Pulse Peak Power Research Articles

Beam Self‐Cleaning of 1.5 μ$\umu$m High Peak‐Power Spatiotemporal Mode‐Locked Lasers Enabled By Nonlinear Compression and Disorder

AbstractThe realization of beam self‐cleaning in a cavity is more challenging than in the outside cavity. The peak power of intracavity pulses needs to be high to reach the threshold of beam self‐cleaning, which usually relies on additional diffraction grating to compress pulses in a positive‐dispersion cavity. Here, it is first experimentally and numerically demonstrated that self‐cleaning can be observed in an all‐fiber high peak‐power Er‐doped spatiotemporal mode‐locked (STML) laser at all‐negative‐dispersion. Through the nonlinear compression of graded‐index multimode fiber, the pulses are compressed along with the emergence of beam self‐cleaning. Besides, the inherent disorder of multimode fiber accelerates the self‐cleaning process. The intracavity pulse energy of ≈13 nJ with a pulse duration of 734.5 fs is derived under a highly multimode excitation, with an output pulse energy of 2.33 nJ. The pulse energy is a nearly fourfold improvement over the previous report in all‐fiber STML at 1.5 m. Temporal‐dependent characteristics and nonlinear polarization dynamics of beam self‐cleaning are also experimentally uncovered. It is demonstrated that the STML fiber laser will enable new insights into nonlinear pulse propagation in cavities and related applications.

Millimeter-Wave Pulsed Heating in Vitro: Effect of Pulse Duration

The aim of this work is to compare the response of A375 melanoma cells following 90 min of exposure to trains of 1.5 or 6 s millimeter-waves (MMW)-induced thermal pulses with the same temperature dynamics. Phosphorylation of heat shock protein 27 (HSP27) and activation of cleaved Caspase-3 were used as markers of cellular stress and apoptosis, respectively. Immunofluorescence was used to observe and precisely quantify the cellular response as a function of the spatial distribution within the exposed area. Results show that cellular response was stronger when cells were exposed to a train of 1.5 s compared to 6 s heat pulses despite the same average temperature dynamics. Cellular apoptosis induced by 1.5 s pulses was about 50% greater compared to the one induced by 6 s pulses in the area of maximal thermal stress. Similarly, HSP27 phosphorylation was approximately 20% stronger than the one induced by 6 s pulses, and mainly focused within a small area of a few mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Cellular response to MMW induced by pulsed heating does not only depend on the peak, average, and minimum temperature. It is a function of combination of the pulse parameters, including duration, peak power, and period. MMW-induced heat pulses can be efficiently used to induce cellular stress and apoptosis in melanoma cells as a promising innovative tool for the treatment of superficial skin cancer. Adaptative therapies might be envisaged by tuning the pulse shape as a function of the desired effect.

Spectral broadening in convex-concave multipass cells.

Since its first demonstration in 2016, the multi-pass spectral broadening technique has covered impressive ranges of pulse energy (3 µJ - 100 mJ) and peak power (4 MW - 100 GW). Energy scaling of this technique into the joule-level is currently limited by phenomena such as optical damage, gas ionization and spatio-spectral beam inhomogeneity. These limitations can be overcome by the novel multi-pass convex-concave arrangement, which exhibits crucial properties such as large mode size and compactness. In a proof-of-principle experiment, 260 fs, 15 µJ and 200 µJ pulses are broadened and subsequently compressed to approximately 50 fs with 90% efficiency and excellent spatio-spectral homogeneity across the beam profile. We simulate the proposed concept for spectral broadening of 40 mJ and 1.3 ps input pulses and discuss the possibility of further scaling.

Observation of the "invisible" pulsation of soliton molecules in a bidirectional ultrafast fiber laser.

A novel optical soliton dynamics phenomenon, called "invisible" pulsation, has gradually attracted extensive interest in recent years, which can only be identified effectively with the help of real-time spectroscopy technique, i.e., dispersive Fourier transformation (DFT). In this paper, based on a new bidirectional passively mode-locked fiber laser (MLFL), the "invisible" pulsation dynamics of soliton molecules (SMs) is systematically studied. It is indicated that the spectral center intensity, pulse peak power and relative phase of SMs are periodically changed during the "invisible" pulsation, while the temporal separation inside the SMs is constant. The degree of spectral distortion is positively correlated with the pulse peak power, which verifies that self-phase modulation (SPM) is the inducement of spectral distortion. Finally, the universality of the SMs "invisible" pulsation is further experimentally verified. We believe our work is not only conducive to the development of compact and reliable bidirectional ultrafast light sources, but also of great significance to enrich the study of nonlinear dynamics.

On modelling Nd:Yag nanosecond laser milling process by neural network and multi response prediction methods

In this paper, the milling effects on AISI 316 L steel by nanosecond pulsed laser was studied under different parameters as laser pulse peak power, laser repetition rate, scanning speed and focal point. Based on a full factorial design, 108 tests were conducted. MD varied from 15.58 to 60.14 µm; MRR from 0.0028 to 0.0195 mm3/s; Ra from 0.13 to 1.49 µm. The study showed that the laser power and scanning speed have a great influence on material removal. When the laser spot was focused on the upper sample surface, the removing material process was improved. Moreover, Response Surface Methodology and Artificial Neural Network were used to analyze and predict the milling depth, the material removal rate, and the surface roughness. The predictive capabilities of the methods were compared. The predicted R-square for RMS model were 99.70%, 77.79% and 67.73%, while for FF-BPNN were 99.99%, 99.85% and 81.98% for MD, MRR and Ra respectively. Therefore, both models demonstrated strong ability to match the responses. Neural network model exhibited superior predictive power.

486 nm pulsed Nd:YLF laser with intracavity sum-frequency mixing

An intracavity sum-frequency pulsed laser emitting at 486 nm was demonstrated in a combined cavity for two electro-optically Q-switched Nd:YLF fundamental lasers emitting at 908 nm and 1047 nm respectively. Pumped by two 806 nm LDs at 50 Hz repetition rate, while the intracavity pulse energy reached 6.25 mJ at 908 nm and 2.57 mJ at 1047 nm, maximum output pulse energy of 0.26 mJ at 486.4 nm wavelength was successfully achieved by intracavity sum-frequency. The corresponding spectral bandwidth was less than 0.08 nm, and the pulse width was about 11.8 ns. The peak power of the blue laser pulse was up to 21.8 kW, and the results provided a new blue pulsed laser source around 486 nm for ocean detection applications.

Black Phosphorus Coated D-Shape Fiber as a Mode-Locker for Picosecond Soliton Pulse Generation

We demonstrate the production of a picosecond pulse from an Erbium laser cavity using black phosphorous (BP) on side-polished fiber saturable absorber (SA) as a mode-locker. The surface of the fiber was removed utilizing a polishing wheel, and then BP was mechanically deposited onto it to develop an excellent evanescent field on the polished surface area. The SA device was used in a 56 m long Erbium-doped fiber laser (EDFL) ring cavity to generate soliton mode-locked pulses with a center wavelength of 1556.2 nm and a 3 dB spectral bandwidth of 2.2 nm. Stable 3.48 MHz soliton pulses with pulse width as short as 1.17 ps were achievable by setting the pump power within 92 mW to 145 mW. The highest pulse energy and peak power obtainable were 5.4 nJ and 4.7 kW, respectively. The results show that BP deposited onto side-polished fiber can be used as an SA in an EDFL cavity. Its easy construction makes it suitable for producing a portable mode-locked laser source.

355 nm ultraviolet laser output based on a PPMgLN crystal.

This paper reports the method of generating a 355nm ultraviolet (UV) quasicontinuous pulse laser by using two periodically poled Mg-doped lithium niobate (PPMgLN) crystals in a single-pass cascade. In the first PPMgLN crystal with a length of 20mm and a first-order-poled period of 6.97µm, the second-harmonic light of a 532nm laser with 780mW is generated from the 1064nm laser with an average power of 2W; After that, in the second PPMgLN crystal with a length of 15mm and a third-order-poled period of 5.30µm, the 532nm laser generated was combined with the 1064nm laser remaining through the first PPMgLN crystal to obtain a 355nm UV laser with a maximum output average power of 20mW, a repetition rate of 40kHz, a pulse width of 49ns, and a peak power of 10W. Compared with existing reports, we have higher peak power and single pulse energy, which is an important application of the PPMgLN crystal. This paper will provide an important case for the realization of a 355nm UV quasicontinuous or a continuous laser.

Energy characteristics for nanosecond current interrupter of semiconductor-magnetic pulse generator’s terminal stage

Introduction. A semiconductor diode based on reverse current interruption is used to increase a pulse amplitude and peak power delivered on the process load. Usually, a current interrupter is located in the last stage of semiconductor-magnetic pulse generator (SMPG) and is connected in parallel to the load. Problem. Most of publications on this topic mostly concern with analysis of physical processes in the diode structure itself within its oscillating circuit, which is separated from previous SMPG’s pulse compression stages under condition of unidirectional energy transfer from the generator to the load. In this sense, the efficiency of conversion should be determined by the joint of electromagnetic interaction between non-linear compression stages, current interrupter and process load. Goal. Develop a mathematical model of nanosecond current interrupter to determine its electrical and energy characteristics as part of a high-voltage parallel circuit with magnetic pulse compression, depending on the duration and moment of current interruption, the equivalent circuit for load resistance, and to set the most optimal modes of its operation. Methodology. In this work, it is proposed to use a comprehensive approach aimed at the study of electromagnetic processes in the SMPG circuit with a nanosecond current interrupter, which takes into account the topology of circuit, the design parameters of switching reactor, the magnetization curve, the equivalent load resistance, as well as the time parameters of power switches. Results. Analytical expressions describing the electrical and energy characteristics of the interrupter when it operating on the active load are obtained. A numerical simulation of interrupter in the SMPG’s double-loop pumping circuit is carried out, taking into account a nonlinearity of SR’s magnetization curve. Three operation modes of interrupter is described, depending on the initial moment of reverse conduction current interruption. The analysis of interrupter operation on the load with an active-capacitive component is carried out. Practical meaning. The results of the research can be applied in the development of high-voltage SMPG scheme with improved energy-dynamic parameters.

Efficient continuous wave and passively Q switched Er:GdScO3 laser using Fe:ZnSe at 2.8 µm.

We report on diode-pumped continuous wave and passively Q switched Er:GdScO3 crystal lasers at around 2.8 µm. A continuous wave output power of 579 mW was obtained with a slope efficiency of 16.6%. Using Fe:ZnSe as a saturable absorber, a passively Q switched laser operation was realized. A maximum output power of 32 mW was generated with the shortest pulse duration of 286 ns at a repetition rate of 157.3 kHz, leading to a pulse energy of 204 nJ and a pulse peak power of 0.7 W.

Graphitic carbon nitride modulated short pulse generation in an Erbium-doped fiber laser

In the present study, a few layered graphitic carbon nitrides (g-C3N4) nano-sheets were successfully manufactured by the calcination method. It demonstrates nonlinear optical (NLO) property with modulation depths of ∼4.26% at 1.5 μ m. The index-matching gel adhesion effect was used to place the g-C3N4 nano-sheets on the fiber ferrule surface to produce short-pulsed lasers. The g-C3N4 saturable absorber (SA) based Q-switched erbium-doped fiber laser (EDFL) emits at 1560.5 nm wavelength with 1.2 nm of spectral bandwidth at 3 dB. The radio frequency's signal-to-noise ratio (SNR) is 42 dB at first harmonic, demonstrating excellent pulse stability. As the pump power increases, the frequency increases from 27.2 to 108 kHz, and the pulse shortens from 14.6 to 4.2 μ s, correspondingly. The highest pulse energy, peak power, and average output power are measured to be 48.7 nJ, 11 mW, and 5.18 mW at the highest pump power of 479.1 mW. Besides, the morphology and structure of g-C3N4 were characterized by scanning electron microscopy (SEM) and X-rays powder diffraction (XRD), photoluminescence (PL) spectra, Raman spectroscopy, Fourier transform infrared spectra (FT-IR), and UV- diffuse reflectance spectroscopy (DRS) have been also presented. Additionally, the stability of g–C3N4–SA was also measured. These findings suggest that few layered g-C3N4 nano-sheets have a substantial role as a SA in optical modulation devices and nonlinear optical properties at the near and mid-infrared band.

MP23-08 SHORT PULSE VS. LONG PULSE ABLATION WITH THE THULIUM FIBER LASER, AN IN VITRO STUDY

You have accessJournal of UrologyCME1 Apr 2023MP23-08 SHORT PULSE VS. LONG PULSE ABLATION WITH THE THULIUM FIBER LASER, AN IN VITRO STUDY Francois Soto Palou, Robert Medairos, Junqin Chen, Jodi Antonelli, Michael Lipkin, Glenn Preminger, and Pei Zhong Francois Soto PalouFrancois Soto Palou More articles by this author , Robert MedairosRobert Medairos More articles by this author , Junqin ChenJunqin Chen More articles by this author , Jodi AntonelliJodi Antonelli More articles by this author , Michael LipkinMichael Lipkin More articles by this author , Glenn PremingerGlenn Preminger More articles by this author , and Pei ZhongPei Zhong More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003248.08AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The thulium fiber laser (TFL) is becoming of interest to Urologists due to its unique properties. The TFL pulse profile consists of rectangular pulses, designed for enhancing photothermal ablation. Energy for each pulse may be modified by altering pulse duration or peak power. Our aim for this study is to compare short pulse (SP) versus long pulse (LP) for common 10 W dusting settings using the TFL platform. METHODS: All tests were conducted using an IPG Photonics TLR-50 W TFL system and a 200 μm fiber on “soft” (5:2) Begostone phantoms. The most popular 10 W dusting settings (Figure 1) among endourologists familiar with TFL were evaluated.[1] Four different standoff distances (0.2 mm, 0.5 mm 1 mm, 2 mm), and a clinically significant scanning speed of 1 mm/sec was used. The pulse profiles were altered for each energy setting to produce a short pulse (SP) and a long pulse (LP) design. The laser fiber was scanned in a 15 mm straight line with a 3D positioning system across a polished and submerged Begostone surface. Ablation volumes were quantified by optical coherence tomography (OCT). RESULTS: Overall, SP provided greater ablation volume when compared to LP. The greatest difference observed between SP and LP was at 1J/10 Hz and SD of 0.2 mm (2.51 mm3 vs. 0.35 mm3) and this difference was statistically significant (p<0.005). Out of the 20 performed trials there were only two instances in which LP outperformed SP in terms of ablation volume: 0.4J/25 Hz at SD of 2 mm (0 mm3 vs. 0.15 mm3) and 0.2J/50 Hz at SD of 0.2 mm (0.79 mm3 vs 0.81 mm3). In the latter case, however, the difference was not found to be statistically significant (p=0.7). CONCLUSIONS: TFL short pulse profile offers superior trough ablation volumes than long pulse during dusting under clinically relevant scanning speed of 1 mm/s with a time average power of 10 W. [1] Sierra A, Corrales M, Piñero A, Traxer O. Thulium fiber laser pre-settings during ureterorenoscopy: Twitter's experts' recommendations. World J Urol. 2022;40(6):1529-1535. doi:10.1007/s00345-022-03966-9. Source of Funding: N/A © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e308 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Francois Soto Palou More articles by this author Robert Medairos More articles by this author Junqin Chen More articles by this author Jodi Antonelli More articles by this author Michael Lipkin More articles by this author Glenn Preminger More articles by this author Pei Zhong More articles by this author Expand All Advertisement PDF downloadLoading ...

MP35-12 ASSESSMENT OF DUST QUALITY WHILE ABLATING WITH THULIUM FIBER LASER, AN IN VITRO STUDY

You have accessJournal of UrologyCME1 Apr 2023MP35-12 ASSESSMENT OF DUST QUALITY WHILE ABLATING WITH THULIUM FIBER LASER, AN IN VITRO STUDY Francois Soto Palou, Robert Medairos, Junqin Chen, Jodi Antonelli, Michael Lipkin, Glenn Preminger, and Pei Zhong Francois Soto PalouFrancois Soto Palou More articles by this author , Robert MedairosRobert Medairos More articles by this author , Junqin ChenJunqin Chen More articles by this author , Jodi AntonelliJodi Antonelli More articles by this author , Michael LipkinMichael Lipkin More articles by this author , Glenn PremingerGlenn Preminger More articles by this author , and Pei ZhongPei Zhong More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003269.12AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Previous benchtop studies have shown that optimal stone ablation with the thulium fiber laser (TFL) is achieved with short pulse and maximum peak power. Furthermore, in vitro TFL studies have also demonstrated that at equivalent power, the combination of higher energy and lower frequency offers the most efficient dusting settings. Holmium based benchtop studies have shown that low pulse energy produces small fragments while high pulse energy produces larger fragments.1 No such studies have been performed with the TFL platform, and thus with this study we aim to assess the quality and size of fragments produced at different pulse energies. METHODS: All tests were conducted using an IPG Photonics TLR-50W TFL system and a 200 μm fiber on “soft” (5:2) Begostone 6 mm×6 mm (H×D) phantoms. We tested six different pulse energies (0.05 J, 0.1 J, 0.2 J, 0.4 J, 0.5 J, and 1 J) at varying frequencies to produce either 10 W or 20 W of power. Our previous benchtop studies have shown that short pulse provides superior ablation, so all pulse profiles were adjusted to maximum peak power and short pulse. The laser fiber was advanced beyond the distal end of a flexible ureteroscope (Dornier AXISTM, 3.6 F working channel) and the stone phantoms were treated in a test tube filled with water and immersed in a water bath at room temperature (Figure 1). Continuous dusting was performed for 1 minute with the 10 W settings, and 30 seconds with the 20 W settings. Each pulse energy was tested three times with three different stone phantoms. Resultant fragments were sieved, dried for 24 hours and examined under the microscope. RESULTS: At all tested pulse energies, no stone phantoms were broken into large fragments. All stone materials were pulverized into small dust. When examined under the microscope, individual dust particles were smaller than 20 μm for all the tested settings (Figure 1). Exact measurements were not obtained and deemed not clinically relevant. CONCLUSIONS: Unlike Holmium lithotripsy where higher pulse energy results in larger fragments, in Thulium lithotripsy higher pulse energy did not result in increased fragment size. Reference: 1. Sea J, Jonat LM, Chew BH, Qiu J, Wang B, Hoopman J, Milner T, Teichman JM. Optimal power settings for Holmium:YAG lithotripsy. J Urol. 2012 Mar;187(3):914-9. doi: 10.1016/j.juro.2011.10.147. Epub 2012 Jan 20. PMID: 22264464. Source of Funding: N/A © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e474 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Francois Soto Palou More articles by this author Robert Medairos More articles by this author Junqin Chen More articles by this author Jodi Antonelli More articles by this author Michael Lipkin More articles by this author Glenn Preminger More articles by this author Pei Zhong More articles by this author Expand All Advertisement PDF downloadLoading ...

High-Energy Single-Frequency Core-Pumped Er-Doped Fiber Amplifiers

In this article, we studied high-energy single frequency transform-limited Er-doped amplifiers core pumped by a specially developed Yb-doped fiber laser at 980 nm and a Raman laser at 1480 nm. It was demonstrated that pumping at 1480 nm allows achieving slightly higher maximum pulse energy for long pulses in the absence of nonlinear effects. At the same time, amplifiers with a pump at 980 nm have a higher threshold of stimulated Brillouin scattering (SBS), and higher peak power of shorter pulses can be achieved in such a scheme. Lasers with more than 730 μJ pulse energy and with higher than 3.5 kW peak power were demonstrated.

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.

High beam quality yellow laser at 588 nm by an intracavity frequency-doubled composite Nd:YVO4 Raman laser.

High beam quality 588 nm radiation was realized based on a frequency-doubled crystalline Raman laser. The bonding crystal of YVO4/Nd:YVO4/YVO4 was used as the laser gain medium, which can accelerate the thermal diffusion. The intracavity Raman conversion and the second harmonic generation were realized by a YVO4 crystal and an LBO crystal, respectively. Under an incident pump power of 49.2 W and a pulse repetition frequency of 50 kHz, the 588 nm power of 2.85 W was obtained with a pulse duration of 3 ns, corresponding to a diode-to-yellow laser conversion efficiency of 5.75% and a slope efficiency of 7.6%. Meanwhile, a single pulse's pulse energy and peak power were 57 µJ and 19 kW, respectively. The severe thermal effects of the self-Raman structure were overcome in the V-shaped cavity, which has excellent mode matching, and combined with the self-cleaning effect of `Raman scattering, the beam quality factor M2 was effectively improved, which was measured optimally to be Mx 2 = 1.207, and My 2 = 1.200, with the incident pump power being 49.2 W.

Time- and Position-Dependent Breakdown Volume Calculations to Explain Experimentally Observed Femtosecond Laser-Induced Plasma Properties

Focusing of femtosecond laser pulses in gases can produce different gas breakdown phenomena depending on the focusing conditions: from simple optical breakdown like laser “sparks” to a nonlinear optical breakdown like filamentation. The dynamics of such plasmas after the pulse exposure is dependent on the energy deposited by the laser in the breakdown volume. Using a time- and position-dependent breakdown model, we estimate the breakdown volume and show that the energy deposited by the laser in this breakdown volume determines the characteristics of laser-induced plasma in the post-pulse exposure regime. Experimentally we find that for different focal lengths there exists a threshold value of the energy density beyond which a transition from an ellipsoidal shape to a spherical shape can be observed, followed by a toroidal expansion of the produced plasma. When electron density and electron temperature are expressed as a function of the energy density, deviations from the parabolic dependence on irradiance are observed. They imply additional ionization by multiphoton ionization in the plasma volume that occurs when the peak power of the laser pulse is above the critical power for self-focusing in air. The relevance of this experimental and theoretical study is to prevent undesired self-focusing conditions during material processing, a step toward well-controlled laser-plasma etching without laser ablation.

Comparative study on passive Q-switching laser properties of Yb:CaWO4 and Yb:NaY(WO4)2 crystals

Yb:CaWO4 and Yb:NaY(WO4)2 are two tetragonal tungstates, possessing exactly the same crystal symmetry and local site symmetry for the Yb ion. In this work, a detailed comparison of spectroscopic properties was made between the two tungstates, showing a large degree of similarity in their polarized absorption and emission features. Stable passive Q-switching of an Yb:CaWO4 laser was demonstrated, generating 0.40 W of pulsed output power at 1024.7 nm at a repetition rate of 33 kHz; the resulting pulse energy, duration, and peak power were, respectively, 12.1 μJ, 50 ns, and 242 W. Compared to an Yb:NaY(WO4)2 laser operating under the same passive Q-switching conditions, while most of the output characteristics were similar, the pulse energy generated by the Yb:CaWO4 laser proved to be much higher. This may imply the greater potential of Yb:CaWO4 in generating high-energy laser pulses.

High-Peak-Power Passively Q-Switched Laser at 589 nm with Intracavity Stimulated Raman Scattering

A novel scheme was developed for a diode-pumped passively Q-switched Nd:YVO4/KGW Raman laser at 589 nm with a diode-to-orange conversion efficiency reaching 11.4%. The compact near-concentric cavity was designed to achieve the criterion of good passive Q-switching and to contain a coupled resonator for intracavity stimulated Raman scattering (SRS) and second harmonic generation (SHG). The dependence of the output performance on the initial transmission of the saturable absorber was explored in detail. Furthermore, the output performance was studied by considering the influence of the pump-to-mode size ratio. By using an initial transmission of 50%, the highest pulse energy and peak power were 110 μJ and 118 kW, respectively, at a pump duration of 40 μs and a pump frequency of 10 kHz.

Counterpropagating radiation emitted by an electron in the field of a Gaussian laser pulse

The transition from the nonlinear Thomson scattering (electron initially at rest) to the classical limit of Compton scattering (electron moving towards the laser pulse) is considered. The radiation emitted by an electron in the form of plane waves in the far zone is analyzed, and the intensity distribution over the solid angle is obtained. By constructing radiation diagrams, we find numerically the dependences of the intensity and power of radiation on the initial energy of the electron The backscattering intensity as is find analytically is proportional to six power in initial energy and to the peak power of the laser pulse. It is shown that as the initial energy of the electron increases, the effective solid angle of the scattered radiation decreases monotonically and becomes constant.