2010 Vol. 3, No. 4
Up-conversion luminescence in rare earth doped materials is an important approach for the optical frequency conversion as well an important aspect in the researches of luminescent materials. On the basis of the introduction of fundamental concepts of the up-conversion luminescence, the research history of up-conversion luminescence of rare earth doped materials was briefly reviewed and the up-conversion mechanisms including energy transfer, excited state absorption, co-operative sensitization, co-operative luminescence, two-photon absorbed excitation and photon avalanche processes in rare earth doped materials were summarized and compared with each others. Then, the up-conversion luminescence mechanisms for various rare earths doped materials were summarized and the host materials such as phosphors, crystal and non-crystalline solids for rare earth were introduced. Finally, the factors influencing the up-conversion luminescence efficiency were analyzed. It was pointed out that the absorptions of pumping light and emitting light, phonon energies of host materials, the choices of doping ions and pumping routes must be considered in the designs of up-conversion luminescence materials.
With the large applications of the two-mirror optical system with hyperboloidal secondary mirror to astronomical and spacial fields, the aperture and relative aperture of the mirror grow larger and larger, which demands the measurement techniques to be improved greatly. According to the parameters of internationally typical hyperboloidal secondary mirrors, the basic specification and developing trends of secondary mirror is analyzed. The surface measurement method in overseas for the secondary mirror is emphatically introduced, and the corresponding key techniques and applicability are analyzed. In addition, the status of surface measurement method in our country for the mirror is also introduced. Finally, the developing trends of surface measurement technology for the secondary mirror are summarized and prospected, it points out that the research on measurement method in future should focus on the transmission materials with high homogeneity, high precision and large aperture auxiliary components and the measurement methods and data processing based on sub-apeature stitching.
The reasons which effect on the surface quality of vitreous optics was investigated and the surface micro-crakes were regarded as a main source that could change the surface strength. The causes of the surface micro-cracks were analyzed based on the mechanical grinding and forming process, then, the crack tip stress concentration and the Griffith energy balance theory were used to analyze the crack propagation mode. Combined with the surface structure defect theory and grinding crafts, the removal mechanism of micro-cracks and the effect of HF etching method were described. Finally, the methods to enhance glass strength by manufacture technology were proposed, which focus on the some surface processing, such as ion exchanging, coating and HF eting. It suggests that the HF etching would be more suitable for the removal of surface micro-cracks in processing the vitreous optics..
Dynamic Infrared Scene Projection(DIRSP) technology is a major method to evaluate the performance of infrared imaging measurement and tracking systems. The developments and applications of DIRSP technology at home and abroad are reviewed in this paper. Some of the popular DIRSP technologies and their characteristics are provided, then the operating principle and mechanical structure of a Digital Micromirror Device(DMD) are given. A new projection display technology based on DMD called Digital Light Processing(DLP) is briefly introduced, which can be divided into three types according to the number of DMD chips contained. The different features and applications of the DLP are also described. Furthermore, this paper lays particular emphasis on a DIRSP system based on DMD, namely, Micromirror Array Projector System(MAPS). It analyzes its operating principle, basic design, performance capabilities and technical advantages and discusses the key technical issues to be used as a DIRSP. In the end, based on the application background and research status of DIRSP, it presents the following step of research work.
The current international levels of stray light measurement technologies for a space-borne imaging spectrometer are introduced and the definition of stray light and it's source and harmfulness are discussed. The cut-off filter method, spectrum method, spectral stray light factor method, series transmission method, oxygen absorption spectra and parameter fit method, convolution method and correcting matrix method are described to compare their advantages and disadvantages in the stray light measurement, then the specific requirement of the stray light measurement of space-borne imaging spectrometer are given. Finally, the trends of development of stray light measurement for space-borne imaging spectrometers are summarized, which point out that the independent measuring method for stray light can not meet the needs of practical engineering and the compound measuring technologies will be a developing direction for stray light measurements of space-borne imaging spectrometers.
By applying a traveling-wave coupling field, a standing-wave grating field, and a static magnetic field to a cold atomic ensemble, a dynamically controlled cavity consisting of two Bragg regions of high reflection and an electromagnetically induced transparency region with high transmission is realized. With modulating all the three fields in time, a weak probe pulse is sent into the coherently induced optical cavity to achieve several periodic oscillations and then it is retrieved after a short time. This physical phenomenon is accompanied with little energy loss and can be regarded as an efficient scheme for dynamic light storage. This paper simulates the dynamic light storage scheme, discusses numerically its advantages and presents the developing trend of the scheme.
Diffraction properties of high-density gratings are polarization-dependent, which are different from those of conventional gratings. For TE- and TM-polarized incident waves with a wavelength of 1 550 nm and a duty cycle of 0.5, diffraction efficiencies in the 0th and-1st orders are calculated using Rigorous Coupled-wave Analysis(RCWA). It indicates that more polarization-dependent characteristics are shown for the period 1 200 nm compared with 1 550 nm. Especially, with the period 890 nm, the diffraction efficiency of TE-polarized wave changes with grating depth sinusoidally, while the efficiency of TM-polarized wave which has polarization-selectivity is always concentrated on the 0th order. According to modal method, modes excited by the incident wave are investigated for different periods and the accumulated phase differences of the two modes with different effective indices are calculated when they propagate through the grating region. Moreover, diffraction efficiencies in the 0th and-1st orders are simulated based on two-beam interference. Experimental result shows that the numerical calculation result using RCWA coincides well with the theoretical predictions of modal method, which can explain the physical mechanism of polarization-selectivity of high-density phase gratings.
In order to calculate the atmospheric transmittance more correctly, the empirical expression of atmosphere transmittance which should be considered in the design of lidar systems based on Mie theory was analyzed in this paper, and the disadvantage of the empirical expression was demonstrated. In consideration of the merits both the empirical expression and MODTRAN software, they were combined to calculate the atmospheric transmittance. As a result, a modified transmittance expression was achieved. The atmospheric transmittance experiments of CO2 laser were completed under the theory above. The actual results and the theory have some differences without considering the atmosphere turbulence, but there is no impact on the practicability of the theory. The experimental results show that the energy drift ratio of the laser is 6.18% at the output window, and 8.3% and 50.2% at the distances of 50 m and 1000 m, respectively, which means the ratios increase with the enlargement of distance. The main reason of the drift is the atmospheric transmission according to the experimental environments. Excluding the drift ratios at the output window of the CO2 laser, the energy drift ratios are 2.12% and 44.02% at 50 m and 1 000 m, respectively. The experimental results demonstrate that the energy twitter has been so fiercely at 1 000 m, therefore, the adaptive optics compensation is very important in the long-range atmospheric transmission.
A new design of illuminating system used in fundus cameras was proposed. The design was a improved system based upon Kohler illumination, and it used the near infrared light which could not be felt by human eye to deal with the problem of iris shrinking effect when illuminating light flashed. The design had only four lenses and the illuminated area could be adjust continuously, meanwhile the energy of the illumination light could be used efficiently. By inserting black dot boards and a ring stop in the light, the design could shield almost 99% stray light, and the Ratio of Signal to Noise(S/N) of the system could be up to 20 dB. The Gullstrand_Le standard eye model was used in the system, and a uniform illuminated area with the uniformity of 95% could be achieved.
The same optical product can show different stray light coefficients in different measuring conditions, and it is impossible to compare the different results correctly. According to this situation, the stray light coefficients of several kinds of optical lenses have been experimentally investigated in different measuring conditions, such as sizes of block body, receiving apertures of photoelectric device and mounting the collimating objective or not, and the theoretical analysis and experimental results supply the dependences of stray light coefficients on test conditions. The experimental results indicate that the larger size of the black body, the smaller value of stray light; the larger receiving aperture of photoelectric receiving device, the larger value of stray light; the use of collimating objective will induce new stray lights which increase the value of stray light in experiments, but the increased part can be deducted from the results, as the value can be seen a fixed one.
A novel active hyperspectral imaging system in which a digital filter is specially designed as a creative component is developed for calculating the spectral cube and spectral response of an object. Based on the refit of a general WDF Wadsworth monochromator, the system enhances the exit flux and improves the optical intensity radiated on the object when the light incident keeps a constant. Furthermore, the optical narrowband filter is replaced by a digital filter. The hyperspectral imaging system resolves the problem of the system with a number of optical filters which can not be adjusted continuously, and it has lower cost than other filters. Meanwhile, the system is easy to implement, wavelength tunable, and band variable. According to the characters of the system and image gathering, the calculation method is supplied and the inaccuracy is less than 2 nm. The spectral cube and response of green leaves are successfully achieved, and the system is suitable for the spectral measurements with a small view in laboratory.
In order to ensure that photoelectric instruments can identify and track elliptical objects accurately, a new algorithm based on Hough transform is proposed. The new algorithm randomly samples two points, and then searches the third point using the characters of ellipse's pole and pole chord, and eliminates lots of invalid samples. In the following, it uses the three points as the centers to make three square windows, and then all the points in the windows are used to fit the ellipse. When a candidate ellipse is validated, a new method is proposed to judge if edge points are on the ellipse, and an adaptive threshold is supplied to confirm real ellipses. The experiment indicates that the algorithm's average length error is 0.5 pixel, average angle error is 0.6, and the average time needed is 79 ms. In conclusion, the algorithm has high precision and high speed, and shows a good capability of detecting ellipses.
We demonstrate an all-optical switching of the magnetic resonance properties associated with a metallic Split Ring Resonator(SRR) array. The periodically spaced elements are fabricated on a high-resistivity silicon wafer and probed by using conventional Terahertz(THz) time-domain spectroscopy. We use a continuous-wave laser diode to generate carriers in the gaps of the SRR elements. Using a sufficient power, this optical excitation can create an effective short gap, which would switch the resonant properties of the metamaterial from that of an SRR array to that of a closed ring resonator array and leads to dramatic changes in the THz transmission. In the present experiment, the optically induced switching is associated with the magnetic resonance. However, with appropriate changes in the device structure, this approach can be extended to switch a medium with a negative real index of refraction to a medium with a positive real index of refraction. This opens the way to creat a broad new range of active devices.
The surface temperature measurement of temperature target based on a medium wave infrared detector was researched theoretically and experimentally in this paper. The constitution and measurement principle of the system were introduced and a temperature measurement model for the infrared detector was established. The gray drift characteristics of the infrared detector in a calibration were analyzed, and the drift disciplinarians were summarized by four kinds of different experiments. Meanwhile, the drift compensation method was proposed based on the drift disciplinarians. Finally, a temperature measurement experiment was carried out, and the results show that the measurement error before and after drift compensations are 1.965 ℃ and 0.335 ℃, respectively, which indicates that the measurement precision has been improved in a great degree after the compensation.
In order to test the air quality in real-time, an optical and mechanical structure of on-truck infrared detection equipment is designed. Using large aperture optical system, high precision scanning structure and unfocus reflecting telescope, the system achieves 0-360 scanning in orientation and pitching. The structural static analysis of the system is performed using finite element method and the results meet the optical and mechanical design requirements. A modal test is done by hammer beat method and a vibration test is carried out under the on-truck environment. Comparing the two results above, the first-order frequency of the optical and mechanical structure is 52 Hz, which has sufficient dynamic stiffness corresponding to the 12.5 Hz in the on-truck environment and can ensure the stable operation of infrared detection devices.