Spin-polarized electron sources have important applications in electron spectroscopies. Such electron spectroscopies can provide considerable insight into the electronic structure of magnetic materials. A spin-polarized electron gun, based on photoemission from a GaAs cathode, has been designed for spin- polarized inverse photoemission and spin-polarized electron scattering. Our spin-polarized electron source is used in combination with a Geiger-Muller isochromat photon detector (for inverse photoemission), a small electron energy analyzer or Mott detector (for electron spin scattering), and a pulsed magnetic field (to saturate the magnetization of the sample). It is important that such sources have very stable emission, well defined electron polarization, and excellent focus for spectroscopy applications. Much of this depends on a stable laser and associated optical systems in the near infra-red. In the instrument we describe, the geometry of the incident circularly polarized light with respect to the direction of electron emission, as well as the electron optics, are designed so that the electron spin polarization is consistently in the plane of the sample for any incident angle in an angle resolved measurements for electron wave vector dependent studies. We provide examples of the types of the novel new measurements that are possible with such instrumentation.

A compact, reliable semiconductor laser source for materials processing, medical and pumping applications is described. This industrial laser source relies on a combination of technologies that have matured in recent years. In particular, effective means of stacking and imaging monolithic semiconductor laser arrays (a.k.a., bars), together with advances in the design and manufacture of the bars, have enabled the production of robust sources at market-competitive costs. Semiconductor lasers are presently the only lasers known that combine an efficiency of about 50% with compact size and high reliability. Currently the maximum demonstrated output power of a 10-mm-wide semiconductor laser bar exceeds the 260 W level when assembled on an actively cooled heat sink. (The rated power is in the range of 50 to 100 W.) Power levels in the kW range can be reached by stacking such devices. The requirements on the stacking technique and the optic assembly to achieve high brightness are discussed. Optics for beam collimation in fast and slow axis are compared. An example for an optical setup to use in materials processing will be shown. Spot sizes as low as 0.4 mm X 1.2 mm at a numerical aperture of 0.3 and output power of 1 kW are demonstrated. This results in a power density of more than 200 kW/cm². A setup for further increase in brightness by wavelength and polarization coupling will be outlined. For incoherent coupling of multiple beams into a single core optical fiber, a sophisticated beam-shaping device is needed to homogenize the beam quality of stacked semiconductor lasers.

This paper describes a novel, high-brightness, multi-laser- diode system that provides great flexibility for use in a wide array of applications. The system consists of eight individual, field-replaceable laser diodes, whose outputs are optically combined to provide a collimated beam. Field replaceability of the diodes and mechanical robustness of this system make it particularly suitable for highly demanding environments. CW optical power greater than 90 Watts at 915 nm was focused to a spot size of 140 X 130 micrometer and a numerical aperture of 0.22 NA. This high CW power density (approximately 5 X 10⁵ W/cm²) was achieved by polarization coupling of two multi-laser-diode systems. Optical power in excess of 52 W was obtained from a single-end pumped, grating stabilized Yb:fiber laser at 1100 nm. This paper will also present results on digital printing, CD-RW disk initialization and solid-state laser pumping. A unique feature of this system is the ability for direct-diode coupling to fiber, eliminating any splicing or connector- related losses.

High power diode laser bars and stacks are of great interest in industrial applications due to their high electro-optical efficiency, their small type of construction and maintenance free operation. With highly sophisticated beam shaping optics diode lasers can be used as pumping sources for solid state and fiber lasers and direct for material processing, e.g. welding, soldering and marking metals. We have developed different fiber coupled diode laser systems with output power up to greater than 2 kW cw into a spot 0 1.0 mm (power density greater than 250 kW/cm²) and systems with output power 170 W cw into a spot 0 0.38 mm (power density about 150 kW/cm²). The 2 kW system operates with a 0 1.5 mm fiber (N.A. 0.32) and consists of polarization and wavelength coupled stacks with an overall electro-optical efficiency of 23%. The smaller system operates either with a 0 0.6 mm (N.A. 0.22) or 0 0.4 mm (N.A. 0.33) fiber and consists of a single stack. Polarization and wavelength coupling will be realized in future. The overall electro-optical efficiency is about 27%.

The development of didoe-pumped self-frequency doubling (SFD) YCA₄O(BO₃)₃ (YCOB) crystals doped with ND³⁺ or YB³⁺ ions offers an attractive alternative to traditional intra-cavity doubling techniques using a separate non-linear crystal. Here, we summarize the progress of scaling SFD lasers to higher powers. Moreover, we examine the potential and limitations of these devices. While SFD lasers are potentially more compact and less costly, scaling to higher powers in the visible region requires careful assessment of mode matching and cavity mode brightness. Combining optical gain and frequency conversion in the same material requires a compromise between the ideal cavity mode for mode matching and generating the largest available power density of the laser mode for optimum frequency doubling. The lack of adjustment of the cavity mode inherently limits scaling of SFD laser operation when using low brightness high power laser diodes. We have employed a new source developed by Polaroid Corp. using multiple high-brightness laser diodes to investigate the potential of increasing SFD laser output. We have then compared the efficiency of this novel pump technique to a single diode pumped system to determine the importance of brightness of the pump source to SFD operation.

Commercially available high power diode lasers (HPDLs) with output powers of up to 6 kW have been recognized as an interesting tool for industrial applications. In certain fields of application they offer many advantages over Nd:YAG and CO₂ lasers because of their low maintenance, compact design and low capital costs. Examples of successful industrial implementation of HPDLs include plastic welding, surface hardening and heat conduction welding of stainless steel and aluminum. The joining of plastics with an HPDL offers the advantages of producing a weld seam with high strength, high consistency and superior appearance. One example is the keyless entry system introduced with the Mercedes E-class where the microelectronic circuits are embedded in a plastic housing. Other applications include instrument panels, cell phones, headlights and tail lights. Applications in the field of surface treatment of metals profit from the HPDL's inherent line-shaped focus and the homogeneous intensity distribution across this focus. An HPDL system is used within the industry to harden rails for coordinate measurement machines. This system contains a customized zoom optic to focus the laser light onto the rails. With the addition of a temperature control, even complex shapes can be hardened with a constant depth and minimum distortion.

A laser diode-based multilaser system of extremely high brightness is presented. The high brightness of the system is achieved by summing anomorphous radiation of individual powerful diode lasers with an original optical design SuperFocus to give an isomorphous output beam. Application of wavelength feedback and injection locking effect to enhance the performance of multilaser diode systems is studied. It is shown that the injection locking using a fiber laser as a master is one of the ways to significantly improve the performance of such systems. A very narrow-band high-power optical output and, hence, a significant increase in the spectral brightness of the multilaser system are achieved by an optimum combination of the parameters of the master laser and the slave multilaser system.

The design, fabrication, and testing of a new anamorphic microlens for laser diode circularization is presented. The microlens is fabricated using photolithography, gray scale masks, and reactive ion etching. A front-to-back mask aligner is used to precisely align two anamorphic aspheric microlenses on opposite sides of a single wafer, creating the ability to circularize or collimate a laser diode with only a single monolithic element. The entire fabrication process is highly nonlinear. This requires that accurate surface metrology methods be incorporated into the process as a feedback loop for iterative corrections to the gray scale mask. We discuss the measurement process and the effects of surface errors for circularizers and circularizer/collimators. This device has been under development for about two years at MEMS Optical. The most recent fabrication and test results of an actual device are presented.

Point triangulation probes (PTBs) fall into a general category of noncontact height or displacement measurement devices. PTBs are widely used for their simple structure, high resolution, and long operating range. However, there are several factors that must be taken into account in order to obtain high accuracy and reliability; measurement errors from inclinations of an object surface, probe signal fluctuations generated by speckle effects, power variation of a light source, electronic noises, and so on. In this paper, we propose a novel signal processing algorithm, named as EASDF (expanded average square difference function), for a newly designed PTB which is composed of an incoherent source (LED), a line scan array detector, a specially selected diffuse reflecting surface, and several optical components. The EASDF, which is a modified correlation function, is able to calculate displacement between the probe and the object surface effectively even if there are inclinations, power fluctuations, and noises.

Wavelength modulation spectroscopy was employed to investigate water vapor absorption lines in the 1.462 micrometer wavelength region using an external-cavity diode laser. These measurements were necessary in the development of a lidar (light detection and ranging) instrument for differential absorption measurement of the concentration and movement of water vapor in the Earth's atmosphere. Differential absorption measurements require that the laser frequency remain stable throughout the duration of the measurement. To ensure this stability, the laser output wavelength is monitored and a feedback control loop set up to minimize laser line drift. Three lines were investigated in the 1.462 micrometer region. The first-harmonic spectroscopic signal of the strongest of these lines was used as an error signal for the stabilization feedback loop. The derivative-like nature of harmonic signals provides a zero crossing for odd harmonics which can be used to determine the polarity of the requisite feedback voltage and compensate the laser wavelength accordingly. The feedback control loop utilized the virtual instrument capabilities of Labview and locking to within plus or minus 5.2 MHz was achieved using this method.

The use of VCSELs in spectrally-demanding applications is considered. Vertical cavity lasers with emission in the (lambda) equals 763 nm, 780 nm and 852 nm wavelength ranges have been developed and optimized for spectrally-pure emission. Measurements of output spectra, linewidth, noise, polarization and spectral aging properties are considered in detail. Typical linewidth values below 5 MHz are seen, which makes these lasers very attractive for a variety of spectroscopic applications. Two of these optically-demanding applications are considered, namely oxygen sensing and pump sources for atomic clocks; performance results for the former are presented.

In the last fifteen years, initiated by the needs of the laser atom cooling community, grating-stabilized diode laser systems have emerged that cover a variety of scientific and increasingly, technical applications. The paper is intended to give an overview to the non-specialist on today's grating- tunable diode laser technology and its recent extensions, focusing on the two most frequently used designs. While the Metcalf-Littman approach is designated for far mode-hop free detuning, using mostly high quality anti-reflection-coated laser diodes, the Littrow set-up offers highest output power and most rigid operation at fixed wavelengths. The key advantage of the Littrow approach is its simplicity and the usage of standard commercial laser diodes without any special treatment. Reliable single frequency operation at about a tenth of the linewidth of the free-running laser diodes, mechanical tunability and active frequency control with diode lasers in the range from 390 to 1690 nm earn these diode laser systems a strong position in many research laboratories today. Using subsequent semiconductors the light can be amplified up to 1 Watt or frequency-doubled with an efficiency of more than 30% without loss of coherence.

This paper presents a comparison between interferometric heterodyne measurements of a commercial system (Axiom 2/20, Zygo) with its frequency stabilized He-Ne laser source and the same apparatus whose laser source has been replaced by our wavelength stabilized laser diode. The aim of this paper is only to demonstrate the feasibility of length measurements by interferometric techniques using new type of laser source which is insensitive to fluctuations of the refractive index of air.

Wavelength modulation spectroscopy using semiconductor lasers is a sensitive tool for identifying species and measuring concentrations, velocities, and temperature in gaseous media. One advantage of modulation spectroscopy is that detection is carried out at frequencies far from the base-band noise, improving the signal-to-noise ratio. An additional benefit of performing wavelength modulation spectroscopy is that it allows for detection at harmonics of the modulation frequency. When a sinusoidal modulation is imposed, the harmonic detection signals resemble the frequency derivatives of the absorption profile, where the derivative order corresponds to the harmonic detection order. For this reason, the higher harmonic signals can be exploited to obtain more sensitive measurements of spectroscopic parameters, such as lineshape profile, absorption cross-section, temperature, and concentration. Wavelength modulation of semiconductor lasers, such as Fabry-Perot, vertical cavity, and external-cavity lasers, is discussed along with the advantages and disadvantages associated with each laser source. Applications of wavelength modulation spectroscopy are explored and it is shown that the higher harmonic detection signals exhibit structure and magnitude variations that are extremely useful in many spectroscopic applications.

The portable Diode Laser Colorimetric Spectrometer has been developed for analysis of glucose as an application of the Diode-Laser/Fiber-Optic Colorimetric System (DL-FOCS) previously reported. The spectrometer was calibrated by standard solutions of glucose with the conventional enzymatic method (GOD-POD method). The relationship between the colorimetric absorption signal and the concentration of glucose was linear in the region between 0.02 mg/dL and 20 mg/dL with a correlation coefficient of 0.9946.

Multi-degree-of-freedom (MDOF) displacement measurement systems are needed in many application fields; precision machine control, precision assembly, vibration analysis, and so on. This paper presents a new MDOF displacement measurement system that is composed of a laser diode (LD), two position- sensitive detectors (PSDs), and a conventional diffraction grating. It utilizes typical features of a diffraction grating to obtain the information of MDOF displacement. MDOF displacement is calculated from the independent coordinate values of the diffracted ray spots on the PSDs. Forward and inverse kinematic problems were solved to compute the MDOF displacement of an object. Experimental results show maximum absolute errors of less than plus or minus 10 micrometers in translation and plus or minus 30 arcsecs in rotation.

In the present study, we show the experimental results that we obtained in order to measure vibrations and small displacements using a self mixing technique. In our experimental set up, we achieved a strong optical feedback with a high power, low cost, multimode laser diode. Sweeping the laser diode injection current, and simultaneously gathering the photomonitor current, we obtained the output power vs. current with a reduction of the current threshold and the increase of the device efficiency due to feedback. Also, we present the signal applied to a PZT and the response on the laser's photodiode, as well as the calibration curve at different amplitudes of the stimulus with their corresponding responses. We have been able to experimentally reproduce the results obtained by modeling for the self-mixing technique applied to measuring vibrations.

The fiber optic sensor system, that consists of 6 - 8 fiber sensor heads and can measure the salt-content in the water of near-coastal region of 1 Km², is presented. The fiber optic sensor head was made by polishing the end of a double fiber in the form of a prism, with reflecting coating on one side, and had a dimension of 250 - 300 microns. The fiber optic sensor with lead-in power of 3 - 15 mW from visible laser diodes was tested for measuring salt content in the seawater from 0 to 4 wt.%. The results are repeatable and the accuracy less than 10^-3 is suitable for controlling the salinity degree in the range of 0.5 - 1.7% in the near coastal shrimp farms, especially for the childhood shrimp fields.

Inclusion of a small amount of Bi in InAs and GaAs changes the temperature dependent behavior of the band gap. Both InAs_{1- x}Bi_x and GaAs_1-xBi_x tend to have temperature insensitive band gap with increasing Bi content. Raman scattering has been performed on the epilayers of InAs_{1- x}Bi_x and GaAs_1-xBi_x compounds grown by MOVPE technique for varying Bi content. Good single crystalline growth with spatial homogeneity was confirmed using micro- Raman technique. Vibrational modes of InBi and GaBi were observed in the two materials, respectively. In addition, vibrational modes corresponding to Bi and phonon-plasmon coupled modes were also observed. Experimental results indicate that Bi atoms homogeneously replace some of the As atoms in both InAs as well as in GaAs to provide good crystalline structures of InAs_1-xBi_x and GaAs_{1- x}Bi_x compounds, respectively.

With the increasing use of higher strength steels, the hydrogen content necessary to promote hydrogen assisted cracking (HAC) has become very small. This much lower hydrogen content level is approaching the uncertainty level of present diffusible hydrogen analytical practices, thus requiring the development of new analytical techniques. Efforts are being made to develop more sensitive and less time consuming methods for hydrogen measurement. An advanced design for a transition metal oxide based fiber optic diffusible hydrogen sensor has therefore been developed. The sensor allows measurement of hydrogen content directly from a welded structure, eliminating the need for duplicate welded coupons. The sensor generates the necessary analytical signal in less than one hour, and has been calibrated to yield results in ml H₂100 g weld metal. The sensor is also extremely sensitive to hydrogen and relatively inexpensive. The sensor shows excellent promise as an advanced hydrogen measurement technique, and research is continuing to establish procedures for transfer to industry.

All optical demultiplexing of a 40 Gb/s signal into four channels at 10 Gb/s each and an 80 Gb/s signal into eight channels at 10 Gb/s each have been successfully demonstrated using four wave mixing and phase modulation in traveling wave semiconductor amplifiers. The latter is carried out with the amplifiers in a Mach-Zehnder configuration. Our calculations show that four wave mixing is expected to perform the demultiplexing function for signal speeds to 1 Tb/s.

Selective proton bombarded buried stripe lasers have been developed using the tungsten filaments as a mask to proton bombard the current-blocking area. High reliability has been shown in high temperature accelerated aging tests. For the selective proton bombarded buried crescent laser diodes, the output power of 150 mW, the small signal modulation bandwidth in excess of 11 GHz for the 250 micrometer cavity length and full area electrode, and the shortest gain switched laser pulses of 7 ps FWHM by combined DC and microwave current injection are achieved.

We have measured the oscillation characteristic shifts of laser diodes originated from a magnetic field. We observed wavelength shifts toward the longer wavelength side, i.e., a red shift, by using the beat note between test and reference lasers at room temperature in more than five different laser types, whereas the experiments in early 60s showed a blue shift at extremely low temperature and in a very strong magnetic field. We also observed output power shifts toward the lower power side. Both characteristic shifts showed the same tendencies at increased temperature. So, we considered the magnetic field increases the temperature of the laser diodes and then two characteristics will change. Our experiment, however, showed that the amounts of changes in temperature, estimated from each characteristic shift, do not coincide with each other. At the first stage of our experiment, we removed the packaging parts of laser diodes because they are made of ferromagnetic materials. However, we recently observed the wavelength shifts using the laser diodes with the packaging parts. We are now expecting the changes of the current flow around the active region in the magnetic field can explain this discrepancy by using the correlation analysis between these two shifts.

As a result of the overwhelming demand for bandwidth, the number of channels offered in commercially available DWDM systems has climbed from 8 to 160 in just a few short years. With the growth in channel counts comes increasing demands placed upon optical amplifiers for the long haul market. High powers, flatter gain profiles, extended bandwidths (both C- and L-band), dispersion compensation, longer distances and greater control at the optical level are all capabilities that future networks will require. Today's optical amplifiers must be capable of supporting these services in advance of their installation to prepare networks for these foreseeable demands. Optigain's expertise and focus on optical amplifiers for the telecommunications industry has enabled it to achieve a technology leadership position in the field of optical amplification. Optigain's leadership position in the development of high power amplifiers based upon fiber laser technology will permit the Company to obtain favorable pricing and to gain significant market share in high growth markets. Figures 1 and 2 show the EDFA future global market shares.

A low cost and highly reliable fiber coupled laser diode is demonstrated with up to 1.0 W output power in 0.14 NA out of a 60 micrometer core fiber. Package reliability with extended operation at 600 mW is shown for over 600 hours at 85 degrees Celsius, and with stringent environmental tests, including thermal cycling, high temperature storage, and two sec. on two sec. off power cycling.

A 1.48-micrometer unstable-cavity laser is coupled into a single-mode fiber using three microlenses. Reproducible coupling of very high power is demonstrated with different types of lenses (plano-convex or bi-convex, with different apertures). Over 550 mW in single-mode fiber were reproducibly reached; to our knowledge, it is the highest power coupled into a single-mode fiber from a single semiconductor laser at this wavelength. Tolerance measurements on all of the coupling elements of a three-lens system are reported for the first time; an unexpected very large tolerance on the axial displacement of the second lens was measured. Results and interpretation with the aid of Gaussian and aberration simulations are also presented. Finally, we report on the first realization of a module with 46% chip to fiber coupling efficiency.

High power diode lasers can be used for a lot of applications such as pumping of solid state lasers, direct material processing (for example welding, soldering, annealing) and printing. The successful use of high power diode lasers depends on their high efficiency and reliability in combination with a long lifetime. For a further increase in the quality of high power diode lasers the properties of semiconductor laser bars have to be improved as well as the mounting techniques for these bars onto specially designed heat sinks. For most applications the electro-optical properties of the high power diode lasers have to be known exactly. Detailed information on the propagation characteristics and the transverse mode distribution of diode laser beams is necessary for the optimization of the overall performance. In addition the electro-optical characterization is a first test for the quality of high power diode lasers. An automated test set-up developed at the Fraunhofer-Institut fur Lasertechnik will be presented. The electro-optical data such as threshold current, slope efficiency, center wavelength, spectral width, total conversion efficiency and cw-output power can be measured as a function of driving current as well as the beam divergence angles in fast and slow direction of the high power diode lasers. Different methods to determine the exact divergence angles will be discussed. A high power test set-up is developed which allows driving currents up to 360 A. Using diode laser bars developed at the Fraunhofer- Institute fur Angewandte Festkorperphysik a record cw-output power of 267 W could be achieved at 333 A.

We have developed high power and highly reliable single-mode 980 nm laser diodes (LDs) as an excitation light source for erbium doped fiber amplifiers (EDFAs) for practical communication usage. We designed buried-stripe type 980 nm LDs with a weakly index guided structure to maintain a stable single transverse mode even in high power output operation. Regarding the typical initial device characteristics, a kink level of 315 plus or minus 15 mW was realized and the devices showed maximum light output powers of over 550 mW at 25 degrees Celsius and complete thermal rollover characteristics measured at temperatures up to 150 degrees Celsius with 800 mA current injection. In electrostatic discharge (ESD) tests, no significant change of light output and/or voltage versus current characteristics after forward bias discharges typically up to about plus 12 kV and reverse up to -30 kV (equipment limitation) was found. Regarding the reliability, we carried out long-term aging tests at 120 mW light output power at 50 degrees Celsius. In the tests, we confirmed no sudden failure and very stable spectral characteristics. In addition, we obtained similar degradation rates over different device groups. Furthermore, 150 - 250 mW light output aging tests also showed stable operation. The characteristics of these devices make them suitable for practical communication applications.

A single laser diode bar design, based on the AlGaAs material system, has been developed for high power, high reliability operation at a variety of CW and QCW operating conditions. The bar has a cavity length of 750 micrometer and a fill factor of 40%. Typical CW operation has a threshold current of approximately 10A and a conversion efficiency of greater than 45% at 40W. A variety of lifetests have been conducted at both CW and QCW operating conditions from the same bar design. On- going 3000 hr CW operation at 45C and 40W shows an extrapolated median lifetime (20% current increase) of 16,500 hrs at 45C or approximately 50,000 hrs at 25C (with 0.45eV activation energy). On-going 3000 hr QCW operation at 60C/60W and 35C/100W, with a pulse width of 200 microseconds and a duty factor of 2%, shows a median lifetime of approximately 10 billion shots and approximately 5 billion shots, respectively. In addition to single bar operation, this bar design can be stacked in various 2-D configurations. A 4 bar linear stack operating at 160W CW and a 6 bar vertical stack operating at 240W CW have been developed with superior performance. Results for high duty and low duty QCW stacks will also be presented.

We report device properties and results of lifetime tests for Al-free InGaAs/InGaAsP/InGaP broad-area (BA) laser diodes, emitting at 950 nm. The epitaxial layers were grown by metal organic vapor phase epitaxy (MOVPE). The mounted diode lasers have a high wallplug efficiency around 60%, for a resonator length of 2 mm, and about 50% for 4 mm long devices due to low threshold current densities of j_th equals 110 . . . 140 A/cm², high slope efficiencies of 75% and the typical low series resistance of the Al-free material. The lasers were mounted on copper heatsinks, episide-down as well as episide- up. Lifetime tests were performed with a facet load of 15 mW/micrometers at temperatures between 25 degrees Celsius and 70 degrees Celsius and with a facet load of 20 mW/micrometers at 25 degrees Celsius. All diodes survived 3000 h with degradation rates lower than 6 X 10^-5h^-1 at 50 degrees Celsius and 1 X 10^-4h^-1 at 70 degrees Celsius as well as 2000 h with a low degradation rates of 2 X 10^-5h^-1 at 20 mW/micrometer. As far we know, the results belong to the best ones reported until now for Al-free BA laser diodes.

Spatially resolved photo-luminescence (PL) line-scans were performed in a specific optical micro-probe to determine the soldering-induced local stresses in GaAs/GaAlAs laser diode arrays designed for high-power operation at 808 nm. In this approach, the sign and magnitude of the local stress are deduced from the spectral shift associated with band-to-band transitions in the GaAs substrate. The sensitivity (minimal equivalent hydrostatic stress that can be detected) is better than 10 MPa. The spatial resolution of the micro-PL technique (of the order of 1 micrometer), together with the short acquisition times, allows for detailed investigations of the stress profiles along the whole laser bars with a large number of data points. Different aspects of the mechanical stress distribution at the various steps of the process could thus be revealed. Finally, correlations between solder-induced stress distribution and estimated lifetimes were established. In particular, << V-shaped >> defects, which are known as a failure mechanism on this type of devices, were observed only on the laser bars for which the micro-PL indicates the strongest compressive stress. This leads to consider the micro-PL approach proposed here as a cost- effective screening technique for the high-power GaAs/GaAlAs laser diode arrays.

A compact optical sensor for the measurement of distance and displacement has been developed by using the self-mixing effect of a laser diode. Although the principle of self-mixing interference is different from conventional interference, it is shown that FFT analysis technique can also be used to detect the signal phase and increase the measurement precision of self-mixing interferometry. The optical phase of self- mixing interference is detected by FFT analysis, and the phase error caused by the laser frequency fluctuation was reduced by using a reference reflector. By these techniques, we can determine the distance from centimeters to a few meters and the displacement with nanometer precision.

High-power 980 nm-diode laser bars have been fabricated in the AlGaAs/GaInAs material system. The bars are 1 cm wide and comprise 25 broad area lasers with 200 micrometer aperture and 2 mm resonator length. Hence, the fill factor is 50%. To reduce the power density at the facet, we used an LOC structure with low modal gain, which also helps to prevent filamentation. The measured threshold current was 14 A and a record output power of 267 W cw was achieved at 333 A with an electro-optical conversion efficiency of 40%. With less thermal load, at 150 W output power the conversion efficiency was as high as 50% and the corresponding slope efficiency was 0.9 W/A. Microchannel copper heat sinks with a thermal resistance of less than 0.29 K/W were used for mounting the bars. The coolant temperature was set for all measurements to 22 degrees Celsius and the flux was 0.9 l/min. Additionally, the top electrode of the p-side down mounted bars was cooled by a second heat sink, which was pressed gently on the top electrode.

Improvement in the sensors used for the measurement of static and dynamic strain is a critical area of concern to developers of fiber-optic sensors. Polarimetric fiber sensors are considered as sensitive and simple in exploitation. We propose a modification of polarimetric fiber-optic sensor promising better stability compared with earlier versions.

The characteristics of different confined structures of AlGaInP/GaInP laser diodes grown by low-pressure multi-wafer metal-organic chemical vapor deposition have been discussed in this work. The constraint effect on the light and carriers in confining layers has been analyzed as well. To enhance the efficiency, the relatively low refractive index of AlInP was adopted as the cladding layer, in which the doping level of p- cladding layer was over 1 X 10¹⁸ cm^-3. Meanwhile, the GRIN-SCH structures were applied as confining layers to achieve optimum constraints of light and carriers. The threshold current was measured at 10.6 mA from the laser diodes emitting at (lambda) equals 652 nm with resonant cavity of 3.5 micrometer X 300 micrometer and 16.8 mA from the laser diodes emitting at (lambda) equals 639 nm with resonant cavity of 3.5 micrometer X 300 micrometer.