Blue-green Laser Research Articles

Study of current-voltage characteristic in a ZnSe-based II-VI laser diode

High operating voltage in a blue-green laser diode was explained quantitatively by the tunneling process through the barrier at a metal/p-ZnSe interface. The barrier height at the metal/p-ZnSe interface was evaluated considering the tunneling and thermionic emission processes in the realistic diode structure.

Compact blue-green lasers get down to business

The development of solid-state, blue-green lasers, which are emerging as viable alternatives to air-cooled argon and helium-cadmium lasers for such applications as flourescent bioanalysis, optical inspection, and high-end reprographics, is summarized. Methods of efficient doubling in diode-pumped lasers, direct doubling, second harmonic generation in waveguides, and intracavity frequency mixing are discussed. The limited marketing impact of these technologies is also discussed. >

Randomized Comparison of Krypton versus Argon Scatter Photocoagulation for Diabetic Disc Neovascularization: The Krypton Argon Regression Neovascularization Study Report Number 1

The Krypton Argon Regression of Neovascularization Study (KARNS) was designed to compare the efficacy of red krypton versus blue-green argon laser photocoagulation for the management of high-risk proliferative diabetic retinopathy. A prospective, randomized clinical trial was performed in 24 clinical centers. Patients (n = 696, 907 eyes) with diabetes and neovascularization of the disc (NVD) of one-third disc area or greater in extent were assigned at random to either argon or krypton laser scatter (panretinal) photocoagulation. The major endpoint of the regression of NVD to less than one-third disc area in extent at 3 months was evaluated by comparisons of gradings of the fundus photographs obtained at baseline and follow-up. At 3 months' follow-up, the proportion of eyes with regression of NVD to less than or equal to one-third disc area in extent were 41.1% in the argon-treated group and 41.8% in the krypton-treated group (P = 0.92). The odds of regressing to this extent of NVD at 3 months for argon-treated eyes versus krypton-treated eyes was 0.98 (95% confidence interval, 0.74-1.31). Scatter laser photocoagulation with either krypton red or argon appears to be equally effective in the treatment of proliferative diabetic retinopathy with NVD.

Development and characterization of II–VI blue-green diode lasers

In this paper, we report the growth and characterization of II–VI devices grown by molecular beam epitaxy (MBE). The n-type doped ZnSe epilayers were obtained using iodine fom an electrochemical cell and nitrogen from a RF plasma source was used for p-type doping. Capacitance-voltage ( C-V) electrochemical profiling of layers and devices has been used to ensure uniform n-type and p-type doping. The nitrogen doped epilayers show a compensation process which leads to the suggestion of a new deep donor which is a complex, such as the (V Se-Zn-N Se) single donor which involves native Se vacancies. The fabrication of pn laser diodes and ZnSe/Zn 0.82Cd 0.18Se quantum well (QW) laser diodes is reported. The pn junctions show blue laser emission between 448–473 nm under pulsed current conditions at 4.2 K and the QW laser diode shows an excellent mode structure and emits at 474.8 nm at 77 K in pulsed mode operation.

Theoretical aspects of blue-green II–VI strained quantum well lasers

In this article, a theoretical overview of blue-green quantum well lasers with emphasis on ZnSe-based materials is presented. The effects of biaxial strain on the linear and nonlinear optical gains of a strained-layer II–VI quantum-well blue-green laser are studies with band mixing effects taken into account. The gain and gain-suppression coefficient of a strained quantum well laser are calculated from the complex susceptability obtained by the density matrix formalism. The calculated gain of a CdZnSe-ZnSSe quantum well shows enhancement with increasing biaxial compressive strain in a quantum well. It is shown that the theoretical model employed in this study gives very good agreement on the L-I curve as well as the peak gain position of the quantum well structure with experiment. Feasibility of ZnSSe-MgZnSSe quantum wells with tensile strain and CdZnTe-ZnTe quantum wells with compressive strain on the optoelectronic device applications is also studied.

Room temperature continuous operation of blue-green laser diodes

Continuous-wave operation in wide-gap II-VI semiconductor current injection laser diodes at room temperature has been demonstrated for the first time. Stimulated emission was observed at a wavelength of 523.5 nm with a threshold current of 45 mA (1.4 kA/cm2) from ZnCdSe/ZnSe/ZnMgSSe single-quantum-well (SQW) separate-confinement heterostructure (SCH) laser diodes.

Panretinal photocoagulation in diabetic retinopathy: Argon versus dye laser coagulation

The range of wavelengths used in ophthalmic photocoagulation treatment has been greatly enlarged by the development of the dye laser. To investigate the efficacy and possible side effects of orange dye laser light in the treatment of diabetic retinopathy, we performed a prospective, controlled clinical study comparing argon blue-green and orange dye laser light. In 14 patients with diabetic retinopathy of equal severity in both eyes one eye was randomly assigned to either blue-green argon (488 and 514.5 nm) or orange dye (600 nm) panretinal laser treatment. The total coagulated area was the same in both eyes. Subjective parameters (visual acuity, perimetry, color vision) as well as objective functions (electroretinography, electro-oculography) and the clinical course were studied preoperatively and then postoperatively over a period of 6 months. Dye laser coagulation proved as effective and safe as blue-green argon laser coagulation in the panretinal treatment of diabetic retinopathy. No significant differences in postoperative retinal function were detected. However, orange laser coagulation proved significantly more painful than blue-green argon laser treatment (P = 0.002).

Optical physics and laser devices in II–VI quantum confined heterostructures

We review some of the recent advances in wide-gap II–VI heterostructures, with emphasis on device physics and engineering of quantum confinement in ZnSe-based multilayer structures for blue-green diode lasers and LEDs. An important element in these quantum well configurations are quasi-two-dimensional exciton effects which dominate absorption but are also of relevance in both spontaneous and stimulated emission processes.

Blue-green II–VI laser diodes

The first blue-green laser diodes were demonstrated in our laboratories in early April 1991 using wide band gap II–VI semiconductors. Since then, devices with emission wavelengths from 508 to 535 nm have been obtained in the pulsed mode at room temperature with threshold current densities about 1000 A/cm 2. Continuous wave devices have also been operated at 80 K emitting more than 3 mW/facet. These diodes are separate confinement devices with single Cd x Zn 1− x Se strained quantum wells within ZnSe p-n junctions. Optical confinement is accomplished by surroundings the ZnSe guide with ZvS 0.07Se 0.93 cladding layers. Characteristics of these devices and the issues standing in the way of commercializing II–VI LEDs and diode lasers are discussed.

Heavy p-doping of ZnTe by molecular beam epitaxy using a nitrogen plasma source

The successful p-doping of ZnSe and Zn(S,Se) using a nitrogen plasma source during growth by molecular beam epitaxy has been an important factor leading to the recent realization of blue-green diode lasers and light-emitting diodes. This letter reports the results of the nitrogen doping of ZnTe using similar techniques. Doping levels approaching the 1019 cm−3 range are reported along with electrical, optical, and microstructural characterization. Highly doped ZnTe provides an opportunity for forming an ohmic contact to p-ZnSe.

Pulsed room-temperature operation of a blue-green ZnSe quantum-well diode laser

Low-threshold current density operation has been obtained from (Zn, Cd)Se/Zn(S, Se) quantum-well diode lasers in the blue-green spectrum. The devices, with reflective facet coatings, have been operated at room temperature under pulsed conditions with threshold current densities of I(th) approximately 1 kA/cm(2).

Blue-green buried-ridge laser diodes

Summary form only given. An attempt is being made to develop short wavelength (green and blue) laser diodes with performance suitable for use in optical data storage systems. Buried-ridge laser diodes operating in the blue-green ( lambda =511 nm) are reported. The starting material is a separate-confinement heterostructure consisting of a strained, pseudomorphic CdZnSe quantum well, ZnSSe light-guiding layers, and MgZnSSe cladding layers. The II-VI layers are grown by MBE (molecular beam epitaxy) and are nominally lattice-matched to the GaAs substrate. Ridges, typically 2 or 3 mu m wide, are formed using ion beam etching, and are subsequently buried with ZnS in a self-aligned process that results in a planar surface. Laser diodes with room-temperature pulsed threshold currents of 2.5 mA have been obtained. Single lateral model operation is indicated by the far-field pattern of these devices. >

Light Emission from Quantum Well Structures Containing ZnS, ZnSe, and Related Alloys

Properties of blue and blue-green laser diodes with ZnCdSe single- and multiple-quantum-well active regions are discussed. Blue, blue-green, and green light emitting diodes which employ ZnCdSe or ZnSTeSe as the active region of double heterostructure devices have also been prepared and tested. Properties of ZnS-ZnSSe and ZnS-ZnCdS quantum well structures are also reported. These structures emit intense photoluminescence in the ultraviolet spectral region.

Report on Topical Meeting of Advanced Solid State Lasers and Compact Blue-Green Lasers.

Report on Topical Meeting of Advanced Solid State Lasers and Compact Blue-Green Lasers.

Epitaxial Growth, Fabrication, and Performance of Ingaas Strained Quantum Well Laser Structures

ABSTRACTThere is considerable interest in InGaAs/GaAs strained quantum well lasers for applications within the 0.9 to 1.1 μm wavelength range, such as high power lasers for Efdoped fiber amplifiers and rare-earth-ion solid state lasers, obtaining blue-green laser emission by frequency doubling, and optoelectronic integrated circuits. Epitaxial growth of these structures by organometallic vapor phase epitaxy, molecular beam epitaxy, and gas source molecular beam epitaxy will be discussed. The relative merits of AlGaAs and InGaP cladding layers will be examined with respect to growth challenges, laser processing and performance, and device reliability. Several device structures which provide transverse and lateral confinement will be reviewed. Reduction of the transverse far-field angle, which improves fiber coupling efficiency, can be accomplished through the use of periodic index separate confinement and depressed index cladding heterostructures. The performance of ridge waveguide lasers, which require accurate control of the ridge height, can be improved through the incorporation of etch-stop layers, either InGaP or AlAs, in the AlGaAs cladding layer. Nonplanar growth over mesas etched into the substrate is a convenient method to obtain buried heterostructure lasers. Carbon-doped planar InGaAs/AlGaAs lasers, using CC14 as an extrinsic dopant, have been fabricated with an impurity-induced layer disordering process. Microcylinder lasers have been fabricated out of InGaAs/InGaP layer structures.

Adsorption and Dissociation Mechanism of Excited N2 on ZnSe Surface

Nitrogen molecular adsorption and dissociation on the ZnSe (100) surface has been examined by ab initio molecular orbital theory. Based on the electronic structure and energetics, the excited (3Σu+) nitrogen molecule can be selectively adsorbed and dissociated on a Zn atom of the ZnSe surface. This result supports the contention recently presented that the p-type ZnSe layers grown by plasma discharge, which successfully realized blue-green lasers, is grown by the excited (3Σu+) nitrogen molecular beam.

High-resolution study of stimulated emission from blue-green laser diodes

The first high-resolution study of emission spectra from ZnSe-based blue-green laser diodes is reported.

Distributed feedback operation of optically pumped ZnSe quantum-well lasers in the blue-green

Distributed feedback operation of optically pumped (Zn,Cd)Se/ZnSe quantum-well lasers has been realized at room temperature. The periodic grating structure was fabricated by short wavelength holographic lithography and dry etching techniques. These results are relevant also in the context of the new blue-green diode lasers, based on this same quantum-well system.

Translacrimal Laser Dacryocystorhinostomy-Reply

In Reply. —I thank Dr Christenbury for his kind comments regarding our original description of endonasal laser dacryocystorhinostomy (ENL-DCR) for the treatment of lacrimal outflow obstruction. I offer the following comments regarding his work. In our initial cadaver research we investigated transcanalicular passage of a 300-μm quartz fiberoptic catheter to produce a laser DCR fistula using a 16-W argon blue-green laser. The optical fiber suffered damage when used in this contact mode, causing reduced tissue cutting efficiency and increased collateral tissue damage as evidenced by post-procedure dissections. The quartz fiber described by Dr Christenbury is intended for intraocular endophotocoagulation and would be expected to present the same disadvantages. When using a transcanalicular technique, it is more difficult to control the exact site of fistula placement, and lacrimal sac mucosal damage is not directly observed. Although this route may be less cumbersome and more familiar to the ophthalmologist, the intranasal approach

Activation of N-Acceptor in MOCVD-ZnSe by Excimer Laser Annealing

ABSTRACTThe recent success in obtaining blue-green diode lasers using ZnSe-based heterostructures has been mainly due to the successful p-doping of ZnSe using a N plasma source in an MBE system. P-type ZnSe can also be grown by MOCVD, using NH3 as the dopant source. Dopant concentrations of up to 1018 cm−3 have been obtained but net acceptor concentrations are in the range of only about 1015 cm−3 Activation of the remaining N has been achieved to some extent (NA -ND∼3*1016cm−3 ) by rapid thermal annealing. However, this has had limited success. We have used fast surface annealing by an excimer laser to activate the N. We have observed an increase in the ratio of Acceptor Bound Exciton peak intensity to Free Exciton peak intensity on annealing and this effect increases as we increase the laser power density from 10 to 30 MW/cm2. Electrical measurements ( C-V ) give a net acceptor concentration of ∼2*1016 cm−3 and thus confirm the increase in carrier concentration after annealing.