Pulsed Diode Research Articles

Effects of Current Distortion on DC Link Inductor and Capacitor Lifetime in Variable Frequency Drive Connected to Grid With Active Harmonic Filter

In this research article, new investigation and comprehensive analysis is done on the current distortion effects of dc link inductor and capacitor in variable frequency drive (VFD). Shunt active filter (SAF) is the most prominent solution for harmonic mitigation at the point of common coupling in the power distribution system. However, SAF connectivity reduces the grid impedance ( ZTH ) seen at the input of six pulse diode bridge rectifier in VFD. Commutation behavior of the diode rectifier is changed due to this grid impedance variation resulting in increased harmonic current distortion (THD i ) at the input of the rectifier bridge. This effect increases the ripple current of dc capacitor, dc link inductor losses, and diode rectifier conduction losses. This study investigates the drive dc link inductor and capacitor lifetime reduction with and without SAF, under various grid operating conditions of 3% voltage unbalance and 8% predistortion. Moreover, the high frequency (2–9 kHz) impact on dc link inductor core and copper losses is detailed. A 250 kW VFD with SAF of 180 A capacity is used for test measurement under various operating conditions. Current distortion effects are analyzed, and test results are compared with MATLAB simulation. Grid impedance variation due to SAF and its effect on the reliability of the VFD front-end components were not covered in detail in any of the earlier research. Lifetime estimation of dc link inductor and capacitor due to grid impedance variation is one among the significant outcomes of this investigation.

Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source

The production of negative ions in cesium sputter ion sources is generally considered to be a pure surface process. It has been recently proposed that ion pair production could explain the higher-than-expected beam currents extracted from these ion sources, therefore opening the door for laser-assisted enhancement of the negative ion yield. We have tested this hypothesis by measuring the effect of various pulsed diode lasers on the O− beam current produced from Al2O3 cathode of a cesium sputter ion source. It is expected that the ion pair production of O− requires populating the 5d electronic states of neutral cesium, thus implying that the process should be provoked only with specific wavelengths. Our experimental results provide evidence for the existence of a wavelength-dependent photo-assisted effect but cast doubt on its alleged resonant nature as the prompt enhancement of beam current can be observed with laser wavelengths exceeding a threshold photon energy. The beam current transients observed during the laser pulses suggest that the magnitude and longevity of the beam current enhancement depends on the cesium balance on the cathode surface. We conclude that the photo-assisted negative ion production could be of practical importance as it can more than double the extracted beam current under certain operational settings of the ion source.

Laser gain module small-signal gain increase due to suppression of parasitic generation with pump geometry optimization

A method for optical pump scheme optimization for a laser gain module with pulsed diode arrays for Nd:YAG rods (Ø10 × 130 mm & Ø10 × 160 mm) is presented. The goal is to maximize the small-signal gain of the laser gain module while maintaining a flat-top amplification profile. A possible way of the overall small-signal gain reduction due to amplified spontaneous emission is discussed and a method to deal with this phenomenon is given. As a result of optical pump scheme optimization, the gain module with the maximum pump power of 40 kW for 250 µs pulse duration at repetition rates of up to 25 Hz is created. The maximum small-signal gain G = 100 at 1.064 is achieved.

Asymmetric-waveguide, short cavity designs with a bulk active layer for high pulsed power eye-safe spectral range laser diodes

It is shown, by calculations calibrated against the authors’ recent experimental data, that an eye-safe wavelength range InGaAsP/InP high pulsed power laser design using a bulk active layer, which has a large refractive index step with respect to the optical confinement layer and is located close to the p-cladding, can provide substantial performance improvement compared to the best results achieved so far for this operating regime and wavelength. The dependence of the laser performance on the design parameters such as the thicknesses of the active layer and the waveguide, as well as the cavity length, are analysed. It is shown that the relatively thick bulk active layer in such InGaAsP/InP lasers allows the use of short cavity lengths (∼1 mm or even shorter), for achieving high pulsed power while maintaining a low p-cladding series resistance (making for high efficiency) and a narrow far field (making for high brightness). A single-asymmetry structure with the asymmetric active layer location but symmetric optical confinement layer/cladding refractive index steps gives performance only marginally inferior to that of a double-asymmetric one including asymmetric refractive index steps.

Deep-blue DBR laser at room temperature from single-crystalline perovskite thin film

Abstract Organic-inorganic hybrid perovskite semiconductors as gain materials have been widely investigated in various lasing structures. Here, we construct a vertical cavity surface-emitting deep-blue laser device in one step. A high-quality CH3NH3PbCl3 single-crystalline film as gain material is in situ grown in solution confined between a pair of distributed Bragg reflectors, which naturally form an optical microcavity. The thickness of the perovskite film can be easily adjusted from submicron to several microns by changing the applied pressure on the substrates. At room temperature, the resulting device can lase in a range of 414–435 nm when pumped by an 8 ns pulsed semiconductor laser diode, exhibiting a typical threshold of 211 μJ/cm2. The lasing wavelength and the number of modes are tunable due to the adjustable thickness of the perovskite film.

640-nm Pr:YLF regenerative amplifier seeded by gain-switched laser diode pulses.

We demonstrated the regenerative amplification of picosecond laser pulses generated by a gain-switched laser diode at 640 nm with a Pr:YLF crystal that was continuously pumped by a multimode blue laser diode. A 0.7-pJ seed pulse energy sufficiently suppressed the self-oscillation in the amplifier. The amplified pulse energy reached 33 µJ at a repetition rate of 10 kHz. The spatial beam quality was nearly TEM00. We also demonstrated second- and third-harmonic generation and obtained 320- and 213-nm pulse energies of 18 and 0.83 µJ at 10 kHz.

Efficacy of Microwave Pulse Diode Laser and Argon Laser Trabeculoplasty in Patients with Primary Open Angle Glaucoma

Purpose: To compare the efficacy of the microwave pulse diode laser and argon laser trabeculoplasty in primary open angle glaucoma.
 Study Design: Quasi experimental study.
 Place and Duration of Study: Shaheed Mohtarma Benazir Bhutto Medical College Lyari and Sindh Government Lyari General Hospital, Karachi, from October, 2017 to March, 2018.
 Material and Methods: One hundred and sixty patients, between 42 to 61 years with visual acuity of perception of light to 6/36 were enrolled. Patients diagnosed with POAG were included and patients with intraocular pressure of more than 40 mm Hg, previous glaucoma surgery or laser treatment and narrow angle on gonioscopy were excluded. Ophthalmic examination included visual acuity, slit lamp examination, fundus examination and visual field status using Humphrey perimeter. Patients were divided into two groups. Group A received microwave pulse diode laser (810) and Group B received argon laser trabeculoplasty. Average follow up period was 6 months. Success was assessed objectively by measuring intra ocular pressure and subjectively by visual acuity.
 Results: The average time-period for each procedure was 15 ± 5 minutes. In Group A, mean IOP at first week, first month, third month and sixth month was 20.79, 16.34, 16.21and 16.09 mm Hg respectively. While in Group B, IOP at first week, first, third and sixth month was 16.52, 15.76, 13.62, and 12.54 mm Hg at (P < 0.001 in both groups).
 Conclusion: Both microwave pulse diode laser and argon laser trabeculoplasty are effective in lowering intra ocular pressures in patients with primary open angle glaucoma.

Effects of temperature on luminescent properties of Gd2O3:Er, Yb nanophosphor

In this study we analyze nano powder Gd2O3 doped with Er3+ and Yb3+. Material was synthesized by simple and efficient solution combustion method. The nano phosphor was optically excited at 980 nm by using pulsed laser diode. We have obtained time resolved upconversion luminescence spectra of nano powder samples of Gd2O3:Er,Yb using a streak camera and analyzed temperature dependence of erbium optical line emission intensities. The possibilities of using Gd2O3:Er,Yb for temperature sensing were analyzed by means of luminescence intensity ratio method. We show that synthesized Gd2O3:Er,Yb material is useful for temperature measurements up to 550 K.

Treatment of Sebaceous Hyperplasia by Laser Modalities: A Review of the Literature and Presentation of Our Experience With Erbium-doped Yttrium Aluminium Garnet (Er:YAG)

Sebaceous hyperplasia (SH) is a common skin presentation in adults. Due to their unwanted yellow papular appearance, patients may desire their removal. Although several treatment modalities have been reported, the full range and efficacy of options are unclear. To determine the efficacy of laser modalities in the treatment of SH. The authors will also specifically assess the efficacy, recurrence rate and side effect profile of SH treatment with Er:YAG wavelength using a variable long pulsed (VLP) Er:YAG laser (SP Dynamis Fotona laser, Ljubljana, Slovenia) Methods & Materials: A comprehensive literature search was performed through PubMed, EMBASE, and Web of Science, using the search terms [(sebaceous hyperplasia)] and [(laser[s], Er:Yag, Er:Glass, Fraxel, CO2, PDL, Pulse dye laser, Diode, Xe-Cl, Excimer, Argon, KTP, Ruby, Alexandrite or Nd:YAG)]. The search yielded a total of 119 results and 8 were identified as relevant to this reviewResults: Pulse dye laser (PDL) provides a wide range of treatment results from complete reduction to flattening of the SH without significant adverse events; recurrence rates were unreported. Short PDL showed faster treatment response than long PDL. CO2 laser can produce considerable positive cosmetic outcomes with marked clinical improvement without any recurrence, but significant adverse effects have been reported. The 1450-nm diode laser has been described to produce good (75%) clinical improvement and lesion shrinkage ranging from 50% to greater than 75% without lasting adverse effects. In our clinic, Er:YAG has provided very significant cosmetic outcomes with a low recurrence rate and minimal adverse effects. Laser modalities can provide satisfactory results for removing SH. It is crucial that the laser is being used by an expert who is familiar with the device as well as understand the laser tissue interaction to minimize patient adverse effects while providing the best cosmetic outcome. In our experience, Er:YAG laser can provide a safe and highly effective solution for SH. J Drugs Dermatol. 2020;19(5)   doi:10.36849/JDD.2020.3971.

In vivo detection of venous sinus distension due to intracranial hypotension in small animal using pulsed-laser-diode photoacoustic tomography.

Intracranial hypotension (IH) is a pathophysiological condition of reduced intracranial pressure caused by low cerebrospinal fluid (CSF) volume due to dural injuries from lumbar puncture, surgery, or trauma. Understanding the prognosis of IH in small animal models is important to gain insights on the complications associated with it such as orthostatic headache, cerebral venous thrombosis, coma, and so forth. Photoacoustic tomography (PAT) offers a novel and cost-effective way to perceive and detect IH in small animal models. In this study, a pulsed laser diode (PLD)-based PAT imaging system was used to examine the changes in the venous sinuses of the rat brain due to IH, induced through CSF extraction. After the CSF extraction, an increase in the sagittal sinus area by ~30% and width by 40% ± 5% was observed. These results provide supportive evidence that the PLD-PAT can be employed for detecting changes in sagittal sinus due to IH in rat model.

Spontaneous loss versus stimulation gain in pump-probe microscopy: a proof of concept demonstration.

.Significance: The large background, narrow dynamic range, and detector saturation have been the common limiting factors in stimulated emission (SE)-based pump-probe microscopy, attributed to the very small signal overriding the very intense laser probe beam. To better differentiate the signal of interest from the background, lock-in detection is used to measure the fluorescence quenching, which is termed spontaneous loss (SL). The advantages are manifold. The spontaneous fluorescence signal can be well separated from both the pump and the probe beams with filters, thus eliminating the background, enlarging the dynamic range, and avoiding the saturation of the detector.Aim: We propose and demonstrate an integrated pump-probe microscopy technique based on lock-in detection for background removal and dynamic range enhancement through SL detection.Approach: The experimental setup is configured with a pulsed diode laser at a wavelength , acting as a pump (excitation) and a mode-locked Ti:sapphire laser at a central wavelength , serving as the probe beam (stimulation). Both pulse trains are temporally synchronized through high precision delay control by adjusting the length of the triggering cables. The pump and probe beams are alternatively modulated at different frequencies and to extract the stimulated gain (SG) and SL signal.Results: SG signal shows saturation due to the irradiation of the intense probe beam onto the photodetector. However, the detector saturation does not occur at high probe beam power for SL detection. The fluorescence lifetime images are acquired with reduced background. The theoretical signal-to-noise ratios for SG and SL are also estimated by photon statistics.Conclusion: We have confirmed that the detection of SL allows the elimination of the large background without photodetector saturation, which commonly exists in SG configuration. This modality would allow unprecedented manipulation and investigation of fluorophores in fluorescence imaging.

Inactivation of Salmonella and quality changes in wheat flour after pulsed light-emitting diode (LED) treatments

Several low water activity (aw) foods have been recently associated with Salmonella related outbreaks and recalls. The use of high intensity light pulses generated by light-emitting diodes (LEDs) is a novel approach to achieve microbial inactivation. This study compares the ability of light emitted by LEDs at wavelengths of 275, 365, 395, and 455 nm to inactivate microorganisms at different environmental relative humidity (RH) conditions. The exposure to LED radiant energy of 1199 J/cm2 at wavelengths of 365, 395, and 455 nm resulted in Salmonella reductions of 2.22, 2.48, and 1.61 logs CFU/g, respectively. Reductions in Salmonella cell counts of 1.07, 2.42, 3.67, and 2.64 CFU/g were observed in wheat flour after 60 min of 275, 365, 395, and 455 nm LED treatments, respectively, at 25 °C and an RH of 75%. Significant drying, oxidation of gluten proteins, and changes in the secondary structure of gluten were observed after LED treatments at all the light wavelengths tested. Significant color change of wheat flour was observed for all wavelengths LED except 275 nm. The results of this study will aid selection of LED wavelengths appropriate for inactivating microorganisms in low aw foods. This study presents the potential of LED treatment for simultaneous drying and microbial decontamination of foods.

纳秒半导体激光器的时间抖动和触发同步特性

纳秒半导体激光器的时间抖动和触发同步特性

纳秒半导体激光器的时间抖动和触发同步特性

纳秒半导体激光器的时间抖动和触发同步特性

OPTIMIZATION OF THE CONVERTER CHARACTERISTICS IN BRAKING TRANSITION MODES OF TRACTION ENGINE

Described conditions of converter optimization for DC engine braking modes. Braking minimizes the level of current ripple when using various methods of current regulation. Solving problems of efficient use of a DC traction engine and create safe modes of operation by ensuring optimal mode. The introduction of additional elements in the scheme allows to reduce the rate of attenuation of the current in the brake coils. A significant advantage of the proposed circuit modernization is the introduction of diodes in the circuit, which will allow the use of self-excitation of the electric motor for electrical braking. The proposed solution simplifies the technical implementation and reduces costs due to the lack of an additional independent power source for the brake coils. A significant factor in increasing the profitability of electric transport in general may be the replacement of an existing traction electric drive (TEP) with their more modern types. Simulation models have been developed to allow the study of electromechanical processes in a serial DC engine. Introduction to the circuit of a pulsed regulator diode, which shunts the excitation winding, reduces the rate of attenuation of the current in this winding. The proposed modernization of the circuit is to introduce into the circuit the diodes, an energy storage, which allows the use of brake modes for self-excitation of the motor and to avoid the use of additional independent sources of current.

Non-contact acquisition of brain function using a time-extracted compact camera

A revolution in functional brain imaging techniques is in progress in the field of neurosciences. Optical imaging techniques, such as high-density diffuse optical tomography (HD-DOT), in which source-detector pairs of probes are placed on subjects’ heads, provide better portability than conventional functional magnetic resonance imaging (fMRI) equipment. However, these techniques remain costly and can only acquire images at up to a few measurements per square centimetre, even when multiple detector probes are employed. In this study, we demonstrate functional brain imaging using a compact and affordable setup that employs nanosecond-order pulsed ordinary laser diodes and a time-extracted image sensor with superimposition capture of scattered components. Our technique can simply and easily attain a high density of measurement points without requiring probes to be attached, and can directly capture two-dimensional functional brain images. We have demonstrated brain activity imaging using a phantom that mimics the optical properties of an adult human head, and with a human subject, have measured cognitive brain activation while the subject is solving simple arithmetical tasks.

Lightsheet fluorescence lifetime imaging microscopy with wide-field time-correlated single photon counting.

We report on wide‐field time‐correlated single photon counting (TCSPC)‐based fluorescence lifetime imaging microscopy (FLIM) with lightsheet illumination. A pulsed diode laser is used for excitation, and a crossed delay line anode image intensifier, effectively a single‐photon sensitive camera, is used to record the position and arrival time of the photons with picosecond time resolution, combining low illumination intensity of microwatts with wide‐field data collection. We pair this detector with the lightsheet illumination technique, and apply it to 3D FLIM imaging of dye gradients in human cancer cell spheroids, and C. elegans.

Laser induced autofluorescence lifetime to identify larynx squamous cell carcinoma: Short series ex vivo study

Laser induced autofluorescence (LIAF) lifetime is useful to distinguish between normal laryngeal tissues and squamous cell carcinoma (SCC) based on variations of their biochemical composition and structure alterations. LIAF was collected from samples constituted by pairs of normal and malignant tissue, which were excised from three patients. Exclusion criteria for samples harvest were: (i) macroscopic changes of normal vocal cord observed during surgery; (ii) previous surgical intervention on vocal cord, (iii) patients treated only with chemotherapy or radiotherapy for carcinoma. Inclusion conditions: men, aged 57–68, non-smokers. A pulsed laser diode excited LIAF at 375 nm and 31 MHz repetition rate; beam full-time width at half-maximum was 87 ps at an average power of 0.49 mW. Mean LIAF lifetime for normal tissues was (3.75 ± 0.49) ns and for malignant (4.37 ± 0.85) ns: it is longer in malignant than in normal tissue. Variance analysis made with Fisher's test has shown no significant difference between patients for normal tissues; the same was true for malignant. Though, when malignant tissue was compared to normal for the same patients as well as between patients, a significant difference (significance level of 5%) was evidenced. Time-resolved LIAF may allow better differentiation between normal and malignant tissues in patients diagnosed with larynx SCC.

Frequency-multiplexing photon-counting multi-beam LiDAR

We report a frequency-multiplexing method for multi-beam photon-counting light detection and ranging (LiDAR), where only one single-pixel single-photon detector is employed to simultaneously detect the multi-beam echoes. In this frequency-multiplexing multi-beam LiDAR, each beam is from an independent laser source with different repetition rates and independent phases. As a result, the photon counts from different beams could be discriminated from each other due to the strong correlation between the laser pulses and their respective echo photons. A 16-beam LiDAR system was demonstrated in three-dimensional laser imaging with 16 pulsed laser diodes at 850 nm and one single-photon detector based on a Si-avalanche photodiode. This frequency-multiplexing method can greatly reduce the number of single-photon detectors in multi-beam LiDAR systems, which may be useful for low-cost and eye-safe LiDAR applications.

Lasers for reduction of unwanted hair in skin of colour: a systematic review and meta-analysis.

Light-based therapies are one of the most effective and widely used strategies for removal of undesired hair, with a broadly favourable safety profile. However, subjects with pigmented skin are found to be more prone to laser-related adverse events. While prolonged pulse-width and longer treatment duration were proposed to minimize adverse events, the optimal treatment option among available phototherapy modalities - long-pulsed (Nd:YAG), pulsed diode and alexandrite lasers as well as intense pulsed light (IPL) - remains unclear, particularly for skin of colour. To determine superiority in terms of effectiveness and tolerability, we conducted a systematic review of literature on different types of in-office laser and IPL for hair removal in subjects with Fitzpatrick skin types III-VI. The meta-analysis was performed using Review Manager (RevMan) version 5.3 and included 12 eligible comparative trials (nine randomized controlled trials and three quasi-randomized). In terms of hair count reduction, pooled effect estimates for long-pulsed ND:YAG laser [OR: 0.26, 95% CI (0.1, 0.78)] and diode laser [standardized mean difference (SMD): -0.11, 95% CI (-0.62, 0.39)] were not statistically significant from those of IPL; in contrast, alexandrite laser was found to be superior to IPL in reducing hair count [SMD: -1.7, 95% CI (-2.6, -0.78)]. In terms of adverse events, the pooled effect estimates favoured long-pulsed Nd:YAG laser to IPL with respect to postinflammatory hyperpigmentation [OR: 0.26, 95% CI: (0.1, 0.78)]. However, both pulsed diode and alexandrite lasers exhibited a comparable safety profile to IPL, despite higher pain scores with lasers. In conclusion, this systematic review suggests that treatment outcomes for different in-office laser devices and IPL in subjects with skin type III-VI are broadly similar; nevertheless, we observed a trend towards greater hair reduction following laser therapy compared with IPL.