Optimizing the ordering of the Hadamard masks of ghost imaging suitable for the efficient face reconstruction using the max-projection method.

One crucial component of ghost imaging (GI) is the encoded mask. Higher-quality reconstruction at lower sampling rates is still a major challenge for GI. Inspired by deep learning, max-projection method is proposed in the paper to reorder the Hadamard masks for its efficient and rapid reconstruction. The simulations demonstrated that max-projection ordering with only 20 face training images yielded excellent reconstruction outcomes. In noise-free simulations, at an ultralow sampling rate of 5%, the PSNR of the max-projection ordering was 1.1 dB higher than that of the cake-cutting ordering with the best performance in the reference group. In noisy simulations, at ultralow sampling rates, the retrieved images remained almost identical to their noise-free counterparts. Irrespective of the presence or absence of noise, the max-projection ordering guaranteed the highest fidelity of image reconstruction at ultralow sampling rates. The reconstruction time was reduced to mere milliseconds, thereby enabling swift visualization of dynamic phenomena. Accordingly, the max-projection ordering Hadamard matrix offers a promising solution for real-time GI due to its higher reconstruction quality, stronger noise immunity and millisecond reconstruction time.

Synchrotron radiation stability with meV-level energy resolution: in situ characterization.

One of the most critical parameters in synchrotron radiation (SR) experiments is the stability of the photon energy, which is primarily affected by the stability of the light source and the optical elements in the beamline. Due to the characteristics of SR and the use of dispersive elements such as monochromators in the beamline, the change of the beam position is usually accompanied by the change of energy and flux, while most traditional beam monitoring methods are based on the direct or indirect measurement of total flux, and are therefore sensitive to the beam position only, having no energy resolution. In this paper, an in situ monitoring system has been designed to measure the short-term (jitter) and long-term (drift) characteristics of the energy variation in the SR beamline. The system consists of a double-crystal monochromator, an orthogonal analysis crystal, and an X-ray imaging detector, which could decouple the angle and energy spread of the photon beam based on the dispersion effect in Bragg diffraction. The time response and the energy resolution of the system could reach millisecond and millielectron volt level, respectively.

Characterization of the error of the speckle-based wavefront metrology device at Shanghai Synchrotron Radiation Facility.

A metrology device based on the near-field speckle technique was developed in the x-ray test beamline at the Shanghai Synchrotron Radiation Facility to meet the at-wavelength detection requirements of ultra-high-precision optical elements. Different sources of error that limit the uncertainty of the instrument were characterized. Two main factors that contribute to the uncertainty of the measurements were investigated: (1) noise errors introduced by the electronics and the errors introduced by the algorithm and (2) stability errors owing to environmental conditions. The results show that the high measurement stability of the device is realized because it is insensitive to the effect of the external environment. The repetition accuracy of the device achieved 9 nrad (rms) when measuring the planar mirror that produces weak phase curvature.

Generation of picosecond pulses with variable temporal profiles and linear polarization by coherent pulse stacking in a birefringent crystal shaper.

We report the study and demonstration of a new laser pulse shaping system capable of generating linearly polarized picosecond laser pulses with variable temporal profiles including symmetric intensity distributions, as well as non-symmetric distributions, which are highly desired by various applications. It is found that both high transmittance and high stability of the shaped pulse can be achieved simultaneously when crystals are set at a specific phase delay through fine control of the crystal temperature. Although multi-crystal pulse stacking with different configurations was reported before particularly for flattop pulse generation, this new configuration leads to new opportunities for many potential applications over a wide range of laser wavelengths, pulse repetition rate, time structures and power levels. A practical double-pass temporal shaping configuration that significantly reduces the number of crystals is also proposed in this paper as a result of present study.