled rate equations with the spatial overlap effect for four-level passively Q-switched lasers are fully considered. A transcendental equation is derived for the residual fraction of the inversion density after the finish of the Q-switched pulse. Comprehensive calculations for the transcendental equation were executed to attain an analytical function for precisely fitting the residual fraction of the inversion density. With the fitting function, a pedagogical model with the correction for high output coupling is developed to straightforwardly analyze the output pulse energy and peak power. Detailed experiments are carried out to validate the model.

Highly efficient, high-energy, picosecond, synchronously pumped Raman laser at 1171 and 1217 nm based on PbMoO4 crystals with single and combined Raman shifts.

For the first time to our knowledge, the operation of a synchronously pumped ultrafast Raman laser that uses a PbMoO4 crystal as the active medium has been demonstrated. We achieved efficient Raman conversion in PbMoO4 from pumping 1063 nm into 1171 and 1217 nm, respectively, at single and combined frequency shifts on stretching and bending Raman modes. The output pulse energy (up to 160 nJ) and peak power (up to 11 kW) of the output picosecond radiation is the highest among all-solid-state synchronously pumped Raman lasers published to date. The strongest pulse shortening at 1217 nm down to 1.4 ps was obtained that is close to the bending mode dephasing time.

Octave-Spanning Dispersive Slot Waveguide Based Chip-Level Ultrashort Pulse Stretcher

A silicon nitride horizontal slot waveguide with silicon dioxide cladding is designed to achieve flat negative dispersion ( $\text {nm}\cdot \text {km}$ )) over an octave-spanning bandwidth (782 to 2100 nm). Simulations show that, when a 10-fs pulse with 1-W peak power is input into a 5-cm long waveguide, the pulse width becomes 448 times wider and its peak power is reduced to $2.23\times 10^{-3}$ W. After passing through another ideal positive dispersion element, we find that the output pulse peak power can be recompressed close to 1 W in the case of different input pulse widths. Moreover, for the input pulse with a much higher peak power, the pulse width of the output pulse can be compressed to a much narrower level because of the spectral broadening introduced by optical nonlinearity. A 100-fs input pulse with 10-kW peak power can be compressed to 12.5 fs with a peak power of 63 kW. Considering the time-domain broadening and the peak power reduction, such a slot waveguide with a flat negative dispersion could be used as a time stretcher for 10-fs level pulse in on-chip chirped pulse amplification (CPA) system.

Dissipative soliton resonance and its depression into burst-like emission in a holmium-doped fiber laser with large normal dispersion.

We report on dissipative soliton resonance (DSR) and its transformation into a type of burst-like emission in a holmium-doped fiber (HDF) laser in the large normal dispersion regime. A nonlinear amplifying loop mirror incorporating ∼118 m large normal dispersion fiber acts as an artificial saturable absorber. To the best of our knowledge, the HDF laser has the largest net normal dispersion so far. As the pump power is increased from ∼1.72 W to ∼4.80 W, the produced single pulse linearly broadens from ∼6.7 ns to ∼68.0 ns, while the output pulse peak power is clamped around ∼180.5 mW due to the peak-power-clamping effect with DSR. The sharp spectral peak indicates that DSR is realized with a large normal dispersion. With further manipulation of the polarization state, DSR can evolve into a type of burst-like emission. It is further revealed that this burst-like emission could be caused by a type of peak-power-depressing effect, which results from the competition between DSR and soliton formation.

Diode-pumped high-efficiency passively Q-switched Yb:CaYAlO4 laser

We experimentally demonstrated a high-efficiency passively Q-switched Yb:CaYAlO4 (Yb:CYA) laser based on a semiconductor-saturable absorber mirror (SESAM), and the output characteristics of the laser including the average output power, repetition frequency, pulse duration, pulse energy and pulse peak power were investigated by adopting output mirrors with different transmittances. When the transmittance of the output mirror was 5% and the pump power was set at about 7.76 W, a maximum average output power of as high as 2.480 W was achieved with a slope efficiency and light-to-light efficiency of the Q-switched Yb:CYA laser of up to 37.1% and 31.2%, respectively.

Short pulse generation in active Q-switched Yb-doped all fiber laser and its amplification

Generation of stable sub-cavity round-trip time pulses have been achieved in all-fiber Ytterbium-doped Q-switched fiber laser by controlling the modulation window ON-time of acousto-optic modulator (AOM). Short pulses (anomalous pulses) of duration in the range of 50–55 ns have been achieved in experimental configurations with the cavity round-trip time of ∼130 ns, when modulation window “ON-time” of AOM was equal to or shorter than the pulse build-up time of the normal Q-switched pulses. In the case of normal AO Q-switching, pulses of duration more than 1.3 µs with an average power of 30 mW and pulse energy of 0.38 µJ at 80 kHz of repetition rate were obtained at 2 W of pump power. At the same value of the pump power, the anomalous pulses of ∼55 ns with an average power of 12 mW were generated, which are ∼24 times shorter than pulses obtained with conventional Q-switching process (normal pulses). The peak power of the anomalous pulses are higher than the normal pulses by the factor of eight at the same value of the pump power. The anomalous pulses from the AO Q-switched oscillator with 55 ns pulse duration have been amplified in single mode Ytterbium doped all fiber amplifier in two stages. Amplified average output power of ∼19 W was achieved with the output pulse energy and peak power of 240 µJ and 4.4 kW respectively in all fiber configuration.

Highly efficient picosecond all-solid-state Raman laser at 1179 and 1227 nm on single and combined Raman lines in a BaWO4 crystal

We present a highly efficient ring-cavity all-solid-state BaWO4 Raman laser generating at both the long-shift (ν1=925 cm-1) and short-shift (ν2=332 cm-1) Raman lines under external picosecond synchronous pumping at the wavelength of 1063nm. Very high slope efficiencies and output pulse energies of 68.8% and 103nJ at the ν1-shifted Stokes wavelength of 1179nm, and 38.6% and 53nJ at the (ν1+ν2)-shifted Stokes wavelength of 1227nm have been achieved. Self-mode locking of the (ν1+ν2)-shifted Stokes field under intracavity pumping by the ν1-shifted Stokes field allowed to realize 12-fold shortening of the 1227nm radiation pulse down to 3ps close to the shorter dephasing time of the ν2 Raman line at the output pulse peak power 1.5 times higher than the pump peak power.

Theoretical and Experimental Investigations on a Gaussian-Like Beam Output System for Ku-Band Gyro-TWT

Theoretical and experimental investigations on an output system, consisting of waveguide horn, phase-shift section, RF window, and monitoring section, capable of outputting a Gaussian-like beam rather than a circular waveguide TE1,1 mode, for a Ku-band gyrotron-traveling-wave tube, have been carried out. An azimuthally symmetric Gaussian-like beam has been observed at the output port in both the low-power and high-power measurements. The experimental results showed that the mode purity of output Gaussian beam is over 98% from 14.5 to 16.5 GHz. There is no arcing monitored when the output pulse peak power is over 160 kW when the pulsed tube operates with 10% duty cycle. The output Gaussian-like beam can be directly usable for low-loss transmission as well as for effective antenna feeding and no extra mode converter is needed, which can improve the transmission efficiency of the transmission line system and form a compact high-power system.

Linearly frequency-modulated pulsed single-frequency fiber laser at 1083 nm.

A linearly frequency-modulated, actively Q-switched, single-frequency ring fiber laser based on injection seeding from an ultra-short cavity is demonstrated at 1083 nm. A piezoelectric transducer is employed to obtain linearly frequency-modulating performance and over 1.05 GHz frequency-tuning range is achieved with a modulating frequency reaching tens of kilohertz. A maximum peak power of the stable output pulse is over 3.83 W during frequency-modulating process. This type of pulsed fiber laser provides a promising candidate for coherent LIDAR in the measurement of thermosphere.

Theoretical study on generating mid-infrared ultrashort pulse in mode-locked Er3+: ZBLAN fiber laser

Fiber lasers show several advantages over other types of lasers. They are efficient, compact, and rugged since they require few bulk components and are virtually unaffected by the surrounding environment. Mode-locked mid-infrared (mid-IR) lasers are essential for a wide variety of applications. The promising applications of mode-locked fiber lasers at wavelengths near 3 m include combs generation (metrology), spectroscopic sensors, infrared countermeasures, laser surgery, high-efficient pump sources for longer-wavelength oscillators and mid-IR supercontinuum source pumping. Based on the nonlinear Schrdinger equation (NLSE), a theoretical model of passively mode-locked Er3+-doped fluoride fiber laser using a saturable absorber is set up. Some mechanisms for generating mid-IR ultrashort pulse in fiber lasers are investigated. When the dispersion of the cavity is managed properly, the numerical simulation mainly focuses on the evolution process of mid-IR ultrashort pulse in fluoride fiber oscillators. Influences of the intracavity net dispersion and the small-signal gain on the generation of mode-locked pulses are analyzed in detail. And the reasonable parameter windows are given. Just as the simulated results showed, for a case of 4 m Er3+-doped fluoride fiber, small-signal gain g0= 0.6 m-1 and unsaturated loss l0 = 0.7, the stable mode-locked pulses are achieved by tuning the net intracavity dispersion within a certain range from 0.72 ps2 to 0.83 ps2. As the net intracavity dispersion increases, the output pulse duration increases gradually, while the spectrum width (FWHM) and peak power decrease accordingly. In addition, for the case of 4 m Er3+-doped fluoride fiber, unsaturated loss l0 = 0.7 and net intracavity dispersion of 0.8 ps2, the stable mode-locked pulses can also be obtained by tuning the small-signal gain within a certain range from 0.55 to 0.70 m-1. As the small-signal gain increases, the output pulse duration, spectral width, and peak power increase gradually. This work may be beneficial to the design of experiments for achieving more narrow pulse duration, wide spectral width, and high peak power mid-infrared ultrashort pulse.

Operation of a Microwave Pulse Compressor With a Laser-Triggered Plasma Switch at Different Laser Beam Directions

A resonant microwave pulse compressor with laser triggering of the plasma discharge in its switch was studied for the influence of the unfocused laser beam direction with respect to the RF electric field. The compressor was realized as a rectangular waveguide-based cavity connected to an $H$ -plane waveguide tee with a shorted side arm filled with pressurized helium and pumped by a conventional pulsed $S$ -band magnetron. It was found that neither the direction, nor the intensity of the laser beam significantly affect the compressor output pulse peak power and waveform. Meantime, the delay between the moment of plasma discharge initiation and the appearance of the microwave output is shorter and the time jitter for this delay is smaller if the laser beam is directed along the RF electric field. The same effect was observed when increasing the intensity of the laser beam. Time-resolved optical emission spectroscopy was used to evaluate the plasma density, and numerical simulations of the RF energy release from the system with the appearance of plasma showed a good agreement with the experimentally obtained characteristics of the plasma and microwave output pulse.

High-power passively mode-locked Nd:YVO(4) laser using SWCNT saturable absorber fabricated by dip coating method.

Passive mode locked laser is typically achieved by the Semiconductor Saturable absorber Mirror, SESAM, saturable absorber, which is produced by expensive and complicated metal organic chemical vapor deposition method. Carbon based single wall carbon nanotube (SWCNT), saturable absorber, is a promising material which is capable to produce stable passive mode-locking in the high power laser cavity over a wide operational wavelength range. This study has successfully demonstrated the high power mode locking laser system operating at 1 micron by using SWCNT based absorbers fabricated by dip coating method. The proposed fabrication method is practical, simple and cost effective for fabricating SWCNT saturable absorber. The demonstrated high power Nd:YVO(4) mode-locked laser operating at 1064nm have maximum output power up to 2.7W,with the 167MHz repetition rate and 3.1 ps pulse duration, respectively. The calculated output pulse energy and peak power are 16.1nJ and 5.2kW, respectively.

Plasma density temporal evolution in a high-power microwave pulse compressor switch

Time-resolved optical-emission spectroscopy measurements are used to evaluate plasma density in an interference switch during the extraction of a nanosecond output pulse from a high-power microwave compressor. The compressor represents a resonant cavity connected to an H-plane waveguide tee with a shorted side arm filled with helium at a pressure of ; the plasma discharge in the tee side arm is triggered by a Surelite laser. A nanosecond-scale dynamics of the plasma density is obtained by analyzing the shape of the helium spectral lines. The analysis of the experimental data evidences a correlation between the rise time of the plasma density and the peak power of the microwave output pulse. Numerical simulations of the microwave energy release from the cavity with the appearance of the plasma yield results in good agreement with the measured output pulse peak power and waveform.

Numerical simulations of output pulse extraction from a high-power microwave compressor with a plasma switch

Numerical simulations of the process of electromagnetic energy release from a high-power microwave pulse compressor comprising a gas-filled cavity and interference switch were carried out. A microwave plasma discharge in a rectangular waveguide H-plane tee was modeled with the use of the fully electromagnetic particle-in-cell code MAGIC. The gas ionization, plasma evolution, and interaction with RF fields accumulated within the compressor were simulated using different approaches provided by the MAGIC code: particle-in-cell approach accounting for electron-neutral collisions, gas conductivity model based on the concept of mobility, and hybrid modeling. The dependences of the microwave output pulse peak power and waveform on parameters that can be controlled in experiments, such as an external ionization rate, RF field amplitude, and background gas pressure, were investigated.

Stimulated Brillouin scattering generation in ns pulsed double-cladding fiber amplifier

This paper proposes a study both in theory and experiment on the phenomenon of stimulated Brillouin scattering (SBS) in a double-cladding fiber amplifier. The distortion characteristic of the 200-ns is observed through a stationary coupled-wave SBS model including the second-order Stokes wave for double-cladding fiber amplifier. The first-order Stokes wave is amplified during backward propagation to such an intense peak power that it can generate second-order Stokes wave. The stochastic aspect of pulse distortion induced by SBS is also experimentally demonstrated in the single frequency 200ns pulse amplifier with 12-m Yb3+ doped double-cladding fiber. The backward SBS pulse is observed when the pulse peak power is up to 3.3W, and the pulse width of SBS is narrower than that of the input signal. In the meantime, to overcome the difficulty of the pulse spectrum measurement, a novel method is put forward to measure the SBS frequency shift using the F–P interferometer with free spectral rang of 30G, showing a good agreement with the theoretical estimation. SBS is the main factor that limits the output pulse peak power in the amplification of the single-frequency pulse.

High-pulse-stability double-end continuous-grown YVO4/Nd:YVO4/YVO4 acousto-optically Q-switched laser at high repetition rates

High pulse amplitude stability of 0.62% (rms) is achieved at 60 kHz repetition rate in fundamental mode with double-end continuous-grown YVO4/Nd:YVO4/YVO4 composite crystal. The average output power and pulse peak power are 32.9 W and 27.7 kW, respectively, with 19.8 ns pulse width and 548 μJ pulse energy. The pulse amplitude stability is investigated experimentally. The stability gets improved with the decrease of repetition rate and output transmission. From theoretical analysis, the reason of pulse instability at high repetition rates is that the initial population inversion doesn’t saturate and the final population inversion doesn’t approach zero. With the decrease of repetition rate and output transmission, the final population inversion decreases and the interaction between two adjacent pulse periods is weakened. Therefore, pulse stability improves.

Continuous-wave and Q-switched laser operation of Yb:NaY(WO_4)_2 crystal

Diode-pumped continuous-wave (cw) and Q-switched laser operations were demonstrated, for the first time to our knowledge, with a disordered Yb:NaY(WO(4))(2) crystal. A cw output power of 5.2 W at 1045 nm was generated with an optical-to-optical efficiency of 37%. The slope efficiency in the absence of thermal losses was 50%. With a Cr(4+):YAG saturable absorber to passively Q-switch the laser, an average output power of 2.0 W was obtained with a slope efficiency of 35%. The output pulse energy, duration, and peak power were 145 muJ, 26 ns, and 5.6 kW, respectively.

Self-terminated laser amplifier with an enhanced peak output pulse power

A method for increasing the peak radiation pulse power of self-terminated amplifiers without changing the pump power of an active medium and energy extraction is discussed. The first experimental results obtained by using the active media of copper vapour lasers are presented. A nearly twofold increase in the output pulse peak power is achieved.

Stimulated emission in the blue wavelength region from a copolymer containing PPV segment

The lasing properties of a soluble conjugated polymer, Poly[1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-3,5-dimethoxy-1,4-phenylene] (CNMBC-Ph) in chloroform solution were investigated. The third harmonic radiation of a Nd:YAG laser was used as the pump light. The stimulated emission with a linewidth of 15 nm was observed in the blue wavelength region with the peak at 450 nm. The threshold pulse peak power was about 2.8 MW/cm 2. The energy conversion yield of the laser was estimated to be about 3.4%. The maximum peak power of the laser output pulse reached 40 kW.