Output Pulse Peak Research Articles

A narrow pulse width and high peak power passively Q-switched laser based on the saturable-absorption characteristic of 2-layer TeSe2

We prepared TeSe2 saturable-absorption nanosheets. The match of band-gap energy with laser wavelength was analysed, and the TeSe2 SA was applied in solid-state lasers to obtain narrow temporal-width and high peak pulse output.

Strain-balanced InGaAs/AlInAs/InP quantum cascade laser grown on GaAs by MOVPE

A systematic study was performed to elucidate the properties of strained-layer InGaAs/AlInAs superlattices (SL) on metamorphic buffer layers grown by MOVPE on GaAs substrates. Differences observed in surface morphology indicate relatively tight control over the SL average net-strain is required for the growth of micron-thick SL structures, as needed for quantum cascade laser (QCL) active regions. Using such conditions, 5.7 μm-emitting, strain-balanced InP-based QCLs grown on (001) GaAs were demonstrated with comparable device performance to their counterparts grown on native InP substrate. 3 mm-long and 25 μm-wide uncoated-facets devices, grown on GaAs and having epi-side lateral contacts, provide peak-pulsed output powers of 2.65 W per facet at room temperature. The corresponding threshold-current density and maximum wall-plug efficiency is 1.61 kA/cm2 and 6.0% respectively. HR-XRD measurements of the strain-balanced QCL grown on GaAs show broadened satellite peaks which are well aligned with the peaks from their counterparts grown on InP.

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.

Rock breaking mechanism of electrode bit in heterogeneous granite formation and its optimization

Electro-pulse-boring (EPB) technology is one of the most potential and nearly industrialized new rock breaking methods in geothermal drilling. However, the mechanism of EPB is not clear, and the structural parameters of EPB electrode bit are not well matched with the corresponding strata parameters and voltage parameters, which seriously hindered the commercialization process of this technology. Based on the dynamic electrical breakdown model (DEBM), a single electric breakdown of rock is realized by coupling the circuit field, the current field and the breakdown field. At the same time, considering the heterogeneity of rock, the three-dimensional numerical simulation of full-bit electrical breakdown using five kinds of electrode bits with different structures is conducted. From these five kinds of electrode bits, an electrode bit suitable for EPB is selected. Finally, the adaptability between the structural parameters and voltage parameters of the selected electrode bit is studied. The results show that the initiation and development of electrical breakdown are affected by the mineral composition, mineral quantity and mineral position of the rock. The petal-structural electrode bits with the same clearance between the high voltage electrode and all ground electrodes are more suitable for EPB drilling due to their higher chip removal function. Moreover, the minimum initial output pulse peak voltage, i.e., the adaptive voltage, of petal-structural electrode bit under different structural parameters is calculated by fitting, which is the best rock breaking voltage parameter. This research can provide reliable help for the design of EPB electrode bit, the optimization of structural parameters and voltage parameters of electrode bit to increase geothermal resources.

Numerical Simulation Study on Gain Nonlinearity of Microchannel Plate in Photomultiplier Tube

Microchannel plate-photomultiplier tubes (MCP-PMTs) with high dynamic ranges and strong outputs are still challenges for the future inertial confinement fusion (ICF) studies, aiming at detecting the large-scale intensities of the radiation pulses. In this article, to investigate the influence factors of the gain nonlinearity causing high-linearity limits of the MCP-PMTs, 3-D microchannel plate (MCP) channel models were built in computer simulation technology (CST) Particle Studio. The Monte Carlo and particle-in-cell methods were carried out to simulate the electron cascade processes in the channels of the MCPs. The dependences of MCP gain nonlinearity on the number of incident electrons, operating voltage, and secondary electron emission (SEE) yield properties were studied. The gains obtained by the simulations for the conventional one-stage and two-stage MCPs are in good agreement with the available experimental data, which verifies the reliabilities of the 3-D MCP models. The simulation results show that the gain of the MCP single channel decreases as the number of incident electrons increases due to the space charge effects. The higher the operating voltage and SEE yield of the MCP, the faster the gain deteriorates. To mitigate the gain saturation effect of MCP single channels, a novel structural design of MCP-PMTs has been proposed by adjusting the design of the MCP chevron pair. A significant improvement in the output pulse peak can be obtained.

High-Power 300 GHz Solid-State Source Chain Based on GaN Doublers

A high-power 300 GHz solid-state source chain based on GaN doublers is proposed. The two doublers working at 150 GHz and 300 GHz are designed and fabricated. The pulsed output power exceeds 1000 mW at 148 GHz to 152.5 GHz with an efficiency of 21 % to 29 %. At 151 GHz, a peak pulsed output power of 1322 mW with 27 % efficiency is derived, while a peak efficiency of 33.1 % is determined at 150 GHz with an input power of 2.3 W. The fabricated 300 GHz doubler delivers pulsed output power that is greater than 110 mW from 292 GHz to 305 GHz with an efficiency of 11.3 % to 14.7 %. A peak output power of 183.4 mW with 13.9 % efficiency is obtained at 302 GHz.

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.

Scalable High Pulsed Power VCSEL Arrays With Transparent Top Electrodes

We demonstrate an innovative approach to fabricating scalable VCSEL arrays for high-pulsed-power applications. The VCSEL arrays consist of tightly-packed, small-diameter mesas that are planarized and passivated with SU-8 resin, and connected by a large-area top transparent electrode made of indium tin oxide. Peak pulsed output power exceeding 100 kW/cm 2 of active area was achieved in arrays with very smoothly etched and passivated sidewalls, without the need of oxide aperture formation.

High pulsed power VCSEL arrays with polymer microlenses formed by photoacid diffusion.

We demonstrate millimeters-long VCSEL linear arrays with SU-8 epoxy-based microlenses that are directly patterned and cross-linked on the output apertures by a simple, photoacid-diffusion-aided photolithography technique. The linear arrays are capable of delivering >7 W of peak pulsed output power. By exploiting the photoacid diffusion effect, it is possible to produce a range of microlens structures with height and radius of curvature ranging from approximately ten to tens of microns. Simulation and experimental results show that the far-field beam divergence can be reduced by a factor of up to 7 in VCSELs integrated with optimal microlens dimensions.

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.

Application of ethanol infiltration for ultra-flattened normal dispersion in fused silica photonic crystal fibers

This paper proposes a new design for an ultra-flattened normal dispersion photonic crystal fiber (PCF) with ethanol infiltration. The optimization process allow us to achieve a symmetric ultra-flat (1 ps/nm/km) normal dispersion in the range of over 500 nm, which is not possible with standard air hole silica fiber. This fiber allows for supercontinuum (SC) generation in the normal dispersion regime. Numerical simulations show that a PCF fiber of length 20 cm, with the pump wavelength of 1550 nm, pulse energy of 4 nJ and duration of 80 fs can generate 945 nm of flattened broadband SC spectrum in the infrared wavelength range; the output pulse peak is also very stable. In addition, the same optical fiber with air holes and under the same stimulated conditions generates the SC spectrum in the anomalous dispersion regime. The proposed PCF structure could be very helpful in large-scale engineering applications, such as dispersion compensation, ultra-short soliton pulse propagation, spectroscopy applications etc.

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.

High-power, surface-emitting quantum cascade laser operating in a symmetric grating mode

Grating-coupled surface-emitting (GCSE) lasers generally operate with a double-lobed far-field beam pattern along the cavity-length direction, which is a result of lasing being favored in the antisymmetric grating mode. We experimentally demonstrate a GCSE quantum-cascade laser design allowing high-power, nearly single-lobed surface emission parallel to the longitudinal cavity. A 2nd-order Au-semiconductor distributed-feedback (DFB)/distributed-Bragg-reflector (DBR) grating is used for feedback and out-coupling. The DFB and DBR grating regions are 2.55 mm- and 1.28 mm-long, respectively, for a total grating length of 5.1 mm. The lasers are designed to operate in a symmetric (longitudinal) grating mode by causing resonant coupling of the guided optical mode to the antisymmetric surface-plasmon modes of the 2nd-order metal/semiconductor grating. Then, the antisymmetric modes are strongly absorbed by the metal in the grating, causing the symmetric mode to be favored to lase, which, in turn, produces a single-lobed beam over a range of grating duty-cycle values of 36%–41%. Simulations indicate that the symmetric mode is always favored to lase, independent of the random phase of reflections from the device's cleaved ends. Peak pulsed output powers of ∼0.4 W were measured with nearly single-lobe beam-pattern (in the longitudinal direction), single-spatial-mode operation near 4.75 μm wavelength. Far-field measurements confirm a diffraction-limited beam pattern, in agreement with simulations, for a source-to-detector separation of 2 m.

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.

Experimental Study of Microwave Pulse Compression Using a Five-Fold Helically Corrugated Waveguide

This paper presents the experimental study of microwave pulse compression using a five-fold helically corrugated waveguide. In the experiment, the maximum power compression ratio of 25.2 was achieved by compressing an input microwave pulse of 80-ns duration and 9.65-9.05-GHz frequency swept range into a 1.6-ns Gaussian-envelope pulse. For an average input power of 5.8 kW generated by a conventional traveling-wave tube, a peak pulse output power of 144.8 kW was measured corresponding to an energy efficiency of 66.3%.

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.