GaAs Laser Diodes Research Articles

ChemInform Abstract: Electronic Properties of 1,4-Dithioketo-3,6-diphenyl-pyrrolo(3,4-c) pyrrole in Solution and in the Solid State.

The near IR optical absorption of the title compound (DTPP) is of practical importance for laser printers and information storage applications based on GaAs laser diodes. Electronic properties of DTPP have been investigated in solution and in the solid state from the standpoint of deprotonation and intermolecular hydrogen bonding. The electronic state of the dithioketopyrrolopyrrole chromophore is found to be most sensitively affected by an environment of proton acceptors which interact with the NH group. The deprotonation (= N−) in solution leads to increased electron density on the nitrogen atom. As a consequence, there is more overall electron density in the chromophore which contributes to a large bathochromic displacement. A similar increase in electron density is also operative in the solid state through the inter-molecular hydrogen bonds between the NH group of one DTPP and the sulfur of the neighboring molecule. This is responsible for the large bathochromic shift of DTPP from the solution to the solid state. The visible absorption in the solid state is attributed to transitions along the molecular plane. On the other hand, the strong near IR absorption is interpreted as being due to interplanar π — π interactions along the stacking axis perpendicular to the molecular plane.

The Use of Surgical Diode Laser in Oral Hemangioma: A Case Report

To review the literature regarding the use of surgical lasers in hemangioma treatment and to report a clinical case involving diode laser. Hemangiomas are benign vascular proliferations consisting of numerous capillary structures and are especially common on the tongue, lips, jugal mucous membrane, and gums. A number of treatment modalities have been proposed for hemangioma treatment. The patient was referred for evaluation complaining of chewing difficulty because of swelling in the right area of the upper lip, with no previous trauma. The lesion was located in the internal right jugal mucous membrane, measured 4 x 4 cm(2), presented a bluish coloration, and was diagnosed as a hemangioma. The treatment selected was surgical removal using gallium arsenide (GaAs) diode laser at 980 nm wavelength, with 4.0 W of power. During surgery, complications including hemorrhage were not observed, and no scarring developed after surgery. The use of GaAs high-potency diode laser in the treatment of hemangioma reduced bleeding during surgery, with a consequent reduction in operating time, and promoted rapid postoperative hemostasis. It is safe for use on large lesions and easy to manage, and postoperative problems, including potential scarring, and discomfort are minimal.

Supermodes in Broad Ridge (Al,In)GaN Laser Diodes

Broad area (Al,In)GaN laser diodes (LDs) are suitable for high optical output power in the near UV to blue spectral range. But for ridge widths larger than a few micrometers, the occurrence of filamentation is well known. We present experimental evidence that the single filaments tend to be phase-locked with defined phase offset and build up a so called supermode. Depending on driving current a coherent or incoherent superposition of different supermodes can be observed, which has a significant impact on the corresponding lateral far-field pattern. By a simulated reconstruction of the lateral mode profile of the laser mode propagating in free space we retrieve the field and phase distribution of the laser mode in the waveguide. In this context the coupling mechanism is discussed and the mode behavior is compared to supermodes in GaAs laser diode arrays.

Influence of Deposition Method on Refractive Index of SiO2and TiO2Thin Films for Anti-reflective Multilayers

Anti-Reflective (AR) thin film coatings of SiO₂ (n=1.48) and TiO₂ (n=2.17) were deposited by ion-beam assisted deposition (IBAD) with End-Hall ion source and conventional electron beam (e-beam) evaporation to investigate the effect of deposition method on the refractive indicies (n) of the films. Green-light generation using a GaAs laser diode was achieved via excitation of the second harmonic. The latter resulted from the transmission of the fundamental guided-mode wave of 1064 nm through periodically poled LiNbO₃. Large differences in the refractive indicies of each of the layers in the multilayer coating may improve AR performance. IBAD of SiO₂ reduced its refractive index from 1.45 to 1.34 at 1064 nm. Conversely, e-beam evaporation of TiO₂ increased its refractive index from 1.80 to 2.11. In addition, no fluctuations in absorption at the wavelength of 1064 nm were found. The results suggest that films prepared by different deposition methods can increase the effectiveness of multilayer AR coatings.

Efficient Laser-Diode End-Pumped Passively Q-Switched Mode-Locked Yb:LYSO Laser Based on SESAM

We report an efficient Q-switched laser action based on a semiconductor saturable absorber mirrors (SESAMs) as passively Q-switched laser starter and a Yb:LYSO alloyed crystal as gain material pumped directly by 974 nm In GaAs laser diodes. The output pulse duration is measured to be about 7μs, while the average power and the repetition rate of the pulse chain are about 0.92 W and 6.2kHz, respectively, under 12.5 W absorbed pumping power. The Q-switched mode-locked pulse train is also observed in this setup. The laser performance shows that Yb:LYSO is a promising laser gain medium for laser-diode pumped compact solid-state lasers.

Low-Level Laser Therapy Applied Transcranially to Mice following Traumatic Brain Injury Significantly Reduces Long-term Neurological Deficits

Low-level laser therapy (LLLT) has been evaluated in this study as a potential therapy for traumatic brain injury (TBI). LLLT has been found to modulate various biological processes. Following TBI in mice, we assessed the hypothesis that LLLT might have a beneficial effect on their neurobehavioral and histological outcome. TBI was induced by a weight-drop device, and motor function was assessed 1 h post-trauma using a neurological severity score (NSS). Mice were then divided into three groups of eight mice each: one control group that received a sham LLLT procedure and was not irradiated; and two groups that received LLLT at two different doses (10 and 20 mW/cm(2) ) transcranially. An 808-nm Ga-As diode laser was employed transcranially 4 h post-trauma to illuminate the entire cortex of the brain. Motor function was assessed up to 4 weeks, and lesion volume was measured. There were no significant changes in NSS at 24 and 48 h between the laser-treated and non-treated mice. Yet, from 5 days and up to 28 days, the NSS of the laser-treated mice were significantly lower (p < 0.05) than the traumatized control mice that were not treated with the laser. The lesion volume of the laser treated mice was significantly lower (1.4%) than the non-treated group (12.1%). Our data suggest that a non-invasive transcranial application of LLLT given 4 h following TBI provides a significant long-term functional neurological benefit. Further confirmatory trials are warranted.

Kelvin probe force and surface photovoltage microscopy observation of minority holes leaked from active region of working InGaAs∕AlGaAs∕GaAs laser diode

A method for direct observation of carrier leakage from active regions of working semiconductor light-emitting diodes and lasers is suggested. In this method, Kelvin probe force and surface photovoltage microscopies are used to measure local changes in the surface potential of the device mirror on which a high concentration of the leaked carriers is expected. The applicability of the method is demonstrated by studying in detail the leakage current on the mirrors of high-power InGaAs∕AlGaAs∕GaAs laser diodes in action. It is shown that minority holes arrive at the mirror surface from the active zone of the laser and spread over to regions of the n emitter and n substrate. This observation is confirmed by exposing the mirror to external light with photon energy exceeding the band gap of the laser structure and measuring the generated surface photovoltage. Owing to surface channels formed by the surface band bending, the holes can move tens of micrometers from the place of their generation. The leakage currents are evaluated on the basis of the surface potential distributions observed. It is found that as the injection current of the laser increases, the leakage current grows until onset of lasing.

Low-Level Laser Therapy Applied Transcranially to Rats After Induction of Stroke Significantly Reduces Long-Term Neurological Deficits

Low-level laser therapy (LLLT) modulates various biological processes. In the present study, we assessed the hypothesis that LLLT after induction of stroke may have a beneficial effect on ischemic brain tissue. Two sets of experiments were performed. Stroke was induced in rats by (1) permanent occlusion of the middle cerebral artery through a craniotomy or (2) insertion of a filament. After induction of stroke, a battery of neurological and functional tests (neurological score, adhesive removal) was performed. Four and 24 hours poststroke, a Ga-As diode laser was used transcranially to illuminate the hemisphere contralateral to the stroke at a power density of 7.5 mW/cm2. In both models of stroke, LLLT significantly reduced neurological deficits when applied 24 hours poststroke. Application of the laser at 4 hours poststroke did not affect the neurological outcome of the stroke-induced rats as compared with controls. There was no statistically significant difference in the stroke lesion area between control and laser-irradiated rats. The number of newly formed neuronal cells, assessed by double immunoreactivity to bromodeoxyuridine and tubulin isotype III as well as migrating cells (doublecortin immunoactivity), was significantly elevated in the subventricular zone of the hemisphere ipsilateral to the induction of stroke when treated by LLLT. Our data suggest that a noninvasive intervention of LLLT issued 24 hours after acute stroke may provide a significant functional benefit with an underlying mechanism possibly being induction of neurogenesis.

Impact of N on the lasing characteristics of GaInNAs∕GaAs quantum well lasers emitting from 1.29 to 1.52μm

The origin of the degradation with N of the threshold current density (Jth) and external differential quantum efficiency (ηd) of 1.29 to 1.52μmGaInNAs∕GaAs laser diodes is analyzed. Adding N to InGaAs leads to a ∼25% reduction of the carrier injection efficiency and thus to an increase of Jth and a decrease of ηd. This effect is likely related to carrier recombination losses in the barriers and is independent of the N content. The optical absorption losses and the internal transparency current density are found to increase with N content, accounting for the rest of the degradation in Jth. Modeling of the transparency carrier and radiative current densities identifies the increase of the defect-related recombination coefficient in GaInNAs as the dominant effect leading to the N dependence of Jtr.

Low-Power Laser Treatment for Shoulder Pain

The objective of this study is to investigate the effect of low-power gallium-arsenide laser treatment on the patients with shoulder pain. Low-energy laser therapy has recently been popularized in the treatment of various rheumatologic, neurologic, and musculoskeletal disorders such as osteoarthritis, rheumatoid arthritis, fibromyalgia, carpal tunnel syndrome, rotator cuff tendinitis, and chronic back pain syndromes. A total of 40 patients who applied to our clinic with shoulder pain and complied with the selection criteria were included in the study. The patients were randomly assigned into Group I (n = 20, laser treatment) and Group II (n = 20, control). In Group I, patients were given laser treatment and an exercise protocol for 10 sessions during a period of 2 weeks. Laser was applied over tuberculum majus and minus, bicipital groove, and anterior and posterior faces of the capsule, regardless of the existence of sensitivity, for 1 min at each location at each session with a frequency of 2000 Hz using a GaAs diode laser instrument (Roland Serie Elettronica Pagani, wavelength 904 nm, frequency range of 5-7000 Hz, and maximum peak power of 27 W, 50 W, or 27 x 4 W). In Group II, placebo laser and the same exercise protocol was given for the same period. Patients were evaluated according to the parameters of pain, palpation sensitivity, algometric sensitivity, and shoulder joint range of motion before and after treatment. Analysis of measurement results within each group showed a significant posttreatment improvement for some active and passive movements in both groups, and also for algometric sensitivity in Group I (p < 0.05-0.01). Posttreatment palpation sensitivity values showed improvement in 17 patients (85%) for Group I and six patients (30%) for Group II. Comparison between two groups showed superior results (p < 0.01 and p < 0.001) in Group I for the parameters of passive extension and palpation sensitivity but no significant difference for other parameters. The results of our study have shown better results in palpation sensitivity and passive extension, but no significant improvement in pain, active range, and algometric sensitivity in laser treatment group compared to the control group in the patients with shoulder pain.

1.50 [micro sign]m CW operation of GaInNAs∕GaAs laser diodes grown by MOCVD

Room-temperature continuous-wave operation of a 1.5 µm range GaInNAs laser grown by metal organic chemical vapour deposition is reported. The lasing wavelength of the GaInNAs/GaAs double quantum well laser was 1.50 µm and the threshold current was 245 mA. The characteristic temperature between 10 and 50°C was about 119 K under pulse operation.

9.7 GHz small-signal bandwidth of three-quantum well GaInNAs∕GaAs laser diodes operating at 1.35 [micro sign

High frequency characterisation of three-quantum well GaInNAs/GaAs lasers operating at 1.35 µm is reported. A relaxation frequency as high as 7.4 GHz and a 9.7 GHz small-signal bandwidth are demonstrated, indicating the potential for high bit rate (10 Gbit/s) direct modulation of these dilute nitrides on GaAs devices.

THE POSSIBLE APPLICATION OF LOW REACTIVE-LEVEL LASER THERAPY (LLLT) IN THE TREATMENT OF MALE INFERTILITY: A preliminary report

The clinical use of low reactive level laser therapy (LLLT) has been reported in several aspects of bioactivation. This study reports an investigation into the possible application of LLLT for the treatment of male infertility. Four azoospermic and 16 oligospermic male patients were treated with a 6 mW HeNe12.5 mW pulsed GaAs diode laser with a dose of 1.3 i/cm2. Although no improvement was noted in the azoospermic subjects. the sperm count increased from 2 to 5 times in the oligospermic subjects. In addition, ejaculation of abnormal spermatozoa decreased in several subjects. Libido also increased in 15 of the 20 patients. From these findings it was concluded that LLLT offers a possible treatment for the oligospermic patient, particularly for the subfertile.

Structure optimisation of 1.3 μm (GaIn)(NAs)∕GaAs in-plane lasers

The comprehensive three-dimensional fully self-consistent model of the 1.3 /spl mu/m in-plane stripe-geometry (GaIn)(NAs)/GaAs diode laser has been applied to optimise its structure and to simulate its continuous-wave (CW) performance characteristics at and above room temperature (RT). To reduce the RT CW lasing threshold, optimal value of the laser stripe width has been found to be about 9 /spl mu/m. The current-spreading part of the p-type cladding layer below etched areas on both sides of the mesa should be as thin as possible for technological reasons. For a 130 K temperature increase over RT (= 300 K), the T/sub 0/ laser parameter has been determined to be 122 K. Its value is steadily reduced from 130 K (just above RT) to 116 K (at around 400 K).

Fabrication of GaAs laser diodes on Si using low-temperature bonding of MBE-grown GaAs wafers with Si wafers

We present a study of the properties of III–V structures integrated on Si by low-temperature GaAs–Si wafer bonding, using an intermediate spin-on-glass layer. Transmission electron microscopy revealed the good quality of the bonding and the absence of micro-cracks or dislocations in the semiconductor material. Photoluminescence measurements on GaAs/AlGaAs multiple quantum well structures bonded on Si confirmed that the structural integrity of the quantum wells was preserved during the wafer bonding and thinning process. Photoreflectance measurements at temperatures in the range of 80–300 K showed that the bonded GaAs layers were practically stress free at room temperature, while a tensile stress appeared at lower temperature, due to the different thermal expansion coefficients of GaAs and Si. Laser devices with etched mirrors were fabricated on silicon and exhibited similar performances with reference devices fabricated on a GaAs substrate.

Effect of low-power laser irradiation on cell growth and procollagen synthesis of cultured fibroblasts.

In dentistry, low-power lasers have been used in the treatment of dentin hypersensitivity, gingivitis, periodontitis, and different forms of oral ulcers. This in vitro study focuses on the biostimulation of NIH-3T3 fibroblasts by a low-power Ga-As-pulsed laser. We have studied cell growth and procollagen synthesis of cultured fibroblasts submitted to low-power laser irradiation with energy densities varying from 3 to 5 J/cm(2) over a period of 1-6 days. The light source was a 120 mW Ga-As diode laser (lambda = 904 nm). Growth curves and procollagen immunoprecipitation were obtained. Irradiation of 3 and 4 J/cm(2) increased the cell numbers about threefold to sixfold comparing to control cultures. However, this effect was restricted to a small range of energy densities since 5 J/cm(2) had no effect on cell growth. The energy density of 3 J/cm(2) remarkably increased cell growth, with no effect on procollagen synthesis, as demonstrated by the immunoprecipitation analysis. Our results showed that a particular laser irradiation stimulates fibroblast proliferation, without impairing procollagen synthesis.

Optical Absorption Rate Determination, on the Front Facet of High-Power GaAs Laser Diodes, by Means of Thermoreflectance Technique

Very-high-resolution thermoreflectance measurements have been used to study the light absorption occurring on the front facet of GaAs laser diodes, which is responsible for their damage. We determined the activation of the induced surface heat source for an injected current higher than the laser emission threshold current. This varying thermal behavior of the laser diode according to the value of the injected current has been used to determine the contribution to heat dissipation due to the surface source only. By identification using a thermal model we could evaluate for the first time the surface absorption rate both on coated and noncoated laser diodes. We propose it as a new reliability criterion, which enables discrimination of laser diodes both according to their coating and to their aging.

33-µm microcavity light emitter for gas detection

A room-temperature resonant-cavity light source emitting at 3.327 microm is presented. It combines a CdHgTe light-emitting layer, grown by molecular beam epitaxy, and two evaporated YF(3)-ZnS Bragg mirrors. The emitter is optically pumped by a commercial low-power GaAs laser diode. Compared with an unprocessed sample, this microcavity device shows a drastic (10-fold) linewidth reduction, a 3.3-fold intensity increase at 3.327 microm , and a 2.4-fold angular-spread decrease. The emitted optical power is 15 microW , and the device is used as a light source in a basic gas-detection setup. Measurements of a butane-propane mixture in the 1 to 5x 10(-3) bar range with a 5-cm-long single-path gas cell are demonstrated.

Cell Viability and DNA Denaturation Measurements by Two-Photon Fluorescence Excitation in CW Al:GaAs Diode Laser Optical Traps

Cell viability and DNA denaturation are measured through two-photon fluorescence excitation using a single diode laser beam as the trapping and exciting source simultaneously. Two-photon fluorescence emission spectra are presented for CHO cells and T lymphocytes loaded with various fluorescent probes. This single beam method is demonstrated to be a safe tool to monitor the viability of optically trapped cells, even under intense 809 nm diode laser illumination (∼106 W/cm2). The dynamics of cellular necrosis is monitored by adding ethanol to the cell suspension during trapping. Thermal damage to heat-treated samples is assessed by recording shifts in the emission spectra from trapped cells loaded with the nucleic acid probe, acridine orange. © 1999 Society of Photo-Optical Instrumentation Engineers.

GALLIUM ARSENIDE LASER TREATMENT OF CHRONIC LOW BACK PAIN: A PROSPECTIVE, RANDOMIZED AND DOUBLE BLIND STUDY

Patients of more than 60 years of age and affected by chronic low back pain were randomly assigned to two groups. Group A, consisting of 38 patients, was irradiated with a pulsed GaAs diode laser, 904 nm, pulse width 200 nsec, pulse frequency 10,000 Hz, peak power of 20 W, average power 40 mW, spot size 150 cm2 in area, and an angle of divergence of 6°. The laser was applied in the point technique with a dose of 4 J/cm2 per point in the area of pain. Group B, consisting of 33 patients, was treated with sham irradiation with a deactivated laser system. Neither the patient nor the operator knew to which group each patient was randomly assigned. The use of analgesic drugs and physical therapy was excluded in both groups. Ten daily consecutive sessions were carried out once per day. Pain was evaluated through an analogue and visual scale at the beginning and at the end of the treatment. Laser treatment was considered effective when pain relief was more than 60%. A follow up was carried out over the following 6 months. The treatment was effective in 71% of patients in group A, and 36.4% of group B (p < 0.007). The pain disappeared completely in 44.7% of group A and 15.2% of group B (p < 0.01). During the six month follow-up period, in those patients in whom the response to the treatment was effective, the pain recurred in 34.8% of group A and in 70% of group B. No cutaneous, ophthalmologic or systemic side effects were observed. These results suggest that irradiation with GaAs laser at the doses used and techniques applied in this study, relieves chronic low back pain in older patients in a statistically significant percentage of the patients but without causing any adverse side effects.