Search Results (46)

Background: Clinical diagnostics, food industries, and biotechnological processes typically use an enzyme called alpha-amylase to metabolize carbohydrates. Objective: The aim of this study is to investigate how low-level laser irradiation (LLLI) affects alpha-amylase activity towards determining the usability of LLLI in non-invasive enzymatic modulation. Methods: Enzyme solutions were irradiated at 10, 20, 30, and 40 J/cm² utilizing 589 nm and 532 nm diode-pumped solid-state lasers. The iodine–starch colorimetric method was used to quantify post-irradiation enzymatic activity, with inverse correlations found between absorbance and activity levels. Modulation was determined by the wavelength and dosage. Results: Enzymatic activity significantly improved when utilizing 589 nm irradiation at lower doses, maximizing at 120% at 20 J/cm² (p < 0.01). Neutral or inhibitory effects were revealed when higher doses were applied. Enzymatic activity showed progressive inhibition when 532 nm irradiation was applied, declining to 75% at 40 J/cm² (p < 0.01). Conclusions: These outcomes indicate that conformational flexibility and catalytic efficiency occur when applying lower-energy photons at 589 nm, whilst oxidative stress and impaired enzymatic function are induced by higher-energy photons at 532 nm. This is consistent with the biphasic dose–response characteristic of photobiomodulation. Full article

Research on the thermal analysis of laser diode (LD) side-pumped amplifiers is a critical step in the design of high-power solid-state laser systems. Instead of adopting a standard solid modeling approach that only considers a laser rod, a fluid–structure interaction model is employed for analysis using the FLUENT 2021 R1 software. This model integrates the cooling structure, coolant, and laser rod, incorporating their relevant material parameters. By considering both uniform and non-uniform inlet velocity distributions as loading conditions, the study reveals remarkably different thermal simulation results. The correlation between thermal analysis outcomes and the total inlet flow rates is calculated, while temperature and stress distributions are obtained under a varying internal heat source. It was observed that the non-uniform inlet velocity distribution has little impact on the rod’s maximum temperature but significantly influences the maximum equivalent stress. This finding underscores the necessity of accounting for non-uniform inlet distributions during the design of laser amplifiers to achieve more accurate thermal simulation results and optimize structural reliability. Full article

We report on a 1064 nm master oscillator power amplifier (MOPA) system based on pulse-modulated laser diode seed sources combined with fiber preamplifiers and a Yb-doped tapered double-clad fiber (T-DCF) amplifier used as an all-fiber master oscillator and a two-stage side-pumped solid-state power amplifier. The combination of two master oscillators and a single power amplifier allowed us to obtain pulses with a duration ranging from 10 ns to 10 μs with energy up to 137 mJ at 100 Hz. For the first time, we demonstrate a widely tunable pulse duration and a solid-state MOPA system with over 100 mJ energy based on a T-DCF fiber seed laser. Full article

The critical pump power for achieving passively continuous-wave mode-locking in a solid-state laser is analytically derived from the spatially dependent rate equations and the criterion for the intracavity pulse energy. A prompt way is proposed to straightforwardly design the cavity for passively mode-locked solid-state lasers. Complete experiments are performed to demonstrate the proposed cavity design and, simultaneously, to verify the theoretical model for the critical pump powers. It is interestingly observed that even though a larger modulation depth causes a higher critical pump power, it can generate a shorter pulse width in return. Full article

Salt, one of the most commonly consumed food additives worldwide, is produced in many countries. The chemical composition of edible salts is essential information for quality assessment and origin distinction. In this work, a simple laser-induced breakdown spectroscopy instrument was assembled with a diode-pumped solid-state laser and a miniature spectrometer. Its performances in analyzing Mg and Ca in six popular edible sea salts consumed in South Korea and classification of the products were investigated. Each salt was dissolved in water and a tiny amount of the solution was dropped and dried on the hydrophilicity-enhanced silicon wafer substrate, providing homogeneous distribution of salt crystals. Strong Mg II and Ca II emissions were chosen for both quantification and classification. Calibration curves could be constructed with limits-of-detection of 87 mg/kg for Mg and 45 mg/kg for Ca. Also, the Mg II and Ca II emission peak intensities were used in a k-nearest neighbors model providing 98.6% classification accuracy. In both quantification and classification, intensity normalization using a Na I emission line as a reference signal was effective. A concept of interclass distance was introduced, and the increase in the classification accuracy due to the intensity normalization was rationalized based on it. Our methodology will be useful for analyzing major mineral nutrients in various food materials in liquid phase or soluble in water, including salts. Full article

We report a diode-pumped solid-state (DPSS) laser used for intracavity pump-enhanced difference frequency generation (DFG) to create a 3.5-micron laser. Using a 50 mm-long periodically poled lithium niobate (PPLN) crystal inside the cavity of an Nd:YVO₄ solid-state laser at 1064 nm with 4.5 W pump power at 808 nm, and a 310 mW C-band signal at 1529 nm, up to 31 mW of mid-infrared output power at 3499 nm is obtained. The cavity requires no active stabilization and/or locking, and the entire cavity is <8 cm in length. The obtained output power corresponds to a black-box efficiency of 2.20%W⁻¹, which is the highest value reported to date for continuous-wave DFG based on a bulk nonlinear optical crystal with no active stabilization. Potential future applications in free-space optical communication are also discussed. Full article

A diode-end-pumped self-mode-locked Tm,Ho:LuLiF₄ (LLF) laser is demonstrated for the first time, to the best of our knowledge. At the incident pump power of 3.4 W, the stable self-mode-locked operation of the Tm,Ho:LLF laser was realized without any additional devices in the resonator. Further increasing the incident pump power to 6.8 W, the maximum average output power of 1.07 W was achieved at 2068 nm with a pulse width of 746 ps and a repetition frequency of 468 MHz. The experimental results indicate that the Tm,Ho:LLF crystal is promising to generate the high-power self-mode-locked solid-state laser at 2 μm waveband. The self-mode-locked Tm,Ho:LLF laser has potential applications in optical communication, remote sensing, material process, and nonlinear frequency conversion. Full article

The buildup dynamics of diode-pumped passively mode-locked solid-state laser is thoroughly explored using the real-time measurement with temporal sampling rate of up to 40 GHz. A concise cavity is developed to ensure the transient dynamics purely arising from the gain medium and saturable absorber. Experimental results reveal that the laser output in the buildup process exhibits numerous passively Q-switched pulses followed with a damped relaxation oscillation prior to the stable mode locking. Furthermore, it is confirmed that the laser output has already displayed single clean mode-locked pulses inside the first several Q-switched envelopes before stepping into the stage of relaxation oscillation. The present real-time exploration is expected to provide important information for practical applications with temporal modulation of the pump intensity. Full article

In this study, an optical sensor using thermo-sensitive phosphor and its measurement system for visualizing and measuring the temperature distribution in an arbitrary cross-section of transmission oil using one type of phosphor, whose peak wavelength changes with temperature, is proposed. Because the intensity of the excitation light is gradually attenuated by the scattering of the laser light owing to microscopic impurities in the oil, we attempted to reduce the scattering effect by increasing the excitation light wavelength. Therefore, Pyrromethene 597 was selected as the optical sensor using thermo-sensitive phosphor, and a DPSS (Diode Pumped Solid State) laser with a wavelength of 532 nm was used as the excitation light. Using this measurement system, we measured the temperature distribution of a vertical buoyant jet of transmission oil and validated the measurement method. In addition, it was shown that this measurement system could be applied to the measurement of the temperature distribution in transmission oil with cavitation foaming. Full article

Laser diode pumped solid-state lasers (DPSSLs) have been widely used in many fields, and their thermal effects have attracted more and more attention. The laser diode (LD) side-pumped amplifier, as a key component of DPSSLs, is necessary for effective heat dissipation. In this paper, instead of the common thermal analysis based only on a crystal rod model, a fluid–structure interaction model including a glass tube, cooling channel, coolant and crystal rod is established in numerical simulation using ANSYS FLUENT for the configuration of an LD array side-pumped laser amplifier. The relationships between cooling layer thickness, coolant velocity and maximum temperature, maximum equivalent stress, inlet pressure and the convective heat transfer coefficient are analyzed. The results show that the maximum temperature (or maximum equivalent stress) decreases with the increase in the coolant velocity; at low velocity, a larger cooling layer thickness with more coolant is not conductive enough for improved heat dissipation of the crystal rod; at high velocity, when the cooling layer thickness is above or below 1.5 mm, the influence of the cooling layer thickness on the maximum temperature can be ignored; and the effect of the cooling layer thickness on the maximum equivalent stress at high velocity is not very significant. The comprehensive influence of various factors should be fully considered in the design process, and this study provides an important reference for the design and optimization of a laser amplifier and DPSSL system. Full article

We report a novel, miniaturized gas sensor configuration with ppbv (parts-per-billion by volume) sensitivity, where detection of the gas sample concentration is realized inside a Nd:YVO₄/YVO₄/Air-Gap structure (2 × 2 × 14 mm³) of the double-beam, monolithic diode-pumped solid-state laser (DPSSL) resonator operating at 1064 nm. Both generated probe and reference beams are passed through an ultra-compact sensing volume (4 μL) of the air-gap section filled with gas molecules. Simultaneously, an auxiliary laser beam is targeted on the absorption line of a measured gas sample and focused on a 1064 nm probe beam only. Due to the absorption effect, excited gas molecules are heated locally, resulting in a negligible change in a gas refractive index (RI), which is inherent to the photothermal effect (PT). Hence, the PT-induced variations of the gas RI inside the laser resonator are modulating the optical path-length of the probe beam, which resulted in a significant optical frequency shift of the probe beam against the reference one. The optical frequency changes were measured by applying the heterodyne detection technique, where both 1064 nm beams were coupled onto the near-infrared (near-IR) high-speed photodiode (PD), resulting in a beat note signal readout down-converted into the radio-frequency (RF) domain. The RF mixer was used to shift the beat note in frequency accordingly to the frequency modulation (FM) demodulator range. The demodulator converts the beat note frequency changes into a proportional voltage signal. To provide better gas sensor properties, a typical wavelength modulation spectroscopy (WMS) technique was additionally used. The solid-state laser intra-cavity photothermal sensor (SLIPS) is a unique approach to gas spectroscopy, which provides tens of ppbv sensitivity, more than 5000 signal-to-noise (SNR) ratio, baseline-free measurements, miniature, versatile and non-complex sensor setup based on inexpensive DPSSL technology. The SLIPS has no limitation in terms of the excitation wavelength because only one near-IR detector for signal retrieval is needed. Full article

A wide variety of applications require high peak laser intensity in conjunction with a narrow spectral linewidth. Typically, injection-locked amplifiers have been employed for this purpose, where a continuous wave oscillator is amplified in a secondary external resonant amplifier cavity using a pulsed pump laser. In contrast, here we demonstrate a setup that combines a CW Ti:sapphire oscillator and pulsed amplifier in a single optical cavity, resulting in a compact system. Dichroic beam combination of blue wavelength semiconductor diodes and the green wavelength of a Nd:YAG laser allowed the simultaneous excitation of the Ti:sapphire crystal by both continuous wave and pulsed pump sources. A linewidth of <2 MHz is achieved in continuous wave operation, while the linewidth increases to about 10 MHz in the combined CW+pulsed mode with a pulse duration of 73 ns. A peak pulse intensity of 0.2 kW is achieved, which should enable efficient single-pass second harmonic generation in a nonlinear crystal. Full article

A static modulated Fourier transform spectrometer composed of a modified Sagnac interferometer was implemented for real-time remote sensing of the spectral property changes in a solid dye. In the spectrum obtained from the implemented spectrometer, the relationship between spectral resolution and dependent factors was discussed to prevent aliasing. As a target material, a solid-state dye of rhodamine-6G was fabricated in the laboratory. When an intense pumping laser light was irradiated to a solid dye, with increasing irradiating time, photodissociation occurred due to the accumulated heat and the fluorescence intensity decreased rapidly. The fast change in the fluorescence spectrum of the solid dye due to photodissociation could be measured and analyzed in real time using a static modulated Fourier transform spectrometer implemented in the laboratory. As the pumping light source, a diode laser of 1 W output power at 530 nm, in which pulse width modulation was possible, was used. When the solid-state dye sample was irradiated with a 10 Hz pulse repetition rate and 2.5 ms pulse duration for 900 s, the fluorescence intensity decreased by 44%, the fluorescence peak wavelength shifted from 590 to 586 nm, and the maximum temperature of the irradiated portion rose up to 45 °C. Under the same conditions, when the pulse duration was increased by 4 times to 10 ms, the fluorescence intensity decreased by 65%, the fluorescence peak wavelength shifted from 590 to 580 nm, and the maximum temperature of the irradiated portion rose up to 76 °C. The spectrometer proposed in this study was effective in measuring and analyzing the spectral properties of rapidly changing materials in real time. Full article

This paper is devoted to reviewing the latest results achieved in solid-state lasers based on thulium-doped mixed-sesquioxide ceramics, i.e., (Lu,Sc,Y)₂O₃. The near- and mid-infrared regions are of interest for many applications, from medicine to remote sensing, as they match molecular fingerprints and cover several atmospheric transparency windows. These matrices are characterized by a strong electron–phonon interaction—which results in a large splitting of the ground state—and by a spectral broadening of the optical transition suitable for developing tunable and short-pulse lasers. In particular, the manuscript reports on the trivalent thulium laser transitions at 1.5, 1.9, and 2.3 µm, along with the thermal and optical characteristics of the (Lu,Sc,Y)₂O₃ ceramics, including the fabrication techniques, spectroscopic and optical properties, and laser performances achieved in different pumping regimes, such as continuous-wave (CW), quasi-CW, and pulsed modes. A comparison of the performance obtained with these mixed-sesquioxide ceramics and with the corresponding crystals is reported. Full article

We report the first ever demonstration of a wavelength-locked Alexandrite laser using a volume Bragg grating (VBG) as a wavelength-selective mirror. Output power of 3.3 W with a diffraction limited beam quality of M${}^2=1.1$ was obtained at a lasing wavelength of 762.2 nm and a linewidth (FWHM) of 2.5 GHz. Full article