Wavefront coding for athermal technique can effectively ensure the stability of the optical system imaging in large temperature range, as well as the advantages of compact structure and low cost. Using simulation method to analyze the properties such as PSF and MTF of wavefront coding athermal system under several typical temperature gradient distributions has directive function to characterize the working state of non-ideal temperature environment, and can effectively realize the system design indicators as well. In this paper, we utilize the interoperability of data between Solidworks and ZEMAX to simplify the traditional process of structure/thermal/optical integrated analysis. Besides, we design and build the optical model and corresponding mechanical model of the infrared imaging wavefront coding athermal system. The axial and radial temperature gradients of different degrees are applied to the whole system by using SolidWorks software, thus the changes of curvature, refractive index and the distance between the lenses are obtained. Then, we import the deformation model to ZEMAX for ray tracing, and obtain the changes of PSF and MTF in optical system. Finally, we discuss and evaluate the consistency of the PSF (MTF) of the wavefront coding athermal system and the image restorability, which provides the basis and reference for the optimal design of the wavefront coding athermal system. The results show that the adaptability of single material infrared wavefront coding athermal system to axial temperature gradient can reach the upper limit of temperature fluctuation of 60°C, which is much higher than that of radial temperature gradient.
A measurement region extended differential laser Doppler velocimeter with multipoint illumination was proposed. The arrangement used two types of ruled diffraction gratings to form the extended region with several independent measuring volumes. The measurement model was then given, demonstrating that a solid object passed through a single measuring volume or two measuring volumes simultaneously. Signal processing technique efficiently enhanced the signal-to-noise ratio. Experimental results showed that the measurement range along the optical axis could be extended to 109.73 mm with a beam angle of 9.557 deg. The mean error of velocity ranging from 7 to 13 m/s was 1.52% by using the frequency spectrum correction method. The results indicated that the proposed method has great potential for realizing the velocity measurement of solid objects in a large measuring region.
A modified Michelson interferometer for spatial phase shifting speckle shearography is presented. The interferometer consists of one slit aperture, one beam splitter, and two spherical mirrors. Spatial carrier frequency and shear are both generated by one translated spherical mirror. The slit aperture controls the speckle size. These arrangements make the system simple and easy to align. The shear is proportional to the translation of the spherical mirror. Shear distortion due to the rotated mirror in a traditional Michelson interferometer is avoided as well. The carrier frequency is proven to be constant in image plane and can be conveniently adjusted by translating the spherical mirror without changing imaging setup. Fourier analysis method is applied to accurately calibrate carrier frequency. Finally, experimental dynamic deformation results of a center loaded metal plate using the proposed method are provided.
Dynamic speckle pattern interferometry has been widely applied to measure vibration or continuously-deformation. As a
promising technique, temporal phase analysis reduces the 2D phase retrieval task to 1D and gives wider measurement
range. In this paper, some classical and recently proposed temporal phase retrieval techniques, such as windowed Fourier
transform, wavelet transform and Hilbert transform, are comparatively studied. The advantages and drawbacks of each
algorithm are discussed and evaluated in simulation experiments.
Dynamic speckle interferometry using temporal phase analysis has larger measurement range and is easier to setup over
phase-shifting based speckle interferometry. Hilbert transform (HT) is a widely used approach to implement analytic
method based phase retrieval. To fulfill the requirements of HT based phase retrieval, EMD (Empirical Mode
Decomposition) can be applied to remove the bias intensity. With the low noise assumption, the first IMF was taken as
the input for HT. However, according to our experiments, some dynamic speckle signals are not as good as assumed. In
many cases, the first IMF is not the proper one. To find the proper IMF, we proposed to adaptively find the IMF of
largest similarity with the input signal. And the similarity is evaluated by mutual information. Simulation experiments
were given to verify the validity of the proposed algorithm.
In order to measure the 3D architecture of tire size code, Digital Speckle Pattern Interferometry (DSPI) and Phase
Shifting interferometry(PSI) were integrated to capture its phase. With capturing speckle pattern interferogram by
reference-wave interferometry, the illumination laser diodes of DSPI-PSI interferometer were arranged to enlarge the
illumination area; and the viewing field was also expanded by battery of lens containing field lens and imaging lens. To
generate a phase difference associated with height of test surface, the illumination beam was rotated by motor. The
experiment results show the viewing field was more than 60 degree, the resolution of surface profile match the tire size
code height as 1mm.
Using Digital Speckle Pattern Interferometry (DSPI) method measuring the large object in practice, the
primarily problem is uniform illumination. This paper presents a method that using multiple laser
beams to enlarge the illumination area and analysis the non-uniform illumination influences for
interferogram. We design an illumination model using 10 semiconductor lasers for interferometer, and
corresponding experiment shows that this method is suitable for industrial measurement in large area
The article mainly focused on mobile on-line air quality monitoring system. By deeply analyzed DOAS theory, we designed this new air quality monitoring system. It is mobile and may monitoring many pollution sources on-line everyday.
The Differential Optical Absorption Spectroscopy (DOAS), based on the work by U. Platt and co-workers, is becoming increasingly popular for environment monitoring. DOAS may measure many trace gases like NO2, O3, BrO, NO3 , and SO2. It is designed for the measurement of primary and secondary urban air pollutants with high precision and little cross interference. In the DOAS technique, the spectrum of an artificial light source within a given bandwidth is measured after passing through the open atmosphere for between 100 m and 10 km. After removing the emission spectrum of the light source, the remaining differential absorption features are compared with the absorption cross sections of relevant trace gases. This allows both the qualitative and quantitative determination of their concentration in the light path.
After deeply research, we design this new system. It uses fiber spectroscopy, and it is mobile. User may monitor many pollution sources in a car. This makes auto-monitoring more easily.
Our DOAS system has these merits: New Light Emission-Receiver Unit which united emission,receiver and collimation lenses. New Background Elimination Fiber. And dynamic-feedback self-adapting program. In our experiment by this design idea, we get accurate data.
High-power red laser are of great interest in the fields of medical application, laser display and also as a pumping source for tunable lasers such as Cr:LiSAF. This letter reports the generation of a 12W Q-CW red laser beam by intracavity frequency-doubling of a Nd:YAG laser operating at 1.3μm with a KTP crystal. A laser module that consisting of a Nd:YAG rod side-pumped by thirty 20W LDs of a triangle radial pump geometry, a acousto-optic Q switch and a KTP crystal were used in the experiment. Because the efficiency of SHG is sensitive to the type II phase-matching angles of KTP, we calculate the value of phase-matching angles according to several of Sellemier equations of KTP, and modify the phase-matching angles to θ=59.9° and φ=0° by experiment. The maximum average power of 12W of red laser is achieved at 10KHz when the pump power of LDs is about 470W.
We present a theoretical study of a double microcavity resonators system with absorption or gain. The output intensity and the power intensity inside the microresonator are derived. Some interesting features and their possible application are discussed. The results may be useful for modulator, amplifier, laser and sensor.
A solid-state laser source with flat-top wide beam profile was designed and made. The laser source was mainly made up of an Nd:YAG solid-state laser at 1064 nm and a maximum 267 x collimating telescope. A 2 W laser diode (LD) pumped Nd:YAG laser with flat-concave cavity was adopted as the primary laser source at 1064 nm. Then the output laser (1064 nm) was injected into a collimating telescope. We designed three schemes according to spherical wave theory and chose the best one based on our experiments. We found out the spherical aberration (including axial and off-axial points) must be corrected. At last, an output laser beam with 80 mm diameter, 0.4 mrad divergence angle, > 50 mW output power, and ±10% intensity distribution of cross section, was obtained.