Laser Module Research Articles

Characterization of semi-infinite delaminations using lock-in thermography: Experimental results

Delaminations are flat subsurface flaws parallel to the sample surface. Lock-in infrared thermography with optical stimulation is proposed to size the geometrical parameters of a delamination. Here we deal with semi-infinite delaminations, which are characterized by three geometrical parameters: length, depth and thickness. In a recent paper we calculated analytically and numerically the temperature oscillation of a sample containing a semi-infinite delamination when illuminated by a homogeneous and modulated laser beam. In this work, we present lock-in infrared thermography experiments performed on calibrated delaminations manufactured on AISI-304 stainless steel. We fit the numerical model to the experiments to retrieve the delamination length, depth and thickness. The agreement between nominal and retrieved values confirms the validity of the method and paves the way for characterization of finite delaminations.

An automated method for stem diameter measurement based on laser module and deep learning

BackgroundMeasuring stem diameter (SD) is a crucial foundation for forest resource management, but current methods require expert personnel and are time-consuming and costly. In this study, we proposed a novel device and method for automatic SD measurement using an image sensor and a laser module. Firstly, the laser module generated a spot on the tree stem that could be used as reference information for measuring SD. Secondly, an end-to-end model was performed to identify the trunk contour in the panchromatic image from the image sensor. Finally, SD was calculated from the linear relationship between the trunk contour and the spot diameter in pixels.ResultsWe conducted SD measurements in three natural scenarios with different land cover types: transitional woodland/shrub, mixed forest, and green urban area. The SD values varied from 2.00 cm to 89.00 cm across these scenarios. Compared with the field tape measurements, the SD data measured by our method showed high consistency in different natural scenarios. The absolute mean error was 0.36 cm and the root mean square error was 0.45 cm. Our integrated device is low cost, portable, and without the assistance of a tripod. Compared to most studies, our method demonstrated better versatility and exhibited higher performance.ConclusionOur method achieved the automatic, efficient and accurate measurement of SD in natural scenarios. In the future, the device will be further explored to be integrated into autonomous mobile robots for more scenarios.

Real-Time Monitoring of Human Breathing Using Wearable Tilted Fiber Grating Curvature Sensors

Respiration rate and volume are important physiological indicators of human health. They can indicate cardiovascular health status and cardiopulmonary function. Here, we demonstrate a compact breath monitoring system based on a wearable tilted fiber Bragg grating (TFBG) curvature sensor for human respiration monitoring. With the assistance of a custom designed breathing tube, TFBGs provide a very reproducible highly sensitive, real time response to curvature changes during respiration. The miniaturized and cost effective sensing system which we propose consists of a tunable laser module, a field programmable gate array acquisition control circuit module, and a sensor module. Different breathing patterns can be successfully identified from the optical amplitude and frequency output of the sensor. The robust instrument displays high repeatability and real-time tracking.

High Average Power Green Laser Based on LED-Side-Pumped Q-Switched Nd:YAG Laser

In this paper, we demonstrated a watt-level acousto-optic (A-O) Q-switched intracavity frequency-doubled green laser with high average power and beam quality operation based on an efficient LED-pumped Nd:YAG laser module. For the quasi-continuous wave (QCW) running operation, the average output power of fundamental laser at 1064 nm was as high as 10.3 W at a repetition rate of 100 Hz, corresponding to the highest optical conversion efficiency of 25.4% and a slope efficiency of 31.3%, and the maximum energy of single pulse was up to 100mJ. By optimizing the incidence angle of the KTP crystal to meet the non-critical phase matching condition, greater than 3.8 W of 532 nm average power at a repetition rate of 10 kHz was generated with duration of 192 ns and a beam quality factor of M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.6 and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.7, corresponding to a frequency doubling conversion efficiency of 45.5%. To the best of our ability, this is the highest average power and high beam quality of an LED-pumped A-O Q-switched intracavity frequency-doubled green laser with watt-level output reported so far.

Transient optical properties, laser induced avalanche effect, and all optical switching in molecular aggregates

Organic dyes have attracted expressive research interest in recent years due to their wide range of applications. Self-aggregation occurs in a variety of organic molecules, a phenomenon that changes the photochemical and photophysical properties of dyes. Laser beams with wavelengths of 663 nm and 532 nm were used for thermal modulation of the aggregation states of the methylene blue dye, which led to the discovery of a novel avalanche phenomena in the molecular/supramolecular level and observations of not yet reported material optical behaviors. The obtained experimental data reveals the existence of asymmetric optical responses of aggregated dyes under laser excitation with wavelengths at the monomer or at the dimer absorption bands. The observed optical behaviors, resulting from the laser modulation of the molecular aggregation states, may find applications in the field of organic electronics and devices, such as optical logical gates and optical power limiters. A dual mechanism all optical switching driven by the simultaneous action of the cooperative effects of the laser induced disruption of dimeric dye units and thermal lensing was achieved.

In‐Plane Integrating Unidirectional 1D CsPbBr3 Waveguide Arrays with Heterogeneous Semiconductor Wires for Photonic Integrated Circuits

Abstract1D semiconductor wires have great potential in on‐chip integrated photonics systems. However, it is still challenging to efficiently integrate various semiconductor wires on a large scale for complex functional devices. This study reports a universal route to in‐plane integrate unidirectional metal halide perovskite CsPbBr3 wire arrays with Sb2Se3, PbSeand CdS wires on mica substrates, respectively. It is found that the growth of the unidirectional wire arrays is controlled by a synergistic effect of the promoted initial nucleation on the transferred heterogeneous wires and the thermodynamically favored epitaxy on mica. The optical characterizations show that the CsPbBr3 wire arrays can act as both the light emitting media and waveguide, where the emission in the CsPbBr3 wires can be efficiently guided into the backbone Sb2Se3 wire. Importantly, the constructed CsPbBr3 waveguide arrays/Sb2Se3 wire photodetector system shows 73.4 nA photocurrent with the on/off ratio of 111, by exciting the CsPbBr3 wires at 174 mW cm−2 of 405 nm laser. The frequency dependent photoresponse characterizations exhibit a response capability of 2000 Hz modulated laser pulse and a 3 dB frequency above 300 Hz, indicating the rapid response speed. This study promotes the application of semiconductor wires in on‐chip multifunctional integrated photonic devices.

All-optical plasma modulation by the plasma channel induced in the molybdenum disulfide dispersion solution

The molybdenum disulfide (MoS2) nanosheet is successfully synthesized using a hydrothermal Li-intercalation exfoliation method. We experimentally show that the MoS2 dispersion solution can be used for optical modulation and all-optical switching based on the plasma channel induced by control pulses. The modulated signal light has a good transmission property in free space. The spatial modulation of the signal laser can be easily adjusted through the power of control lasers and the suspension concentration. The influence of suspension concentration and type on the free-space propagation of modulated signal light is also investigated. Results reveal a potential application of MoS2 as an all-optical modulator for diversified photoelectric applications.

Low frequency photothermal excitation of AFM microcantilevers

Photothermal excitation at frequencies below the mechanical resonance of the atomic force microscopy (AFM) microcantilever can be utilized in force modulation microscopy, fast force displacement curve acquisition, and tip-based mass spectroscopy. To understand the microcantilever bending response in these modes, accurate models of the thermoelastic response of the AFM microcantilever are needed. We study the sub-resonance photothermal vibrational response of coated and uncoated AFM microcantilevers as a function of laser modulation frequency and spot location. The sub-resonance microcantilever response shows distinct thermoelastic regimes. Below the microcantilever's thermal roll-off frequency, the vibration amplitude is mostly constant. Past this frequency, the vibration amplitude decreases with increasing frequency. At modulation frequencies below the thermal roll-off frequency, the most efficient photothermal laser spot to excite harmonic motion is near the free end of both coated and uncoated microcantilevers. For the tested coated microcantilevers, the most efficient photothermal laser location migrates from near the free end of the microcantilever to near the fixed end as modulation frequency increases. For the tested uncoated microcantilever, the most efficient photothermal laser location remains unchanged at the tested frequencies. To predict the bending response of the coated microcantilever, a bilayer bending model is implemented. At low frequencies, this model underpredicts the bending response compared to experiments by up to 90%. This may be due to neglecting microcantilever bending contributed by a through-thickness temperature gradient. Our results illustrate different aspects of the frequency-dependent photothermal laser spot optimization that can guide users to maximizing microcantilever response to a given input power.

High–Power 792 nm Fiber–Coupled Semiconductor Laser

The pumping of Tm-doped crystal or fiber by a 792 nm semiconductor laser is an important way to generate a mid-infrared laser, which is widely used in various fields. In this paper, a high–power 792 nm fiber–coupled semiconductor laser module was successfully fabricated with the output power of 232 W at a 10 A continuous current and the electro-optic conversion efficiency of 48.6%. The laser module is coupled with 24 chips into a fiber by spatial multiplexing and polarization combination technology. For a single emitting laser chip, the continuous wave (CW) output power and threshold current are 10.45 W at 10 A and 1.55 A, respectively. A polarization as high as 94% can also be realized, which is more suitable for laser spatial beam combining. The laser module was aged for more than 4000 h at 12 A and 25 °C without obvious power degradation.

Frequency modulation laser spectroscopy method for methane isotopologue ratio and total concentration measurements at 1661 nm

Source identification and accurate measurements of methane gas concentration are key tools necessary for climate change management. Here we present a method for methane isotopologue ratio measurement using a laser-based frequency modulation (FM) spectroscopy technique in the near infrared at 1661 nm. We provide line shape analysis and discuss a fitting algorithm for accurate isotopologue ratio metrology and investigate and minimize the effects of residual amplitude modulation on the experimentally produced FM signal line shape. This FM technique is further evaluated for future development of a cavity-enhanced and noise-immune system capable of isotopologue ratio as well as ultrasensitive trace gas measurements, all accessible using a single distributed feedback laser.

Dual pulse heterodyne distributed acoustic sensor system employing SOA-based fiber ring laser

Distributed Acoustic Sensor (DAS) has potential in applications such as hydroacoustic detection. In this paper, a dual-pulse heterodyne distributed acoustic sensor (DAS) system using a semiconductor optical amplifier (SOA)-based fiber ring laser (FRL) is proposed. Unlike the previous DAS system configurations, the SOA-based FRL replaces the narrow linewidth laser (NLL) and pulse modulator, reducing costs and simplifying the system. The system is demonstrated theoretically and validated experimentally. The adaptability of the SOA-based FRL in the heterodyne DAS system has been demonstrated in the experiments. Using the dual-pulse heterodyne detection method, the sensor system responds well to distributed acoustic detection and achieves accurate demodulation and positioning. A high signal-to-noise ratio (SNR) of 42.51 dB at 3 kHz is demonstrated as a demodulation result. The system’s frequency range is 5 Hz to 5 kHz with a spatial resolution of 12 m. The proposed approach shows a broad application prospect for low-cost, large-scale, high-SNR distributed acoustic detection in maritime surveillance.

An injection-locking diode laser at 671 nm with a wide tuning range up to 6 GHz

We present a compact injection-locking diode laser module to generate 671 nm laser light with a high output power up to 150 mW. The module adopts a master–slave injection-locking scheme, and the injection-locking state is monitored using the transmission spectrum from a Fabry–Pérot interferometer. Beat frequency spectrum measurement shows that the injection-locked slave laser has no other frequency components within the 150-MHz detection bandwidth. It is found that without additional electronic feedback, the slave laser can follow the master laser over a wide range of 6 GHz. All the elements of the module are commercially available, which favors fast construction of a complete 671-nm laser system for the preparation of cold 6Li atoms with only one research-grade diode laser as the seeding source.

Measurement of 124-GHz E/O Modulation Bandwidth in Hybrid Modulation Laser

We analyzed and measured the intrinsic modulation characteristics of a hybrid modulation laser with a medium cavity length of 410 μm. The intra-cavity loss modulation section acting as an external cavity induces both a gently sloped modulation response at high frequencies and the photon-photon resonance effect in a directly modulated laser, which can efficiently widen the modulation bandwidth. We analytically and experimentally confirmed that a wide 3-dB E/O bandwidth of more than 124 GHz can be achieved by using a hybrid modulation laser.

Based on adaptive modulation laser communication multi-microgrids scheduling system

In order to improve the data sharing and comprehensive information processing capabilities between multi-microgrids in the power system, the multi-microgrids scheduling system based on laser communication has been proposed. In order to reduce the error rate of laser communication and reduce the impact of atmospheric turbulence on signal acquisition, an adaptive modulation algorithm has been designed. A mathematical model for laser communication modulation and demodulation based on adaptive modulation algorithm has been constructed. In simulation analysis, the target signal was extracted from the original signal superimposed with atmospheric turbulence noise through filtering and demodulation. The energy fluctuation of the extracted signal decreased from 47.3 to 5 mV. The energy attenuation trend of communication lasers within the range of 0–6 km was experimentally tested. Within 2.0 km, the energy demodulation results of both algorithms are similar, both below 10%. After exceeding 2.0 km, the calculation error of the adaptive modulation algorithm remains basically unchanged, while the error of traditional algorithms increases by about twice. For the APD response value, the adaptive modulation algorithm demodulation has a higher response range concentration ratio and the higher envelope recognition. Under different nominal atmospheric turbulence values, the maximum error rates of the adaptive modulation algorithm are 5.8 × 10−8, 8.9 × 10−8, and 1.2 × 10−7, respectively, while the maximum error rates of the amplitude coherent algorithm are 2.9 × 10−5, 6.3 × 10−5, and 1.05 × 10−4, respectively. It can effectively suppress the impact of atmospheric turbulence on the error rate of laser communication by adaptive modulation algorithm.

Na5Rb7Sc2(WO4)9: Yb3+, Er3+: Luminescence Properties and Prospects for Non-Contact Thermometry

Trigonal solid solutions Na5Rb7Sc1.95Yb0.05 – xErx(WO4)9 (x = 0.0025–0.0375) and Na5Rb7Sc2 – 5y-Yb2yEr3y(WO4)9 (y = 0.005–0.015) based on ternary tungstate Na5Rb7Sc2(WO4)9 have been obtained by ceramic technology and their luminescence properties have been studied. Excitation of powders by infrared radiation of the laser module (λex = 980 nm, Pmax = 45 mW/mm2) leads to the appearance of a bright green emission. The highest intensity of the bands at 515–540 nm (2H11/2 → 4I15/2), 540–575 nm (4S3/2 → 4I15/2), and 645–680 nm (4F9/2 → 4I15/2) is observed for sample Na5Rb7Sc1.95Yb0.02Er0.03(WO4)9. For a given composition, the power and temperature dependences of optical characteristics have been studied, a mechanism for energy transfer between optical centers has been proposed, and chromaticity coordinates have been determined. Based on the data obtained, it has been concluded that Na5Rb7Sc1.95Yb0.02Er0.03(WO4)9 can be used as a material for non-contact luminescent thermometry.

Compact LD side-pumped Nd:YAG oscillator at 100 Hz without water-cooling

A high-repetition-frequency side-pumped electro-optical (E-O) Q-switched Nd:YAG laser without water cooling is reported. A 100 Hz laser module without water-cooling was designed and the related parameters of crystal are simulated. The crystal is annularly pumped in both ends and is conductively cooled in the middle. The heat generated by crystal and laser diode is dissipated by thermoelectric cooler (TEC), fins and fan. The 1064 nm maximum output energy is 68 mJ with a pulse width of 31 ns and a repetition rate of 100 Hz. The optical–optical conversion efficiency is 10.6%. To the best of our knowledge, this is the first report of 100 Hz repetition rate operation for a E-O Q-switched Nd:YAG rod laser without water-cooling.

Modulation of carbon dots hybrids lasers for high security flexible multi-level anti-counterfeiting

Anti-counterfeiting materials development has been raised for a long time to improve the level of security against counterfeiting. Increasing counterfeiting difficulties as well as reducing difficulties of materials preparation are two major concerns in the development of anti-counterfeiting materials. Herein, carbon dots (CDs) and triethyl 1,3,5-benzenetricarboxylate (Et3BTC), both of which show two random lasing peaks located around 325 nm and 450 nm at 265 nm excitation are chosen as two lasing mediums to form hybrids. Moreover, lasing intensity ratio of the two lasing bands from the hybrids can be tuned by changing the working temperature, excitation area, and even bending angle of substrate. As a result, a strategy of dual random lasing medium modulation based high security flexible multi-level anti-counterfeiting technique is developed. Thus, it is suitable for anti-counterfeiting of high-value items due to its high security and excellent waterproofness. This work will provide a perspective to boost the development of high security anti-counterfeiting techniques.

Computation and Verification of Spatial Rate Equations for an Electro-Optically Q-Switched Laser-Diode Side-Pumped Nd:YAG Laser

In a side-pumped laser module, we simulate the pumping power distribution across the cross-section of Nd:YAG rods at varying diameters. The coupled rate equations with the spatial overlap efficiency for a four-level actively Q-switched side-pumped laser are considered complete. After a Q-switched pulse terminates, the expressions of laser output parameters are derived. We assess the single pulse energy, pulse width, and peak power using the analysis function. The 200 Hz Q-switched side-pumped Nd:YAG laser with a peak power of 103 kW and beam quality factors M2 = 1.67 is developed to the validity of theoretical models.

Synthesis and investigation of nonlinear optical properties of biphenyl ethylene derivatives with different substituents

Three biphenyl ethylene derivatives (BPED1, BPED2 and BPED3) with different substituent groups were synthesized by Schiff base reaction. The influence of substituent types on nonlinear optical properties of materials was studied. Three derivatives are reverse saturated absorption and have good optical limiting performances. The third harmonic strength of BPED1, BPED2 and BPED3 is 18 times, 27 times and 37 times that of SiO2, respectively. The optical limiting threshold and third harmonic signal show that three derivatives will have good application potential in the field of laser protection, laser modulation and conversion.

Highly sensitive measurement method for photosensitizers based on dual-excitation laser modulation technique

A dual-excitation laser modulation technique for the sensitive measurement of photosensitizers in tumor is proposed. The technique is based on the difference in optical absorption properties of photosensitizers and biological tissues at 405 nm and 450 nm. The 405 nm and 450 nm laser beams, with the same modulation frequency and 180° phase difference, were coupled into a single fiber simultaneously. A periodic signal with a frequency of 1 kHz was generated in alternating excitation, and was processed by phase sensitive detectors. The weak photosensitizer fluorescence masked by tissue autofluorescence can be effectively separated through the proposed method, so that the final signal intensity is only related to the concentration of photosensitizer. The method with a sensitivity of 0.22 mL/ng was determined by measuring the low concentration of protoporphyrin IX (PpIX) solution, and the detection limit of instrument reached 0.5 ng/mL. The puncturable optical probe with a diameter of 675 µm ensures that PpIX in can be detected with spatial resolution, which was performed in the measurement of PpIX in tumor bearing nude mice.