Visible Laser Diodes Research Articles

Phase-locked optical divide-by-3 system for visible radiation

An optical divide-by-3 system has been developed to phase lock a diode-pumped Tm:YAG laser at 148 THz (2022 nm) to a frequency near 1/3 that of an ultrastable diode laser system at 445 THz (674 nm). The 148-THz radiation is frequency doubled in angle-tuned AgGaS(2) and frequency differenced with the 445-THz radiation in noncritically phase-matched LiNbO(3) , generating two signals at 297 THz, which are mixed on a photodiode. An electronic servo system is used to control the frequency of the Tm:YAG laser and to phase lock it to the visible diode laser output. Phase-locking periods of several minutes are routinely obtained.

Absolute distance meter based on a frequency-modulated laser diode

This article describes a distance measuring instrument based on a frequency-modulation continuous wave interferometer implemented in a compact setup suitable for industrial applications. The prototype uses a visible laser diode that is frequency-modulated with a triangular wave form. Measurements carried out with a cooperative target show a measuring range from 130 to 300 mm with a relative accuracy of 1.2×10−3.

Visible diode laser induced fluorescence detection for capillary electrophoretic analysis of amantadine in human plasma following precolumn derivatization with Cy5.29.OSu

Visible diode laser induced fluorescence (VDLIF) detection (620–700 nm) has become important in bioanalysis due to the increased sensitivity and selectivity that can be achieved in biological matrices. A selective and sensitive capillary electrophoretic method employing VDLIF detection has been developed for the analysis of amantadine in plasma. Amantadine was extracted from plasma into toluene under alkaline conditions and the residue was derivatized with the far-red label Cy5.29.OSu. The reaction mixture was dried under nitrogen, reconstituted and then injected onto a laboratory constructed capillary electrophoresis system equipped with a laboratory constructed visible diode laser detector temperature tuned to oscillate at 647.8 nm. The selectivity of the technique was evaluated by demonstrating a lack of interfering peaks in extracts of blank plasma. A calibration curve ranging from 1.8 to 461.1 ng ml −1 was shown to be linear. The precision and accuracy of the assay ( n=6) were determined to be within 17% R.S.D. and 15% difference from the nominal concentration respectively. The limits of detection for unextracted amantadine and for amantadine from the extracted concentrate from plasma were determined to be 9.5 fmol and 115 amol respectively.

High-performance 670-nm AlGaInP/GaInP visible strained quantum well lasers

We have grown high-performance AlGaInP/GaInP visible (670 mn) strained quantum well lasers by low-pressure metalorganic chemical vapor deposition. With AlInP cladding layer, a high-power AlGaInP/GaInP visible laser diode is achieved. Its threshold current is about 30 mA. The output power of this laser diode can maintain, at least, at 32 mW under continuous-wave (CW) operation at room temperature. High slope efficiency (0.8 mW/mA) and differential quantum efficiency (0.87) can be achieved. To improve beam quality, AlGaInP/GaInP visible lasers with and without depressed index cladding layer are theoretically and experimentally studied. From experimental results, the transverse beam divergence can be reduced from 41.4/spl deg/ to 26.2/spl deg/ while maintaining a low threshold current (from 36 mA to 46 mA). By using the transfer matrix method, our theoretical calculations are in good agreement with the experimental results.

Portable autocollimators using the laser diode and the position sensitive detector

We were able to simplify the structure of the autocollimators and enhance the performance by using one- and two-axis PSDs (position-sensitive detectors) which have spatial resolution of 0.1 and 2.5 μm, respectively, with little dependence on the spot size of incident beam and the visible laser diodes as the light source. Two kinds of portable autocollimators which can measure angles with resolutions 0.01″ and 0.1″, respectively, were made. They were calibrated by the reference angle generator which employed the laser interferometer. The characteristics of temporal stability were evaluated and the profile of a test surface was measured.

Low-threshold laterally oxidized GaInP-AlGaInP quantum-well laser diodes

Low-threshold, high-efficiency edge-emitting visible AIGaInP-GaInP laser diodes using a buried AlAs native oxides for carrier and optical confinement are described. The lasers incorporate a thin AlAs layer in the upper cladding region, which when laterally wet oxidized, forms a narrow aperture. The lasers operate with room temperature, continuous-wave (CW) threshold currents of 11 mA with external differential quantum efficiency of 34% per facet for an uncoated 300-/spl mu/m-long 3.5-/spl mu/m-wide device. As-fabricated lasers exhibited modest performance under CW operation. Post-fabrication annealing was shown to dramatically improve the device characteristics.

Frequency stabilization of 0.68μm InGaAIP visible laser diode

This paper describes a method for obtaining a frequency stabilized laser diode with a Fabry-Perot resonator as a frequency standard, if which resonance frequency is slightly modulated, ie, wobbled. It was confirmed that AFC circuit functioned normally.

Laterally oxidized GaInP/AlGaInP quantum well visible laser diodes

High efficiency, low threshold visible AlGaInP/GaInP laser diodes using a buried AlAs native oxide for carrier and optical confinement are described. The lasers incorporate a thin AlAs layer in the upper cladding region, which when laterally wet oxidized, forms a narrow aperture. The lasers exhibited modest performance under continuous wave (cw) operation. Low temperature (400 °C) post-fabrication annealing was shown to dramatically improve the device characteristics. The lasers operate with room temperature cw threshold currents of 20 mA with external differential quantum efficiencies of 27% per facet (0.25 W/A per facet) for an uncoated 625-μm-long, 3.5-μm-wide device.

Pulse duration limitations in a diode-pumped femtosecond Kerr-lens mode-locked Cr:LiSAF laser

We describe the results of experimental investigations into the minimisation of the pulse duration from a diodepumped Kerr-lens mode-locked Cr:LiSAF laser. Specifically, the effects on performance of changing the intracavity dispersion characteristics and the laser cavity mirrors are investigated and described. Pulse durations of less than 20 fs have been recorded. PACS: 42.55R; 42.60F In recent years there have been exciting developments in femtosecond laser technology, exploiting the wide bandwidth of solid-state laser materials such as Ti:sapphire and Cr:LiSAF. There have been significant improvements in both the convenience and performance of femtosecond pulse lasers, and this has encouraged a rapid expansion in the application of such sources, e.g. in time-resolved spectroscopic studies, biological imaging, and nonlinear optics. One aspect of femtosecond laser technology that has attracted special attention is the development of all-solid-state diode-pumped femtosecond solid-state lasers (DPFSSLs). These systems bring well-known advantages such as efficiency, compactness, reliability, and stability, all of which will help bring about the fullest exploitation of the potential of ultrashort pulse lasers. A number of alternative approaches to DPFSSLs have been demonstrated. The most attractive option, at least in terms of convenience and simplicity, is the direct-diode pumping of a suitable broadband gain material. Systems to date have typically used the material Cr3+:LiSrAlF6 (Cr:LiSAF) [or its sister material Cr3+:SrGaF6 (Cr:LiSGAF)] pumped with visible 670-nm laser diodes. Recently, the technique of Kerr-lens modelocking (KLM) (also known as self-mode locking) has been optimised for use in these diode-pumped lasers [1, 2] and proven to be both reliable and flexible. Semi-conductor saturable absorbers have been used as an alternative mode∗Current address: Microlase Optical Systems Ltd., 141 St. James Road, Glasgow, G4 ONG, UK locking technique, and several designs have been used successfully, see e.g [3–5]. Although a wide range of DPFSSLs have been reported, most of the progress in reducing the minimum pulse duration obtained from femtosecond lasers has occurred in systems which are not all-solid-state. Work in this field has been dominated by KLM Ti:sapphire laser systems, pumped with an argon ion laser (or frequency doubled flashlamp pumped Nd:YAG laser). Recently, there has been considerable progress in this field, for example [6, 7], and pulses as short as 7.5 fs have been produced [7]. This dramatic progress has been important in enabling new applications and studies to be made in previously inaccessible regimes. Ti:sapphire is used because it has a very wide emission bandwidth, and because its excellent thermal and spectroscopic properties allow high output powers. However, the absorption regions of Ti:sapphire are not compatible with direct diode pumping and this may act as a barrier to the full exploitation of the very short pulses which have been produced in these systems. In this paper we report on investigations into minimising the pulse duration from a diode-pumped Cr:LiSAF laser. Cr:LiSAF clearly has the required bandwidth, at 1900 cm−1 to support much shorter pulse durations than the 30 fs or longer typically seen in systems reported to date [2, 8–11], and there are many applications which would benefit from obtaining pulse durations closer to the sub-10-fs regime, in a convenient all-solid-state laser source. 1 Experimental background 1.1 The diode-pumped KLM Cr:LiSAF laser The Cr:LiSAF laser used for the experiments described in this paper is similar in design to the first reported KLM diodepumped Cr:LiSAF laser [1]. In a higher-power version of this laser we have previously reported routine operation with output powers of up to 42 mW at pulse durations down to 34 fs [2]. Also, in a similar laser we have reported on the generation of pulses as short as 18 fs in duration [12], al-

Low operating current and high temperature operationof650 nm AlGaInP visible laser diodes with real refractiveindex guided self-aligned structure

High temperature operation at up to 90°C has been achieved in 650 nm-band AlGaInP visible laser diodes with a real refractive index guided self-aligned structure using an AlInP current blocking layer. The operating current is as low as 45 mA under CW operation at 60°C and the characteristic temperature is 120K from 20 to 60°C.

Observation of CO and CO_2 absorption near 157 µm with an external-cavity diode laser

Near-IR and visible room-temperature diode lasers in broadly tunable external-cavity configurations are becoming commercially available for gas-sensing applications. Near 1.57 mum, a coincidence of overtone and combination-band transitions from CO, CO(2), OH, and H(2)O is particularly interesting for combustion and combustor emissions monitoring. We report initial observations of the room-temperature absorption of CO and CO(2) made with a commercial external-cavity diode laser.

Low-noise 650-nm-band AlGaInP visible laser diodes with a highly doped saturable absorbing layer

Stable self-sustained pulsating and low-noise 650-nm-band AlGaInP visible laser diodes were demonstrated by adopting a novel structure, which has a highly doped saturable absorbing (SA) layer. Short carrier lifetime, which is indispensable for self-pulsation, was realized by applying high doping concentration to the p-type SA layer. 500-/spl mu/m-long devices with 51%/51% coated facets were fabricated, resulting in the threshold current of 75 mA at 20/spl deg/C. The temporal output power was measured at the average output power of 5 mW and the stable self-pulsation was observed up to an ambient temperature of 60/spl deg/C. Therefore, the relative intensity noise (RIN) was kept about -140 dB/Hz in temperature ranging from 20/spl deg/C to 60/spl deg/C. Since the refractive index difference could be kept large and the optical mode could be confined effectively, the astigmatism in this work was below 3 /spl mu/m at 5 mW against dc injection current. The lasers operated over 1350 h under the average output power of 5 mW at 60/spl deg/C.

A High Sensitivity Laboratory Constructed HPLC - VDLIF Detector Evaluated with An Oxazine Reagent

An HPLC - visible diode laser induced fluorescence detector (VDLIF) has been constructed and its performance evaluated using nile blue, a far red oxazine reagent. The divergent output beam of the diode laser was collimated to an elliptical shaped beam using a collimating lens. The spot size of the collimated beam was then reduced to a diameter of 200 μm × 135 μm using a microscope objective lens. The diode laser beam illuminated a volume of 21 nanoliters in an 8.0 microliter rectangular flow cell. The energy flow through the VDLIF detector was determined, both theoretically and experimentally, with similar values being obtained. The linear dynamic range of the VDLIF detector extended over six orders of magnitude (1 × 10−9 M - 1 × 10−14 M). A limit of detection (S/N= 3) of 5 × 10−15M was obtained by injection of 50 μL aliquots of nile blue onto a reversed phase column.

Reliability study on 50-100-mW CW operation of 680-nm visible laser diodes with a window-mirror structure

We have studied reliability of 680-nm visible laser diodes (LDs) with a window-mirror structure formed by zinc-diffusion-induced disordering of GaInP quantum wells. Aging tests under the condition of CW output power in the range of 50-100 mW for ambient temperature from 40/spl deg/C to 70/spl deg/C have been carried out for 650-/spl mu/m-long LDs and 900-/spl mu/m-long LDs with three kinds of the front facet reflectivities (1.5%, 6% and 13%). In all tests, laser operation was stable for over 5000 h. For example, reliable 500-10000-h operation of the 900-/spl mu/m LDs was realized under the conditions of output power of 50 mW at 70/spl deg/C, 70 mW at 60/spl deg/C, and 100 mW at 40/spl deg/C for the first time. By various aging test results, dependence of the temperature and the output power on increase of the operating current has been investigated. Also, influences of the facet reflectivities and the cavity lengths on the reliability have been studied with focus on the optical power density and the current density. Consequently, it has been clarified that the degradation of the window LDs rather strongly depends on the operating current density than the optical power density. Moreover, it has been proven that the reliability of the window LDs is effectively improved by the reduction of the operating current density due to extension of the cavity length.

High-Power 650-nm-Band AlGaInP Visible Laser Diodes Fabricated by Reactive Ion Beam Etching Using Cl 2/N 2 Mixture

High-power 650-nm-band AlGaInP visible laser diodes having stable fundamental-transverse-mode at high temperatures were produced using electron cyclotron resonance reactive ion beam etching (ECR-RIBE). Epilayers were etched using a Cl2/N2 mixture gas, resulting in very smooth surfaces and symmetric laser mesas. Lasers that are 700-µm-long and 6%/80% coated were fabricated. The typical threshold current of these devices was as low as 46 mA at room temperature, and a stable fundamental-mode operation over 30 mW is obtained up to 70°C. The lasers operated for over 1000 h at 60°C under an output power of 25 mW, and their degradation rate was as low as lasers fabricated by the ordinary wet etching process.

Fabrication of AlGaInP/GaInP Laser Diodes by Molecular Beam Epitaxy

Room temperature pulse operation for AlGaInP/GalnP visible laser diodes prepared by gas source molecular beam epitaxy (GSMBE) have been successfully fabricated and demonstrated. In this report, two kinds of laser structures, the lattice-matched quantum well double heterostructure (DH) and the grade-index separate- confinement heterostructure (GRIN-SCH) stained quantum well structure are characterized. Measurements of photoluminescence (PL) intensity, L-I curves and wavelength spectra of these two structures all exhibit lasing properties. At room temperature, it is found that induced lasing phenomena has a full width half maximum (FWHM) of 2.1 nm and 0.5 nm, respectively. The emitting wavelengths range from 6500 Å to 6850 Å.

Development of a 2D solid state LDA for velocity measurements in turbulent bearing flow

A two-dimensional solid state LDA system was developed for the measurement of turbulent flow in a test journal bearing. Visible laser diode and avalanche photodiode were employed in the design of the LDA optics and optical frequency shifts were used to separate signals and remove directional ambiguity. Special techniques were tested to minimize the influence of the diffused light from the shaft surface and make valid measurements near the walls. Two-component measurements were made in a journal bearing with a minimum gap of 0.49 mm and velocity profiles under different Reynolds numbers were obtained.

Application of Rhodamine 800 for Reversed Phase Liquid Chromatographic Detection Using Visible Diode Laser-Induced Fluorescence

This study reports the application of rhodamine 800, a far-red dye, suitable for excitation using visible diode laser-induced fluorescence (VDLIF) detection. A reagent synthesized from rhodamine 800 was evaluated as a precolumn reagent for derivatization with amino-containing analytes. The derivative of this reagent with primary amine analytes showed a loss of fluorescence. Rhodamine 800 was then applied as a mobile phase additive in the indirect mode for quantitation of valproic acid in plasma using reversed phase HPLC in combination with VDLIF detection. A visible diode laser (output power 8.50 mW) temperature-tuned to oscillate at 674.70 nm was used as a light source for a laboratory constructed HPLC fluorescence detector. A liquid/liquid extraction procedure was applied to human blank plasma. The selectivity of this method was validated by demonstration of a lack of interfering peaks in extracts of plasma (n = 3 sources). A calibration curve for valproic acid between 40 and 200 μg/mL was shown to be linear (r = 0.9932). The recoveries of valproic acid at concentrations of 50 and 100 μg/mL were evaluated and determined to be 73 and 72%, respectively. The precision and accuracy (n = 5) of the assay was within 7.0% RSD and 8.0% difference from the spiked concentration, respectively. The limits of detection (S/N = 3) for extracted and unextracted valproic acid were 15.0 and 11.54 μg/mL, respectively. The theoretical (C(lim)) and practical (C(det)) limits of detection in the detector flow cell for unextracted valproic acid at a S/N = 1 were found to be within 15%.

An oxazine reagent for derivatization of carboxylic acid analytes suitable for liquid chromatographic detection using visible diode laser-induced fluorescence

This study reports the use of Nile Blue, an oxazine dye, as a derivatization reagent that fluoresces in the far-red spectral region and is suitable for derivatization with carboxylic-acid-containing analytes. Model carboxylic acid analytes such as benzoic acid, acetic acid, phenylacetic acid and hexanoic acid have been reacted as acid chlorides to form Nile Blue derivatives. The synthesis product of the Nile Blue benzoic acid derivative was confirmed using electrospray-mass spectrometry, infrared spectrometry, 1H and 13C nuclear magnetic resonance, reversed phase liquid chromatography (RP-HPLC), normal phase-thin layer chromatography, and spectral characterization. The synthesized Nile Blue derivatives, separated from reaction by-products with RP-HPLC, all demonstrated an approximately 10-fold drop in molar absorptivity and relative quantum yield. In addition, a 40 nm increase in Stokes shift was observed. A portion of the fluorescence was regained through post-column ionization of the Nile Blue benzoic acid derivative at pH 12. A RP-HPLC limit of detection of 88.25 fmol on column has been reported with conventional fluorescence detection-post-column ionization of the Nile Blue benzoic acid derivative. A limit of detection of 1.99 fmol on column (3.98 × 10 −11M) has been demonstrated for the Nile Blue benzoic acid derivative with the use of a laboratory-constructed visible diode laser fluorescence detector.

Visible laser diodes grown by metal organic vapourphase epitaxy (MOVPE)

Visible (682 nm) InAlGaAs oxide stripe lasers have been fabricated on atmospheric pressure MOVPE grown material. Lowering the oxygen residue of the metal organic reagents allows uniform deposition of high optical quality InAlGaAs QWs at ~600°C. A separate confinement heterostructure laser using a single QW lased at room temperature with J∞ of 1.23 kAcm-2.