Highest Single Pulse Energy Research Articles

All-PM Yb-doped mode-locked fiber laser with high single pulse energy and high repetition frequency

We demonstrate an all-polarization-maintaining (PM) ytterbium (Yb)-doped fiber laser with a figure-of-9 structure to generate mode-locked pulses with high single pulse energy and high repetition frequency. By exploiting the nonlinear amplifying loop mirror, a stably self-started mode-locking is achieved with a spectrum bandwidth of 13 nm and a pulse duration of 4.53 ps. The fundamental frequency is 97.966 MHz at the maximum output power of 143 mW in single pulse mode-locked operation, corresponding to the single pulse energy is 1.46 nJ. The output pulses maintain both high repetition frequency and high single-pulse energy. This laser oscillator can be an ideal seed source for applications such as high-energy amplifiers.

Investigation of pulse burst characteristics in an LD end-pumped Er:Yb:Glass/Co:MALO microchip 1.5 μm laser

Burst mode lasers, characterized by a sequence of high-intensity pulses, are integral to applications such as the examination of turbulent flows and optical metrology. This study investigates a 1.5 μm passively Q-switched pulse burst microchip laser, end-pumped by a 940 nm laser diode. Utilizing Er:Yb:glass as the gain medium and Co:MALO for passive Q-switching, delivering a pulse width of 5.5 ms and a repetition rate of 10 Hz. When the initial transmittance of the saturable absorber was 93 % and the maximum absorbed pump energy reached 85 mJ, we successfully generated up to 12, 8, and 4 pulses within a burst at 1.5 μm. These results corresponded to cavity lengths of 12 mm, 13 mm, and 14 mm, respectively. By using a saturable absorber with an initial transmittance of 90.5 %, a higher single pulse energy and a narrower pulse width were realized. The narrowest pulse width was reduced to 6.2 ns, with a corresponding single pulse energy of 272 μJ. The peak power in the Er:Yb:glass/Co:MALO pulse burst laser reached an estimated 43.9 kW.This research provides valuable experimental and theoretical insights for the development of human eye-safe lasers with adjustable pulse sequences.

Development of the 2.7 μm to 3 μm Erbium-Doped Laser

The 3 μm wavelength band laser is located on the strong absorption peak of water and the atmospheric transmission window. The 3 μm laser with high single pulse energy is used in medical treatment for cutting soft tissues and bones during surgery. It is used as a pump source for optical parametric oscillators, and Fe lasers can realize 3~5 μm or 8~14 μm laser output, which has an irreplaceable role in certain areas (e.g., optoelectronic countermeasures, LIDAR, atmospheric monitoring, etc.). Commercial semiconductor-pumped Er lasers are capable of achieving 3 μm laser output of 600 mJ with the maturation of a 970 nm semiconductor laser. The conversion efficiency is significantly improved. However, the energy is lower than a flash-lamp-pumped Er laser. There are still serious crystal thermal effects and an inefficient conversion process. In this paper, the energy-level systems of 3 μm Er-doped lasers are discussed. A summary of the current state of research on Er lasers using different matrices and the commercialization of Er-doped lasers with wavelengths ranging from 2.7 μm to 3 μm is also provided. Several technical means are given to enhance laser performance. Furthermore, the development of Er-doped solid-state lasers with wavelengths between 2.7 and 3 μm is envisaged in the near future.

A good beam quality Ho:GdVO4 laser pumped by thulium‐doped fiber laser at 1940 nm

AbstractWe demonstrate a Ho:GdVO4 solid‐state laser pumped by a thulium (Tm)‐doped fiber laser at 1940nm. In continuous wave mode, a maximum output power of 6.1 W was obtained under the absorbed pump power of 31.9 W with the slope efficiency of 24.3% at the temperature of 18°C. The wavelength of output laser was 2048.53 nm with full width at half maximum of 0.2 nm. In Q‐switched mode, a maximum single pulse energy of 0.94 mJ was obtained with a minimum pulse duration of 7.3 ns at the pulse repetition frequency of 5 kHz, corresponding to a peak power of 129 kW and an average output power of 4.7 W. The beam quality factor of M2 was 1.01 under the maximum absorbed pump power. To the best of our knowledge, 0.94 mJ is the highest single pulse energy in single holmium (Ho) doped GdVO4 laser pumped by Tm‐doped fiber laser at 1940 nm, and 1.01 is the best beam quality factor of M2 in Ho:GdVO4 laser pumped by a Tm‐doped fiber laser.

Mid-infrared lightly Er3+-doped CaF2 laser under acousto–optical modulation

A 1.7-at.% Er:CaF2 crystal was synthesized by temperature gradient method. The Er:CaF2 crystal was applied in acousto-optically Q-switched laser at mid-infrared region for the first time. Using a TeO2-based crystal as Q-switcher, we obtained a laser diode (LD) end-pumped Er:CaF2 laser with the highest single pulse energy up to 0.49 mJ and maximum peak power of 0.56 kW under 6.34-W absorbed pump power. The implication of these results is that the low-doped Er:CaF2 crystal exhibits promising optical properties in solid-state lasers.

Sub-nanosecond diode-pumped passively Q-switched Nd:LuAG ceramic microchip lasers

Diode-pumped continuous-wave and passively Q-switched Nd:LuAG ceramic microchip lasers at 1064 nm and 1053 nm have been demonstrated, for the first time to our knowledge. For the continuous-wave operation, the achieved maximum output powers of the two lasers reaches 1.62 W and 0.75 W, respectively. Using Cr:YAG crystal as saturable absorber, the two lasers can also been operated in passively Q-switched regimes with sub-nanosecond pulse durations of 489 ps and 556 ps, respectively. The maximum single pulse energy and pulse peak power for the 1064 nm and 1053 nm lasers are calculated to be about 22.25 μJ and 45.49 kW, as well as 12.74 μJ and 22.91 kW. All solid-state microchip lasers give the tremendous potential for high performance laser generation with sub-nanosecond short pulse duration, high single pulse energy and high pulse peak power.

Application of quantitative analysis for aluminum alloy in femtosecond laser-ablation spark-induced breakdown spectroscopy using one-point and multi-line calibration

To achieve the quantitative elemental analysis of aluminum alloy samples, the one-point and multi-line calibration (OP-MLC) method and femtosecond laser-ablation spark-induced breakdown spectroscopy (fs-LA-SIBS) were combined in this study. An ultrafast Ti: sapphire laser with high single-pulse energy and high repetition–rate operation was used as the laser source to ablate the sample at a 1k Hz pulse repetition rate and achieve re-excitation using spark discharge. Subsequently, an enhanced spectral peak intensity was achieved, which increased the sensitivity and analytical capabilities of laser-induced breakdown spectroscopy (LIBS) technique. Considering only one confirmed sample, the OP-MLC method was used to calculate the concentration ratios of trace elements Mg, Cr, Cu, Mn and Zn in four aluminum alloy samples to the calibration samples by the integral intensity ratio of the elemental characteristic lines between the two samples. The average relative errors with the identified concentrations were 3.99%, 15.13%, 8.76%, 9.30% and 9.64%, respectively. The results showed that the combination of OP-MLC method and fs-LA-SIBS has good accuracy in the quantitative analysis of elements, and has the advantages of simplicity, rapidity and high sensitivity.

Folded-resonator LD side-pumped acousto-optically Q-switched Nd:YAG/SrWO4 solid-state Raman laser

A folded cavity of LD side-pumped acousto-optically Q-switched Nd:YAG/SrWO4 solid-state Raman laser is designed. The effects of the thermal focal length and resonator length on the resonator modes are analyzed. The appropriate mode sizes at laser crystal and Raman crystal are designated to realize low SRS threshold, high conversion efficiency and high beam quality. The folded-resonator LD side-pumped acousto-optically Q-switched Nd:YAG/SrWO4 solid-state Raman laser is realized, and the 1st Stokes laser at 1180 nm with high output power, high single pulse energy and high beam quality is obtained. The maximum output power of the 1st Stokes laser at 1180 nm is 2.89 W, optical–optical efficiency is 4 %, the single pulse energy is 0.96 mJ, and the shortest pulse is 35.5 ns. By analyzing the output spectrum and beam quality, it is shown that the beam spatial profile mode is well distributed, and the experimental results verify the rationality of the cavity mode design.

Surface morphology and microstructure of the hole sidewall during drilling of Polyether-Ether-Ketone(PEEK) via single-pulse laser

Polyether-ether-ketone (PEEK), as one kind of thermoplastic polymers, exhibits a great deal of remarkable properties and plays an important role in aerospace, electronics, automotive and medicine. An investigation of single-pulse laser drilling on Polyether-ether-ketone (PEEK) was reported to show the influence of irradiation energy on the hole sidewall. In-situ evolution of drilling process was observed by the high-speed camera. The surface morphology and microstructural characteristics of the hole sidewall were evaluated by different characterization techniques. The hole sidewall was divided into three parts: expanded zone at the entrance, linear zone in the middle, and U-shaped zone at the bottom. It was found that the quality of inner sidewall could be obviously improved under high single-pulse energy (>1 J), in terms of the surface morphology with small heat-affected zone (HAZ) thickness and surface roughness, as well as the least adhesion. Besides, chemical and structural characteristics of the hole sidewall changed a lot under high energy. The C content of three parts increased as the energy increased. The crystallinity of the hole sidewall decreased from 35 % to 25 % after laser-energy irradiation, but there was little change under different single-pulse energy. New diffraction peaks appeared in X-ray diffraction images and the intensity of the relative peaks in Raman spectra decreased when the energy was over 1 J. It was proven that some chemical bonds (phenyl ring (1597 cm−1) and C–O–C (1148 cm−1)) would break under high energy, contributing to mass removal of the keyhole. Moreover, the HAZ thickness of the hole sidewall was calculated based on a viscous flow model, which showed a good consistency with experimental results. These results reveal material-removal mechanism accompanying the appearance of direct decomposition of the material and breaking of chemical bonds under high energy. It can provide references for understanding mechanisms of HAZ formation and material-removal and improving surface quality for laser drilling of polymers.

Rapid quantitative analysis of potassium in soil based on direct-focused laser ablation-laser induced breakdown spectroscopy

A fast quantitative analysis method of soil potassium based on direct-focused laser ablation-laser induced breakdown spectroscopy (direct-focused LA-LIBS) was proposed and tested. A high single-pulse energy laser (200 mJ/pulse) beam was focused on the aerosols near the focus of the 10 kHz fiber laser to generate plasma spectra, and the analytical capability of the direct-focused LA-LIBS system was compared with traditional LIBS system using a high single-pulse energy laser (SP-LIBS). The result showed that for moist soil samples the data stability of the direct-focused LA-LIBS method was significantly improved and the R2 factor of the calibration curve improved from 0.64 to 0.93, the limit of detection improved from 159.2 μg/g to 140.9 μg/g. Three random soil samples from different areas of Beijing suburbs were analyzed by the direct-focused LA-LIBS method, and the results were consistent with AAS. The direct-focused LA-LIBS method proposed is different from the traditional double-pulse technology and laser ablation-assisted technology because it not only does not need carrier gas, but also can overcome the matrix differences better, especially the influence of moisture, which provides a new idea for the rapid detection of nutrient elements in field soils.

Control effects of a high-frequency pulsed discharge on a hypersonic separated flow

The control effects of a high-frequency pulsed discharge on a hypersonic separated flow induced by a 42° compression ramp are studied with high-speed schlieren imaging. A discharge is generated between an electrode pair upstream of the ramp to introduce strong disturbances into the boundary layer. The discharge frequencies used are fd = 10, 20, 30, and 40 kHz, with corresponding single-pulse energies Esp = 22.2, 20.3, 12.0, and 8.7 mJ. The results show that the discharge can reduce the separation area, especially with relatively low frequencies of 10 or 20 kHz. The flow mechanism induced by the discharge is scrutinized using a reduced-order method based on the information from time-resolved schlieren images, including proper orthogonal decomposition and dynamic mode decomposition. The results identify an unsteady mode representing regular energetic eddies within the shear layer of the separation zone. This mode has the same characteristic frequency as the discharge. These eddies enhance the mixing of the shear layer and the main flow stream, accelerating the destruction of the shear layer and reducing the separation zone size. The control effectiveness correlates with the scale of the energetic eddies. At frequencies of 10 or 20 kHz, the discharge is more conducive to attenuating the separation because large-scale eddies, excited by higher single-pulse energy, are enhanced as they propagate downstream in the shear layer. By contrast, the control effectiveness deteriorates when the discharge frequency is 30 or 40 kHz because the induced eddies have smaller scales and decay during propagation.

Passively <i>Q</i>-switched and mode-locked 1.9 μm Tm-doped fiber laser based on pure water as saturable absorber

All-fiber laser with short pulses possesses many advantages, such as superior stability, compact structure, and high single pulse energy. Recently, short pulse laser working in a 1.8–2.0 μm spectral region has received considerable attention due to its wide applications in laser spectroscopy, biomedicine, optical communications and sensing. The passive <i>Q</i>-switched and mode-locked operations by saturable absorber (SA) have been considered to be convenient and low-cost ways to achieve short pulses. Recently, pure water has been reported as the ideal SA because of its advantages of high damage threshold, low prices, good thermal diffusivity and stability. In this work, Tm-doped all-fiber pulse laser based on pure water as the SA is demonstrated. The pure water is fixed between two FC/PC fiber patchcord by the ceramic cannula, so we can change the loss of SA easily. The <i>Q</i>-switched and mode-locked operations can be obtained by adjusting the water layer thickness. The maximum output power at <i>Q</i>-switched state is 0.531 mW, the repetition frequency is 53.45 kHz, and the pulse width is 3.01 μs. The maximum output power at mode-locked state is 2.28 mW, the repetition rate is 17.69 MHz, and the pulse width is 1.42 ps. To our knowledge, this is the first passive mode-locked fiber laser using pure water as a saturable absorber, and provides a new scheme for thulium-doped all-fiber pulse lasers.

Passively Q-switched operation based on Sb2Se3 and self-power near infrared photodetector

In this paper, Antimony selenide （Sb2Se3） nanorods are prepared by the hot solvent method, the Sb2Se3 is detected by near-infrared detectors with good photoelectric properties. Afterwards its nonlinear optical performance was tested, compared with metal chalcogen compounds, the prepared Sb2Se3 has great bandwidth saturation absorption response, higher modulation depth (43.27%) and lower saturation intensity (2.13 MW/cm2), which is very suitable for making saturable absorber (SA) devices. In addition, we integrate Sb2Se3 SA into a 1.5 μm erbium-doped fiber laser and realize Q-switching for the first time. Our results show the obtained Q-switched laser has high single pulse energy and low self-starting threshold and good stability. Moreover, by adjusting the polarization state, a stable double wavelength spectrum appears. This indicates that Sb2Se3 has outstanding application potential in optical switching devices and pulse laser engineering.

Research on hole depth in femtosecond laser deep micropore processing technology based on filament effect

Ceramic-based composites have been applied to turbine components of new-generation aerospace engines due to their excellent properties. Despite the superior high-temperature resistance of SiC/SiC composites, it is necessary to combine with film cooling technology to guarantee normal function of turbine components. However, SiC/SiC composites are typical difficult-to-process materials，and the depth of film cooling holes have increasingly high requirements, which have become one of the major problems in the manufacturing of aerospace engine turbine parts. In this paper, the spatial energy density distribution based on filament effect of femtosecond laser was theoretically studied, it is revealed that the filament effect of femtosecond laser with high single pulse energy will lead to the peak of energy density shift towards the negative defocus direction. Based on the theoretical research, the experimental study on the processing of deep micropore in SiC/SiC composites by femtosecond laser was carried out, main results show that in equal conditions, the depth of micropore in feed trepanning is deeper than that in trepanning, and that in trepanning is deeper than that in direct punching. This research provides both theoretical and technical support for processing of micropore with high aspect ratio by ultrafast laser on the difficult-to-process materials, which have high practical value in the aerospace field.

An adaptive laser focus auto-positioning method for non-datum complex components based on 3D vision

For the advantages of high single-pulse energy and non-contact processing, laser is used to process easily deformable, high-hardness, and high-brittle materials. For some rough, easily deformed, and no-datum workpieces, it is difficult to locate the laser focus on the machining datum, resulting in processing deviation. This paper aims to solve the problem of automatic positioning of the laser focus on complex workpieces without positioning datum in three-dimensional laser processing. A calibration method of 3D scanner and five-axis laser machine tool is proposed, which combines the laser-processed circular hole, calibration ball and the virtual geometric features formed by the high-precision movement of the machine tool as the calibration objects. Based on the calibration results and the principle of homogeneous coordinate transformation, the kinematic model of five-axis laser machine tool is established dynamically. Then, according to the geometric information of the key points obtained by visual measurement, the automatic positioning of the laser focus on non-datum complex components is realized. Finally, the method proposed in this paper is verified by using planar ceramic components and non-datum complex ceramic components as positioning objects respectively. The results show that the method provided in this paper can effectively realize the automatic positioning of laser focus for non-datum complex components. And the positioning error is less than 45µm. The method proposed in this paper has been applied in the actual ceramic core trimming.

The 266-nm ultraviolet-beam generation of all-fiberized super-large-mode-area narrow-linewidth nanosecond amplifier with tunable pulse width and repetition rate

We report on a compact, stable, all-fiberized narrow-linewidth (0.045 nm) pulsed laser source emitting laser beam with a wavelength of 266 nm, and tunable pulse width and repetition rate. The system is based on all-fiberized nanosecond amplifier architecture, which consists of Yb-doped fiber preamplifiers and a super-large-mode-area Yb-doped fiber power amplifier. The fiber amplifier with a core of 50 μm is used to raise the threshold of the stimulated Brillouin scattering (SBS) effect and to obtain high output power and single pulse energy. Using lithium triborate (LBO) crystal and beta-barium borate (BBO) crystal for realizing the second-harmonic generation (SHG) and fourth-harmonic generation (FHG), we achieve 17 μJ (1.73 W) and 0.66 μJ (66 mW), respectively, at wavelengths of 532 nm and 266 nm and a repetition rate of 100 kHz with pulse width of 4 ns. This source has great potential applications in fluorescence research and solar-blind ultraviolet optical communication.

Self-cleaning effect in an all-fiber spatiotemporal mode-locked laser based on graded-index multimode fiber

We demonstrate an all-fiber spatiotemporal mode-locked laser based on graded-index multimode fiber. Due to the high damage threshold of graded-index multimode fiber devices, the output single-pulse energy reach up to 11.67 nJ. The beam quality at mode-locked state is significantly improved compared with continuous wave state as a result of the self-cleaning effect. By amplifying the pulse in the multimode fiber amplifier, high power pulses with high beam quality can be obtained in the all-fiber system based on graded-index MMFs. We present an approach to get high single-pulse energy in the all-fiber multimode laser with a near single-mode output beam.

High peak power passively Q‐switched 2 μm solid‐state laser based on a MoS2 saturated absorber

AbstractA 2 μm passively Q‐switched Tm:YAP solid‐state laser with MoS2 as saturated absorber was demonstrated in this work. MoS2 two‐dimensional materials were prepared by using the method of chemical vapor deposition. The laser achieved high peak power of 21.2 W and high single pulse energy of 19.5 μJ, while maintaining a short pulse width of 916 ns. This is the first time that the peak power of a Tm:TAP solid‐state laser based on a MoS2 saturated absorber has reached 21.2 W. The beam quality factor was M2x = 1.08 and M2y = 1.10.

Stable growth of large-size organic 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate crystal and its optical, dielectric and THz properties

Results of an experimental study on the stable growth of large-enough and crack-free organic nonlinear optical 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystal by seed crystal fixing method with reasonable growth speed are reported. It is found that large and high-quality crystal with size of 25 × 22 × 2 mm3 under lower concentration of the solution for a growth rate of 0.47 mm/day can be obtained. Terahertz (THz) waves based on the crystal were generated using difference frequency generation (DFG) method. Tunable THz-wave in the broad range of 0.3-19.6 THz was obtained. At 18.9 THz, the maximum output energy of THz waves reaches 870.4 nJ/pulse, and the corresponding energy conversion efficiency is 1.036 × 10−4. It is also found that the single-pulse energy of DAST crystal varies with the crystal thickness (140, 400 and 610 μm). DAST crystals with a thickness of 140 μm have high single-pulse energy. The UV-vis-NIR spectrum, dielectric properties, photoluminescence spectrum, and Raman spectra of crystalline samples were also investigated.

High single pulse energy passively Q-switched mode-locked Tm, Ho: LLF laser

High single pulse energy passively Q-switched mode-locked Tm, Ho: LLF laser