Fiber-coupled Laser Diode Research Articles

High-performance 320-nm continuous-wave solid-state laser

For the first time, to our knowledge, we realized a high-performance 320-nm continuous-wave (CW) laser with a fiber-coupled blue laser diode as the pump source. A V-shaped folded cavity is constituted by three mirrors, with a Pr3+:LiYF4 (Pr:YLF) as the laser crystal and a LiB3O5 (LBO) as the frequency doubling crystal, respectively. Under an absorbed pump power of 19.5 W, the maximum 320-nm output power reaches 4.26 W, corresponding to an optical conversion efficiency of 21.8% and a root-mean-square (RMS) power fluctuation of 0.61%, which give the best results of a 320-nm CW laser up to now. The excellent performance will make this ultraviolet laser source very suitable for practical applications, including semiconductor detection, spectral analysis, microscopic imaging, and biotechnology.

B-174 Quantification of vitamin C in serum as a biomarker using the Laser Diode Thermal Desorption technique “LDTD”/Mass Spectrometry (Luxon)

Abstract Background Ascorbic acid (AA) or vitamin C, is a crucial substance that is involved in numerous physiological processes in living beings, including collagen production and antioxidant activity. When ascorbic acid is exposed to moisture, air, heat, light and oxygen, it oxidizes and turns into dehydroascorbic acid (DHAA). Our objective is to describe the sample preparation procedure and total quantification of AA and DHAA in human serum sample based on LDTD-MS/MS, and demonstrate its efficiency in quantification, combined with analysis selectivity and rapidity. Methods The Luxon is a sample introduction and ionization source that used a fiber-coupled laser diode to thermally desorb neutral molecules and charge them using a corona needle so they can be analyzed by mass spectrometry. Due to the instability of ascorbic acid, plasma samples were enriched and stabilized with an acidic solution. Sample preparation utilized a phosphate-containing buffer to minimize interferents and help volatize the analyte, followed by a precipitation step using acetonitrile to further clean the extract. Stable isotope-labeled internal standard (13C6 ascorbic acid) and homemade calibration curve and water quality controls were used for quantification. The analysis was performed using a Sciex 6500+ Triple Quad in APCI (Atmospheric Pressure Chemical Ionization) negative mode. Calibration curves ranging from 1 to 100 μg/mL and QCs were prepared in ascorbic acid-depleted serum (kept at room temperature/exposed to light for 4 days). The peak area against the internal standard (IS) ratio was used to normalize the signal. The calibration curves were plotted using the peak area ratio and the nominal concentration of standards. The following parameters were assessed for quantitative analysis: linearity, precision, accuracy, carryover and parallelism. A linear regression model with 1/X2 weighting was used to obtain the calibration curve equation and determine the correlation coefficient (r2). Parallelism was assessed by comparing the correlation coefficient of calibration curves prepared in water to six curves prepared with biological matrixes. Intra and inter assay precision and accuracy were determined by measuring QC samples ranging from low to high concentration in five replicates for 3 consecutive days. Results Calibration curves (n=3) showed excellent linearity. The calibration curve resulted in a linear response throughout the concentration range, the correlation coefficient was 0.99. For each quality control concentrations CVs were <10% complying with desirable specifications for imprecision and accuracy. Intra-assay CVs were 3.0-8.89% and inter-assay CVs were 7.64-9.79% for precision which reflects the agreement between repeated measurements. The results for accuracy showed similar results, intra-assay CVs were 3.83-9.20% and inter-assay CVs were 5.0-9.7%. Conclusions The new LDTD-MS/MS method described here has been validated as an effective technique to reliably and rapidly quantify ascorbic acid. Simple sample preparation, rapid acid stabilization combined with high yield allow analysis without degradation responses.

Microstructural Evolution and Wear Resistance of Surface Alloyed AISI 316L Stainless Steel with Equi-atomic CoCrFeMnTi by Continuous Wave Diode Laser

In this investigation, a multicomponent alloyed surface was developed on AISI 316L stainless steel (AISI 316L SS) substrate by melting it with a fiber coupled diode laser having 3.6 mm beam diameter (using argon as shrouding gas) along with simultaneous melting of equiatomic pre-mixed elemental powders of cobalt (Co), chromium (Cr), iron (Fe), manganese (Mn) and titanium (Ti) (high entropy alloy). The process parameters used in the experiment were laser power (1800–2200 W) and scan speed (6 mm/sec to 8 mm/sec). Following laser surface alloying (LSA) a detailed microstructural characterization of the surface and evaluation of surface mechanical properties (micro/nano hardness, Young’s modulus and wear resistance) were undertaken. Due to LSA there is formation of near eutectic microstructure consisting of FCC and BCC phase mixtures along with the precipitates of Fe2Ti randomly distributed in the microstructure which was confirmed by X-ray diffraction (XRD) and electron back scattered diffraction (EBSD) analysis. There is an increase in microhardness in the processed zone from 180 VHN (of as received AISI 316L SS) to 309–650 VHN. In addition, there is an increase in Young’s modulus from 208 GPa for as received AISI 316L SS to 228–301 GPa for laser surface alloyed zone. The wear resistance (against WC ball in fretting wear mode) property of AISI 316L SS substrate after LSA was superior to the substrate. The wear mechanism was established.

Crystal growth, polarized spectral properties, and 2.3 µm laser performance of Tm:LuVO4 crystal

We report on the Czochralski crystal growth, polarized optical spectroscopy, and the first continuous-wave laser operation of 1.5 at.% Tm:LuVO4 crystal on the 3H4 → 3H5 transition. The polarized absorption and stimulated-emission properties of Tm3+ ions in LuVO4 were revised and the crystal-field splitting of the Tm3+ multiplets was determined by low-temperature (12 K) spectroscopy. The maximum stimulated-emission cross-section for the 3H4 → 3H5 transition is 2.48 × 10−20 cm2 at 2363 nm for π-polarization corresponding to an emission bandwidth of 28 nm. Evidence of phonon-assisted emissions of Tm3+ ions above 2 µm is presented. The broadband emission properties of the Tm:LuVO4 crystal make it promising for ultrashort pulse generation. Additionally, pumped by a 796 nm fiber-coupled laser diode, the Tm:LuVO4 laser generated a Watt-level output power at 2279-2295 nm with a slope efficiency of 9.2% and linearly polarized emission (π-polarization).

Integrated-path multi-gas sensor using near-infrared diode lasers: An alternative to vehicle-driven point gas analyzer

Sensors for quantitative monitoring of greenhouse gases from high-emission facilities, such as wastewater treatment and industrial plants, are becoming essential to enforce regulatory compliance in climate action initiatives. A predominant sensing technique is the tracer-gas dispersion method (TDM) using closed-path gas analyzers typically installed in a vehicle to measure concentration as the gas plume is transected. Here, we validate for the first time the use of integrated-path gas sensors in TDM, measuring instantaneously the concentration along a predetermined laser beam path, thereby facilitating a stationary setup with orders of magnitude higher update rate and without the need for vehicles or road access. Our approach relies on a sensitive, integrated-path multi-gas sensor for real-time emission quantification using tunable diode laser absorption spectroscopy. An optical sensor head with spectral coverage from 1.52 μm to 1.65 μm is demonstrated, supporting multiplexed gas sensing in a modular fashion using low-power fiber-coupled diode lasers. The sensor measures real-time integrated-path concentrations of CO2 and CH4, and the tracer-gas C2H2 at 130 Hz with 0.5 ppm, 3 ppb, and 2 ppb sensitivity, respectively, at 1 s averaging. The integrated-path sensor is systematically benchmarked for absolute accuracy against a state-of-the-art point sensor, revealing an excellent match over 16 hours. Furthermore, the integrated-path sensor is deployed outdoors for emission quantification using TDM. A comparison to the gold-standard point sensor reveals identical results, demonstrating the integrated-path sensor as a potent substitute for vehicle-driven point sensors.

Buried Depressed-Cladding Waveguides Inscribed in Nd3+ and Yb3+ Doped CLNGG Laser Crystals by Picosecond-Laser Beam Writing.

Buried depressed-cladding waveguides were fabricated in 0.7-at.% Nd:Ca3Li0.275Nb1.775Ga2.95O12 (Nd:CLNGG) and 7.28-at.% Yb:CLNGG disordered laser crystals grown by Czochralski method. Circular waveguides with 100 μm diameters were inscribed in both crystals with picosecond (ps) laser pulses at 532 nm of 0.15 μJ energy at 500 kHz repetition rate. A line-by-line writing technique at 1 mm/s scanning speed was used. Laser emission at 1.06 μm (with 0.35 mJ pulse energy) and at 1.03 μm (with 0.16 mJ pulse energy) was obtained from the waveguide inscribed in Nd:CLNGG and Yb:CLNGG, respectively, employing quasi-continuous wave pumping with fiber-coupled diode lasers. The waveguide realized in RE3+-doped CLNGG crystals using ps-laser pulses at high repetition rates could provide Q-switched or mode-locked miniaturized lasers for a large number of photonic applications.

Titanium carbide (TiC) dispersed surface on titanium based alloy (Ti-13Nb-13Zr) by in-situ laser composite surfacing and its wear performance

Ti-13Nb-13Zr is a promising titanium-based alloy for bioimplant applications due to its low Young’s modulus (80 GPa). However, it undergoes mechanical and mechano-chemical degradation after long-term application in the human body. The present study concerns the development of TiC dispersed surface on Ti-13Nb-13Zr by preplacement of graphite and subsequent melting with a continuous wave (CW) fiber-coupled diode laser using varied power (1000 W to 1400 W) and scan speed (10 mm/s to 20 mm/s). Laser composite surfacing leads to the formation of dispersion of carbide (TiC) in the beta (β) matrix. There is an improvement in microhardness from 257 VHN (for as-received) to 360–519 VHN for laser composite surfaced Ti-13Nb-13Zr and varied with process parameters. There is an increase in nanohardness value from 3.6 GPa (for as-received Ti-13Nb-13Zr) to 5.14–9.224 GPa and increased in Young’s modulus from 100 MPa (for as-received Ti-13Nb-13Zr) to 103.22–120.85 MPa due to laser composite surfacing. A significant improvement in wear resistance (5.8 times) and a decrease in coefficient of friction (COF) (2.8 times) against the WC ball in fretting wear mode was noticed. The wear mechanism has been schematically presented and discussed in details.

Kerr-Lens Mode-Locked Yb:BaF2 Laser

We present sub-50 fs soliton pulse generation from a diode-pumped Kerr-lens mode-locked laser based on an Yb3+-doped BaF2 crystal. Utilizing a spatially single-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:BaF2 laser generates pulses as short as 46 fs at 1060.1 nm with an average output power of 45 mW at a pulse repetition rate of ~65.6 MHz via soft-aperture Kerr-lens mode locking. To the best of our knowledge, this represents the first demonstration of Kerr-lens mode-locked operation of the Yb:BaF2 crystal, as well as the shortest pulse duration ever achieved from any diode-pumped mode-locked laser based on an Yb3+-doped alkaline-earth fluoride crystal.

High-speed full-color computer-generated holography using a digital micromirror device and fiber-coupled RGB laser diode.

Computer-generated holography (CGH) can be used to display three-dimensional (3D) images and has a special feature that no other technology possesses: it can reconstruct arbitrary object wavefronts. In this study, we investigated a high-speed full-color reconstruction method for improving the realism of 3D images produced using CGH. The proposed method uses a digital micromirror device (DMD) with a high-speed switching capability as the hologram display device. It produces 3D video by time-division multiplexing using an optical system incorporating fiber-coupled laser diodes (LDs) operating in red, green, and blue wavelengths. The wavelength dispersion of the DMD is compensated for by multiplying plane waves on the hologram. Fourier transform optics are used to separate the object, conjugate, and zeroth-order light, thus eliminating the need for an extensive 4f system. The resources used in this research, such as the programs used for the hologram generation and the schematics of the LD driver, are available on GitHub.

SESAM mode-locked Yb:GdScO3 laser.

We report on the investigation of continuous-wave (CW) and SEmiconductor Saturable Absorber Mirror (SESAM) mode-locked operation of a Yb:GdScO3 laser. Using a single-transverse-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:GdScO3 laser delivers 343 mW output power at 1062 nm in the CW regime, which corresponds to a slope efficiency of 52%. Continuous tuning is possible across a wavelength range of 84 nm (1027-1111 nm). Using a commercial SESAM to initiate mode-locking and stabilize soliton-type pulse shaping, the Yb:GdScO3 laser produces pulses as short as 42 fs at 1065.9 nm, with an average output power of 40 mW at 66.89 MHz. To the best of our knowledge, this is the first demonstration of passively mode-locking with Yb:GdScO3 crystal.

Compact Diode-Pumped 946 nm Nd:YAG Laser with Good Beam Quality

A continuous-wave (CW), high-power, quasi-three-level Nd:YAG laser operating at 946 nm is reported. The beam quality of the laser is greatly improved. The laser consists of a composite Nd:YAG rod end pumped by a fiber-coupled diode laser inside a simple concave-plane cavity. At an incident pump power of 31 W, a maximum CW output of 9.98 W was obtained at 946 nm, with a beam quality factor of M2~5. The corresponding optical-to-optical efficiency was 32.2% with respect to the incident pump power. To the best of our knowledge, this is the highest output power at 946 nm with such a beam quality ever generated by diode-pumped Nd:YAG laser with bulk crystals.

Continuous-wave and SESAM mode-locked operation of a Yb:YSr3(PO4)3 laser.

We report on the continuous-wave (CW) and, for what we believe to be the first time, passively mode-locked (ML) laser operation of an Yb3+-doped YSr3(PO4)3 crystal. Utilizing a 976-nm spatially single-mode, fiber-coupled laser diode as pump source, the Yb:YSr3(PO4)3 laser delivers a maximum CW output power of 333 mW at 1045.8 nm with an optical efficiency of 55.7% and a slope efficiency of 60.9%. Employing a quartz-based Lyot filter, an impressive wavelength tuning range of 97 nm at the zero level was achieved in the CW regime, spanning from 1007 nm to 1104 nm. In the ML regime, incorporating a commercially available semiconductor saturable absorber mirror (SESAM) to initiate and maintain soliton-like pulse shaping, the Yb:YSr3(PO4)3 laser generated pulses as short as 61 fs at 1062.7 nm, with an average output power of 38 mW at a repetition rate of ∼66.7 MHz.

Growth, spectroscopy and SESAM mode-locking of a "mixed" Yb:Ca(Gd,Y)AlO4 disordered crystal.

We present the growth, spectroscopy, continuous-wave (CW) and passively mode-locked (ML) operation of a novel "mixed" tetragonal calcium rare-earth aluminate crystal, Yb3+:Ca(Gd,Y)AlO4. The absorption, stimulated-emission, and gain cross-sections are derived for π and σ polarizations. The laser performance of a c-cut Yb:Ca(Gd,Y)AlO4 crystal is studied using a spatially single-mode, 976-nm fiber-coupled laser diode as a pump source. A maximum output power of 347 mW is obtained in the CW regime with a slope efficiency of 48.9%. The emission wavelength is continuously tunable across 90 nm (1010 - 1100 nm) using a quartz-based Lyot filter. With a commercial SEmiconductor Saturable Absorber Mirror to initiate and maintain ML operation, soliton pulses as short as 35 fs are generated at 1059.8 nm with an average output power of 51 mW at ∼65.95 MHz. The average output power can be scaled to 105 mW for slightly longer pulses of 42 fs at 1063.5 nm.

Laser emission from buried depressed-cladding waveguides inscribed in Nd:YAG ceramics by picosecond-laser beam writing

Buried, depressed-cladding waveguides were inscribed in a 1.1-at.% Nd:YAG ceramic by direct writing with a picosecond-laser beam. Laser emission performances were investigated under the pump with fiber-coupled diode lasers. For quasi-continuous-wave pumping, a circular waveguide with 100 μm diameter yielded laser pulses at 1.06 μm with 2.4 mJ energy for 12.8 mJ pump pulse energy at 807 nm (corresponding to an overall optical-to-optical efficiency of 0.19); the slope efficiency was 0.22. Continuous-wave output power of 0.35 W at 1.06 μm with overall optical-to-optical efficiency of 0.09 was obtained from the same waveguide; the slope efficiency amounted to 0.12. Furthermore, the circular waveguide yielded laser pulses at 1.32 μm with 0.4 mJ energy (at an overall optical-to-optical efficiency of 0.03); the slope efficiency amounted to 0.03.

NGHIÊN CỨU CHẾ TẠO MÔ ĐUN CHUYỂN HƯỚNG BỨC XẠ LASER BÁN DẪN GHÉP SỢI QUANG 650 NM ỨNG DỤNG TRONG QUANG TRỊ LIỆU VÀ QUANG SINH DIỆT KHUẨN

Currently, diode lasers in the red wavelength region, especially at 650 nm, are extensively utilized in phototherapy and photodynamic inactivation of bacterials by numerous research groups in the field of lasers for biomedical application. These devices offer exceptional advantages, such as their compact size, ease of design and integration, user-friendliness, and high safety for both operators and patients. Among these, fiber-coupled diode lasers provide an efficient solution for delivering radiation from the laser chip to the desired location. However, further optimization is still required for the fabrication technological development of these devices to meet specific application needs. This includes aspects like reducing manufacturing costs, improving component usability during operation, and meeting specialized usage requirements. To develop the technology for device fabrication, addressing the aforementioned demands, we conducted research on the design, fabrication, and characterization of fiber-coupled semiconductor lasers operating at a wavelength of 650 nm. The characterization results demonstrate that the manufactured devices can operate at maximal pumping current of 100 mA and under varying temperatures from 25oC to 40oC. Additionally, a radiation output orientation module has been designed and integrated at the end of the optical fiber to meet various demands in phototherapy and photodynamic inactivation of bacterials.

High-power fiber-coupled diode laser welding of 10-mm thick Inconel 617 superalloy

In the present study, a high beam quality fiber-coupled diode laser was effectively utilized to weld 10-mm thick Inconel 617 superalloy in single pass. Influence of critical parameters of focusing distance and welding speed on weld characteristics was systematically investigated and optimized. At optimum process conditions with the power density of ≈106 W/cm2, crack-free full-penetration weld with minimal distortion, porosity, and no underfill/undercut/root-hump defects were obtained with 97%–99% joint efficiency. The weld joint quality produced was on par with multipass employing conventional lasers and advanced laser-hybrid welding techniques and sufficient enough to apply in various applications of thermal power plants, ship building, and heavy industries.

Efficient Continuous-Wave Deep-Red Pr :YLF Laser Double-Pass-Pumped by a Fiber-Coupled Blue Laser Diode

Efficient Continuous-Wave Deep-Red Pr :YLF Laser Double-Pass-Pumped by a Fiber-Coupled Blue Laser Diode

Latest developments in coaxial multiwire high-power laser cladding

Laser cladding is widely used in the industry to precisely apply tailored surface coatings, as well as three-dimensional deposits for repair and additive manufacturing of metallic parts. However, the processing of larger components is economically challenging mainly because of low deposition rates. At Fraunhofer IWS, a Laserline fiber-coupled diode laser with 20 kW power has been employed for over a decade to develop competitive coating solutions with powder-based laser cladding. The deposition rates achieved with this technology is comparable to common PTA technique at the same time bringing significant advantages in terms of reduced heat affected zone, distortion, and savings in material resources. While high-power powder-based laser cladding is an industrially established coating technology, for example, to coat hydraulic cylinders or most recently brake discs, a high-productivity solution for wire-based processes is still challenging. Fraunhofer IWS has developed a new nozzle for high-power high-productivity laser wire cladding for coating and additive manufacturing, the so-called COAXquattro. This system enables to feed at the same time four wires into the melt pool, reaching deposition efficiencies in the same range as a powder-based laser process. For selected materials, the improvement in coating quality compared to powder laser cladding is achieved. Furthermore, with COAXquattro system simultaneous feeding of powder particles to wire cladding presents a great potential for in situ alloying and cost-effective production of new compositions on material alloying or hardmetal-reinforced composites for coating application and 3D additive manufacturing.

Combined super-Gaussian pump intensity profile model and its application to a solid-state laser

The modeling of a combined super-Gaussian profile distribution for fiber-coupled laser diode beam intensity is investigated in this paper. By fitting the measured beam intensity distribution to the combined super-Gaussian model, the coefficient of determination is better than that of the Gaussian function and super-Gaussian function with order of 2. Applying this theoretical model to the fiber-coupled laser diode end-pumped Nd:GdVO4 laser at 1342 nm, the theoretical calculations are in good agreement with the experimental results.

High-resolution 3D nanoprinting based on two-step absorption via an integrated fiber-coupled laser diode.

Three-dimensional (3D) laser nanoprinting with high resolution and low cost is highly desirable for fabricating arbitrary 3D structures with fine feature size. In this work, we use a 405-nm integrated fiber-coupled continuous wave (cw) laser diode to establish an easy-to-build 3D nanoprinting system based on two-step absorption. Two-dimensional (2D) gratings with a sub-150-nm period and 3D woodpile nanostructures with a lateral period of 350 nm have been printed at a low speed. At a faster scan velocity of 1000 µm/s, 2D gratings with sub-200-nm resolution and sub-50-nm linewidth can still be fabricated with laser power less than 1 mW. The two-step absorption of the used benzil initiator enables us to use a second cw laser with 532-nm wavelength to enhance the polymerization with sub-100-nm feature size when starting with insufficient 405-nm laser power, which possess the potential to find applications in high-speed high-resolution parallel-writing and in situ manipulation.