Laser Module Research Articles

Modeling of a solid-state laser module with pulse transverse diode pumping of Nd<sup>3+</SUP>:YAG active medium

In this work, a laser module (quantron) with transverse pulse diode pumping of a cylindrical Nd3+:YAG active element by the method of non-sequential ray tracing in the Zemax software environment is modeled. Numerically obtained distributions of the absorbed pump radiation power over the cross section of the active element and calculated the pumping efficiency of the quantron. A methodology for optimizing the quantron design is proposed, which results in an increase in the pumping efficiency of the active element.

When do we need Pbps photonic chips and what are the challenges?

We estimate the capacity requirement for optical input/output chips boosted by artificial intelligence in computing centers. It is expected that petabits per second (Pbps) capacity on a single chip may be achieved in ten years or so in laboratories. We then study the key challenges in the implementation of such photonic chips, focusing on technical bottlenecks such as laser integration, modulation speed, MUX/DEMUX scaling, photodetector efficiency, and packaging density. We also discuss potential solutions, including novel materials and integration techniques, to enhance performance and reduce power consumption. Our analysis suggests that significant innovations in these areas could lead to the development of compact and efficient Pbps photonic chips by 2035, paving the way for next-generation optical interconnect systems.

Investigating the transverse jitter in ultrashort electron beam generation with optical compression

Optical compression scheme is a highly potential candidate for the generation of ultrashort electron beam. This scheme utilizes a tightly focused radially polarized laser to compress the electron beam from the photocathode radio frequency (RF) gun. However, the unavoidable relative transverse jitter between the electron beam and the modulation laser leads to a performance degradation of the compressed pulse duration. To address this issue, we propose a method for correcting this transverse jitter through a specific design of optical system and an optimized decoupled solenoid. This method concentrates on the transverse jitter caused by the pointing instability of the laser. Its objective is to align both the transverse jitter direction and magnitude of the modulation laser with that of the electron beam. The simulation results demonstrate that the deleterious impact of transverse jitter can be effectively mitigated by this method, thereby ensuring the sustained generation of high-quality ultrashort electron beams.

Microstructure Control and Hot Cracking Prevention During Laser Additive Manufacturing of Cobalt-Based Superalloy

Hot cracking is a frequent and severe defect that occurs during laser additive manufacturing of superalloys. In this work, a pulsed-wave (PW) laser modulation process was employed to control the solidification microstructure and reduce the hot cracking susceptibility of laser additive manufactured cobalt-based superalloy. The effects of continuous-wave (CW) and PW laser processing modes on the dendrite morphology, element segregation, eutectic phase, and hot cracking of fabricated Co-based superalloys were investigated. Optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize the microstructural characteristics of samples. A two-color pyrometer was used to measure the molten pool temperature variation under different laser processing modes. The results show that coarse columnar dendrites, chain-like eutectic carbides, and hot cracks were observed in the CW sample. In contrast, the fine equiaxed crystals, discrete eutectic carbides, and low-level residual stresses were obtained to avoid hot cracks, owing to the high cooling rate and the periodic melting and solidification of the molten pool under the PW laser processing mode. This work provides a new method for controlling solidification structure and hot cracking of laser additive manufactured Co-based superalloy.

Experimental and computational studies on hot cracking in single laser tracks of aluminium alloy AA2024 and related implications for laser powder bed fusion

Laser powder bed fusion of high-strength aluminium alloys remains challenging due to the formation of hot cracks during the printing process. Hot cracking is a complex phenomenon involving a complex thermo-mechanical and metallurgical interplay. Such relationship needs to be fully understood to reap the benefits of advanced laser modulation (temporal and spatial) capabilities, now becoming available in PBF-LB. To this end, we explore the formation of hot cracks in single tracks produced using a simple spatial–temporal laser modulation characterised by laser pulses of various distance. The formation of cracks is then rationalised by physical and numerical modelling using multi-physics CFD simulation. We demonstrate that the area of the mushy zone at the back of the moving melt pool, dynamically contracts and expands according to the laser temporal regimes and find maxima in correspondence to the largest laser pulse distance and the time steps between exposures. By then analysing in detail in the crack observed in the printed parts fabricated with the same laser modulation, it is possible to conclude that the mechanisms leading to hot cracks in these specimens is analogous. In turn, the insights on single tracks can be extended, for the most part, to the case of bulk specimens. Nevertheless, printed specimens appear to be more sensitive to the erratic movement of the melt pool, due to the presence of a larger number of highly energetical grain boundaries and unintended microstructural defects (voids and inclusions), from which cracks can nucleate.Graphical

Fast modulation of a long-wave infrared laser based on the two-photon absorption of CO2

In this work, we report a long-wave infrared (LWIR) modulator based on the two-photon absorption of CO2 gas. The effect of gas pressure and laser power on the modulation under different wavelengths is discussed. A maximum modulation depth of 21.5% with a rise time (full time) less than 20 ns for a 9.36 μm laser was achieved. The gaseous modulator, which adopts a 2.75 μm laser as the pumping source, is capable of converting the pulse characteristics of the pump light into the modulation of the long-wave infrared light. It demonstrates promising potential for applications in the rapid optical modulation of LWIR lasers.

Laser modulation of the FePS3 memristors.

Ternary two-dimensional (2D) material-based memristors have garnered significant attention in the fields of machine learning, neuromorphic computing due to their low power consumption, rapid learning, and synaptic-like behavior. Although such memristors often exhibit high ON/OFF ratios and exceptional pulse response characteristics, they have also to face some challenges concerning reusability and switching cycles, which arise from the filament instability issues.. Here we propose a modulation strategy to improve performance of 2D-material memristors with synaptic and flexible features. By laser-modulating few-layer FePS3, we induced the formation of conductive filaments, realized a major improvement in performance of the FePS3 memristors, achieving an on/off ratio of nearly 104, low power consumption at approximately 10-7 W of single switching operation, and maintaining stability even after over 500 cycles. The performance promotion has been ascribed to enhancement of conductive filament induced by laser-modulation. Furthermore, we have identified the effectiveness of our laser modulation under strain by building the high-performance flexible FePS3 memristor. Meanwhile, we discovered a novel strain-dominant erasure method for the flexible memristors. Our work confirms that laser modulation is a viable method for enhancing the performance of 2D material-based memristive devices.&#xD.

Coherent instabilities in thulium-based fiber amplifiers induced by laser frequency modulation.

Frequency modulation of narrow-linewidth lasers can cause coherent backscattering in cladding-pumped fiber amplifiers. This detrimental effect can be observed in Tm-based fiber amplifiers and can be an additional limitation for power scaling applications. We investigate such instabilities in Tm- and Tm/Ho-doped fiber amplifiers for a wide range of design parameters (active fiber length, pumping scheme, dopant type) and operation regimes (laser frequency tuning rate, amplifier gain). For each amplifier configuration, the backward-propagating (BP) signal is found to peak at a specific laser frequency tuning rate, with an amplitude and a frequency that increase with increasing amplifier gain and fiber length.

Laser modulation to plateau region and intensity of high-order harmonic generation in monolayer MoTe2

Abstract Through solving semiconductor Bloch equations, we theoretically investigated the high-order harmonic generation in monolayer MoTe2 under laser modulation. Adjusting the laser parameters, the plateau region and intensity of harmonics can be effectively regulated. Changing laser wavelength can regulate the width of platform region and the cutoff order of harmonic spectrum. Platform region widens with the increase of laser wavelength. Under different laser wavelengths, the number of photons that need to be absorbed for electron transition varies, which affects the inter-band transition of electrons. Laser vector potential also varies with the wavelength, affecting the intra-band motion of electrons. Laser field strength can significantly change the harmonic intensity. As the laser field strength increases, the harmonic intensity increases and may generate new plateau in the high-energy region. The emergence of new platform is due to the transition of electrons between conduction bands. Our work provides a theoretical exploration for generating high quality harmonics and understanding the micro mechanism of high-order harmonic generation.

Widefield optical coherence tomography by electro-optical modulation.

Optical coherence tomography (OCT) is a unique imaging modality capable of axial sectioning with a resolution of only a few microns. Its ability to image with high resolution deep within tissue makes it ideal for material inspection, dentistry, and, in particular, ophthalmology. Widefield retinal imaging has garnered increasing clinical interest for the detection of numerous retinal diseases. However, real-time applications in clinical practice demand the contrast of swept-source OCT at scan speeds that limit their depth range. The curvature of typical samples, such as teeth, corneas, or retinas, thus restricts the field-of-view of fast OCT systems. Novel high-speed swept sources are expected to further improve the scan rate; however, not without exacerbating the already severe trade-off in depth range. Here, we show how, without the need for mechanical repositioning, harmonic images can be rapidly synthesized at any depth. This is achieved by opto-electronic modulation of a single-frequency swept source laser in tandem with tailored numerical dispersion compensation. We demonstrate experimentally how real-time imaging of highly-curved samples is enabled by extending the effective depth-range 8-fold. Even at the scan speed of a 400 kHz swept source, harmonic OCT enables widefield retinal imaging.

Coherent high-harmonic generation with laser-plasma beams

Active energy compression scheme is presently being investigated for future laser-plasma accelerators. This method enables generating laser-plasma accelerator electron beams with a small, ∼10−5, relative slice energy spread. When modulated by a laser pulse, such beams can produce coherent radiation at very high, ∼100th harmonics of the modulation laser wavelength, which are hard to access by conventional techniques. The scheme has a potential of providing additional capabilities for future plasma-based facilities by generating stable, tunable, narrow-band radiation. Published by the American Physical Society 2024

Dual-module combination with littman crosstalk external cavity for narrow-linewidth blue diode laser

The dense spectral beam combination is vital for achieving high power and brightness output in diode lasers. High-power narrow-linewidth laser modules have been widely studied as the fundamental units. This study presents a dual-module shared external cavity linewidth compression structure with a transmission diffraction grating. With a driving current of 2.4 A and a cooling temperature of 20 °C, the blue diode laser’s external cavity achieved an output power of 49.8 W, a spectral linewidth of 0.321 nm, and a tuning range of 0.817 nm, with an external cavity spectrum locked efficiency of approximately 80.6 %. Additionally, it is observed that crosstalk has a significant influence on the linewidth of the two modules. When one module current locked at 2.4 A and the other increased from 0 A to 2.4 A, the linewidth was reduced from 0.377 nm to 0.321 nm, and linewidth locking was implemented over an output power range from 27 W to 49.8 W. This work reports the highest output power for a blue diode narrow-linewidth external cavity laser.

SiPM-based LiDAR with multipulse sequence modulation and multithreshold signal processing.

A light detection and range technology (LiDAR) system that enables rapid ranging under extremely low signal-to-noise ratios (SNRs) during daylight conditions based on a SiPM (silicon photomultiplier) detector is proposed. The system emits a sequence of modulated laser pulses by controlling the semiconductor laser and then processes the SiPM response signals using dynamic multithreshold. The experimental result shows that, under extremely low SNR of daylight, the system achieves a 100% success rate in continuous ranging of a low reflectivity target at 125 m, with a ranging precision of less than 20 cm and a ranging time of less than 10 µs. Our system provides a significant reference value for achieving high-speed, noise-resistant, miniaturized, practical, and low-cost LiDAR based on a SiPM.

Prototype optical enhancement cavity for steady-state microbunching.

The innovative mechanism of steady-state microbunching (SSMB) promises a potent light source, featuring high repetition rate and coherent radiation. The laser modulator, comprising an undulator and an optical enhancement cavity, is pivotal in SSMB. A high-finesse prototype optical enhancement cavity for SSMB with an average power of 55 kW is described in this paper. Preliminary design of the laser modulator, experimental setup, and methods to address frequency degeneracy and power coupling issues are discussed. D-shaped mirrors are utilized to successfully suppress the modal instability. This study is the first to illustrate the finesse reduction caused by high-order mode damping during experiments. The experimental and simulation results match closely. A cavity power coupling model is established, and the experimental results verify the correctness of the coupling model. A method for estimating the absorption coefficient through thermal-induced evolution of cavity mode has been implemented. Experimental results demonstrate a high-average-power enhancement cavity with a finesse of 16 518 ± 103 and an estimated average absorption coefficient of 12 ppm for the cavity mirrors. The findings contribute to the advancement of SSMB by providing insights into the design and operation of high-power optical enhancement cavities.

Implementation of the Internet of Things in Centrifuge Calibrators

The implementation of Internet of Things (IoT) technology in centrifuge calibrators brings innovation by enhancing accuracy and efficiency in medical device calibration. This research develops an IoT-based centrifuge calibrator capable of storing calibration data digitally and providing real-time access, using the E18-D80NK sensor for rotational motion detection, which is more cost-effective than conventional laser modules. Measurement results demonstrate high accuracy across various RPM settings (1000, 1500, 2000, 2500, and 3000 RPM), with minimal error and stability within acceptable tolerance limits. The key advantage of IoT implementation lies in efficient calibration data management, enabling real-time access and integration with other systems for effective analysis and monitoring of calibration outcomes. Overall, IoT technology in centrifuge calibration not only enhances healthcare service quality with reliable results but also supports efficient and transparent equipment management in medical settings, offering long-term benefits to healthcare facilities and patients.

Effective bandwidth of optical pre-emphasis by photon-photon resonance in hybrid modulation laser diode

Effective bandwidth of optical pre-emphasis by photon-photon resonance in hybrid modulation laser diode

Electro-optic frequency comb generation via cascaded modulators driven at lower frequency harmonics.

Electro-optical modulation of a continuous wave laser is a highly stable way to generate frequency combs, gaining popularity in telecommunication and spectroscopic applications. These combs are generated by modulating non-linear electro-optic crystals with radio frequencies, creating equally spaced side-bands centered around the single-frequency seed laser. Electro-optic frequency comb architectures often choose between optical bandwidth (cascaded GHz combs) or higher mode density (chirped RF generation). This work demonstrates an electro-optic frequency comb with > 120 GHz of bandwidth and an 80MHz repetition rate. The comb has three cascaded electro-optic modulators driven at sequentially lower harmonics, the last megahertz modulation dictating the repetition rate. This architecture can modulate at any individual harmonic and repetition rate without changes to the components. This comb can be used in any applications where a stable and tunable repetition rate is needed.

Design and Development of an Automatic Layout Algorithm for Laser GNSS RTK.

At the current stage, the automation level of GNSS RTK equipment is low, and manual operation leads to decreased accuracy and efficiency in setting out. To address these issues, this paper has designed an algorithm for automatic setting out that resolves the common problem of reduced accuracy in conventional RTK. First, the calculation of the laser rotation center is conducted using relevant parameters to calibrate the instrument's posture and angle. Then, by analyzing the posture information, the relative position and direction of the instrument to the point to be set out are determined, and the rotation angles in the horizontal and vertical directions are calculated. Following this, the data results are analyzed, and the obtained rotation angles are output to achieve automatic control of the instrument. Finally, a rotating laser composed of servo motors and laser modules is used to control the GNSS RTK equipment to locate the set-out point, thereby determining its position on the ground and displaying it in real-time. Compared to traditional GNSS RTK equipment, the proposed automatic setting out algorithm and the developed GNSS laser RTK equipment reduce the setting out error from 15 mm to 10.3 mm. This reduces the barrier to using GNSS RTK equipment, minimizes human influence, enhances the work efficiency of setting out measurements, and ensures high efficiency and stability under complex conditions.

Semi-in-situ thermal transport characterization of thermal interface materials through a low-frequency thermoreflectance technique

Thermal transport characterization of thermal interface materials (TIMs), especially in their application scenario is so far challenging. Herein, we demonstrate a low-frequency frequency domain thermoreflectance technique to measure the semi-in-situ thermal transport properties of TIMs in a sandwiched structure. The measurement ability is first demonstrated by accurate measurement on several well-known materials. Then the thermal conductivity and interface thermal resistance of a thermal gel, a thermal pad composed of phase change materials and an Indium foil, sandwiched in two silicon slides are investigated. Sensitivity analysis emphasized the importance of pump laser spot size and modulation frequency in the measurement. For TIMs with low thermal conductivity, the sensitivity to interface thermal resistance is highly suppressed, while for TIMs with high thermal conductivity, the sensitivity to interface thermal resistance is prominent, which makes it easier to separately determine the TIM thermal conductivity and interface thermal resistance.

High-peak-power nanosecond pulse laser at 915 nm based on all-fiber structure

We demonstrate an all-fiber high-peak-power nanosecond pulse laser operating at 915 nm. The nanosecond pulse laser source is consisting of a 915 nm modulated laser diode and 4-stage Nd-doped fiber amplifiers. A maximum output power of 2.01 W is achieved with a peak power of 2.2 kW. The peak-to-peak fluctuation is less than ±0.2 % and the RMS is 0.084 %. Additionally, the beam quality at output power of 2.01 W is measured to be Mx2 = 1.09, My2 = 1.08, indicative of excellent beam characteristics in the output signal. To the best of our knowledge, it is the first report about high-peak-power Nd-doped fiber laser at 915 nm based on all-fiber structure. This work provides a good candidate for the Automotive Lidar with high imaging resolution and detection accuracy.