Pulsed Laser System Research Articles

Effect of Tm3+ concentration on structure, spectral properties and cross relaxation of Tm:CaF2 crystal.

Through the investigation of spectral characteristics, the evolution of cluster proportions and the cross-relaxation process in Tm:CaF2 crystals as a function of Tm doping concentration has been clarified. A quantitative model has been established to describe the relationship between these factors. At low concentrations (0.01-0.5 at.%), Tm ions rapidly form clusters with negligible cross-relaxation. As the concentration increases from 0.5 at.% to 2 at.%, the cluster ratio surpasses 90%, and its growth rate decelerates, while both the cross-relaxation rate and efficiency significantly increase. When the Tm concentration exceeds 2 at.%, the cluster ratio and cross-relaxation efficiency nearly reach 100% and remain stable. These findings provide valuable insights for the application of Tm:CaF2 in high-energy pulsed laser systems.

Generation of Dark Pulses in Mode‐Locked Erbium‐Doped Fiber Ring Laser Operating in L‐Band Region Using Sc2O3 Absorber

ABSTRACTBy incorporating scandium oxide (Sc2O3) powder into a PVA film, a Sc2O3 saturable absorber (SA) was successfully developed, boasting a modulation depth of 25%. When integrated into a ring erbium‐doped fiber laser, the Sc2O3‐SA facilitated the production of mode‐locked dark pulses featuring multi‐wavelength emission, leveraging its saturable absorbing ability along with the nonlinear properties inherent in the Sc2O3 thin film and the long erbium‐doped fiber. Mode‐locking operation was achieved within a pumping range of 209.3–239.8 mW, resulting in a peak pulse energy of 0.71 nJ. Operating at 1597.8 nm, the mode‐locked laser demonstrated a repetition rate of 10.42 MHz and a pulse width of 23 ns. Domain‐wall dark pulse operation was demonstrated in the L‐band region, achieving a relative stability with a signal‐to‐noise ratio of 55.6 dB, utilizing a Sc2O3 thin film absorber and an 8‐meter‐long active fiber. These findings underscore the promising potential of Sc2O3 to be used in pulsed laser systems, particularly due to its exceptional nonlinear optical properties.

Power output optimization in complex laser systems by means of polarization control

Abstract Recently, a polarimetric method for thermally-induced polarization change-driven power loss (TIPCL) mitigation in complex laser systems has been developed. However, the final optimization relies on a four-parameter numerical process. This article provides a fully analytical direct calculation alternative to this optimization process. The validity of this approach is demonstrated in previously published data from the pulsed laser system Bivoj/DiPOLE100. The new approach provides a deeper insight into the polarimetric method for TIPCL suppression and also brings a more precise, reliable, and faster alternative to the numerical process used earlier.

Single-exposure beam quality analysis via lens-free coherent amplitude modulation imaging.

A single-exposure method for complex amplitude reconstruction in beam quality analysis is proposed, utilizing lens-free coherent amplitude modulation imaging (LF-CAMI). This approach leverages a partially saturated diffraction pattern to reconstruct the complex amplitude of a measured laser beam. The corresponding intensity images near the beam waist along the axial direction are determined directly via the Fresnel diffraction formula. Spatial beam parameters, including the beam quality factor M2, are then calculated following the ISO 11146-1 standard. The feasibility of the proposed method is validated through theoretical analysis and experiments, targeting both static and dynamic laser beams. Experimental results demonstrate that this method yields results consistent with those obtained using commercial beam quality analysis instruments while reducing the total measurement time by approximately 80%. The proposed method is compact, cost-effective, and immune to aberrations and offers a fast and accurate measurement process, making it particularly suitable for beam quality analysis in various laser systems, especially pulsed laser systems.

2.6 GW, mJ-class high-energy femtosecond laser system based on Yb:YAG single-crystal fiber amplifier

High-peak-intensity ultrafast fiber lasers show excellent prospect for ultrafast science and industrial applications. For simplicity as well as efficiency, chirped-pulse amplification (CPA) is an effective technique for the generation of high-energy sources and single crystal fiber (SCF) also shows great potential due to its convenient configuration. In this work, a high-peak-power hybrid CPA pulsed laser system based on a three-stage single-pass end-pumped Yb:YAG SCF amplifier is experimentally demonstrated. The amplification system emitted pulses with the maximum power of 103.2 W at 100 kHz repetition rate and we obtained the compressed output power of 84.2 W, corresponding to the pulse energy of 0.84 mJ. Considering the third order dispersion that induced by the stretcher and the accurate tuning effect for higher-order dispersion compensation of chirped fiber Bragg grating, we have demonstrated a nearly transform limited output pulse duration of 323 fs with the peak power exceeding 2.6 GW. It can be said that we present the results for the first implementation of the shortest pulse duration and highest peak power in such multi-stage Yb:YAG SCF amplifier. The well-preserved beam quality with the measured M2 value of 1.22 and 1.29 for the horizontal and vertical directions at the maximum achieved average power. With such outstanding combined features, the demonstrated high-energy ultrafast fiber lasers would enable broad applications.

Evaluating the therapeutic efficacy of 595 nm pulsed dye laser system for treating capillary malformations

Capillary malformations are the most prevalent low-flow vascular abnormalities. A case of a 30-year-old woman with lateral capillary malformation was presented in this case report. Dermoscopic showed erythematous background and rare telangiectasic vessels for less than 5-10% of the entire area examined. She underwent a single treatment with a 595 nm pulsed dye laser. Excellent response at the end of the session and a clear reduction of the capillary malformation at clinical follow-up 2 months later was achieved. Dermatoscopic and 3D photographic evaluation before and after laser treatment also documented the disappearance of the erythematous background and telengectasic vessels.

Generation of 480 nm picosecond pulses for ultrafast excitation of Rydberg atoms.

Atoms in Rydberg states are an important building block for emerging quantum technologies. While excitation to Rydberg orbitals is typically achieved in more than tens of nanoseconds, the physical limit is in fact much faster, at the ten picoseconds level. Here, we tackle such ultrafast Rydberg excitation of a rubidium atom by designing a dedicated pulsed laser system generating 480 nm pulses of 10 ps duration. In particular, we improved upon our previous design by using an injection-seeded optical parametric amplifier (OPA) to obtain a stable pulsed energy, decreasing the fluctuation from 30 to 6%. We then succeeded in ultrafast excitation of Rydberg atoms with excitation probability of ∼90%, not limited anymore by energy fluctuation but rather by the atomic state preparation, addressable in future works. This achievement broadens the range of applications of Rydberg atoms.

High-power, frequency-doubled all-polarization-maintaining fiber laser system at 925 nm.

We demonstrate a high-power 925-nm pulsed laser system based on a frequency-doubled, all-polarization-maintaining (PM) fiber laser source operating at 1.8 µm. The seed is a figure-9 mode-locked oscillator, which incorporates a nonlinear amplifying loop mirror. After power scaling and pulse compression, the 1.8-µm laser source can provide femtosecond pulses with a repetition rate of 31.3 MHz and an output power of 2.24 W. Through frequency doubling in a nonlinear crystal, the 925-nm laser delivers a pulse duration of 503 fs and an output power of 818 mW, which is the highest power provided by all-PM fiber laser systems at this wavelength, as far as we know. Furthermore, this 925-nm all-PM fiber laser is employed as the excitation light source for two-photon microscopy (TPM) and second-harmonic generation (SHG) microscopy.

Non-ablative laser skin rejuvenation by targeting indigenous chromophores

Three pulsed laser systems: 980 nm semiconductor diode laser, 1064 nm Nd: YAG laser and long pulse- fractional 2940 nm pulsed Er: YAG were used to treat some non-ablative skin rejuvenation applications. These three wavelengths can target the three main indigenous chromophores (melanin, hemoglobin and water) of the skin to treat different skin disorders. The efficacy of these lasers was assessed in the treatment of age spots, enlarged veins and wrinkles. The chromophore type and location of a specific disorder was taken into consideration when working out, in advance, the required laser fluence. The absorption of laser photons and the reabsorbed photon scattering were calculated and used to work out the temperature rise in the targeted tissue. The results indicated very good outcome of age spots with 980 nm laser, excellent clearance of the varicose veins with the use of 1064 nm laser and very good smoothing of fine lines wrinkles on forehead. Advances may involve conducting wavelengths or developing customizable protocols for different skin types. Long-term studies on patient outcomes to help establish standardized protocols and improve efficacy in clinical uses.

Wave mode variation of multi-wavelength photoacoustic guided waves in cortical bone

Abstract Photoacoustic guided waves (PAGWs), excited based on the optical-thermo-mechanical coupling mechanism, have the potential to non-invasion assess the optical properties which associates tissue composition of bones. This study investigates the wave mode variation of PAGWs with the optical transmissivity in a 2mm-thick cortical bone plate. Multi-wavelength PAGWs were generated by lasers of different wavelength with a tunable pulsed laser system; Two piezoelectric transducers with the centre frequency of 500 kHz, symmetrically sticked on the bone surfaces, were used to acquire the signals. The symmetric (S) mode and anti-symmetric (A) mode were extracted by adding and subtracting the signals received by different transducers, respectively. The relative amplitude ratio of A mode and S mode was found to have an inverse relationship with the optical transmissivity of the bone. For the 750 nm laser with high transmissivity, the waves are mainly S mode; the relative amplitude of A mode wave increases with the laser wavelength. The amplitude ratio of A- and S- modes is in exponential attenuation with the transmissivity. The research results suggest that the wave mode variation in signal amplitude is suitable for evaluating the optical properties of bones, which is benefit for the development of quantitative ultrasound assessment of long cortical bone.

Cerium oxide for L-band Q-switched pulse laser generation

Cerium oxide (CeO2), a rare earth metal oxide belonging to the lanthanide group is a mature engineered nanoparticle that has been developed for various industry applications. The nanoparticle features defects in its lattice structure, which is highly advantageous for bandgap tuning, and is acclaimed for its least cytotoxicity among other metal oxides. In this work, CeO2 is employed as a saturable absorber (CeO2-SA) in the generation of an L-band Q-switched erbium-doped fiber laser. Q-switching was attained at 33.33 mW pump power threshold with a central wavelength of 1600.512 nm. Within 33.33 mW to 153.20 mW pump power range, the Q-switched laser obtained pulse repetition rates between 11.00 to 34.48 kHz, and pulse widths between 39.0 to 12.0 µs, with a high maximum pulse energy of 410 nJ. The Q-switched fiber laser remained stable over a 45-minute observation time at 153.20 mW pump power. The room temperature and direct mechanical deposition fabrication technique of the CeO2-SA in this work demonstrates the extreme simplicity and low cost of the device, which would reduce the overall cost and facilitate a wider technology adoption of pulse laser systems.

Artificial intelligence based experimental investigation of underwater fiber laser transmission process during micro-channelling operation on PMMA

Industries that engage in laser-based material processing are increasingly turning to fiber lasers as one of the most effective laser systems available. Using a pulsed fiber laser system, an experimental investigation of underwater laser micro-channelling on hard to machine thick PMMA has been conducted in this research work. Submerged laser transmission cutting which is also known as underwater laser induced backside machining helps to generate clean kerf edge without presence of mushy region, which is very common during laser machining of thick PMMA with wavelength of near infrared region. Submerged conditions are used here for laser transmission micromachining in order to reduce adverse thermal effects and microcracking or charring inside the material. Pulse frequency, working power, and cutting speed have been selected as the input parameters. As machining responses, the depth of the micro-channel, the width of the kerf, and the width of the heat affected zone (HAZ) have been considered. To find the ideal parametric condition for simultaneously achieving numerous goals, Response Surface Methodology (RSM) and AI-based Teaching Learning-Based Optimisation (TLBO) have been used. The TLBO technique determined that the optimal laser machining settings are a power setting of 13.98 %, a pulse frequency of 50 kHz, and a cutting speed of 0.20 mm/sec. These parameters result in a minimum HAZ width of 4.1874 µm, a minimum kerf width of 22.3698 µm, and a maximum depth of cut of 37.1478 µm. Underwater laser processing reduces heat affected zone and redeposition surrounding micro-channels, creating a cleaner, finer structure.

High-Power Lasers

High-power lasers play an important role in modern science, industry, and medicine. A significant milestone was reached on 5 December 2022, when Inertial Confinement Nuclear Fusion (ICF) achieved scientific breakeven, releasing more energy than the input laser energy. Additionally, Extreme Ultraviolet Lithography (EUVL) has enabled the development of microchips with 3 nm process nodes, marking a leap in semiconductor technology. These examples, together with the recent achievement of 10 PW (1015 W) laser output, herald remarkable advancements in technology and science. Laser systems are broadly classified based on their operating regimes into two main categories: Continuous Wave (CW) operation, where the laser is continuously pumped and emits a steady beam of light, and the pulsed regime, in which the laser produces single or multiple pulses at various repetition rates. This review will primarily focus on pulsed laser systems, exploring their various types and recent technological advancements.

Applications of LIF to Document Natural Variability of Chlorophyll Content and Cu Uptake in Moss.

Chlorophyll has long been used as a natural indicator of plant health and photosynthetic efficiency. Laser-induced fluorescence (LIF) is an emerging technique for understanding broad spectrum organic processes and has more recently been used to monitor chlorophyll response in plants. Previous work has focused on developing a LIF technique for imaging moss mats to identify metal contamination with the current focus shifting toward application to moss fronds and aiding sample collection for chemical analysis. Two laser systems (CoCoBi a Nd:YGa pulsed laser system and Chl-SL with two blue continuous semiconductor diodes) were used to collect images of moss fronds exposed to increasing levels of Cu (1, 10, and 100 nmol/cm2) using a CMOS camera. The best methods for the preprocessing of images were conducted before the analysis of fluorescence signatures were compared to a control. The Chl-SL system performed better than the CoCoBi, with dynamic time warping (DTW) proving the most effective for image analysis. Manual thresholding to remove lower decimal code values improved the data distributions and proved whether using one or two fronds in an image was more advantageous. A higher DTW difference from the control correlated to lower chlorophyll a/b ratios and a higher metal content, indicating that LIF, with the aid of image processing, can be an effective technique for identifying Cu contamination shortly after an event.

Laser Powder Bed Fusion and Heat Treatment of the Martensitic Age‐Hardenable Steel (1.2709)

The primary objective of this study is to clarify the fundamental question of whether, in principle, it is possible to dispense with a prior solution annealing process in favor of a direct aging heat treatment for specimens of maraging stainless steel grade X3NiCoMoTi18‐9‐5 (1.2709) produced by laser powder bed fusion (LPBF). The waiver of a solution annealing process would significantly increase the process efficiency and thus support a sustainable and resource‐friendly production of such components. Therefore, the hardness, microstructure, and the present phases of specimens in as‐built + aged condition (AB + A) and solution‐annealed + aged (SOL + A) are examined during this study. Initially, an extended parameter study is performed using a Renishaw AM 250 LPBF system equipped with a pulsed mode laser system to achieve the highest possible apparent density. As test specimens, small cubes are produced for parameter study and are analyzed for porosity by means of optical microscopy. To investigate the relationship between microstructure and hardness in different material states, one series of specimens is aged directly after LPBF processing in the as‐built state (AB + A). For comparison, the other series was solution annealed at 820 °C for 60 min, quenched in water and then aged (SOL + A). A maximum hardness value of 614 HV1.0 is achieved for specimen aged at 490 °C for 120 min in as built condition (AB + A), while 624 HV1.0 was measured for specimen aged at 490 °C for 180 min in conventionally solution annealed + aged (SOL + A) condition. Significant austenite reversion is not observed at aging temperature of 490 °C in both cases. Aging of specimens at temperatures of 540 and 600 °C resulted in reduction of specimen hardness due to higher percentage of austenite reversion. No significant difference between the hardness values of AB + A and SOL + A specimens is observed. It can therefore be concluded that, in principle, conventional solution annealing and ageing can be dispensed with in favor of direct aging. However, as the results are based on small sized specimens, further investigations into the scalability are needed.

Influence of Laser Treatment of Ti6Al4V on the Behavior of Biological Cells.

This article explores the enhancement of material surface properties of Ti6Al4V, potentially applicable to dental implants, through ultra-short pulse laser systems. This study investigates potential connections between surface wettability and biocompatibility, addressing the challenge of improving variability in material properties with specific laser treatment. Several designed microstructures were manufactured using a picosecond laser system. After that, the wettability of these structures was measured using the sessile drop method. The basic behavior and growth activity of biological cells (MG-63 cell line) on treated surfaces were also analyzed. While the conducted tests did not conclusively establish correlations between wettability and biocompatibility, the results indicated that laser treatment of Ti6Al4V could effectively enlarge the active surface to better biological cell colonization and adhesion and provide a focused moving orientation. This outcome suggests the potential application of laser treatment in producing special dental implants to mitigate the issues during and following implantation.

Characterisation of laser-cladded 410 stainless steel for in situ repair of turbine blade

Laser cladding was employed to apply a pure nickel powder coating onto 410 stainless steel turbine blade material, utilising a 50 W pulsed diode fibre laser system. Various process parameters were explored, including average laser power (20 W, 30 W, 40 W) and scanning speeds (SSs) (0.5 mm/s, 1 mm/s, 1.5 mm/s). The pulse width and frequency were fixed to 110 ns and 50 kHz, respectively. Successful deposition of nickel powder was accomplished at an average power of 40 W at various SSs. The microstructure, phase components, clad geometry, tensile properties, and microhardness of cladded specimens were examined. The experimental results show that the cladding layer has a metallurgical bonding with the substrate, having a visual interface with no cracks or defects. The clad layer's height peaked at 1 mm/s (175.889 μm), while the maximum clad depth occurred at 0.5 mm/s (367.797 μm). Predominant intermetallic phases observed included FeNi3, Cr1.36Fe0.52, along with fine carbides (M3C, M7C3, M23C6 where M – Fe, Ni). Enhanced mechanical properties were observed in the cladded samples compared to the substrate. At 1 mm/s SS, the clad zone exhibited the highest microhardness (221.4 HV), tensile strength (482.03 MPa), and Young's modulus (17.97 GPa).

Generation of Q-switched and mode-locked pulses in erbium-doped fiber ring laser using saturable absorption of Ti2SnC

MAX phase materials have garnered significant attention due to their corrosion resistance, impressive antioxidation and high electrical and optical conductivity. One such material, Titanium Tin Carbide (Ti2SnC), has demonstrated notable nonlinear optical properties. The saturable absorption of Ti2SnC, embedded into a polyvinyl (PVA) film, was measured to assess its potential. The Ti2SnC -PVA film exhibited a calculated modulation depth of 7.8%. In the context of practical applications, the Ti2SnC-PVA film was employed as a saturable absorber (SA) in an Erbium-doped fiber laser (EDFL) cavity. This configuration enabled the generation of stable Q-switched and mode-locked pulse trains. Q-switched operation occurred in a pump power range of 51.67 mW–83.83 mW, reaching a peak pulse energy of 110.94 nJ. Transitioning to mode-locking operation, the laser cavity demonstrated efficiency in the pump power range of 105.27 mW–196.39 mW. At a pump power of 196.39 mW, the fiber laser cavity achieved its highest pulse energy of 5.42 nJ, characterized by a pulse width of 2.32 ps and a pulse repetition rate of 1.825 MHz. These results highlight the promising potential of Ti2SnC-PVA thin film as a cutting-edge material for applications in pulsed laser systems. The material's excellent nonlinear optical properties make it a compelling candidate for advancing the field of pulsed laser technology.

Hundreds of picosecond pulses amplifier based on Yb-doped tapered fiber for the generation of 100 W average output power

Hundreds of picosecond pulses amplifier based on Yb-doped tapered fiber can serve as the primary power amplifier stage for an all-fiber and polarization-maintained picosecond pulse laser system. Here, we report a high-power narrow-linewidth amplifier stage by using the Yb-doped tapered fiber. In the regime, we have demonstrated amplification of 201.4 ps pulses centered at 1031.4 nm with a spectral width of 0.54 nm to 105 W average power at a repetition rate of 29.3 MHz. The picosecond pulses had a high beam quality with a measured M2 value of 1.36 ∼ 1.51, and the optical-to-optical conversion efficiency reached 56 %. To the best of our knowledge, this is the first demonstration of a high-power amplifier based on Yb-doped tapered fiber, capable of amplifying hundreds of picosecond pulses beyond the hectowatt-level average power, while maintaining high beam quality. This achievement highlights the immense potential of Yb-doped tapered fiber in the field of picosecond pulse power amplification. At last, we have refined the model for the transmission and amplification of picosecond pulses in Yb-doped tapered optical fibers, thereby enhancing simulation accuracy by 8 % and providing valuable references for the in-depth research of tapered fiber pulse amplifiers.

Laser assisted Powder Bed Fusion of pure Molybdenum using ultrashort laser pulses

Refractory metals are used in applications requiring extreme high temperature resistance, e.g. jet propulsion systems in aerospace applications or for controlling nuclear reactions. However, the traditional manufacturing of these metals is demanding and expensive, especially if fine structures are required. Here, we report on the laser assisted powder bed fusion of pure Molybdenum. The high melting point and thermal conductivity together with high susceptibility to solidification fractures of Molybdenum make it difficult to identify a suitable parameter window for the laser based melting process. Thus, we apply an ultrashort pulse laser system operating at a center wavelength of 1030 nm and a repetition rate of 32 MHz with a pulse width of 270 fs for the additive processing. Using the additional parameter field provided by the pulsed laser source we are able to fabricate thin-walled structures well below 100 µm as well as volumetric parts with a relative density close to 100 %.