Laser annealing of low dose Se-implanted GaAs studied by d.l.t.s.

Deep level transient spectroscopy (d.l.t.s.) has been applied to the study of deep levels in GaAs following post-implantation annealing using a Q-switched ruby laser. High concentrations (> 1015 cm?3) of deep trapping levels are observed in the laser melt region using a forward-bias voltage pulse.     

C.W. modelocking of a GaInAsP diode laser

Active c.w. modelocking of a GaInAsP double-heterostructure laser diode operating in an external cavity is reported. 18 ps pulses (f.w.h.m.) are obtained at a repetition rate of 2.1 GHz and a lasing wavelength of 1210 nm. The pulses were measured by autocorrelation using s.h.g. in LiIO3. They are the shortest pulses ever reported for a c.w. laser diode.     

Generation of surface acoustic waves by means of a c.w. laser

Acoustic surface waves have been generated in a solid by using a c.w. laser modulated at 10 MHz. The arrangement is regarded as potentially useful for a nondestructive testing system in which both the generation and the detection of surface waves is effected by means of a laser.     

Ho:Tm lasers. II. Experiments

For pt.I see ibid., vol.32, no.1, pp.92-103 (1996). Laser performance of Ho:Tm:YLF and Ho:Tm:YAG lasers are compared under a wide variety of experimental situations. Laser diode pumping is simulated using a Cr:BeAl₂O₄ laser tuned to the absorption peak of the Tm³H₄ manifold for the respective laser material. Laser performance is characterized by experimentally determining the threshold and slope efficiency, and compared with predicted results of a rate equation model developed in the companion paper. Energy transfer parameters for the rate equation model are calculated using the theory developed in that paper. For these experiments, four different pump pulselengths, six different output mirror reflectivities, different Ho concentrations and different length laser materials were evaluated. Using Ho:Tm:YAG an optical slope efficiency of 0.36 was achieved while with Ho:Tm:YLF an optical slope efficiency of 0.50 was reached     

在XeCl放电激光器中的回路电感效应

本文研究了电子雪崩放电XeCl准分子激光器放电回路电感对放电特性与激光脉冲输出能量的影响。     

Semiclassical model of semiconductor laser noise and amplitudenoise squeezing. II. Application to complex laser structures

For pt.I see ibid., vol.33, no.11, p.2097-2104 (1997). We present noise studies of distributed feedback (DFB) laser structures, where spatial hole burning (SHB) plays a key role performed using the model described in part I of this paper with particular emphasis on the influence of SHB, on the coupling coefficient κL, and on the laser facet reflectivities. These structures exhibit high amplitude noise and the possible noise reduction is strongly reduced compared to Fabry-Perot structures. Distributed Bragg reflector (DBR) lasers are better candidates even if their performances are also strictly determined by SHB and the loss in the Bragg reflector. Finally, limitations due to gain suppression are demonstrated for such complex lasers structures. We conclude on the optimum laser structure for amplitude squeezed states generation     

Deep-etched distributed Bragg reflector lasers with curved mirrors.Experiments and modeling

A semiconductor laser with deep-etched distributed Bragg reflectors (DBRs) supporting a planar Gaussian mode has been experimentally and theoretically studied. A 90-μm-long laser with two-groove DBRs has a low threshold current of 7 mA and a maximum side mode suppression of 17.6 dB under continuous operation. The laser resonator supports a mode that closely resembles the desired planar Gaussian mode. The reflectivities of the deep-etched DBRs were experimentally determined using broad area devices, and the reflection, transmission, and scattering properties of the DBRs were simulated using a finite-difference time-domain model. The simulations show that deep grooves, covering the full transverse extent of the guided mode, are needed to maximize the reflectivity and to minimize the scattering loss. A beam-propagation model was used to simulate the laser resonator. The simulations (as well as the experiments) show that the laser is sensitive to thermal effects. Thermal lensing narrows the mode waist, and therefore increases the spatial hole burning in the center of the resonator where the intensity is at its maximum. At high drive currents, this leads to a degradation of the spatial mode quality. The simulations also indicate that a laser with optimized DBRs (one one- and one two-groove DBRs with an etch depth of 1 μm) would have a threshold current less than 2 mA and support a high-quality planar Gaussian mode to an output power of 9 mW under continuous operation     

Short-channel polysilicon-gate m.o.s.f.e.t.s fabricated by c.w. argon laser annealing of arsenic-implanted source and drain

Short-channel polysilicon-gate n-channel m.o.s.f.e.t.s have been successfully fabricated using c.w. argon laser annealing of arsenic-implanted source and drain. The turn-on voltage is higher for the laser annealed devices than for those annealed thermally, which were processed identically except for the source and drain annealing. Laser annealing also reduced the n+-layer sheet resistance to about half that of the thermally annealed n+ regions.     

Polarization states of a single-mode (microchip)Nd3+:YAG laser. I. Theory

We present a microscopic mathematical model for the polarization states of a single-frequency Nd³⁺:YAG laser. It is a plane wave, mean field, vector model carried to all orders in the laser field. The crystal is assumed to be optically pumped longitudinally with a laser of specified polarization. For D₂ site symmetry and an odd number of electrons, we establish the phase relationships between the components of the electric dipole matrix elements between the Kramers states. These relationships are central in determining the site-specific coupling between both, the pump and laser fields to the Nd ³⁺ ions. The laser cavity is assumed to be linear and quasi-isotropic. The residual optical anisotropies are included using a round-trip Jones matrix formalism     

脉冲放电及紫外光电离电子密度实验研究

用X波段外差式微波干涉仪,测得了脉冲放电余辉电子密度以及TEACO_2激光器、HF激光器紫外光预电离的电子密度。文中给出等离子体分布不均匀引起的微波相移计算公式。     

Heterodyne detection with an injection laser. II. Signal-to-noiseratio

For pt.I see ibid., vol.26, p.85-93 (1990). In part I a theory of the conversion efficiency of the self-heterodyne laser detector that was first described by R.F. Kazarinov and R.A. Suris (1974) was presented. In this device a light signal is passed into the resonant cavity of an actively oscillating injection laser, causing an electrical signal at the difference frequency between laser and signal to flow through the wire supplying the DC bias to the laser. An expression is derived for the signal-to-noise ratio of the self-heterodyne laser detector. The result shows that in the limit of ideal operation (complete population inversion and no internal losses) the signal-to-noise ratio of the self-heterodyne laser detector reaches one-half of the quantum noise limit     

Large-signal p.c.m. behaviour of injection lasers with coherent irradiation into one of their oscillating modes

The effect of coherent irradiation on the modulation characteristics is investigated theoretically. A p.c.m. simulation has been performed using a multimode rate-equation model. A significant improvement in the modulation behaviour is predicted if the laser is subject to an external irradiation.     

Inside Front Cover: Optical Control and Patterning of Gold‐Nanorod–Poly(vinyl alcohol) Nanocomposite Films (Adv. Funct. Mater. 7/2005)

The micropatterning of optical structures into thin films of poly (vinyl alcohol) (PVA) containing gold nanorods is demonstrated by Pérez‐Juste, Liz‐Marzán, and co‐workers on p. 1065. The nanorods are uniformly distributed in the thin films and can be aligned by stretching the films. The inside cover shows how irradiation with a nanosecond laser, using a TEM grid as mask, selectively reshapes the nanorods into nanospheres (upper and lower TEM images, respectively). Gold nanorods with well‐defined aspect ratios are homogeneously incorporated within poly(vinyl alcohol) thin films and subsequently aligned by heating and stretching the nanocomposite films. The spatial alignment of the nanorods is directly proved using transmission electron microscopy. The polarization‐dependent optical response of the rods is measured and compared with a dipole model. Excellent agreement is found. Additionally, irradiation of the film with nanosecond laser pulses (1064 nm) leads to selective reshaping of the nanorods into nanospheres, and we demonstrate that this effect can be used to micropattern optical structures into the films.     

100 km optical-fibre transmission system at 1.32 ?m using high-power c.w. Nd-y.a.g. laser

An allowable transmission-line loss as high as 65.6 dB has been experimentally obtained by using a newly developed high-power 1.32 ?m Nd-y.a.g. laser with an average fibre input power of +22.0 dBm at 32 Mbit/s in return-to-zero pulses, which ensures 100 km repeater-spacing transmission with presently available low-loss optical fibres     

Cover Picture: Formation of Metal Nano‐ and Micropatterns on Self‐Assembled Monolayers by Pulsed Laser Deposition Through Nanostencils and Electroless Deposition (Adv. Funct. Mater. 10/2006)

The cover illustrates two‐step fabrication of metal micro‐ and nanostructures on self‐assembled monolayers (SAMs) by pulsed laser deposition and electroless deposition. Metal–SAM–metal junctions are a key component of molecular electronic devices. Pt was deposited in a micropattern by pulsed laser deposition through a stencil. XPS maps show how the Pt pattern is developed into a Cu pattern using electroless deposition as reported by Ravoo, Brugger, Reinhoudt, Blank, and co‐workers on p. 1337. The Cu pattern can also be observed by optical microscopy (background). Patterns of noble‐metal structures on top of self‐assembled monolayers (SAMs) on Au and SiO₂ substrates have been prepared following two approaches. The first approach consists of pulsed laser deposition (PLD) of Pt, Pd, Au, or Cu through nano‐ and microstencils. In the second approach, noble‐metal cluster patterns deposited through nano‐ and microstencils are used as catalysts for selective electroless deposition (ELD) of Cu. Cu structures are grown on SAMs on both Au and SiO₂ substrates and are subsequently analyzed using X‐ray photoelectron spectroscopy element mapping, atomic force microscopy, and optical microscopy. The combination of PLD through stencils on SAMs followed by ELD is a new method for the creation of (sub)‐micrometer‐sized metal structures on top of SAMs. This method minimizes the gas‐phase deposition step, which is often responsible for damage to, or electrical shorts through, the SAM.     

Electric tuning of semiconductor laser using acousto-optic device

An electrically tunable semiconductor laser system is given using an acousto-optic (AO) device and a commercially available semiconductor laser. Rapid scanning of laser oscillation frequency is obtained using frequency modulation of the driving RF power for the AO device. Also, simultaneous two-frequency oscillation is realised using two RF power sources.<>     

Diagnostics of TM010-mode microwave cavity discharges inCO2-N2-He laser gas mixtures. II. Measurement ofvibration temperature

For pt. I see ibid., vol., 31, no. 8, p. 1525-32 (1995). The plasma temperatures in microwave discharged CO₂-N₂-He laser gas mixtures were examined using the spectroscopic and electrostatic probe methods. A vibration temperature of N₂ molecules, obtained spectroscopically, was determined to be nearly 7000 K without gas circulation and to be nearly 4000 K at the mass flow rate of 4.2 kg/h. It is found that an efficiency of laser output power exceed 14% (RF to laser output power conversion ratio) below the vibration temperature of 4000 K. The values of vibration temperature obtained were higher than those reported in DC discharges     

Binary weighted averaging of an ensemble of coherently collected image frames.

Recent interest in the collection of remote laser radar imagery has motivated novel systems that process temporally contiguous frames of collected imagery to produce an average image that reduces laser speckle, increases image SNR, decreases the deleterious effects of atmospheric distortion, and enhances image detail. This research seeks an algorithm based on Bayesian estimation theory to select those frames from an ensemble that increases spatial resolution compared to simple unweighted averaging of all frames. The resulting binary weighted motion-compensated frame average is compared to the unweighted average using simulated and experimental data collected from a fielded laser vision system. Image resolution is significantly enhanced as quantified by the estimation of the atmospheric seeing parameter through which the average image was formed.     

Confocal Microscopy for In Situ Multi-Modal Characterization and Patterning of Laser-Reduced Graphene Oxide (Adv. Funct. Mater. 30/2023)

Graphene oxide (GO) films can be readily prepared at wafer scale, then reduced to form graphene-based conductive circuits relevant to a range of practical device applications. Among a variety of reduction methods, laser processing has emerged as an important technique for localized reduction and patterning of GO films. In this study, the novel use of confocal microscopy is demonstrated for high-resolution characterization, in situ laser reduction, and versatile patterning of GO films. Multi-modal imaging and real-time tracking are performed with 405 and 488 nm lasers, enabling large-area direct observation of the reduction progress. Using image analysis to cluster flake types, the different stages of reduction can be attributed to thermal transfer and accumulation. Delicate control of the reduction process over multiple length scales is illustrated using millimeter-scale stitched patterns, micropatterning of single flakes, and direct writing conductive 2D wires with sub-micrometer resolution (530 nm). The general applicability of the technique is shown, allowing fabrication of both conductive reduced graphene oxide (rGO) films (sheet resistance: 2.5 kOhm sq⁻¹) and 3D microscale architectures. This simple and mask-free method provides a valuable tool for well-controlled and scalable fabrication of reduced GO structures using compact low-power lasers (< 5 mW), with simultaneous in situ monitoring and quality control.