Xianfeng Xu

High-precision phase-shifting interferometry with spherical wavefront reference

An advanced phase-shifting interferometry approach with a spherical wavefront reference is proposed to improve the quality of the holographic image by avoiding errors caused by noncollimated reference and lowering the resolution of the recording device. By considering not only the real amplitude but also the phase distribution of a spherical wavefront reference, a singular object-wave reconstruction formula is deduced. The suggested method here can work without using the collimator in the reference wave and can then remove all the errors incurred by it. Computer simulations demonstrate that this technique is more convenient in the recording process and can improve the precision of the reconstructed wavefront by more than one order of magnitude after considering the real reference amplitude. Optical experiment results show the feasibility and effectiveness of this method.

Solitons in PT-symmetric periodic systems with the logarithmically saturable nonlinearity.

We report on the formation and stability of induced solitons in parity-time (PT) symmetric periodic systems with the logarithmically saturable nonlinearity. Both on-site and off-site lattice solitons exist for the self-focusing nonlinearity. The most intriguing result is that the above solitons can also be realized inside the several higher-order bands of the band structure, due to the change of nonlinear type with the soliton power. Stability analysis shows that on-site solitons are linearly stably, and off-site solitons are unstable in their existence domain.

Detection and correction of wavefront errors caused by slight reference tilt in two-step phase-shifting digital holography.

A simple and convenient method, without the need for any additional optical devices and measurements, is suggested to improve the quality of the reconstructed object wavefront in two-step phase-shifting digital holography by decreasing the errors caused by reference beam tilt, which often occurs in practice and subsequently introduces phase distortion in the reconstructed wave. The effects of reference beam tilt in two-step generalized interferometry is analyzed theoretically, showing that this tilt incurs no error either on the extracted phase shift or on the retrieved real object wave amplitude on the recording plane, but causes great deformation of the recovered object wavefront. A corresponding error detection and correction approach is proposed, and the formulas to calculate the tilt angle and correct the wavefront are deduced. A series of computer simulations to find and remove the wavefront errors caused by reference beam tilt demonstrate the effectiveness of this method.

Robust digital holography design with monitoring setup and reference tilt error elimination

A robust digital holography recording design is presented to complete the work of switching between in-line and off-axis recording methods. We precisely supervise the off-axis angle in off-axis holography, so that the original reconstructed image can be separated by a minimum off-axis angle. In the design, we can also monitor and remove the negative effects of the reference tilt error in phase-shifting digital holography. Compared with the conventional digital holographic recording configuration, a supervising unit is introduced to control and to monitor the angle between the reference beam and object beam. By the Fourier analysis on the interferograms recorded by the supervising unit and using the corresponding equations, the off-axis angle, which is crucial to reset the object image in holographic reconstruction, can be calculated accurately and then chosen for the best recording angle. For in-line holography, the error affecting the slight tilt of the reference beam on the retrieved object wavefront can be eliminated completely because the tilt angle is detected by another independent device. Furthermore, by using this advanced design, the experimental arrangement can be transformed flexibly from the in-line recording state to the off-axis state or from the latter one to the former without rebuilding the experimental setup. The availability and effectiveness of this design are verified by a series of experiments.

Compact KTA-Based Optical Parametric Oscillator Driven by a Passively Q-Switched YVO4/Nd:YVO4 Laser

A compact passively Q-switched YVO4/Nd:YVO4/KTA intracavity optical parametric oscillator (OPO) is realized. With an end-pumping diode power of 16.6 W, output signal power of 932 mW and idler power of 415 mW are obtained at a pulse repetition rate of 101 kHz. The pulse widths and the beam quality factors are also analyzed for both signal and idler lasers.

High Quality Wave Front Reconstruction for Phase-Shifting Color Digital Holography

This paper presented a method for recording and reconstructing high-quality digital color holographic images. Digital holography with three different wavelength lasers and a monochrome CCD has been demonstrated. With the phase-shifting of the reference beam, in-line holograms for three wavelengths are recorded successively for derivation of the complex amplitude at each wavelength. The three monochromatic interferograms are reconstructed and combined into full-color images in the computer. Laser power variation for wavelength can be compensated for the reconstruction process.

Wave Front Reconstruction and Error Correction for Three Wavelengths Phase-Shifting Digital Holography Information System

Quality of holographic images reconstructed from digital holographic information system with monochromatic CCD is higher than that from the colorful CCD. We want to use one singular monochromatic CCD to work in the information system of colorful phase-shifting digital holography. After the formulae are deducted and computer programs are designed, we extracted phase shifts, reconstructed the corresponding objective image, and then corrected the chromatic errors induced by different wavelengths. A Chinese fifty cents coin was employed as the colorful object in our investigating experiment with three wavelengths of 632.8 nm, 532nm, and 473nm. The experiment results show that the method proposed here is effective and robust.

Efficient diode end-pumped acousto-optically Q-switched Nd:YAG/BaTeMo 2 O 9 Raman laser

BaTeMo2O9 (BTM) is employed to achieve efficient stimulated Raman scattering conversion in a diode end-pumped acousto-optically Q-switched Nd:YAG laser. With an incident diode power of 8.6 W, 732 mW of 1179 nm first-Stokes average output power was generated at a pulse repetition rate of 10 kHz, corresponding to a diode-to-Raman conversion efficiency of 8.5%.

Preprocessing for Interference Fringe of Spherical Object Wave

A simple preprocessing method for interference fringe of holograms generated between spherical object wave fronts and plane wave reference is suggested. The formulae to calculate the diameters of the interference concentric circle and then to get the radius of spherical wave are deduced strictly and the flowchart for the algorithm is given clearly. By using the proposed method the characteristics of a spherical object wave can be achieved directly with only one recording frame and then a simulated one can be gained by numerical simulation. The corresponding experiments show that this technique is simple, effective and convenient for use.

Effective Algorithm for Detection and Correction of the Wave Reconstruction Errors Caused by the Tilt of Reference Wave in Phase‐shifting Interferometry

In phase‐shifting interferometry (PSI) the reference wave is usually supposed to be an on‐axis plane wave. But in practice a slight tilt of reference wave often occurs, and this tilt will introduce unexpected errors of the reconstructed object wave‐front. Usually the least‐square method with iterations, which is time consuming, is employed to analyze the phase errors caused by the tilt of reference wave. Here a simple effective algorithm is suggested to detect and then correct this kind of errors. In this method, only some simple mathematic operation is used, avoiding using least‐square equations as needed in most methods reported before. It can be used for generalized phase‐shifting interferometry with two or more frames for both smooth and diffusing objects, and the excellent performance has been verified by computer simulations. The numerical simulations show that the wave reconstruction errors can be reduced by 2 orders of magnitude.