Modulated Laser Diode Research Articles

Cladding-pumped, Yb:YAG-core, fiber-like waveguide laser: modeling and experiment.

We developed a model describing the performance of the cladding-pumped, Yb:YAG-core, fiber-like waveguide laser with a large cladding-to-core area ratio. We analyzed how pump absorption and laser output efficiencies depend on the Yb-doping level as well as the waveguide parameters, such as clad-to-core area ratio and waveguide length. We also determined the conditions that maximize both pump and laser efficiency. We showed that, depending on the waveguide design, cavity parameters as well as the core temperature, this laser can operate either at 1030 or 1050 nm. We have also shown that the main factor limiting power scaling of such a waveguide laser is the core temperature. The model was validated by laser experiments with a 174 mm long, double-clad, Yb(20%):YAG-core waveguide, with the cladding-to-core area ratio of 43.4. An output power of 41.6 W and slope efficiency of 73% with respect to the absorbed pump power have been achieved with cladding pumping by a fiber-coupled laser diode module at 933 nm. Our experimental results were in a good agreement with the modeling predictions.

Research and Development of Laser Engraving and Material Cutting Machine from 3D Printer

Abstract This article deals with the adjustment of a 3D printer for laser engraving and material cutting. The print head can be fitted with a solid laser diode module, which achieves a compact size while retaining its useful power. Two paths lead to the use of such a concept. It is possible to equip the existing print head with a module, which also brings a number of disadvantages such as, for example, the reduction of the printing space or the need for a suitable mounting design. A more elegant solution is to consider this in the design of a 3D printer and design a system to exchange the print heads for 3D printing and laser engraving. Such a solution allows full utilization of the workspace and simple installation of the effector for the required type of work. According to the installed power of the laser diode, it is possible not only to engrave but also cut material such as thin wood, veneer or acrylic glass. The use of such a machine is not only for graphic elements but for the creation of various stencils, boxes or simple models, which can be made up of plastic-burning pieces. The laser module is controlled by a driver, which is designed for the device. This is connected to a 3D printer control board. It is, therefore, necessary for the control board to have at least two pins, which can be controlled after adjusting the control firmware. Most laser modules are normally equipped with an adjustable lens, which is used to concentrate the focus of a laser for the given distance against the worktop. Thus, the modified 3D printer can perform its function as a multi-purpose CNC machine, while a basic platform similar for both devices is used.

Measurements and analysis of diode laser modulation wavelength at high accuracy and response rate

Measurements and analysis of diode laser modulation wavelength at high accuracy and response rate

Rancang Bangun Mesin Laser Engraver and Cutter Untuk Membuat Kemasan Modul Praktikum Berbahan Akrilik

In the competence of vocational institution, lecturers, students and PLP staff are expected to make their own appropriate equipment. An educational laboratory as a place to provide adequate practice and supporting equipments. Equipment or innovations that are designed must be packaged in an attractive form as a prototype of a product. As for the research and or as a practical tool in the laboratory. The packaging also serves to protect the device made and increase its life time. Usually the material used to make a casing material is acrylic. The thicker the acrylic, the more difficult it is to make. Laser engraver or laser cutter as a solution to facilitate the manufacture of casings that made from acrylic. User will create a two-dimensional design using a program, such as Inkscape. Then the design is saved or changed into gcode. The resulting gcode file is then sent to the laser engraver to make the design. The power of the laser head used, will determine the thickness of the acrylic to be cut. In this research, 2 mm thick acrylic was tested using a 15W laser diode module.

Extended cavity diode laser master-oscillator-power-amplifier for operation of an iodine frequency reference on a sounding rocket

We present a hybrid microintegrated diode laser module developed for iodine spectroscopy on board a sounding rocket. The laser module is based on a master-oscillator-power-amplifier concept: an extended cavity diode laser serves as the master oscillator, and a ridge-waveguide semiconductor optical amplifier provides the power boost. The module's form factor and mass correspond to 12.5×7.5×2.3cm3 and 750 g, respectively. With an electrical power of 3.75 W supplied to the module, 570 mW of optical power is provided out of a polarization maintaining optical fiber at 1064.490 nm with a technical linewidth of 13 kHz (55 kHz) at a 1 ms (10 ms) time scale. The laser module has successfully passed vibration tests at a level of 8.8g R M S . A nominally identical module has recently been used to demonstrate, for the first time, precision iodine spectroscopy in space.

Watt-level Pr3+:YLF deep red laser pumped by a fiber-coupled blue LD module or a single-emitter blue LD

A power-scaled laser operation of Pr:YLiF4 (YLF) crystal at 720.9 nm pumped by a 443.6 nm laser diode (LD) module was demonstrated. The 20 W module was used to pump the Pr:YLF crystal, and a maximum output power of 3.03 W with slope efficiency of 30.04% was obtained. In addition, a 5 W blue LD was also used to pump the Pr:YLF laser, and a maximum output power of 0.72 W was obtained at room temperature. The output power was limited by the wavelength mismatch between the single-emitter LD and the absorption peak of the crystal.

Monitoring temperature and vibration in a long weak grating array with short-pulse generation using a compact gain-switching laser diode module

Quasi-distributed temperature sensing and single point vibration sensing were performed. Ultrashort pulses generated by a gain-switching laser were used to interrogate a fiber Bragg gratings (FBG) array sensor. Temperature changes were measured down to 1°C with sub-centimeter spatial resolution. The advantages of our fast interrogation setup were exploited, as the higher frequency limit of a dynamic measure that can be sensed is limited by the time needed to generate the optical pulse and to acquire the data from the sensor. The experimental approach described in this paper can sense mechanical vibrations up to a frequency of 245 kHz and a strain resolution as low as 1.2 µɛ.

Self-referenced frequency response measurement of high-speed photodetectors through segmental up-conversion based on low-speed photonic sampling.

A self-referenced electrical method is proposed for measuring the frequency responses of high-speed photodetectors (PDs) through segmental up-conversion based on low-speed photonic sampling. The proposed method provides a very narrow linewidth and ultra-wideband optical stimulus by the segmental electro-optic up-conversion, and eliminates the uneven responses of mode-locked laser diode (MLLD) and electro-optic modulator (MOD) based on the symmetric frequency photonic sampling, which is free of any extra calibration. Moreover, it achieves ultra-wide and scalable frequency response measurement of PDs with 2M-fold measuring frequency range, where the symmetric sweeping frequency up to Nfr/2 of MOD enables the measuring frequency range of M × N×fr. For a proof-of-concept, two commercial PDs are measured with a sampling rate of 96.9 MS/s and a symmetric frequency-swept modulation up to 1.4575 GHz and 2.475 GHz, and their frequency responses are evaluated up to 29.07 GHz (=10 × 30 × fr) and 49.419 GHz (=10 × 51 × fr), respectively. The consistency between our method and conventional methods verifies that the scalable self-referenced measurement provides a simple but accurate method for the performance characterization of high-speed PDs.

Numerical and Experimental Analysis of Optical Frequency Comb Generation in Gain-Switched Semiconductor Lasers

We have performed a systematic experimental and simulation analysis of the optical frequency combs generated by gain-switching single mode laser diodes, either free-running or subjected to optical injection. The simulations have been produced with a dynamical model consisting of three rate equations that include stochastic noise terms. The model parameters have been extracted from experiments. An exhaustive comparison between the simulated and the experimental temporal profiles and optical spectra generated under a wide range of switching and optical injection conditions has been performed. The excellent quantitative agreement found in the entire range of the explored operating conditions supports the validity of the model for the analysis of the comb generation mechanisms. The detailed maps generated provide guidelines for selecting suitable operating conditions for specific comb characteristics.

Effect of ozone and diode laser (635 nm) in reducing orthodontic pain in the maxillary arch\u2014a randomized clinical controlled trial

The effect of ozone, diode laser irradiation, and presence of teeth crowding/spacing on pain perception in orthodontic patient was tested. Overall, 76 patients [55 women and 21 men; age 35.1(6.4) years] who met the inclusion criteria participated in the study. Immediately after fixed orthodontic appliance placement, the patients were exposed to a pain relief treatment (one single session) using either 635-nm diode laser (SmartM, Lasotronix, Warsaw, Poland) or ozone therapy (OzoneDTA, Apoza, New Taipei City, Taiwan) by placing the handpieces in the area of each teeth apex and interdental papillae, from the maxillary right first molar to the maxillary left first molar. Subjects were divided into three groups: control group (G1, n = 26), ozone (G2, n = 26, exposed to ozone therapy, generator probe type 3, working time per point 5 s, 23 points, application time 1 min and 55 s), and laser group (G3, n = 25, exposed to continuous mode diode laser, 400 mW, handpiece diameter 8 mm, spot area 0.5024 cm2, power density per second 1.59 W/cm2, dose 2 J per point, time: 5 s per point, 23 points, total energy per session 46 J, application time 1 min and 55 s). The level of teeth crowding was assessed using the Lundstrom indicator. The patients received a questionnaire for pain assessment (the Numeric Rating Scale, NRS-11, grade level 0–10) and recorded at 7 time points (1 h, 6 h, and 1, 2, 3, 4, and 5 days ) after the fixed orthodontic appliance placement. The mean pain values for the diode laser, ozone, and control group were 3.6 (1.31) (95% CI, 2.95–4.25), 5.25 (3.37) (95% CI, 3.52–6.98), and 5.75 (2.40) (95% CI, 4.69–6.81), respectively. We observed lower pain values in the diode laser group compared to the control group (p = 0.0237). The use of ozone in this study did not result in significant pain reduction in comparison to control (p = 0.8040) and laser groups (p = 0.1029). There were no differences in pain perception between patients with crowded teeth and non-crowded teeth in each group (G1, p = 0.66, G2, p = 0.86, G3, p = 0.24). The use of 635-nm diode laser led to decreased pain perception; however, ozone and presence of teeth crowding/spacing did not affect the pain perception in orthodontic patients during the first 5 days after the fixed orthodontic appliance placement.

Characterization of a carrier-envelope-offset-stabilized blue- and green-diode-pumped Ti:sapphire frequency comb.

Diode-pumping of Ti:sapphire provides a low-cost route to high-quality frequency-comb sources, exploiting the potential of direct diode modulation for wideband control of the carrier-envelope-offset frequency. We present here an fREP- and fCEO-locked, directly diode-pumped Ti:sapphire frequency comb, producing 66-fs pulses at 800nm and employing f-to-2f interferometry and current modulation of a 462-nm blue laser diode to achieve a stabilization bandwidth extending to ∼70 kHz. Characterizations of the fREP and fCEO phase noise are compared to relative intensity noise spectra of the pump diodes to provide insights into how the diode design and performance transfer into the comb stability, suggesting a lower contribution to fREP and fCEO noise from the blue laser diode than from the green diode.

InGaN as a Substrate for AC Photoelectrochemical Imaging.

AC photoelectrochemical imaging at electrolyte–semiconductor interfaces provides spatially resolved information such as surface potentials, ion concentrations and electrical impedance. In this work, thin films of InGaN/GaN were used successfully for AC photoelectrochemical imaging, and experimentally shown to generate a considerable photocurrent under illumination with a 405 nm modulated diode laser at comparatively high frequencies and low applied DC potentials, making this a promising substrate for bioimaging applications. Linear sweep voltammetry showed negligible dark currents. The imaging capabilities of the sensor substrate were demonstrated with a model system and showed a lateral resolution of 7 microns.

Exploiting the aiming beam to increase the safety of laser lithotripsy: Experimental evaluation of light reflection and fluorescence.

In Holmium laser lithotripsy, usually, the surgeon is guided by a visible beam superimposing the infrared (IR) treatment radiation. It has been shown that a green aiming beam excites stone autofluorescence. This fluorescence signal can be used for calculi detection to check the correct fiber position before triggering the IR laser, thus preventing damage to soft tissue and application devices. However, also the directly reflected green light from the fiber tip gives valuable information on fiber position and its surface condition. An external fiber-fiber-coupling-box (fiber core diameter 365 µm) for pulsed holmium laser radiation (2.1 µm) was set up containing a green diode laser module (520 nm, average power on the sample <0.5 mW) and optics and detectors for measuring the reflected light of this aiming beam as well as the fluorescence excited with it. Measurements were done via a lock-in technique with more than 20 human calculi samples and porcine calix in vitro. After the implementation of automatic data storage signals during ongoing in vitro lithotripsy procedures were recorded with the fiber positioned on tissue, stone, or in/on medical equipment (working channel of an endoscope, stone retrieval basket). Stone fluorescence signals measured were a factor of 7 to >100 higher than those of tissue. Stone fluorescence was detectable in "non-contact mode" with a linear signal decrease over a distance up to ~1 mm in front of the fiber tip (core diameter 365 µm) and with severely damaged fibers (max. decrease: 75% with pinched off fiber). Reflection signals of the fiber tip surface in air and water surrounding decreased significantly when the fiber was damaged; measured ratios of intact to damaged fiber found in the air were (5-17):1 and in water (1.6-3.7):1. Surfaces in front of the fiber aggravated the evaluation of fiber condition due to reflections but enabled to detect, for example, the working channel of a flexible endoscope in combination with the (missing) fluorescence signal. Autofluorescence induced by a green aiming beam can be exploited for stone detection in laser lithotripsy. A reflection measurement can give further information on fiber condition and position. Implementing this kind of safety features for an automatic block of IR laser emission in case of weak or missing fluorescence and un-normal reflections can assist the surgeon by avoiding tissue perforation, and damage to medical devices such as endoscopes. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Vibration displacement immunization model for measuring the free spectral range by means of a laser self-mixing velocimeter.

In this paper, a vibration-displacement immunization model is proposed to measure the free spectral range of a resonant cavity by using a laser self-mixing velocimeter. The validity of this method is demonstrated by the experimental results, which can effectively get rid of low measurement accuracy related to the self-mixing vibration system due to the vibratory displacement. According to the periodic waveform separation characteristic of the self-mixing velocity signal, the free spectral range of a multilongitudinal mode diode laser is calculated to be 88.24 GHz. Moreover, the influences of different target velocities and signal sampling frequencies on the free spectral range have been analyzed in detail from the theoretical analysis. In the case of high signal sampling rate and low velocity, from which the undistorted velocity signal waveform at the integral order external cavity mode keeps stable, it is possible to obtain relatively accurate measured results.

Application of the Wiener filtering algorithm for processing the signal obtained by the TDLAS method using the synchronous detection technique for the measurement problem of 13CO2 concentration in exhaled air

It has been shown clearly that using the synchronous detection technique with the pump current frequency modulation of a tunable diode laser emitting near 2 μm wavelength, combined with the application of the Wiener filtering algorithm for the experimental signal, ensures a two-times improvement in the measurement accuracy for the 13CO2 content in exhaled air, and, for the 13CO2 and 12CO2 concentrations ratio, more than seven times.

A temperature effect study on the laser diode module spectral characteristics

The paper presents the study results of the semiconductor laser active medium temperature effect, that changes in time during its operation, on its output spectral characteristics. Experimental dependences of the diode laser emission spectra on the laser crystal temperature in the range from 296 to 320 K are investigated. Using a heat fluxes computer model the possible reasons were analyzed for the time variation of the laser diode module spectral characteristics with several single emitters that are fixed on the ladder platform. The obtained results can be used for the large-scale laser diode modules design, including a large number of emitters, with high requirements for the output characteristics stability. Thermal fields and isothermal surfaces for a laser diode module with total thermal loads exceeding 30 W are studied.

Polarization Multiplexing-Based Ultra-Wideband Over Fiber Communication Employing Direct Modulation and Carrier Re-Use

A cost-efficient ultra-wideband (UWB) over fiber architecture is proposed and demonstrated through simulation results. A directly modulated laser diode at the central unit (CU) is employed to transport and generate downlink UWB signals at a remote access unit (RAU). The directly modulated carrier is re-used at the RAU for transmission of uplink UWB signal. Therefore, all-optical full-duplex transmission of UWB signals at a rate of 2 Gbps is achieved while maintaining very low-bit-error rate (BER) values.

Longitudinal mode seeding in modulated InGaN laser diodes

The modulation of InGaN laser diodes is important for applications such as laser projection in cinemas as well as in virtual and augmented reality applications. Here, a modulation frequency in the 100 MHz to 1 GHz range is necessary. On this timescale, pixel crosstalk is a major issue that affects the intensity and spectral properties. We investigate the spectral and temporal dynamics of InGaN laser diodes driven with different pulse patterns. We identify longitudinal mode seeding as a mechanism between interacting pulses which are spaced by several nanoseconds: photons, remaining in the cavity after the trailing edge of the electric pulse, “seed” consequent pulses and promoting their own longitudinal mode. This leads to a changed spectral–temporal mode pattern of the consequent pulse. The long cavity ring-down time of these photons is a consequence of relatively low losses. Further investigations were performed by streak camera measurements of differently biased laser diodes. For a bias below, but close to, the threshold, the optical gain nearly compensates internal and mirror losses. Additional simulations are performed to confirm the experimental results.

Design and application research of the multi-longitudinal mode laser self-mixing vibration measurement system

The free spectral range of the resonant cavity is calculated to be 78.95 GHz based on 1.90 mm of the waveform separation period as a multi-longitudinal mode laser diode is employed as the light source of the self-mixing vibration measurement system. As such, the influence of the vibration amplitude of the loudspeaker to the self-mixing vibration signal waveform is further researched by means of the feasible theoretical analysis and experimental characterization. The primary experimental results demonstrate that the amplitude limitation ratio coefficient Al of this sensing system is required to design below 2.053 × 10−3 corresponding to an entire waveform separation period, of which is to prevent the self-mixing signal waveform from distorting effectively in the context of the integral order of the external cavity mode. Furthermore, the feedback levels of the multi-longitudinal mode laser self-mixing vibration system are studied in detail. It has been shown that the experimental result of the free spectral range fits well with theoretical value when this system is matched to the applicable amplitude limitation range 0<Al≤2.053×10-3 and the optimum optical feedback regime 0<C<4.6.

Development of a fiber laser diode module in the spectral range of 445–450 nm with an output optical power of more than 100 W

This study considers the possibility of developing a laser diode module with a fiber output, having an output power more than 100 W in the spectral range of 445–450 nm, for processing metals with a low reflectance in this wavelength range, such as gold, silver, and copper. As sources of radiation, 64 blue laser diodes were used in a standard TO-18 case with a diameter of 5.6 mm and an output optical power of 2 W each, combined into a single 8×8 array. The developed optical system for collimation, spatial beam conversion, and radiation focusing on the end face of the optical fiber makes it possible to input optical power of more than 116 W into a fiber with an efficiency of more than 90%.