High Power Short Pulse Research Articles

Achieving high power continuous wave and short pulses of semiconductor laser for use in photodynamic therapy: theoretical work

Achieving high power continuous wave and short pulses of semiconductor laser for use in photodynamic therapy: theoretical work

Effect of peak discharge current on the ion current density on the substrate in the short-pulse HiPIMS

The bombardment of the substrate with accelerated ions from the plasma during the magnetron sputtering process is an effective way of controlling the energy transfer to the coating. One of the ways to increase the ion flux on the substrate is to change the parameters of the discharge power supply pulses. This work investigates the effect of the discharge current pulse amplitude on the average ion current density on the substrate in short-pulse high power impulse magnetron sputtering (s-HiPIMS). During sputtering, the peak discharge current varied from 25 to 250 A with a fixed pulse duration of 6 μs and an average discharge power of 1 kW. Experimental results and theoretical calculations show that the average ion current density on the substrate increases twofold when the amplitude of the discharge current pulses is increased from 25 to 60 A. As the amplitude of the discharge current pulses is further increased, the average ion current density on the substrate stops growing and begins to decrease at currents above 150 A. The paper discusses the reasons for the nonlinear dependence of the average ion current density on the substrate on the amplitude of the discharge current pulses.

Magneto-optical measurement of magnetic field and electrical current on a short pulse high energy pulsed power accelerator

We describe a direct magneto-optical approach to measuring the magnetic field driven by a narrow pulse width (<10 ns), 20 kA electrical current flow in the transmission line of a high energy pulsed power accelerator. The magnetic field and electrical current are among the most important operating parameters in a pulsed power accelerator and are critical to understanding the properties of the radiation output. However, accurately measuring these fields and electrical currents using conventional pulsed power diagnostics is difficult due to the strength of ionizing radiation and electromagnetic interference. Our approach uses a fiber coupled laser beam with a rare earth element sensing crystal sensor that is highly resistant to electromagnetic interference and does not require external calibration. Here, we focus on device theory, operating parameters, results from an experiment on a high energy pulsed power accelerator, and comparison to a conventional electrical current shunt sensor.

Spectral-temporal measurement capabilities of third-order correlators.

We present a method extending scanning third-order correlator temporal pulse evolution measurement capabilities of high power short pulse lasers to spectral sensitivity within the spectral range exploited by typical chirped pulse amplification systems. Modelling of the spectral response achieved by angle tuning of the third harmonic generating crystal is applied and experimentally validated. Exemplary measurements of spectrally resolved pulse contrast of a Petawatt laser frontend illustrate the importance of full bandwidth coverage for the interpretation of relativistic laser target interaction in particular for the case of solid targets.

10 kW peak power, single-frequency 1553 nm nanosecond pulsed fiber laser for time-of-flight LIDAR

A 10 kW peak power, 10 ns duration and 6 kHz repetition rate fiber laser system at 1553 nm based on an Er/Yb co-doped large-mode-area fiber, is demonstrated experimentally. The seed laser is provided by a DFB laser switched with a semiconductor optical amplifier. Its optical spectrum, linewidth, and beam quality are measured and discussed. This pulsed laser with short pulse duration and high peak power could be a candidate for the laser source of time-of-flight light detection and ranging (LIDAR).

Расчет разлета мишени для задач оптимизации лазерного ускорения ионов

At present, a significant part of experiments on the interaction of high-power short laser pulses with solid targets is faced with the problem of target modification under the action of a nanosecond prepulse. In this paper, a series of hydrodynamic calculations of target irradiation with a nanosecond laser pulse is performed, which describes the plasma density profiles arising during the target expansion as a function of the parameters of the laser prepulse/additional pulse. The results obtained can make it possible to improve the efficiency of ion acceleration in the interaction of short laser pulses with a profiled plasma target.

Wavelength-versatile deep-red laser source by intracavity frequency converted Raman laser.

We demonstrate an efficient wavelength-selectable output in the attractive deep-red spectral region from an intracavity frequency converted Nd:YLF/KGW Raman laser. Driven by an acousto-optic Q-switched 1314 nm Nd:YLF laser, two first-Stokes waves at 1461 and 1490 nm were generated owing to the bi-axial properties of KGW crystal. By incorporating intracavity sum-frequency generation and second-harmonic generation with an angle-tuned bismuth borate (BIBO) crystal, four discrete deep-red laser emission lines were yielded at the wavelengths of 692, 698, 731, and 745 nm. Under the incident pump power of 50 W and the repetition rate of 4 kHz, the maximum average output powers of 2.4, 2.7, 3.3, and 3.6 W were attained with the pulse durations of 3.4, 3.2, 4.3, and 3.7 ns, respectively, corresponding to the peak powers up to 177, 209, 190, and 245 kW. The results indicate that the Nd:YLF/KGW Raman laser combined with an angle-adjusted BIBO crystal provides a reliable and convenient approach to achieve the selectable multi-wavelength deep-red laser with short pulse duration and high peak power.

Simple method for broadband amplification in a polarizing-maintained Yb fiber amplifier with a narrow bandpass filter.

We have demonstrated a simple method for achieving broadband amplification and short-pulse generation in a polarizing maintained (PM) Yb fiber amplifier with the implementation of a narrow bandpass filter (NBF). By using an NBF with a spectral bandwidth of 3.3 nm at a wavelength of 1036 nm before the PM Yb amplifier, the spectral bandwidth was extended by self-phase modulation (SPM) in the PM YDF amplifier. The recompressed pulse duration of 125 fs obtained with the NBF was nearly three times shorter than that (350 fs) achieved without the NBF, and therefore the peak intensity of 0.35 MW with the NBF was over two times greater in comparison with that (0.16 MW) obtained without the NBF. We believe that this simple method is useful for developing an all-fiber laser system for high-power short pulse generation.

Design of a Frequency Selective Rasorber With a Waveform Selective Passband

In this letter, a frequency selective rasorber with a waveform selective passband (FSR-WSP) is proposed based on the combination of frequency selective absorber and waveform selective surface techniques to achieve the multiple functions, including absorbing stealth, energy protection, and waveform selection. The structure achieves more than 90% absorptance in the range of 8.4–18.5 GHz (relative bandwidth reaches 75.1%) and a waveform selective transmission band around 3.8 GHz. For waveform selective function, the transmittance reaches more than 80% when a continuous wave is incident, while the transmittance is less than 25% when a high-power short pulse wave is incident. The absorption characteristics and waveform selective transmission mechanism are analyzed and validated by full-wave simulation and cosimulation. Finally, the FSR-WSP is fabricated and measured to verify its functionality.

72-fs Er-doped Mamyshev Oscillator

We demonstrated an all-fiber Er-doped Mamyshev oscillator with short pulse duration and high peak power. Through the dispersion management technique and accumulation of sufficient nonlinear phase shift, stable pulses with repetition rate of 6.55 MHz, 20-dB spectral bandwidth of 78.2 nm, pulse duration of 72 fs and peak power of 86 kW were achieved from output coupler (OC) device directly without extra compression. Simulations have been performed to show the direct generation of ultrafast laser pulse from the Mamyshev oscillator based on the extended nonlinear Schrödinger equation. To the best of our knowledge, this is by far the shortest pulse duration, the highest experimental peak power Er-doped Mamyshev oscillator.

Experimental estimates of the photon background in a potential light-by-light scattering study

High power short pulse lasers provide a promising route to study the strong field effects of the quantum vacuum, for example by direct photon–photon scattering in the all-optical regime. Theoretical predictions based on realistic laser parameters achievable today or in the near future predict scattering of a few photons with colliding Petawatt laser pulses, requiring single photon sensitive detection schemes and very good spatio-temporal filtering and background suppression. In this article, we present experimental investigations of this photon background by employing only a single high power laser pulse tightly focused in residual gas of a vacuum chamber. The focal region was imaged onto a single-photon sensitive, time gated camera. As no detectable quantum vacuum signature was expected in our case, the setup allowed for characterization and first mitigation of background contributions. For the setup employed, scattering off surfaces of imperfect optics dominated below residual gas pressures of 1 × 10−4 mbar. Extrapolation of the findings to intensities relevant for photon–photon scattering studies is discussed.

Safety of high-power short pulse single spot diode laser stapedotomy: an experimental animal study

Background We present a new method of diode laser stapedoplasty – high-power short-pulse mode with preliminary carbonization of the waveguide and a single spot of laser ablation. Aims/objective The aim of our research is the safety evaluation of presented mode 0.98 µm diode laser cochleostomy in guinea pigs. Material and methods Guinea pigs (n = 10) received 0.98 µm diode laser cochleostomy on one ear under general anesthesia. The control group was based on untreated ears (n = 10). The assessment of auditory function was performed using the distortion product otoacoustic emission (DPOAE) before and 7 d after surgery. To assess the degree of damage from the laser cochleas were extracted for histological examination. Results To evaluate the negative impact of laser energy on OHCs and auditory function, we analyzed DPOAE amplitudes for 6400 and 8000 Hz since high frequency. The paired Student’s t-test showed no statistically significant difference between the two groups. The histological examination yielded no statistically significant difference in the number of intact OHCs in the two groups. Conclusion and significance Our study confirms that the proposed method of high-power short pulse diode laser stapedotomy is safe for the inner ear. Further prospective and randomized clinical trials are required to evaluate the possible benefits of this method.

Finite element simulation of temperature field in laser cleaning of TA15 titanium alloy oxide film

<p indent=0mm>Laser cleaning is a noncontact cleaning method that uses a short-pulse high power density laser to irradiate an object. The pollutants are removed by the complex physical and chemical interactions between the laser and the object to be cleaned. The mechanism of laser cleaning is very complex, including photodegradation, photodetachment, and photovibration, which are closely related to the temperature distribution in the laser-cleaning process. In this study, the finite element simulation model of laser cleaning of TA15 titanium alloy oxide film is established by using Comsol Multiphysics commercial simulation software. The influence of spot shape, laser energy, loading mode, and pulse width on the titanium alloy oxide film temperature field is analyzed. The results showed that the substrate was severely damaged by a millisecond pulse laser. The shorter the pulse width, the smaller the surface thermal diffusion. The square flat-top spot was more evenly heated than the Gaussian spot, and the rectangular pulse was less damaged than the Gaussian spot. The laser-cleaning effect of titanium alloy oxide film was the best when the square flat-top laser was loaded in a rectangular pulse.

High Peak Power Electro-Optical Cavity-Dumped Laser at 946 nm Based on Pulse LD Side-Pumped Nd:YAG

Based on the transverse polarization modulation technology of MgO:LN crystal, an electro-optic cavity-dumped 946 nm all-solid-state laser with short pulse duration and high peak power at 200 Hz repetition rate is developed by our research team. Through structural optimization design, the cavity emptying laser has good thermal and insensitivity characteristics, with the repetition frequency in the range of 1 kHz–200 Hz was adjustable, The maximum average output power of the pulsed laser is 15.4 W and 8.4 W were obtained at the repetition frequency of 1 kHz and 200 Hz, the corresponding pulse width of 10.1 ns and 8 ns. The beam quality factors of M2 x is 3.849, M2 y is 3.888, and far field divergence angles θx is 3.46 mrad, θy is 3.55 mrad, respectively at the repetition frequency of 1 kHz.

Comparison of Heating Strategies on Soil Water Measurement Using Actively Heated Fiber Optics on Contrasting Textured Soils

The actively heated fiber optics (AHFO) technique has the potential to measure soil water at high spatial and temporal resolutions, and thus it can bridge the measurement gap from point to large scales. However, the availability of power might restrict its use, since high power is required to heat long fiber optic cables under field conditions; this can be a challenge for long-term soil water monitoring under field conditions. This study investigated the performance of different heating strategies (power intensity and heating duration) on soil water measurement by the AHFO technique on three different textured soils. Different heating strategies: high power–short pulses (20 Wm−1–3 min), low power–short pulses (10 Wm−1–3 min, 5 Wm−1–3 min, 2.5 Wm−1–3 min) and low power–long pulses (10 Wm−1–5 min, 5 Wm−1–10 min, 2.5 Wm−1–15 min) were tested using laboratory soil columns. The study compared the sensitivity of the thermal response, NTcum to volumetric water content (VWC) and the predictive error of different heating strategies and soils. Results of this study showed that the sensitivity of NTcum increased and the predictive error decreased with increasing power intensity, irrespective of the soil type. Low power–short heat pulses such as 5 Wm−1–3 min and 2.5 Wm−1–3 min produced high predictive errors, RMSE of 5–6% and 6–7%, respectively. However, extending the heating duration was effective in reducing the error for both 10 and 5 Wm−1 power intensities, but not for the 2.5 Wm−1. The improvement was particularly noticeable in 5 Wm−1 –10 min; it reduced the RMSE by 1.5% (sand and clay loam) and 2.73% (sandy loam). Overall, the results of this study suggested that extending the heating duration of 10 and 5 Wm−1 power intensities can improve the sensitivity of the thermal response and predictive accuracy of the estimated soil water content (SWC). The results are particularly important for field applications of the AHFO technique, which can be limited by the availability of high power, which restricts the use of 20 Wm−1. For example, 5 Wm−1–10 min improved the predictive accuracy to 3–4%, which has the potential to be used for validating soil water estimations at satellite footprint scales. However, the effects of diurnal temperature variations should also be considered, particularly when using low power intensity such as 5 Wm−1 in surface soils under field conditions.

Short Pulse Width and High Peak Power 457 nm Deep Blue Laser with V-Type Cavity

An intracavity frequency doubling acousto-optically Q-switched Neodymium-doped Yttrium Orthvanadate (Nd:YVO4) 457 nm blue laser by employing a three-mirror folded cavity was demonstrated. With the incident pump power of 40.4 W, the maximum average output power of 439 mW 457 nm laser, and the minimum pulse duration of 86.14 ns and the maximum peak power of 510 W were achieved at 10 kHz. The M2 factors are 1.23 and 1.61 in X and Y directions, respectively. The power stability in two hours is better than 2%.

7 kHz sub-nanosecond microchip laser amplified by a grazing incidence double pass slab amplifier

To obtain short pulse width and high peak power laser, a 7 kHz sub-nanosecond microchip laser amplified by a grazing incidence double pass slab amplifier is experimentally demonstrated in this Letter. We use a compact side-pumped Nd:YVO4 bounce amplifier with grazing incidence beam for achieving high gains and power extraction. Laser output power of 7.37 W at 7 kHz, 1.2 MW pulse peak power with 877 ps duration and 1.05 mJ energy, 25 pm spectral width, and near diffraction limited mode beam quality are achieved, and the optical-to-optical efficiency is 18%. The laser is packaged in a volume of 356 mm × 226 mm × 84 mm and may be used for applications such as laser altimeters and ladar systems.

Analysis of the Influence of High-Power Microwave Short Pulse on IFM Performance

In the working scenario of instantaneous frequency measurement (IFM) system, when the high-power short pulse enters the receiver of IFM system as an interference signal, it will have a certain impact on the receiver’s normal processing of the counter radar signal. This paper discussed the influence a receiver gets while doing frequency measurement, when short pulses are in different part of the received radar signal in time domain and frequency domain.

Uniform atmospheric pressure plasmas in a 7 mm air gap

Homogeneous penetration of atmospheric pressure uniform air plasma (APUAP) into thin gaps is highly warranted for multipurpose processing of materials. Here, we report APUAP generation in a 7 mm discharge gap with ambient air as the working gas, well beyond the presently maximum achievable 4 mm. Driven by a short pulse high voltage power, a 7 mm wide and 60 mm long uniform air plasma sheet is generated. The discharge is robust and the uniformity is not affected by the complex and variable components of ambient air, as is the case for most plasma discharges in air. Ultrafast photography shows that, different from previous reports, the discharge initiates in the whole air gap simultaneously and brightens quickly with the fast rise of the pulsed voltage. The generation of uniform plasma is mainly attributed to the high density of seed electrons and the reduced number density of molecules in air. Moreover, the achievable gas temperature of up to 1300 K indicates that this type of plasma is suitable for processing of a broad range of materials.

RGB laser based on an optical parametric oscillator for single-shot color digital holographic microscopy.

We report on the new technical realization of single-shot color digital holographic microscopy. For this application, we propose to use an original three-wavelength red, green, and blue laser based on the Nd:YAG active element with sequential parametric downconversion and upconversion of optical frequencies into red (634nm), green (532nm), and blue (451nm) spectral intervals. This light source provides high-power short (∼10 ns) pulses and enables simultaneous formation of three color interference patterns in a two-path interferometer. Their registration by a color image sensor provides fast acquisition of phase delay distribution induced by the inspected object at three wavelengths without spectral tuning.