Violet Laser Diodes Research Articles

Wavelength Elongation of GaN-based Laser Diodes

Starting with next generation high density optical disc, commercial use of GaN based violet laser diodes (LD) has been adopted in many new fields, such as bio-medical, reprographic, exposure and etc. Recently, the lasing wavelength has broadened to cover from ultraviolet (UV) to blue-green region, which enabled other new applications. In this paper, current status of GaN based LDs in UV to Blue-green region are reported and next target is discussed.

Microlensed red and violet diode lasers in an extended cavity geometry

We examine the behavior of two microlensed diode lasers at 413 and 661 nm placed in both free-running and extended cavity geometries. The 25 mW free-running 413 nm diode shows current tuning over 40 GHz and the 50 mW, 661 nm diode shows tuning of 55 GHz. In extended cavity the 413 nm diode coarsely tunes 5 nm and finely tunes 6 GHz, with a linewidth of 4 MHz. The 661 nm diode coarsely tunes 11 nm with fine tuning of 6 GHz. Beam profile ratios for the 413 and 661 nm microlensed diodes are 1:1.06 and 1:1.10 respectively.

InGaN violet laser diodes grown by Molecular Beam Epitaxy

We report on the first InGaN quantum well laser diodes grown by molecular beam epitaxy (MBE). Devices were grown by gas-source MBE using ammonia as a source of nitrogen and elemental group III sources. The devices were grown on commercially available GaN template substrates. The lasers consist of a separate confinement heterostructure including an active region consisting of three In 0.1 Ga 0.9 N quantum wells with a nominal thickness of 2 nm. P-type doping of GaN and AlGaN cladding regions was obtained without the use of post-growth thermal annealing. The lasers were fabricated into a ridge-stripe geometry with ridge width of 5 pm and length of 500-1500 μm. Electron cyclotron resonance (ECR) dry-etching was used to fabricate the laser facets. Under pulsed current injection conditions, the lasers exhibit a room temperature threshold current density of 22 kA cm -2 emitting at 400 nm.

Photo‐induced absorption change for InGaN film by violet laser diode

AbstractWe have investigated photo‐induced absorption changes for In0.10Ga0.90N multiple quantum wells and a thin film induced by a continuous‐wave (cw) beam and a femtosecond pulse in the violet region. For the thin‐film sample, nearly the same absorption changes were observed in cw pumping and pulse pumping measurements. Screening of the piezoelectric field in InGaN heterostructures causes absorption changes around the band edge. This screening results from spatial separation of electron–hole pairs to the opposite sides of the InGaN epilayer. These spatially separated carriers are trapped in deep levels and maintain the absorption changes. The trapped charges are considered to be thermally excited to the conduction band and diffuse to attain the equilibrium state. This process takes on the order of 100 μs and such a long decay time of absorption changes allows us to have large absorption changes even by low‐intensity cw pumping. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of UV-excited fluorochromes by flow cytometry using near-ultraviolet laser diodes.

Violet laser diodes have become common and reliable laser sources for benchtop flow cytometers. While these lasers are very useful for a variety of violet and some ultraviolet-excited fluorochromes (e.g., DAPI), they do not efficiently excite most UV-stimulated probes. In this study, the next generation of InGaN near-UV laser diodes (NUVLDs) emitting in the 370-375-nm range have been evaluated as laser sources for cuvette-based flow cytometers. Several NUVLDs, ranging in wavelength from 370 to 374 nm and in power level from 1.5 to 10 mW, were mounted on a BD Biosciences LSR II and evaluated for their ability to excite cells labeled with the UV DNA binding dye DAPI, several UV phenotyping fluorochromes (including Alexa Fluor 350, Marina Blue, and quantum dots), and the fluorescent calcium chelator indo-1. NUVLDs at the 8-10-mW power range gave detection sensitivity levels comparable to more powerful solid-state and ion laser sources, using low-fluorescence microsphere beads as measurement standards. NUVLDs at all tested power levels allowed extremely high-resolution DAPI cell cycle analysis, and sources in the 8-10-mW power range excited Alexa Fluor 350, Marina Blue, and a variety of quantum dots at virtually the same signal-to-noise ratios as more powerful UV sources. These evaluations indicate that near-UV laser diodes installed on a cuvette-based flow cytometer performed nearly as well as more powerful solid-state UV lasers on the same instrumentation, and comparably to more powerful ion lasers on a jet-in-air system, and. Despite their limited power, integration of these small and inexpensive lasers into benchtop flow cytometers should allow the use of flow cytometric applications requiring UV excitation on a wide variety of instruments.

An optical microsensor to measure fluorescent light intensity in biofilms

We have developed an optical microsensor to quantify fluorescent light intensity distribution in biofilms. The optical system consisted of a beam splitter, light couplers, filters and a spectrophotometer able to accept the fiberoptic cable to measure fluorescent light intensity. The emitted light, fluorescence from the biofilm, was collected at the tip of the optical microsensor and was transferred to a spectrophotometer via a fiberoptic cable. The total fluorescent light intensity was evaluated from the emission spectrum by numerical integration. The newly developed fiberoptic microsensor was tested using a Staphylococcus aureus strain producing yellow fluorescent protein (YFP) grown as biofilm. We used a 405-nm violet laser diode for excitation, and measured the emission intensity between 480 nm and 540 nm. The optical microsensor that quantifies fluorescent light intensity is a promising tool in biofilm research which often requires detection and quantification of fluorescent light intensity distribution generated by various fluorescent proteins.

Rb$\mathsf{_{2}}$ diffuse band emission excited by diode lasers

We investigated collisional processes involved in the population of the Rb2 diffuse band through resonant excitation of Rb atoms. Near-infrared (780 nm) and violet (420 nm) diode lasers were used for the Rb first (\(\rm 5 ^{2}S_{1/2}\to 5 ^{2}P_{3/2}\)) and second (\(\rm 5 ^{2}S_{1/2}\to 6 ^{2}P_{3/2}\)) resonant doublet excitations. Laser induced fluorescence spectra were detected and investigated at different rubidium densities, buffer gas pressures and excitation wavelengths.

A novel type of 3-axis lens actuator with tilt compensation for high-density optical disc system

With the increase in recording density of digital versatile disc (DVD), it is necessary to shorten the wavelength of laser such as using violet laser diode and increasing the NA of objective lens in the optical pickup head systems. Thus, the margin for allowable disc tilt due to the wave-front aberration is much tighter than before. The conventional lens actuator can only adjust the lens in tracking and focusing direction to improve the spot quality of laser beam on the disc reflective layer. If the optical disc is not vertical with the laser beam, the lens actuator cannot compensate the aberration. Therefore, a 3-axis lens actuator which can be controlled in tilt direction of lens actuator with a novel structure as well as tracking and focusing directions is developed to diminish the aberration. This paper describes the structure of the actuator and its performance proved by the experimental results.

Using violet laser-induced chlorophyll fluorescence emission spectra for crop yield assessment of cowpea (Vigna unguiculata (L) Walp) varieties

The use of violet laser-induced chlorophyll fluorescence (LICF) emission spectra to monitor the growth of five varieties of cowpea in the University of Cape Coast Botanical Garden is presented. Radiation from a continuous-wave violet laser diode emitting at 396 nm through a fibre is closely incident on in vivo leaves of cowpea to excite chlorophyll fluorescence, which is detected by an integrated spectrometer with CCD readout. The chlorophyll fluorescence spectra with peaks at 683 and 731 nm were used for growth monitoring of the cowpea plants over three weeks and analysed using Gaussian spectral functions with curve fitted parameters to determine the peak positions, area under the spectral curve and the intensity ratio F683/F731. The variation in the intensity ratio of the chlorophyll bands showed sensitive changes indicating the photosynthetic activity of the cowpea varieties. A discussion of the fluorescence result as compared to conventional assessment is presented with regard to discrimination between the cowpea varieties in terms of crop yield performance.

MBE springs blue-violet laser diodes

Developed to comply with Blu-ray standards for next generation DVD storage and video applications, Sharp's demonstration of the world's first MBE produced violet laser diode raises a number of interesting issues.

Optical trapping and fluorescence excitation with violet diode lasers and extended cavity surface emitting lasers

Violet diode lasers and vertical extended cavity surface emitting lasers are used within an optical trapping system. Two distinct but related studies are performed. Firstly, the optical trapping efficiency in terms of the Q parameter for micron and sub-micron sized particles is determined. Secondly, we use the violet diode laser to observe and fluoresce 4'-6- Diamidino-2-phenylindole (DAPI) stained chromosomes, green fluorescent protein (GFP) transfected neuroblastomas, and fluorescent polymer spheres within an optical tweezers using a 1064nm trap laser. This work paves the way for both reduced trap volumes and for biological tagging, chromosome selection, or observing protein dynamics.

Low dislocation density, high power InGaN laser diodes

We used single crystals of GaN, obtained from high-pressure synthesis, as substrates for Metalorganics Vapor Phase Epitaxy growth of violet and UV laser diodes. The use of high-quality bulk GaN leads to the decrease of the dislocation density to the low level of 105 cm−2, i.e. two orders of magnitude better than typical for the Epitaxial Lateral Overgrowth laser structures fabricated on sapphire. The low density and homogeneous distribution of defects in our structures enables the realization of broad stripe laser diodes. We demonstrate that our laser diodes, having 15 μm wide stripes, are able to emit 1.3-1.9 W per facet (50% reflectivity) in 30 ns long pulses. This result, which is among the best ever reported for nitride lasers, opens the path for the development of a new generation of high power laser diodes.

AlGaInN Violet Laser Diodes Grown on GaN Substrates with Low Aspect Ratio

AlGaInN violet laser diodes grown on GaN substrates have been studied. Waveguide simulations have been performed and perpendicular radiation angles have been investigated. A peculiar layer structure has been proposed to reduce the perpendicular radiation angle and compared with a conventional laser. The laser structure has an n-cladding layer consisting of three AlGaN films, the middle film of which has relatively high Al composition. A laser diode with an optimized structure has been fabricated. The threshold current density and slope efficiency have been 2.9 kA/cm2 and 1.4 W/A, respectively. The perpendicular radiation angle has been as small as 16.2°. The AlGaInN violet laser diode with a low aspect ratio of 1.6 and a small threshold current of 29 mA has been realized.

The Evolution of Blue Light-Emitting Devices and Nitride Semiconductors

Breakthroughs in crystal growth and conductivity control of nitride semiconductors during last two decades have led to such developments as high-brightness blue, green and white light-emitting diodes and long-lived violet laser diode and so forth. The high electron saturation velocity in GaN is also suitable for application in high-speed/high power electronic devices. All of these nitride-based devices are the most environmentally-friendly ones available. They are tough and should enable a tremendous saving in energy. Further progress in the area of crystal growth and device engineering is necessary for the development of new frontier devices based on nitride semiconductors.

Discrimination of the Hoechst side population in mouse bone marrow with violet and near-ultraviolet laser diodes.

Discrimination of stem cells with flow cytometric analysis of Hoechst 33342 efflux by the ABCG2 transporter (termed the Hoechst side population, or SP technique) is a valuable methodology for identifying bone marrow progenitors enriched with stem cells. Unfortunately, it requires a ultraviolet (UV) laser source, usually necessitating an expensive and maintenance-intensive argon- or krypton-ion gas laser on a large-scale cell sorter. In this study, we evaluated the ability of recently available violet and near-UV laser diodes to discriminate Hoechst SP on smaller cuvette-based flow cytometers. Violet laser diodes (emitting at 408 and 401 nm) and a near-UV laser diode (emitting at 370 nm) were mounted on a BD Biosciences LSR II and evaluated for their ability to discriminate Hoechst SP in murine bone marrow. The violet laser diodes discriminated the Hoechst SP, but with poorer resolution than with the standard UV gas laser on a large-scale cell sorter. The near-UV laser diode, in contrast, gave excellent Hoechst SP resolution. These evaluations indicated that near-UV laser diodes give excellent Hoechst SP resolution on cuvette-based instruments. As the next generation of cell sorters integrate cuvette-based cell interrogation into conventional jet-in-air cell separation, these laser sources should become applicable for analysis and physical separation of Hoechst SP cells.

A fluorescent natural product for ultra sensitive detection of proteins in one-dimensional and two-dimensional gel electrophoresis.

Lightning Fast is a sensitive fluorescence-based stain for detecting proteins in one-dimensional and two-dimensional polyacrylamide electrophoresis gels. It contains the fluorophore epicocconone from the fungus Epicoccum nigrum that interacts noncovalently with sodium dodecyl sulfate and protein. Stained proteins can be excited optimally by near-ultraviolet light of about 395 nm or with visible light of about 520 nm. The stain can be excited using a range of sources used in image analysis systems including UVA (ca. 365 nm) and UVB (ca. 302 nm) transilluminators; Xenon-arc lamps; 488 nm and 457 nm Argon-ion lasers; 473 nm and 532 nm neodymium: yttrium aluminum garnet (Nd:YAG) solid-state lasers; 543 nm helium-neon lasers, and emerging violet, blue and green diode lasers. Maximum fluorescence emission of the dye is at approximately 610 nm. The limit of detection in one-dimensional gels stained with Lightning Fast protein gel stain is less than 100 pg of protein, rivaling the current limits of matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). Lightning Fast was found to be considerably more sensitive than SYPRO Ruby, SYPRO Orange, silver and Coomassie Brilliant Blue G-250 in matched experiments. Staining takes as little as 3.5 h and stained proteins displayed quantitative linearity over more than four orders of magnitude, thereby allowing visualization of entire proteomes. Lightning Fast protein gel staining is compatible with subsequent peptide mass fingerprinting using MALDI-MS and Edman-based sequencing chemistry.

Recent progress of high power GaN‐based violet laser diodes

High performance laser diodes were fabricated on lateral epitaxial overgrown GaN layers on sapphire substrates. The threshold current of the LDs was strongly dependent on the dislocation density. A low threshold voltage was obtained using highly Mg doped contact layers. The lifetime of LDs was also influenced by the operation voltage. Threshold current density and threshold voltage were 3.74 kA/cm2 and 4.8 V, respectively. The LDs showed a lifetime of 1,000 hs at 50 °C under automatic power controlled conditions of 30 mW. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Efficient magneto-optical trapping of Yb atoms with a violet laser diode

We report the first efficient trapping of rare-earth Yb atoms with a high-power violet laser diode (LD). An injection-locked violet LD with a 25 mW frequency-stabilized output was used for the magneto-optical trapping (MOT) of fermionic as well as bosonic Yb isotopes. A typical number of $4\times 10^6$ atoms for $^{174}$Yb with a trap density of $\sim 1\times10^8/$cm$^3$ was obtained. A 10 mW violet external-cavity LD (ECLD) was used for the one-dimensional (1D) slowing of an effusive Yb atomic beam without a Zeeman slower resulting in a 35-fold increase in the number of trapped atoms. The overall characteristics of our compact violet MOT, e.g., the loss time of 1 s, the loading time of 400 ms, and the cloud temperature of 0.7 mK, are comparable to those in previously reported violet Yb MOTs, yet with a greatly reduced cost and complexity of the experiment.

AlGaInN violet laser diodes grown on GaN substrates with low aspect ratio

AlGaInN violet laser diodes grown on GaN substrates have been investigated. Waveguide simulations have been performed and a triple-cladding-layer (TCL) technique has been proposed for achieving a small radiation angle in the perpendicular direction to the junction plane. A TCL-type laser has been fabricated. The threshold current density and the slope efficiency were 2.9 kA/cm2 and 1.4 W/A, respectively. The radiation angle in the perpendicular direction was as small as 16°. A violet laser diode with a low aspect ratio of 1.6 has been realized. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Super high-power AlGaInN-based laser diodes with a single broad-area stripe emitter fabricated on a GaN substrate

AlGaInN-based blue–violet laser diodes with a single broad-area stripe emitter were successfully fabricated on GaN substrates. Three stripe widths were examined; 10, 50, and 100 μm, and the maximum light output power of 0.94 W under cw operation at 20 °C was achieved for the sample with a stripe width of 10 μm. A super high-power laser diode array was fabricated using 11 of these high-performance laser chips, with a resultant output power of 6.1 W under cw operation at 20 °C. This result represents the highest reported output power for blue–violet laser diodes. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)