We present a novel noncontact ultrasound (US) and photoacoustic imaging (PAI) system, overcoming the limitations of traditional coupling media. Using a lo
We present a novel noncontact ultrasound (US) and photoacoustic imaging (PAI) system, overcoming the limitations of traditional coupling media. Using a long coherent length laser, we employ a homodyne free-space Mach–Zehnder setup with zero-crossing triggering, achieving a noise equivalent pressure of 703 Pa at 5 MHz and a -6 dB bandwidth of 1 to 8.54 MHz. We address the phase uncertainty inherent in the homodyne method. Scanning the noncontact US probe enables photoacoustic computed tomography (PACT). Phantom studies demonstrate imaging performance and system stability, underscoring the potential of our system for noncontact US sensing and PAI.show less
We propose a near-eye display optics system that supports three-dimensional mutual occlusion. By exploiting the polarization-control properties of a phase
We propose a near-eye display optics system that supports three-dimensional mutual occlusion. By exploiting the polarization-control properties of a phase-only liquid crystal on silicon (LCoS), we achieve real see-through scene masking as well as virtual digital scene imaging using a single LCoS. Dynamic depth control of the real scene mask and virtual digital image is also achieved by using a focus tunable lens (FTL) pair of opposite curvatures. The proposed configuration using a single LCoS and opposite curvature FTL pair enables the self-alignment of the mask and image at an arbitrary depth without distorting the see-through view of the real scene. We verified the feasibility of the proposed optics using two optical benchtop setups: one with two off-the-shelf FTLs for continuous depth control, and the other with a single Pancharatnam–Berry phase-type FTL for the improved form factor.show less
We present an effective approach to realize a highly efficient, high-power and chirped pulse amplification-free ultrafast ytterbium-doped yttrium aluminum
We present an effective approach to realize a highly efficient, high-power and chirped pulse amplification-free ultrafast ytterbium-doped yttrium aluminum garnet thin-disk regenerative amplifier pumped by a zero-phonon line 969 nm laser diode. The amplifier delivers an output power exceeding 154 W at a pulse repetition rate of 1 MHz with custom-designed 48 pump passes. The exceptional thermal management on the thin disk through high-quality bonding, efficient heat dissipation and a fully locked spectrum collectively contributes to achieving a remarkable optical-to-optical efficiency of 61% and a near-diffraction-limit beam quality with an M2 factor of 1.06. To the best of our knowledge, this represents the highest conversion efficiency reported in ultrafast thin-disk regenerative amplifiers. Furthermore, the amplifier operates at room temperature and exhibits exceptional stability, with root mean square stability of less than 0.33%. This study significantly represents advances in the field of laser amplification systems, particularly in terms of efficiency and average power. This advantageous combination of high efficiency and diffraction limitation positions the thin-disk regenerative amplifier as a promising solution for a wide range of scientific and industrial applications.show less
Holographic display stands as a prominent approach for achieving lifelike three-dimensional (3D) reproductions with continuous depth sensation. However, t
Holographic display stands as a prominent approach for achieving lifelike three-dimensional (3D) reproductions with continuous depth sensation. However, the generation of a computer-generated hologram (CGH) always relies on the repetitive computation of diffraction propagation from point-cloud or multiple depth-sliced planar images, which inevitably leads to an increase in computational complexity, making real-time CGH generation impractical. Here, we report a new CGH generation algorithm capable of rapidly synthesizing a 3D hologram in only one-step backward propagation calculation in a novel split Lohmann lens-based diffraction model. By introducing an extra predesigned virtual digital phase modulation of multifocal split Lohmann lens in such a diffraction model, the generated CGH appears to reconstruct 3D scenes with accurate accommodation abilities across the display contents. Compared with the conventional layer-based method, the computation speed of the proposed method is independent of the quantized layer numbers, and therefore can achieve real-time computation speed with a very dense of depth sampling. Both simulation and experimental results validate the proposed method.show less
We propose a transfer-learning multi-input multi-output (TL-MIMO) scheme to significantly reduce the required training complexity for converging the equalizers in mode-division multiplexing (MDM
We propose a transfer-learning multi-input multi-output (TL-MIMO) scheme to significantly reduce the required training complexity for converging the equalizers in mode-division multiplexing (MDM) systems. Based on a built three-mode (LP01, LP11a and LP11b) multiplexed experimental system, we thoughtfully investigate the TL-MIMO performances on the three-typed data, collecting from different sampling times, launched optical powers, and input optical signal-to-noise ratios (OSNRs). The dramatic reduction of 40%~83.33% on the required training complexity is achieved in all of three scenarios. Furthermore, the good stability of TL-MIMO in both the launched power and OSNR test bands has also been proved.show less
In this work, we propose a method using frequency modulated continuous waveform (FMCW) laser self-mixing interferometry (SMI) and all-phase fast Fourier transform (APFFT) for simultaneous measur
In this work, we propose a method using frequency modulated continuous waveform (FMCW) laser self-mixing interferometry (SMI) and all-phase fast Fourier transform (APFFT) for simultaneous measurement of speed and distance. APFFT offers superior accuracy in frequency determination by mitigating issues like the fence effect and spectrum leakage, contributing to high-accuracy measurement for speed and distance. Both simulations and experiments have demonstrated relative errors at the level of 10-4 and 10-3 for distance and speed measurements respectively. Furthermore, factors impacting measurement performance have been discussed. It provides a high-performance and cost-effective solution for distance and speed measurements, applicable across scientific research and various industrial domains.show less
The problem of optimizing the parameters of a laser pulse compressor consisting of four identical diffraction gratings is solved analytically. The goal of optimization is to obtain maximum pulse
The problem of optimizing the parameters of a laser pulse compressor consisting of four identical diffraction gratings is solved analytically. The goal of optimization is to obtain maximum pulse power, completely excluding both beam clipping on gratings and the appearance of spurious diffraction orders. The analysis is carried out in a general form for an out-of-plane compressor. Two particular “plane” cases attractive from a practical point of view are analyzed in more detail: a standard Treacy compressor (TC) and a compressor with an angle of incidence equal to the Littrow angle (LC). It is shown that in both cases the LC is superior to the TC. Specifically, for 160-cm diffraction gratings, optimal LC design enables 107 PW for XCELS and 111 PW for SEL-100 PW, while optimal TC design enables 86 PW for both projects.show less
To overcome Yb laser, kilowatt-level 1535 nm fiber laser is utilized to in-band pump an Er:Yb co-doped fiber (EYDF) amplifier. An output power of 301 W narrow-linewidth EYDF amplifier operating
To overcome Yb laser, kilowatt-level 1535 nm fiber laser is utilized to in-band pump an Er:Yb co-doped fiber (EYDF) amplifier. An output power of 301 W narrow-linewidth EYDF amplifier operating at 1585 nm, with 3 dB bandwidth of 150 pm and M2<1.4, is experimentally demonstrated. To the best of our knowledge, it is the highest output power in L band narrow-linewidth fiber amplifiers with good beam quality. Theoretically, a new ion transition behavior among energy levels for in-band pumping EYDF is uncovered, and a spatial-mode-resolved nonlinearity-assisted theoretical model is developed to understand its internal dynamics. Numerical simulations reveal that the reduction in optical efficiency is significantly related to excited-state absorption (ESA). ESA has a nonlinear hindering effect on power scaling. It can drastically lower the pump absorption and slope efficiency with increasing pump power for in-band pumped EYDF amplifiers. Meanwhile, to improve power to kilowatt level via in-band pumping, optimized approaches are proposed.show less