Optics & Laser Technology

Published by Elsevier
Print ISSN: 0030-3992
Publications
Several high-speed pnp phototransistors built in a standard 180 nm CMOS process are presented. The phototransistors were implemented in sizes of 40×40 μm(2) and 100×100 μm(2). Different base and emitter areas lead to different characteristics of the phototransistors. As starting material a p(+) wafer with a p(-) epitaxial layer on top was used. The phototransistors were optically characterized at wavelengths of 410, 675 and 850 nm. Bandwidths up to 92 MHz and dynamic responsivities up to 2.95 A/W were achieved. Evaluating the results, we can say that the presented phototransistors are well suited for high speed photosensitive optical applications where inherent amplification is needed. Further on, the standard silicon CMOS implementation opens the possibility for cheap integration of integrated optoelectronic circuits. Possible applications for the presented phototransistors are low cost high speed image sensors, opto-couplers, etc.
 
The pattern matching for fingerprints requires a large amount of data and computation time. Practical fingerprint identification systems require minimal errors and ultrafast processing time to perform real time verification and identification. By utilizing the two-dimensional processing capability, fast processing speed and non-interfering communication of optical processing techniques, such extremely fast real time fingerprint identification systems can be implemented. Among the various pattern matching systems, the joint transform correlator (JTC) has been found to be inherently suitable for real time matching applications. Among the various JTCs the fringe-adjusted JTC has been found to yield significantly better correlation output compared to alternate JTCs. In this paper, a fingerprint identification system has been developed based on the fringe-adjusted JTC. Since all pattern matching systems suffer from high sensitivity to distortions, the synthetic discriminant function concept has been incorporated in fringe-adjusted JTC to ensure distortion-invariant fingerprint identification
 
Processor arrays with an optical bus are introduced as a new computational model. We use the order statistics problem as an example to demonstrate how to design efficient parallel algorithms on such systems. Besides proposing a new algorithm on the model, some basic data movement operations involved in the algorithm are discussed. We believe that these operations can be used to design other parallel algorithms on the same model. Time analysis indicates that order statistics can be done more efficiently on a linear array with a pipelined optical bus than that with an electronic bus. The initial result is promising, and the author believes that optical buses may emerge as a powerful communication mechanism for connecting large parallel computer systems in the near future
 
The effects of developing agents and activators in the reversal bleach upon the diffraction efficiencies of a Slavich PFG-01 plate to be used for recording transmission holograms were studied. The plates were developed using four different developers: MSC, AAC, PSC, and HSC. The four developers were derived from different developing agents of metol, l-ascorbic acid, phenidone, and hydroquinone, respectively. Sodium carbonate was added to the developer as an activator that accelerates the development by keeping the developer alkaline. A maximum diffraction efficiency of 89.0% was obtained when the AAC developer was used.
 
An experimental study of single shot damage to monocrystal GaAs by a free running laser pulse of 1.06 μm wavelength is described. In order to see the role of surface effects on laser induced damage, samples of different surface finish were prepared. The laser induced damage threshold (LIDT) of lapped GaAs samples is considerably lower than that of the mirror polished samples (ratio ). Damage threshold results are analysed in terms of a thermal model incorporating the temperature dependent thermal and optical parameters of GaAs. The combined effect of the enhanced surface absorption and high surface recombination velocity of photo-excited carriers significantly enhances the surface temperature rise and reduces the damage threshold value of GaAs. The evolution of damage morphology is governed by the mechanical damage caused due to the polishing process.
 
The high power and energy densities in a Q-switched laser beam modify the optical characteristics of a transmitting material and may ultimately cause damage. This paper reviews the mechanisms by which laser-induced damage occurs and summarizes the forms of such damage which are seen in practice. The experimental conditions for making accurate damage threshold measurements are set out, and the apparatus and procedures used in the present work are described. A summary of the laser-induced damage threshold measurements at 1.06 μm on a wide range of materials under the same conditions are presented and compared with other published data.
 
A CW NYAB laser at 1.06 μm end-pumped by a high-power diode-laser-array has been demonstrated. At the incident pump power of 11 W, a maximum output power of 3.2 W was achieved, resulting in an optical conversion efficiency of 29.1%, and average slope efficiency of 37.5%. The output beam quality factor was measured to be M2=1.9. The internal losses caused by the NYAB crystal were measured to be 0.035 cm−1. The NYAB crystal was also found to exhibit very strong thermal lensing under high-power end-pumped conditions.
 
The gain properties and valence subbands of InGaAsN/GaAsN quantum-well structures are numerically investigated with a self-consistent LASTIP simulation program. The simulation results show that the InGaAsN/GaAsN has lower transparency carrier density than the conventional InGaAsP/InP material system for 1.3-μm semiconductor lasers. The material gain and radiative current density of InGaAsN/GaAsN with different compressive strains in quantum well and tensile strains in barrier are also studied. The material gain and radiative current density as functions of strain in quantum well and barrier are determined. The simulation results suggest that the laser performance and Auger recombination rate of the 1.3-μm InGaAsN semiconductor laser may be markedly improved when the traditional GaAs barriers are replaced with the AlGaAs graded barriers.
 
High-power and high beam quality continuous-wave (CW) Nd:GdVO4 lasers operating at 1.34 μm were experimentally demonstrated. The lasers consisted of either one or two crystals, which were both end-pumped by high-power fiber-coupled diode lasers. With one crystal, the maximum CW output power generated was 8.4 W. When two crystals were used, a maximum output power of 15.7 W was achieved with the incident pump power of 76.2 W, showing a slope efficiency of 26.2% and an optical-to-optical efficiency of 20.6%. The beam divergence at an output power of 15 W was measured to be about two times that of the diffraction limit.
 
Thermal, pyroelectric, and photoelectric detectors are discussed with respect to the middle infrared range of 1.5–30μm wavelength. A brief description of the principles governing the operation of the different categories of detector is followed by a more detailed discussion on the performance and applications of individual instruments.
 
A 1.57 μm eye-safe laser is realized by placing a KTP crystal into a diode-end-pumped, acousto-optically (AO) Q-switched Nd:YVO4 laser. For the first time, the 1.06 μm pumping laser with a concave–concave cavity is used to lower the threshold of the intracavity-pumped optical parametric oscillator (IPOPO). The pumping threshold and output characteristics of the OPO are analyzed by changing repetition rate of the AO Q-switch and output mirrors with different transmissivity at 1.57 μm. The results show that the pumping threshold will decrease with the lower output transmissivity and the lower repetition rate, but the narrower output pulse width can be obtained with the higher output transmissivity.
 
High-performance Tm–silica fibre lasers operating at 1.9 μm when pumped at 1319 or 1064 nm have been Q-switched using a rotating mirror mounted at an asymmetric angle. Pumping by 1319 nm gives better performance compared with 1064 nm pumping due to greater excited state absorption (ESA) at 1064 nm. A short Q-switched pulse duration of 25 ns and a peak pulse power of about 2.7 kW has been obtained from a 1.8 m fibre for 3.5 W launched pump power at 1.3 μm. The Q-switch performance has been studied for variation of fibre length and shown that the optimum length under these pumping conditions is around 2 m.
 
A technique for generating short pulses of 10.6 μm radiation is presented. This technique produces pulses of 10−9−10−8 s duration of single-mode radiation with diffraction-limited divergence of the beam and good extraction efficiency of the energy stored in the cavity.
 
Stable single-frequency and single-polarization distributed-feedback (DFB) fiber laser was realized by giving a pressure on the phase shift region of the fiber grating. The output wavelength of the DFB fiber laser is 1053 nm. When the pump power of 980 nm laser diode is 100 and 254 mW, the output power can reach 8.3 and 37.1 mW and the polarization extinction ratio was 26 and 20 dB, respectively. After chopped by Acousto-optic modulator (0.3 Hz), the pulse peak value variance is 4.65%(peak to peak) and 1.098% (RMS) for 31 min.
 
The interaction phenomena of nanosecond time period Q-switched diode-pumped Nd:YAG laser pulses using 1064, 532 and with thick pure-copper foil was investigated at an incident laser intensity range of 0.5–. For each sample, etch rate and surface structure were determined. Analysis of the results of the tests included scanning electron microscopy (SEM). A maximum etch rate of per pulse was obtained for the etch rate tests carried out at . The maximum etch rate obtainable for was per pulse, and for , per pulse. The dramatic decrease in etch rate observed when processing at is thought to occur due the highly reflective nature of copper as the interaction wavelength is increased, plus the nature of the plasma formed above the material during the high-intensity laser–material interaction. This plasma then imparts energy to the surface of the processed area leading to surface melting of the area surrounding the hole as can be seen by the SEM photographs.
 
Seeding high power fiber amplifier employing multi-tone fiber laser is an effective approach to suppress stimulated Brillouin scattering (SBS). In this paper, a two-stage 1064 nm high power fiber amplification system was set up. Single-, two- and three-tone fiber lasers were employed. SBS threshold powers and maximum output powers of the multi-tone cases are enhanced compared with the single-tone case. The multi-tone amplifiers also show comparable optical-to-optical efficiency to the single-tone amplifier. To demonstrate and validate coherence property of the two multi-tone fiber amplifiers, the output laser beams of the amplifiers were self-interfered in our self-made coherent beam combining system. The laser beams of the multi-tone cases showed good coherence property comparable to the single-tone case, which implied that the high power output laser light of the multi-tone fiber amplifiers could be used for coherent beam combining.Highlights► SBS and coherence property of the multi-tone amplifiers are studied experimentally. ► The SBS thresholds of the multi-tone cases are higher than the single-tone case. ► The maximum outputs of the multi-tone cases are enhanced too. ► All the amplifiers have nearly the same optical-to-optical efficiency. ► The high power laser of the multi-tone amplifiers is fit for coherent beam combining.
 
An experimental study has been made of the diffraction efficiency, scattering and stability against printout effect of bleached, photographically recorded two- beam interference gratings using Agfa-Gevaert 10E75 NAH plates. The efficiency is increased by using bleaching processes that convert the silver image into a dielectric image. Plots of the diffraction efficiency and scattering against exposure, and variation of the maximum diffraction efficiency as a function of departure from the Bragg angle, and exposure to white light, for various bleaching processes, are given. A maximum diffraction efficiency of approximately 54% has been achieved by using a potassium iodide and iodine bleach process.
 
A high power dynamic fundamental mode Nd:YAG laser is experimentally demonstrated with a stagger-pumped laser module and a V-shaped resonator. The rod is pumped symmetrically by staggered bar modules. And dynamic fundamental mode is achieved under different pump levels. The maximal continuous wave (CW) output of 124 W (M2=1.4) is achieved with a dual rod. Average output of 112 W, pulse width of 120 ns, pulse energy of 11.2 mJ and peak power of 93 kW are obtained in Q-switched operation of 10 kHz.
 
We propose a novel multiplexing technique to solve the twin image problem in optical scanning holography without the use of a spatial carrier, as commonly used in conventional off-axis holography. The technique involves simultaneously acquiring sine and cosine Fresnel zone-lens plate coded images by optical scanning. A complex addition of the two coded images will then be performed and decoded to give a twin-image rejection reconstruction. Computer simulations will be presented to demonstrate the validity of the idea.
 
An all-fiber, single-wavelength, erbium-doped photonic crystal fiber (PCF) distributed feedback (DFB) loop laser at 1550.08 nm is proposed and demonstrated experimentally for the first time. Two matched fiber Bragg gratings (FBGs) are used as the selective wavelength components in the loop laser. The optical signal to noise ratio and the 3 dB linewidth of lasing wavelength are greater than 30 dB and less than 0.96 nm, respectively. A low pump power threshold (∼17 mW) is obtained. 10-time repeated scans of the laser output spectra with 1 min interval indicate that the lasing wavelength is rather stable at room temperature. The peak power of the laser has a maximal fluctuation no more than 0.06 dBm within 30 min.Highlights► A new single-mode erbium-doped photonic crystal fiber is used as a gain medium. ► The loop laser includes a novel distributed feedback configuration. ► Two matched fiber Bragg gratings are used as the selective wavelength components. ► The lasing wavelength and the peak power of the proposed laser are rather stable.
 
High-speed, oxide-confined, polyimide-planarized 850 nm vertical-cavity surface-emitting lasers (VCSELs) with oxide aperture diameters of 9, 10, 12, 15, 20, and 30 μm have been fabricated and characterized. For a 9 μm oxide aperture diameter, the lasers exhibit a resonance frequency, a 3-dB modulation frequency, and a modulation current efficiency factor (MCEF) up to 12.4, 16.5 GHz, and 10.9 GHz/mA1/2, respectively, at only 7.9 kA/cm2. Threshold voltage and current were 1.45 V and 0.7 mA, respectively. It is demonstrated that increasing the resonance frequency with bias does not guarantee a higher modulation bandwidth. The influence of oxide aperture scaling effect on VCSEL performance is presented.
 
The photophysical properties of DMAPrP have been investigated in different solvents. DMAPrP dye exhibits a large change in dipole-moment upon excitation due to an intramolecular charge transfer interaction. A crystalline solid of DMAPrP give an excimer like emission at 546 nm. The ground and excited state protonation constants of DMAPrP are calculated. DMAPrP acts as good laser dye upon pumping with nitrogen laser in some organic solvents. The laser parameters such as the tuning range, gain coefficient (α), emission cross section (σe) and half-life energy (E1/2) are also calculated. The photoreactivity and net photochemical quantum yield of DMAPrP in chloromethane solvents are also studied.
 
Interaction of a 2.5 kW high power diode laser (HPDL) beam with the ordinary Portland cement (OPC) surface of concrete has been investigated, resulting in the generation of a tough, inexpensive amorphous glaze. Life assessment testing revealed that the OPC glaze had an increase in wear life of 1.3–14.8 times over an untreated OPC surface, depending upon the corrosive environment. Also, variations in the width of the HPDL beam were seen to have a considerable affect on the melt depth. Furthermore, the maximum coverage rate that it may be possible to achieve using the HPDL was calculated as being 1.94 m2/h. It is a distinct possibility that the economic and material benefits to be gained from the deployment of such an effective and efficient large area coating on OPC could be significant.
 
Mixing layer height measurements with an elastic-backscattered lidar were carried out in Hefei, China, during the total solar eclipse of 22 July, 2009. The mixing layer height evolution is studied with the observation of changes in near-ground temperature, relative humidity and wind speed. The lidar emits the laser at the wavelengths of 532 and 355 nm, respectively, and obtains the backscattered signal with the resolution of 10 m. The whole eclipse witnessed the mixing layer change similar to that occurring during sunset. The results also show the mixing layer height decreased to 287 m rapidly during the total eclipse within only more than 1 min from the initial 354 m. The entrainment thickness reached the minimum of 43 m in the eclipse, indicating the weakening of the penetrative convection. Thereafter the thickness kept a constant value of 180 m. The temperature in the whole eclipse is uptrend, increasing only by 0.5 °C as a whole. The wind speed decreased and simultaneously the wind direction changed. The wind speed reached its minimum of 2 m/s at the end of the eclipse.
 
An efficient erbium–ytterbium-doped fiber amplifier (EYDFA) is demonstrated by forward and backward pumping a 3 m erbium/ytterbium co-doped fibers (EYDF) in single- and double-pass configurations using a 20 mW pump. At the input signal wavelength of 1536 nm, the forward- and backward-pumped double-pass amplifiers achieved a maximum low-signal gain of 37.2 and 28.6 dB and a corresponding noise figure of 5.4 and 10.8 dB, respectively. Whereas, the forward- and backward-pumped single-pass amplifiers (at the same wavelength) achieved a maximum low-signal gain of 20.0 and 22.2 dB and a corresponding noise figure of 4.6 and 10.3 dB, respectively. The double-pass design offers an economical solution to high-efficiency and high-gain optical amplifiers.
 
We developed a highly efficient diode side-pumped Nd:YAG ceramic laser with a diffusive reflector as an optical pump cavity. A maximum output power of 211.6 W was obtained with an optical-to-optical conversion efficiency of 48.7%. This corresponds to the highest conversion efficiency in the side-pumped ceramic rod. Thermal effects of the Nd:YAG ceramic rod were analyzed in detail through the measurements of laser output powers and beam profiles near the critically unstable region. A M2 beam quality factor of 18.7 was obtained at the maximum laser output power.
 
We report a high-quality interleaver with frequency spacing of 25 GHz, which is made by a Michelson interferometer with a mirror replaced by a Gires–Tournois etalon. Our optimal design and elaborate manufacture assure its excellent performance. We present the analysis of performance parameters, design of structural parameters, the unique fabrication technology and testing results of this interleaver in this paper.
 
A Cr:Nd:GGG slab laser with an average output power of 300 W was made. The solarization of the Cr:Nd:GGG crystal was prevented by using a filter with a 530 nm cut-off wavelength. The influence of the ultra-violet cut-off filters on the laser performance: thermal lensing, depolarization, laser output energy and average power, was investigated.
 
We report the low-threshold operation of a nanosecond β-BaB2O4 optical parametric oscillator (OPO) pumped by the third harmonic of a Q-switched Nd:YAG laser. Using cylindrical focusing of the pump beam, a threshold pulse energy of ∼0.5 mJ is obtained at the signal wavelength of 560 nm, which is about sixteen times lower than that of a spherical focusing configuration. The importance of diffraction loss in the design of tightly focused OPOs is discussed in terms of a simple extension of the conventional OPO model.
 
Eu2+ activated Ca5(PO4)3Cl blue-emitting phosphors were prepared by the conventional solid state method using CaCl2 as the chlorine source and H3BO3 as flux. The structure and luminescent properties of phosphors depend on the concentrations of Eu2+, the amount of CaCl2 and the usage of the H3BO3 flux were investigated systematically. Eu2+ and Mn2+ Co-doped Ca5(PO4)3Cl with blue and orange double-band emissions were also researched based on the optimal composition and synthesis conditions. The energy transfer between Eu2+ and Mn2+ was found in the phosphor Ca5(PO4)3Cl:Eu2+, Mn2+, and the Co-doped phosphor can be efficiently excited by near-UV light, indicating that the phoshor is a potentional candidate for n-UV LED used phosphor.
 
Using holographic interferometry the three-dimensional structure of unsteady and large-scale motions within subsonic and transonic turbulent jet flows has been studied. The instantaneous 3D flow structure is obtained by tomographic reconstruction techniques from quantitative phase maps recorded using a rapid-switching, double reference beam, double pulse laser system. The reconstruction of the jets studied here reveal a three-dimensional nature of the flow. In particular an increasing complexity can be seen in the turbulence as the flow progresses from the jet nozzle. Furthermore, a coherent three-dimensional, possibly rotating, structure can be seen to exist within these jets. The type of flow features illustrated here are not just of fundamental importance for understanding the behavior of free jet flows, but are also common to a number of industrial applications, ranging from the combustion flow within an IC engine to the transonic flow through the stages of a gas turbine.
 
The non-contact 3D area sensor technology has achieved many successes in a variety of offline measurements. However, it has not been implemented for online measurement in the automotive production lines. The biggest challenge is the capability of simultaneously satisfying the efficiency, reliability, and accuracy requirements. For this purpose, a real-time 3D area sensor based on structured light pattern is proposed. To satisfy the requirement of online measurement, a one-shot pattern using monochromatic light is proposed. Compared with the previous patterns, this pattern is more robust because it can avoid the influence of the ambient light and the inspected part reflective property. Moreover, the requirement of the accuracy performance is achieved by the pattern primitive which is similar to the corner of the checkerboard since it can provide high accuracy performance even when the occlusion occurs; also, the pixel-to-pixel calibration strategy is utilized to increase the accuracy of the inspection system. Such a real-time shape measurement system has been successfully developed in our laboratory. Last, the evaluation experiments are conducted. The experiment results demonstrate the robustness and accuracy of the approach on automotive parts with different surface properties.
 
Tracer based shock visualisation (TSV) is a new optical non intrusive technique to visualise the position and the structure of shocks in a transonic axial compressor. The number per volume density of particles, which are added to the flow and with it the density of the fluid are visualised with a laser light sheet and an intensified CCD camera. structures like normal and oblique shocks, λ-shocks and separation regions can be clearly identified. The 3D-shape and structure of the blade passage shock is reconstructed from the collected data. The results are in good agreement with wall pressure measurements and numerical data. The experimental difficulties of the technique are discussed.
 
Three-dimensional (3D) position and velocity information can be extracted by directly analysing the scattering patterns in velocimetry imaging of seeding particles using real-time CCD cameras. A Fraunhöfer diffraction simplification of generalised Lorenz–Mie theory is shown to yield a representative model of particle position, such that particle position can be approximately deduced from typical experimental particle images. Data are obtained by pattern-matching theoretical to experimental images using a Nelder–Mead algorithm, subject to digitisation considerations and the concept of “locales”. In this way, information about the characteristics of positional error as a function of magnification, pixel size, intensity resolution, and spatial resolution can be derived. This work shows that an optimum magnification exists, beneath which error begins to increase drastically. A practical application is demonstrated. The theory, simulations and experimental verification of this basic problem are discussed.
 
Structured light 3D vision inspection is a commonly used method for various 3D surface profiling techniques. In this paper, a novel approach is proposed to generate the sufficient calibration points with high accuracy for structured light 3D vision. This approach is based on a flexible calibration target, composed of a photo-electrical aiming device and a 3D translation platform. An improved algorithm of back propagation (BP) neural network is also presented, and is successfully applied to the calibration of structured light 3D vision inspection. Finally, using the calibration points and the improved algorithm of BP neural network, the best network structure is established. The training accuracy for the best BP network structure is , and its testing accuracy is .
 
We analyzed a linear cavity for intracavity frequency doubling of a diode-pumped acousto-optic Q-switched Nd:YAG rod laser, and showed that a green laser beam with a short pulse width can be generated efficiently. A green laser output power of corresponding to the 83.9% of maximum IR output power was obtained with a pulse width at a repetition rate. A green output power of with a pulse width was measured at a repetition rate. Minimum laser pulse width of approximately was obtained around repetition rate for both green and IR laser beams.
 
Utilizing a new blood-analysis method which uses the interaction between an Ar+ laser beam and a blood sample, it can be shown that there is a significant difference in the reflectance variation δR between the malignant and benign blood, at 501.7 nm of the Ar+ laser, under a dc magnetic field, for both human and mouse blood. For the malignant mouse-blood with leukaemia, δR tends to be positive with the magnetic field, while for the benign blood it is negative. This is also true for the human blood. This fact is confirmed by the inverted variation of the higher order Fourier pattern obtained by the Fourier pattern analyser from the transmitted beam through the diluted sample, for the malignant and benign mouse-blood under the magnetic field.
 
Experimental investigations are presented on the 540.1 nm Ne laser line, excited directly by a sliding discharge. Laser action is a result of the Ne transitions 2p1 → 1s4 producing relatively intense laser light. The design characteristics of this novel Ne laser and the performance parameters are given and ideas for further improvement of the laser action are discussed.
 
A new laser transition at 1112 nm was obtained after analyzing the parameters of the main laser transitions in Nd:YAG and calculating the transmission loss of the cavity at 1064, 1319, and 946 nm. The maximum output power of the fundamental wavelength was 610 mW, the fundamental wavelength light-to-light conversion efficiency was 38.1%, the maximum output at 556 nm was 109 mW intra-cavity frequency doubled by LBO, the SHG conversion efficiency was 17.8%, and the overall light-to-light efficiency was 6.8% for the pump power of 1.6 W.
 
A He–Ne dual-frequency laser equipped with a bireflectance cavity mirror is described. It is based on the principle that when the incident light is perpendicular to the bireflectance cavity mirror, the phase delays of the reflective light along the mirror's fast and slow axes are different because of the photoelastic effect. The mode coupling is reduced by utilizing transverse Zeeman effect so that two linear and orthogonal polarization components with beat frequency are generated. The effect of the magnetic field's direction on the dual-frequency as well as the polarization property of the laser are investigated by experiments. After stabilizing the frequency, the laser is calibrated with the iodine frequency stabilization laser of Chinese National Institute of Metrology (CNIM). Experimental results indicate that the expanded uncertainty of wavelength in vacuum is 1×10−7(k=3) with a frequency stabilization of 6.6×10−10 (sampled in ).
 
Dye-sensitized solar cells (DSSCs) use two glass substrates (photo electrode and counter electrode) coated with fluorine-doped tin oxide (FTO) to harvest light into the cell and to collect electrons. The space between the photo electrode and the counter electrode are filled with a liquid type electrolyte for electron transfer into the cell. Therefore, an appropriate sealing method is required to prevent the liquid electrolyte leaking out. In this paper, a simple CO2 laser beam with TEM00 mode excited by a 60 Hz AC discharge was used to seal two glass substrates coated with FTO for the fabrication of DSSCs. The sealing technique improved the durability and stability of the DSSCs. The optimal conditions for the sealing of the DSSCs are related to the pin-hole diameter, the discharge current and the moving velocity of the target. Especially, the CO2 laser beam is used as a heat source that is precisely controlled by the pin-hole, which plays an important role in adjusting its spot size. From these results, the maximum laser power was found to be 40 W at 18 Torr and 35 mA. In order to achieve the best sealing quality, the following parameters are required: a pin-hole diameter of 4 mm, input voltage of 10.73 kV, discharge current of 9.31 mA, moving velocity of 1 mm/s and distance from the target surface of 26.5 cm. Scanning electron microscope images show that the sealing quality obtained using the CO2 laser beam is superior to that obtained using a hot press or soldering iron.
 
This paper presents an investigation of laser rapid manufacturing (LRM) for Inconel-625 components. LRM is an upcoming rapid manufacturing technology, it is similar to laser cladding at process level with different end applications. In general, laser-cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near-net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high-power continuous wave (CW) CO2 laser system, integrated with a co-axial powder-feeding system and a three-axis workstation were used. The effect of processing parameters during LRM of Inconel-625 was studied and the optimum set of parameters for the maximum deposition rate was established employing Orthogonal L9 array of Taguchi technique. Results indicated that the powder feed rate and the scan speed contributed about 56% and 26%, respectively to the deposition rate, while the influence of laser power was limited to 10% only. Fabricated components were subjected to non-destructive testing (like—ultrasonic testing, dye-penetrant testing), tensile testing, impact testing, metallographic examinations and micro-hardness measurement. The test results revealed defect-free material deposition with improved mechanical strength without sacrificing the ductility.
 
Optical parameters of bulk animal tissue in vitro, including absorption coefficient (μa), reduced scattering coefficient (μ′s) or scattering coefficient (μs), total attenuation coefficient (μt), anisotropy factor (g) and refractive index (n) are measured at wavelength of 650 nm. Clinical Intralipid-10% is diluted in distilled water into different concentrations to use as tissue phantoms. Four types of animal tissues in vitro are studied. The relationships among the optical parameters are analyzed systemically. For animal tissues, μa, μ′s or μs and n rely on muscle fiber orientations. μs and μt range from 10 to 20 mm−1, μa from 10−2 to 10−3 mm−1 and g from 0.95 to 0.99.
 
We show in our work that very narrow (FSR~0.09 nm) lasing modes can be formed from rhodamine 6G solution confined within quartz (SiO2) cuvette with suitable pumping scheme by Q switched Nd:YAG laser. With introduction of silver nanoparticles of different concentrations in rhodamine 6G we show that such lasing modes can be modulated as well as tuned in intensity, band spacing and emission wavelength. We also show that this system maintains a very high Q value > 6.4*1000 irrespective to change in other parameters.
 
We demonstrate a multi-wavelength semiconductor optical amplifier (SOA) fiber ring laser with a dual-pass Mach–Zehnder interferometer (MZI) filter. Two SOAs with different gain spectra provide sufficient gain and a wider gain spectrum to facilitate multi-wavelength lasing. The dual-pass MZI, configured by adding an optical isolator to the two outputs of the conventional MZI, serves as comb filter for multi-wavelength operation, and its extinction ratio can be enhanced to twofold as that of the conventional MZI in the same parameters. To investigate the influences of a dual-pass MZI filter and a conventional MZI filter on multi-wavelength operation, two different cavity configurations are presented and compared, including a single-SOA ring cavity and a double-SOA ring cavity. Stable simultaneous operation at 82 wavelengths, with a wavelength spacing of 40 GHz and a power deviation of 5 dB, and with a minimum optical signal-to-noise ratio (OSNR) of 28 dB, is observed from the double-SOA ring cavity using a dual-pass MZI filter.
 
A very simple and inexpensive tunable semiconductor diode laser controller is designed for stable operation of the diode laser. The diode laser controller is stable within +/−8 μA and +/−10 mK, respectively. The noise spectrum of the current controller is studied by FFT analysis. We have used our home-made diode laser system in a tunable diode laser absorption spectrometer (TDLAS) to probe weak overtone transitions of water vapour molecule. The diode laser wavelength is coarsely tuned by changing the operating temperature to probe (2, 1, 1)←(0, 0, 0) band overtone transitions of water vapour within 818–835 nm. To demonstrate line shape study, seven transitions are scanned by ramping the drive current of the diode laser (at constant operating temperature) under different perturber (laboratory air) pressures within the sample cell. A balanced detector and a lock-in amplifier are used for phase sensitive detection purpose. Small current modulation amplitude, balanced detection and proper adjustment of the lock-in amplifier help to obtain a S/N ratio ranging from ∼100 to ∼7 using a small sample path length of 1.5 m. Experimentally obtained derivative spectrum is numerically integrated to reveal the original line shape and fitted with a nonlinear least squares fitting program to extract air broadening coefficients and line strength parameters. The spectroscopic line parameters are compared with the results from HITRAN database.
 
A DFB laser emitting at a wavelength around 940 nm in a single longitudinal mode up to an output power of 500 mW with a side mode suppression ratio greater than 50 dB is presented. More than 4 nm tuning range was reached by varying the current between 100 and 800 mA. Up to a power of about 300 mW, the lateral far field revealed stable fundamental mode operation.
 
We report the intracavity-frequency-doubling of a 946 nm Nd:YAG laser with a CMTC crystal at room temperature. A cw output power of 1.64 mW of blue light at 473 nm is obtained. To our knowledge, this is the first time that CMTC crystal has been used to frequency double a 946 nm Nd:YAG laser.
 
By expanding a hard aperture function into a finite sum of complex Gaussian functions, approximate propagation formula is derived in the situation that the beam generated by Gaussian mirror resonator passes through a paraxial ABCD optical system with an annular aperture. The corresponding forms for a circular aperture and a circular black screen are also given. Some numerical simulations are shown to illustrate propagation properties and focusing properties of the beam passing through a paraxial ABCD optical system with the three different kinds of aperture.
 
Top-cited authors
Nanrun Zhou
  • Shanghai University of Engineering Science
Radovan Kovacevic
  • Southern Methodist University
Bekir Sami Yilbas
  • King Fahd University of Petroleum and Minerals
Abdul Ghani Olabi
  • University of the West of Scotland
Sulaiman Wadi Harun
  • University of Malaya