Absolute interferometric testing of spherical surfaces is one of effective methods for ultra-precision testing, which can
eliminate the systematic errors. In this paper, we discuss the absolute measurement of spherical surfaces and analyze the
influence of errors existed in the organism comprehensively. To improve the testing precision, it is necessary to remove
the alignment errors such as tilt and defocus. The traditional methods remove alignment errors by low-level
approximation, so they may be not effective for the small F-number surface. To solve this problem, we propose a novel
measurement with high-order approximation model. The simulation and experiment results show that: while the error
between high-order approximation model and low-level approximate model is small on tilt, it is large on defocus, and the
error will become larger when the F-number of testing surface becomes smaller; alignment errors can be well adjusted by
our high-order approximation model.
The precision measurement on surperfinish surface scratch has been currently paid much attention to on electronic
products. To meet these demands, a novel method has been proposed which is based on heterodyne interferometry that
utilizes birefringent lens as beam splitter and cantilever tip as scanning probe to get the measurement values of sample
topography. But the optical nonlinear errors affect the measurement precision of the system. In this paper, we adopt the
Jones matrix to analyze the elliptic polarization caused by the three factors existing at the same time, which are
polarization ellipticity of laser source, installation orientation error and phase retardation of birefringent lens. The
measurement errors of frequency mixing about these elliptic polarization beams arriving at the photodiode detecter are
studied by vector theory. The results show that the measurement errors are periodic errors, and they will change from
1.24nm to 3.94 nm when the magnitude of orientation error of birefringent lens changes from 1°to 5°. Also, the methods
of reducing measurement errors according to the numerical results in the system are suggested. The measurement
precision will be improved by reducing the orientation error or choosing high performance laser source.
Optical array technology is an attractive method of achieving high power output using diode bars, which is different from using traditional diode stacks. Reflectors are the main optical elements in optical array diode lasers, and their influences of alignment errors on the output beam are analyzed using the matrix method. Analytical expressions of the beam size and deviation influenced by the misalignment of the reflectors are deduced, and the misalignment tolerances are also given. Based on the results, it is helpful to adjust the reflectors to achieve an output beam of good beam quality from the optical array diode lasers.
A kind of novel power splitter built with two-dimensional photonic crystals based on directional coupling is proposed. Different output power levels are achieved by changing the coupling length. The distribution of light intensity in the coupling waveguides is investigated and the dependence of transmission on coupling length is provided. A good agreement between the theoretical and experimental output transmissions is shown. With the low-loss bends, a total transmission up to ~0.96 is achieved. The power in each branch can be easily further split.
The performance of code-division multiple access (CDMA) as a multiple-access technique for optical wireless communications is evaluated. The information data is modulated through dual-amplitude pulse interval modulation (DAPIM). Optical orthogonal code is used as the signature sequence. The upper bound and lower bound on the exact probability of errors per slot and per packet are derived in the presence of ambient background noise. We investigate the performance characteristics for various system parameters, including the SNR of the source information bits, receiver threshold, DAPIM order, and number of users.
A split Monte Carlo algorithm based on Phong's radiation model for the calculation of the impulse response on infrared wireless indoor channels with various reflecting property is presented. It allows evaluation of not only Lambertian-diffuse but also direction-diffuse reflections. The numerical burden can be dramatically reduced with nearly geometric growth in the number of rays compared to classical deterministic algorithm for exponential ray growths.
Non-critical phase-matching KTP OPO pumped by single-cell-SBS and dual-cell SBS phase-conjugation beam, which is generated by backward stimulated Brillouin scattering (SBS) on Nd:YAG laser as pumping source, is presented together with the maximum output energy 21 .6mJ and the corresponding conversion efficiency 32%. And it has obtained tunable pulse-width ranging from less than ins to 6ns and comparatively high conversion efficiency with a low-power pumping laser. The output character of this OPO is also analyzed with experiment results according to characteristics of long-pulse pumping OPO.
Passive Q-switched operation of a LD-pumped Nd:YVO4 laser is studied with a saturable absorber GaAs as a passive Q-switched component and F-P output coupler. Q-switched pulses with pulse duration 47ns, pulse repetition rate 1183 kHz, pulse average power 430mW and beam quality M2=1.13 in a TEM00 mode were produced with Q-switched pumping threshold 1700mw. We performed numerical calculations of coupled wave equations for case of GaAs playing the role as mentioned above, discussing passive Q-switched mechanism and the dependency ofpulse duration and pulse repetition rate on pumping rate, which was well in agreement with the experiments' results. A brief and effective technique for compact Q-switched solid-state laser having multiple functions is provided.
In FTIR film thickness measurement system, traditional process for determining film thickness is optical interference method or absorption method. In practice, both interference effect and absorption effect make a partial contribution to spectrum respectively. When both of the tow effects have influence on measurement, neither interference method nor absorption method can be individually used to determine the film thickness accurately. A new mathematical correction method is described for FTIR film thickness measurement in this case. Employing this new mathematical correction method, the effects of interference and absorption can be apart form each other effectively. The film thickness measurement accuracy of (lambda) /100 has been achieved.
A high-speed automatic agricultural produce grading and sorting system using color CCD and new color identification algorithm has been developed. In a typical application, the system can sort almonds into tow output grades according to their color. Almonds ar rich in 18 kinds of amino acids and 13 kinds of micro minerals and vitamins and can be made into almond drink. In order to ensure the drink quality, almonds must be sorted carefully before being made into a drink. Using this system, almonds can be sorted into two grades: up to grade and below grade almonds or foreign materials. A color CCD inspects the almonds passing on a conveyor of rotating rollers, a color identification algorithm grades almonds and distinguishes foreign materials from almonds. Employing an elaborately designed mechanism, the below grade almonds and foreign materials can be removed effectively from the raw almonds. This system can be easily adapted for inspecting and sorting other kinds of agricultural produce such as peanuts, beans tomatoes and so on.
A measurement system utilizing interferometry and correction method has been developed to conduct fast and accurate measurement of ultrathin film thickness and spacing between two separated surfaces. According to the intensity of the interference pattern and the correction method, the ultrathin thickness or spacing is obtained exactly and quickly. After diffracted by a concave grating, the entire visible spectrum of the interference pattern is received simultaneously with a CCD array. Due to the numerical differentiation and average data processing method, the impacts of the light source, the reflecting surfaces, the grating and the CCD array are eliminated automatically. A numerical filtering technique used in the system significantly reduces the noise, thereby yielding a good signal to noise ratio. An ultrathin thickness of (lambda) /20 ((lambda) is the wavelength) is obtained by a numerical analysis of the measured data, which is remarkably less than the limitation, (lambda) /4, by the conventional method.
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