We demonstrated a 120-W side-pumped Tm:YAG laser with compound parabolic concentrators (CPC's) to couple the pump light into the laser rod. The optical-to-optical efficiency of this laser is 25.2% and the slope efficiency is 31.2%. At such high average power operation, we encountered severe thermal lensing in our Tm:YAG laser rod which prevented us from increasing the diode pump power due to the thermal rollover as the laser cavity become unstable. In this paper, Temperature was measured using IR camera. Temperature and stress distributions are obtained using finite element method. Those data can be used to estimate the fracture limit, the thermal lensing, the thermal distortion of the Tm:YAG laser and subsequently correct the thermal distortion using diffractive optical devices etc.

Passively Q-switching and mode-locking has been realized in a diode-pumped Nd:YAG laser using a GaAs wafer as an output coupler as well as a saturable absorber. The laser has a Z-type cavity to achieve a tight-focused beam at the saturable absorber and to realize an optimum mode matching in the laser crystal simultaneously. At an incident pump power of 13.8 W, the average output power was 1.62 W. The repetition rate and pulse width of the Q-switched pulses are in the range of 29 to approximately 73 kHz and 0.73 to approximately 1.87 microsecond(s) , respectively. The mode-locked pulses were measured to have a repetition rate of 154 MHz and an average pulse duration of 42 ps.

The paper analyzes the performance of plane-concave resonators with internal thermal lenses, and gives out stability and instability regions in terms of dioptric power. Based on stability region's symmetry and stable and unstable resonator's characteristics, relationship between resonators' loss and pump power is obtained, and then, a detailed analysis for output power of cw plane-concave Nd:YAG laser is presented. Experimental results clearly show the existence of two-peak structure predicted by the theoretical analysis.

In this paper, the performance characteristics of diode-pumped miniature CW Yb:YAG laser such as the temperature distribution and thermal lensing effect inside laser rod, and cw laser output are investigated. The laser output power of 2.5 W with the slope efficiency of 48.6% and opt-optical efficiency of 19.8% at the absorbed pump power of 12.6 W are obtained in experiment.

A fundamental understanding of the mechanisms and variables involved in mechanical and chemical material removal can reduce the trail and error involved in designing a polishing schedule. This paper summarizes some key results from the literature on the relationship between damage mechanisms, removal rates, materials properties and polishing machine variables. A case history on development of a schedule for fiber polishing illustrates some practical examples of the challenges encountered, and also discusses the effects of different abrasive materials.

For in situ/real time measurement, a retarder is substituted by a photoelastic modulator (PEM) in a polarimetry. The azimuthal position of the strain axis of PEM is directly determined with respect to the orientation of the transmission axis of polarizer and analyzer. The Mueller matrix of a twisted nematic liquid crystal (TN-LCD) is derived analytically. The phase retardation and the twisted angle of a TN-LCD are numerically obtained through two successive measurements of the Mueller polarimeter.

The paper presents a new method of measuring 3D small angles. In the method, a collimated parallel ray is projected on a double-face-reflector, a CCD detects the position changes of the returned light points. Compared with the traditional autocollimation system, the presented system can distinguish the small change of angle around axis z, therefore, the system realizes the measurement of 3D small angles. By matrix transform, the paper sets up the mathematics model between the position changes of the imaging points on CCD and the changes of spatial small angles. It describes the characteristics of this method and gives its resolving method. By simulations, the paper testifies the correctness of the system model and its resolving method. Furthermore, the paper analyses the effect of the system parameters on the system resolutions. The results can be used as the reference and basis while designing system. When the system parameters apply the values supposed in the paper, the resolutions of alpha and beta can reach 0.025'. The resolution of gamma, less than that of alpha and beta, is about 2'.

A miniature split-optics camera attachment with high index glass was developed for an optical sighting system. The system is designed to clip-on to an exiting eyepiece to monitor and record the sighting activities by the operator. This paper describes an optics design which makes use of very high index glass to prolong the eye-relief of the exiting eyepiece and allow the operator to operate the sighting system with his spectacles.

Silicon micromachines are an emerging technology that will impact almost every area of science and technology. From industries as diverse as automotive, cellular, aerospace, chemical as well as lightwave systems, N/MEMS (Nano/Microelectromechanical Systems) is rapidly becoming the solution of choice for many technical problems. MEMS devices are, in general, built using standard IC techniques. Starting with a silicon wafer and depositing a series of films such as nitrides, polysilicon, oxides and metals, one builds a complex three-dimensional structure in much the same way one builds an IC. However, unlike an IC, one then releases the device by etching away the oxides, producing a structure that can move. This subtle change in processing allows one to produce devices that move including rotary gears, hinges, plates, flexural beams and motors of every imaginable type. In optical fiber communication, MEMS allows one to build a wide range of components including data modulators, variable attenuators, optical switches, active equalizers, add/drop multiplexers, optical crossconnects (OXCs), dispersion compensators, all- optical switches, tunable laser sources, active packages and adaptive optical elements. In this paper, the design and fabrication of MEMS optical devices using readily available standard fabrication facilities for different fiber optical communication applications will be discussed in details.

The Benes network has two major advantages: one is that it has the lowest system insertion loss and the other is that it needs the fewest switches and drivers. However, lower signal- to-noise ratio (SNR) is its major disadvantage. The generally modified dilated Benes (GMDB) network has been proposed to obtain a higher SNR, but this network needs much more drivers. In this presentation, the modified Benes network is proposed to obtain a higher SNR with the same number of drivers as Benes network.

We present a novel technique to produce adjustable chirped fiber gratings that allows the spectral width tuning without center wavelength shift. The chirp rate can be precisely controlled by bending the uniform fiber Bragg grating (FBG) surface-mounted on one side of a simply supported beam. This technique allows the dynamic control of the spectral width of the chirped grating. It has a simple structure with a linear strain gradient. Both compression and tension are simultaneously applied to the beam, so center wavelength shift is avoided. In the experiment, a maximum spectral width of 18.3 nm is obtained, which corresponds to a chirp rate of 3.05 nm/cm. To the best of our knowledge, this is the largest chirp rate produced on a uniform FBG by using strain-gradient beam tuning technique. The proposed technique can also be used to tune the chirp rate of a linearly chirped grating.

We investigated the transmission of the long-period fiber grating (LPFG) with the linear chirp and with the nonlinear citric chirp, and detailed the cross-coupled constant Kac and chirp f, which affect the LPFG's transmission. With various cross-coupled constants, the filter can be of band-pass, band- reject or partial band-passing/reject. The effects of the high order citric chirp on the long-period fiber grating were in transmission and in the shift of the center wavelength.

In this paper, the effects of compression induced birefringence on reflection spectra of fiber Bragg gratings (FBG) is investigated experimentally together with the theoretical analysis. The coupled mode theory has been employed, by considering the LP_x and LP_y modes, to obtain accurate results for optical responses of FBG with compression-induced birefringence. The effects of polarization states of the incident light and compression conditions have also been investigated. Good agreements between experimental results and numerical simulations have been obtained.

A sensitive method based on the principle of photothermal lensing technique to realize optical logic gates is presented. A dual beam thermal lens method using low power cw lasers can be very effectively used as an alternate technique to perform the logical function such as XOR and NAND.

A compact and efficient diode-array pumped high power passively Q-switched N:YAG laser has been used to pump a quasi-phase-matched PPMgLN optical parametric oscillator. Stable laser pulses of duration of 3.0 ns, energy of 69.3 micro-joule and repetition rate of 7.0 kHz were generated from the passively Q-switched Nd:YAG laser at an incident pump power of 6.8 W. The periodically poled MgO-doped LiNbO₃ has an interaction length of 30 mm and a thickness 0.5-mm. The OPO generates signal and idler wavelengths tunable in the range of 1.48-1.59 micron and 3.78-3.21 micron, respectively, by using seven different poling periods. The measured signal output power was approximately 140 mW at an average incident pump power of 485 mW. The OPO was operated at around room temperature and no photorefractive effect was found.

Recently, we have obtained a 23.5 W of 2-micrometers intracavity OPO output which is, to the best of our knowledge, the highest power from an intracavity OPO reported in the literature. To achieve such high average power 2-micrometers OPO output in a simple and compact laser system, we have adopted the diffusion-bonded walk-off compensated (DBWOC) KTP OPO pumped by the anisotropy Nd:YALO laser. The walk-off compensated twin KTP crystals reduce the aperture effect due to Poynting's walkoff in the critically phase-matched parametric generation. At the same time, it increases the acceptance angle for the nonlinear interaction, resulting in more efficient OPO conversion. In addition, the diffusion-bonded configuration eliminates the optical losses at the in/out facets and the need for alignment of the crystals. In order to low down the OPO threshold and increase the effective gain of KTP OPO, we bonded two pairs of crystals together. In this paper, we will compare the recent results of the 2-micrometers KTP OPO results with different pairs of DBWOC KTP OPO. With two pairs of DBWOC KTP device, we observed 78% higher 2-micrometers average output power compared to one pair of KTP device.

This paper presents a novel 4 X 4 free-space polarization- independent bidirectional fiber optical switch based on 2 X 2 optical switch module. The optical architecture of the 4 X 4 optical switch is designed. The routing path for different switching state is analyzed in details. The performance analysis for this 4 X 4 fiber optical switch architecture is derived. The insertion loss of the 4 X 4 optical switch architecture is less than 4.4 dB and the interchannel crosstalk is less than -74 dB. The switch time is in microsecond range. This new kind of architecture of the optical switch grants the features of less optical components, high compactness, low optical interchannel crosstalk, fast switching sped, polarization insensitivity and easiness to optical assembly.

In this paper we reported the results of investigation on surface deformation caused by thermal effect during excimer laser ablation of polyimide. Obvious surface deformation around the hole entrance was observed during the experiment. The surface topology and cross-section of the ablated holes were analyzed using Zygo and SEM. It was shown that ring feature of 17 to 150 nm in height and 1 to 3 micrometers in width was formed above the level of the unablated surface. The deformed surface showed rough and color-changed characteristics. An optical diffraction model was employed to explain the causing of this kind of deformation. It was found that the ablating and heating by near- and under-threshold laser beam became thermal effect to polyimide material ablation, which was contributed by diffraction effect of optical projection system.

Glass is a hard transparent material with many applications in Photonics and advanced display industries. It is a high challenge to achieve crack-free glass microfabrication due to its special material characteristics. Laser-induced-plasma- assisted ablation is applied in this study to get the high quality glass microfabrication. In this processing, the laser beam goes through the glass substrate first and then irradiates on a solid target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed. At a small target-to-substrate distance, there are strong interactions among laser light, target plasma and glass materials at the rear side of the substrate. Light absorption characteristic at the glass substrate is modified since the plasma may soften and dope into the glass in the interaction area. To have a better understanding of this processing, signal diagnostics are carried out to study the dynamic interaction. It is found that glass microfabrication is closely related to laser fluence, target-to-substrate distance, laser spot size and laser beam scanning speed. With proper control of the processing parameters, glass surface marking patterning and cutting can be achieved. With different materials as the targets, color marking of glass substrate can be obtained.

In this paper, a fast process of fabrication of diffractive optical elements by excimer laser ablation of polymer films is mainly described. Dammann grating on PI and PC materials with feature size of 2 micrometers are successfully fabricated.

This paper reports the design and fabrication of holographic diffusers for diffuse infrared wireless home networking. Three optimization methods -- error reduction, input-output and simulated annealing, are employed to calculate the computer- generated holograms (CGHs), which are used to fabricate the holographic diffusers. To evaluate the performance of the CGHs generated using the different techniques, a cost function is defined and calculated for each hologram. The CGH generated from the simulated annealing is found to have the best output compared to the other two techniques. The diffusers are verified by displaying them onto a spatial light modulator. The fabrication of the CGH onto a piece of quartz with a pixel size of 14 micrometers X 14 micrometers using a laser writing system is also achieved.

In this paper we describe how finite difference time domain (FDTD) calculations can be used in the modeling of extremely short external cavity (ESEC) lasers. We concentrate on the applications of ESEC lasers in modern optical data storage systems: we study the operation of direct semiconductor laser read/write heads that utilize either a conventional edge emitting laser or very small aperture laser. The storage medium is assumed to be a first-surface-recorded phase change (e.g. SGT) disc. The external cavity is formed between laser's front facet and disc. The length of the ESEC is typically 0.1 to 1.0 microns. By using FDTD we can study the behavior of the electric field in the ESEC in detail, taking into account the vector field effects resulting from the three-dimensional nature of the data marks and laser apertures. We calculate the distributions of electric field amplitudes, power flow and absorption in/near the external cavity. In addition, we calculate the effective reflectance spectrum of the ESEC and use this data as input into a phenomenological laser model to simulate the readout signal (i.e. laser's output power and/or wavelength) as the disk is scanned. One-dimensional FDTD models were used for qualitative analysis of ESEC laser's wavelength and power characteristics.

In order to investigate numerically the effect of absorption on the photonic band gap, we consider a one-dimensional (1D) composite photonic crystal composed of alternating layers having complex dielectric constants. We perform calculations on the reflective spectra using the transfer matrix technique for the composite photonic crystal and find that the reflectance depends on material loss tangent Im((epsilon) )/Re((epsilon) ) and the scaled frequency (omega) /(omega) 0. It is shown that the absorption in composite photonic crystal breaks the periodic band structure produced by Bragg reflection in perfect photonic crystal. It pushes stop band-edges down, and raises the bottom of the pass band. The absorption makes the discrete stop bands become gradually a continuous stop band in larger-frequency range as material loss tangent Im((epsilon) )/Re((epsilon) ) increases.

An open cell photoacoustic configuration has been employed to evaluate the thermal diffusivity of pure InP as well as InP doped with sulphur and iron. Chopped optical radiation at 488 nm from an Ar-ion laser has been used to excite photoacoustic signals which been detected by a sensitive electret microphone. Thermal diffusivity value have been calculated from phase versus chopping frequency plots. Doped sample are found to show a reduced value for thermal diffusivity in comparison with intrinsically pure sample. The results have been interpreted in terms of the mechanisms of heat generation and transmission in semiconductors.

A new displacement measuring scheme based on simply supported beam is reported and demonstrated. The theoretical formula is derived and the experimental results are given. This device has many characteristics, such as simple structure, high sensitivity and good linearity. It is promising to be used into in-process displacement measurement.

A novel method, which utilizes amplified spontaneous emission (ASE) as a secondary pump source, is presented for implanting a linear cavity erbium-doped fiber laser operating in L-Band. The output wavelength tuned from 1566 nm to 1587 nm, about 21 nm tuning range, was obtained in the experiment and the stability of the laser is very good.

We introduce a novel electric current sensor, which is based on a fiber Bragg grating covered by a uniform coat of aluminum thin film which was deposited on the FBG by a simple evaporation method. The Bragg wavelength of the fiber grating shifts when the current flowing through the film varies due to the Joule heat generated by the current. The relationship between the square of the current intensity and the wavelength shift is basically linear. In the experiment, the maximum current can be measured was 43.1 mA with the wavelength sift of about 4 nm and the current sensitivity was about 2.31 X 10^-3 nm/(mA)².

Without any stabilizing equipment, a multi-wavelength fiber linear cavity laser in L-band was obtained at the room temperature. The cavity was formed by two linear fiber loops. Utilizing the birefringence of the single mode fiber, we can make the reflectivity of these fiber-loops vary periodically with the wavelength. Two polarization controllers (PCs) were inserted into fiber loops. By changing the states of PCs, the number of the lasing wavelengths and wavelength spaces can be controlled.

A portable and practical fiber-type sensor, with which can determine the refractive index and the concentration of the liquid, has been designed and realized. The method combines simplicity of structure, facility of operation, wide range of measurement and low price. It can be used either by immersing the liquid or by pouring one drop of liquid into the sensing head. The measuring resolution of the refractive index is 1.41 X 10^-4 for the refractive indices of 1.33 - 1.70, and the measuring resolution of the concentration is 2.67 X 10^-4 for the salt solution and the sugar solution.

The transmission of polarized light through plastic optical fibers (POFs) is studied. The purpose of this work is to analyze the relationship between the depolarization of the light along the POF and the quality of the fiber. We found that the light polarization is lost for fiber lengths larger than 30 cm. At the fiber output, the polarization state is always partially elliptic, and the rate of depolarized light increases with fiber length. The depolarization also depends on the fiber core radius as well as on the light launching angle.

We demonstrate a wavelength- and bandwidth-tunable reflective filter based on a novel fiber Bragg grating chirping technique. The new technique allows grating to be chirped in a wide range without center Bragg wavelength shift. The tunabilities of the new band reflective filter are based on the responses of the grating pitch to the temperature and the applied strain gradient. It enables wavelength and bandwidth tuning ranges up to 5.2 nm and 10.9 nm, respectively.

Optical coherence tomography (OCT) is used mainly for noninvasive cross-sectional imaging in biological systems. In this technique, a lateral scanning low-coherence interferometer is employed to produce a two-dimensional image of an object's internal microstructure. This paper presents an experimental OCT measurement system based on a bulk-type Michelson interferometer illuminated by a superluminescent light source. The system was used to provide a visual image of multilayer plastics. In addition, the research team conducted experiments to measure the thickness of varnish on top of plywood and experimented with paper measurements. The system produced two-dimensional pictures of multilayer plastics, showing that it is applicable to transparent media.

In this paper, the measurement and analysis of the second-generation image intensifier have been discussed in detail. On the base of analyzing on the noise measurement principle of the second-generation image intensifier, the variable aperture & dynamic scanning noise measurement technique has been put forward. By using photoelectric multiply-tube which is low noise and high gain as the low light detector, the variable aperture & dynamic scanning noise measurement system of the second-generation image intensifier has been developed. The design and the schematic diagram of this noise measurement system have been present. Based on the above, the SNR has been tested and analyzed with variable incidence illumination, variable aperture in fixed-point measurement and scanning measurement condition. The corresponding noise distribution curves have been drawn. At last the characteristics of this noise measurement system of the second-generation image intensifier have been given out. This noise measurement system has important meaning on the design, evaluating and manufacturing of new photoelectric imaging device.

The Shape of an object can be determined by analyzing the distortion of optical grating projected onto it. Many available approaches could be used for this kind of analysis, however most of them require massive computation such as Fourier transformation. Alternatively, direct image processing could be used to give an efficient and accurate result. The profile of the object can be expressed in terms of wire-frame or texture mapped model.

Two-phase flow in pipelines containing elbows represents a common situation in the oil and gas industries. This study deals with the stratified flow regime between the gas and liquid phase through an elbow. It is of interest to study the change in wave characteristics by measuring the wave velocity and wavelength at the inlet and outlet of the elbow. The experiments were performed under concurrent air-water stratified flow in a horizontal transparent polycarbonate pipe of 0.05m diameter and superficial air and water velocities up to 8.97 and 0.0778 m/s respectively. A non-intrusive video imaging technique was applied to capture the waves. For image analysis, a frame by frame direct overlapping method was used to detect for pulsating flow and a pixel shifting method based on the detection of minimum values in the overlap function was used to determine wave velocity and wavelength. Under superficial gas velocity of less than 4.44 m/s, the results suggest a regular pulsating outflow produced by the elbow. At higher gas velocities, more random pulsation was found and the emergence of localized interfacial waves was detected. Wave velocities measured by this technique were found to produce satisfactory agreement with direct measurements.

A postfabrication technique for writing fiber Bragg gratings in H2-loaded fiber with precise wavelength control is reported. The grating wavelength is highly stable and less than 0.01 nm shift was observed after storing at room temperature for 2 months. This technique allows 1 nm of wavelength trimming and significantly enhances the grating thermal stability.

We investigate an attenuated total internal reflection (ATR) modulator, which can be fabricated by depositing an ultra-thin Au film, an electro-optic (EO) polymer film and an Au electrode on a prism. At a certain incidence angle, the incoming TM-polarized beam can excite a surface-plasmon wave (SPW) propagating at the metal-polymer interface. The intensity modulation of the reflected beam is possible because of the sensitivity of the coupling efficiency to the refractive index of the polymer. An alternative design uses a thin dielectric film between the prism and the Au film but gave no better results. The device potentially provides low fabrication cost and very high frequency operation, and the polymer losses are not a significant issue. A modulator structure was optimized with simulations to achieve maximum modulation depth. The optimal thicknesses were in the range of 30 to 35 nm and 1 micrometers for the Au and polymer films, respectively. Nevertheless, the achievable modulation depth is rather small even with polymers of high EO coefficient and the operation of the device is sensitive, especially, to the incidence angle as well as to the polymer thickness due to the coupling of two SPW modes.

From the laser cavity theory, we analyze the stable properties of the cavity in the conditions of various parameters, and then the output power curves of the laser are fully analyzed. The results show that the double-peak shape of the curves does not appear in three special cases of cavity parameters, in two of which there exist wide regions for stable output. Based on heretical analysis, we design a laser with proper cavity parameters and obtain some experimental results, which coincide with the theoretical expectations.

A microprocessor controlled feedback system using a linear variable differential transformer to measure the compression of a fiber Bragg grating with a view to improve the tuning accuracy of a fiber grating laser is reported. This technique overcomes the large hysteresis of the PZT actuator normally used to compress the grating. A tuning range of about 20 nm with a readout wavelength accuracy of better than +/- 0.05 nm was achieved.

An active interrogation technique for a 16-cascaded wavelength-division multiplexing fiber Bragg grating sensor system is proposed. The system has been demonstrated using a combination of a feedback control technique, which makes the transmission of an employed tunable F-P filter track the Bragg wavelength of the interrogated sensor automatically, and a technique for choosing the output wavelength of a ring- compounded-cavity fiber laser by tuning the applied voltage of the filter. Demodulated by using an unbalanced scanning Michelson interferometer, a sensitivity of 1.682 Deg/(mu) (epsilon) has been achieved.

A novel technique to increase the temperature sensitivity of LPGs by exploiting the relatively large thermal coefficient of index-matching fluid to induce a large spectral shift of the LPG is reported in this paper. It is shown that the wavelength shift with temperature for such a LPG sensor can be as much as 1,500 times larger than that of sensors made of fiber Bragg gratings. A LPG-based temperature sensor with a resolution of about 0.03 degree(s)C is reported.

In this paper, we report a compact mid-IR intracavity OPO, which has 4.1 W of 3.5-micron output from a non-critically phase-matched (NCPM), type II, KTiOAsO4 (KTA) optical parametric oscillator (OPO). This KTA OPO was pumped within the cavity of a Q-switched diode-pumped Nd:YALO laser operating at 10 kHz. We adopted the simplest configuration with a compact diode-pumped Nd:YALO module pumping the singly resonant KTA OPO. Besides 4.1 W of 3.5 um, 10.9 W of 1.5 micron and 11.3 W of 1-micron radiation were obtained simultaneously.

In the processing of excimer laser ablation of nozzles on polyimide in air, both gases like CO₂, CO and HCN and solid debris including C₂ approximately C₁₂ are produced in laser ablation area. In this paper, we reported for the first time a Nd:YAG laser cleaning of ablation debris generated in excimer laser ablation of polyimide. It demonstrated effective cleaning with the advantages of shortening cleaning cycle time and simplifying cleaning process. The laser used for the cleaning was a Q-switched and frequency doubled Nd:YAG laser with wavelength of 532 nm and repetition rate of 10 Hz. The laser cleaning effect was compared with conventional plasma ashing. AFM measurement showed that the Nd:YAG laser cleaning had no damage to the substrate. XPS results indicated that the polyimide surface cleaned with laser beam had a lower oxygen/carbon ratio than that of plasma ashing. The study shows that frequency doubled Nd:YAG laser cleaning is effective in ablation debris removal from excimer laser ablated polyimide.

Neodymium-doped strontium fluoro-vanadate is a favorable laser material for diode-pumped, compact, and passively Q-switched lasers. We have constructed a high power passively Q-switched Nd:S-VAP laser with a fiber coupled 10 W laser diode pumping. To avoid severe thermal deposition and thermal induced crystal fracture, several measures have been taken in the laser design. With a Cr⁴⁺:YAG of initial transmission of 80%, stable laser pulses of duration of 3 ns, energy of 45 micro-joule and repetition rate of 23 kHz are obtained at an incident pump power of 7.75 W.

The design of three cavities for a solid-state Nd:YVO₄ laser side-pumped by a diode laser is presented as well as the theoretical model and computed simulation developed to describe each system. The computed results are compared with the experiments demonstrating to be in accordance with each other. It is found that an elliptical cavity provides the best balance between the laser output power and quality of a transversal beam profile.

Luminescence spectra of Tm³⁺ ion have been investigated for YVO₄ and LiNbO₃ crystals by excitation with 798 nm laser diode of high powers in a range from 0.6 W up to 10 W. In addition to the one-photon excited infrared emission bands, emission bands at 700 and 1208 nm are observed in YVO₄ by high power excitation and the similar emission bands are observed at 702 and 1216 nm in LiNbO₃. It is observed that each of the 700 and 1208 nm emission intensities in YVO₄ has quadratic pump-power dependence in a pump power range of 0.6 - 4 W and cubic dependence in 4 - 10 W range. Same result is observed for the 702 and 1216 nm emission in LiNbO₃ but the change from the quadratic to cubic dependence appears at 5 W. Discussion is made on the luminescence process for these up-conversion.

A laser-diode based optical sensor for laser particle counter is described,nd some calculated and test results are reported in this paper. A low-powered 650 nm laser diode is used as the light source. The optical system of the sensor is a right- angle scattering optics, which consists of an illumination system and a wide-angle collection system for scattered light. The sensor features high counting efficiency and high signal- to-noise ratio for smaller particles.