In this paper, we present an auto-focusing and ranging method which is based on light-field imaging spatial refocusing principles and simulation algorithm. The clearest image could be chosen among the refocused image sequences by using image-resolution evaluation functions when we select the window of the object whose distance needs to be measured. Finally, we measure an object on the scene with the auto-focusing and ranging method and analyze its range and accuracy. The experimental results show that the auto-focusing and ranging method could obtain distance information of different objects using one-shooting light-field image and then measure the distances of two or more objects in one scene.
We analyze the influence factors that affect the observed degree of squeezing in generation and detection stages theoretically, including the fluctuations of pump power, the intra-cavity loss of the optical parametric amplifier (OPA) cavity , the phase fluctuation on balanced homodyning stage, the propagation efficiency, the mode matching efficiency, the out-put mirror transmission of the OPA cavity and the quantum efficiency of the detector. The theoretical results show that different loss sources appearing at various stages of the squeezed light generation and detection are far more dominant and in the end limit the squeezing level achievable. The analysis of these parameters will be extremely useful for subsequent experiments.
A reflective beam shaper is designed for the purpose of compensation of the low-order aberrations in high-power slab lasers. A proportional-integral-derivative (PID) control algorithm is used to control the optical parameters of a beam shaper for active compensation of low-order aberrations. Simulations of the PID algorithm show that different combinations of defocus, 0-deg astigmatism, and 45-deg astigmatism, which are the main contributors of beam aberrations in slab lasers, can be well compensated by variation of distance and rotation angle of mirrors. For a beam with large wave aberrations [peak-to-valley (PtV)=87.7λ, root-mean-square (RMS)=19λ], the adjustment of distance between mirrors is less than 100 mm, and the rotation angle about the z-axis is <3.2 deg, and the wavefront distortion is reduced to a level (PtV=0.50λ, RMS=0.09λ) that can be further corrected with one deformable mirror. The effectiveness and performance of low-order aberration compensation with the reflective beam shaper are also verified by experiments.
We investigate the effects of cavity detuning on squeezing in the generation of the squeezed light at 1064 nm with a degenerate optical parametric amplifier (OPA) based on a periodically poled KTiOPO4 crystal. We theoretically analyze several effects that lead to cavity detuning, including the displacement and tilt of the incident laser light and the cavity length fluctuations of the OPA. To reduce the influence of the cavity detuning and increase the degree of generated quantum noise reduction, a side-of-fringe locking technique is applied to achieve the resonance between the OPA cavity and the injected laser beam. The experimental results show that the transmitted power through the locked cavity is increased and the cavity detuning is greatly suppressed. After locking of the cavity, we could expect to get a value for the control loop with an accuracy of 10−9 and the locking time is not less than 2 h, which paves the way for the preparation of the squeezed light.
We demonstrate the methods for increasing the observed squeezing level in the generation of squeezed states of light at
1064 nm with periodically poled KTiOPO4 (PPKTP) crystal. We analyze the technical limits to the reduction of noise in
the squeezed quadrature theoretically, including the intra-cavity loss of the optical parametric amplifier (OPA) cavity, the
normalized amplitude, the detection frequency, and the mode matching on the balanced homodyning stage. To observe a
high degree of squeezing, we improve the quality of mode matching into the OPA cavity and the mode cleaning (MC)
cavity experimentally. By optimizing mode matching of the light into cavities, the finesse of the cavities would be higher
in practice and the desirable spatial mode can be realized. As the intensity noise of the laser light reach the shot noise
limit above the frequency of 1 MHz, which is sufficient for our experiment, so the MC cavity is incorporated to filter
higher-order transverse modes of the local oscillator (LO) beam for the balanced homodyne detection. The experimental
and theoretical results show that it is essential to optimize the mode matching efficiency to generate and detect high
degree of squeezing otherwise an inefficiency mode matching will throw away the squeezing and transform the squeezed
field into a vacuum field.
We analyze the balanced homodyne detection technique in the detection of squeezed light, which is controlled by dither
locking scheme. We discuss how the balanced homodyne detection efficiency influences the detected degree of
squeezing. Also, fluctuation in the relative phase between the local beam and the squeezed light is discussed, since a little
phase fluctuation would decrease the detected degree of squeezing greatly. Then, the dither locking technique is studied
in detail, which is used to lock the relative phase between the local beam and the squeezed light. The simulation
experiments and theoretically results show that the balanced homodyne detection technique and the dither locking
scheme are efficient methods to get more accurate degree of squeezing in the preparation of the squeezed states of light.
The effect of mode matching on the preparation of the squeezed light at 1064 nm with periodically poled KTiOPO 4 (PPKTP) crystal is reported. We can derive the desired mode by improving the spatial mode matching into optical cavities, including the beam from the laser mode matched to the optical parametric amplifier cavity and mode cleaning cavity; also it is useful for the stability of the locking systems. By increasing the fringe visibility between the squeezed light and the local oscillator beam, a squeezing level of −8.75 dB or even higher could be observed, even with the same experimental parameters as described elsewhere.
A stable amplitude squeezed-state light was generated by utilizing the nondegenerate optical parametric amplifier based on periodically poled KTiOPO4 crystal at 1064 nm. We observed −4.93 dB of squeezing with a local oscillator phase locked in homodyne measurement. The imaging experiments of the resolution target have shown that the imaging resolution, which was based on squeezed-state light, is 1.41 times as much as the resolution that was acquired using coherent light as light source. In addition, the squeezed-state light was applied for imaging of the virtual object. It was found that the characters on the board were much more easily discerned with squeezed light as a light source than with coherent light. This result paves the way for further improvements of imaging resolution by use of the squeezed-state light.
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