A 2.5nm-thickness molybdenum diselenide (MoSe₂) saturable absorber (SA) is prepared by electron beam evaporation (EBE) method. Applying the prepared MoSe₂ SA to an acousto-optic (AO) Q-switched fundamental laser, a dual-loss-modulated intra-cavity optical parametric oscillator (IOPO) has been experimentally realized. The signal-pulse train from this IOPO has 0.0053 standard deviation (SD) of pulse amplitude. When the MoSe₂ SA is applied to IOPO, the signal pulse is compressed by maximum 68%, the peak power increases by 274%, and the nonlinear conversion increases by 12.6%. To solve the established rate equation of IOPO, the ground-state and excited-state absorption cross section of MoSe₂ are rationally estimated to be 1.04×10⁻¹⁸cm⁻² and 6.25×10⁻¹⁹cm⁻² from the measured transmittance curve, and the excited-state lifetime is 275.6µs. The numerical solution of the equations fits the experimental data well.

We present a D-shaped photonic crystal fiber (PCF) plasmon sensor based on a large-hole self-reference channel for applications in biological and chemical sensing. Both the Plasmon’s fundamental linear-polarization LP01 and high-order LP11 modes are excited at the interface between the analyte and the silver film based on results of the numerical calculation method. We obtained the transmitted spectrum of the guided mode LP01 in the D-shaped PCF. We found that the peak spectral wavelength of the sensor increases when the refractive index of the analyte increases. The spectral sensitivity clearly increases with the silver film’s thickness on the sensor’s platform, although it is unaffected by other variations of the PCF’s geometry. We obtained an optimal spectral sensitivity for the sensor of 3191.43nm/RIU for a silver film thickness of 50nm.

A geometrically structural parameters insensitive hollow-core photonic crystal fiber (HC-PCF) sensor has been researched to detect the concentration of the water-ethanol solution. Using the full-vector finite element method (FEM), we have obtained the effective refractive index of the guided mode LP01 in the fiber based on surface Plasmon resonance (SPR) and the anisotropic perfectly matched layer (PML) boundary condition. The high-order Plasmon mode LP11 is excited at the adjacent ethanol solution and is sensitive to the change of the concentration. Through simulating transmission spectrum of the sensor, we obtain that the spectral sensitivity doesn’t approximately change when the thickness of the silver film h, these air-holes diameter d and the large air-hole diameter D increase, respectively. The spectral sensitivity of the sensor can be about 1.15nm/% with h =50nm, Λ= 2.8μm, D= 2.2Λ and d = 0.5Λ.

A dual-loss Q-switched laser was realized by applying a home-made 2.5 nm-thick WTe2 to an acoustic-optic (AO) modulated laser. Besides conventional pulse compression, the participation of WTe2 could obviously improve the average output power by 29.6% and reduce the laser threshold by 20%, even with the introduced 8% nonsaturable loss. The average-output-power improvement and pulse compression in this dual-loss modulated laser resulted in a 113.7% increase of peak power. According to the measured spectra of laser and photoluminescence of WTe2, the laser-induced excitonic light-emission may be the reason of this laser gain.

We propose a method for imaging through a turbid medium by using a single-shot decoherence polarization gate (DPG). The DPG is made up of a polarizer, an analyzer, and a weakly scattering medium. Contrary to intuition, we discover that the preferential utilization of sparsely scattered photons by introducing weakly scattering mediums can lead to better image quality. The experimental results show that the visibilities of the images acquired from the DPG imaging method are obviously improved. The contrast of the bar can be increased by 50% by the DPG imaging technique. Furthermore, we study the effect of the volume concentration of the weakly scattering medium on the speckle suppression and the enhancement of the visibilities of the images. The variances of the contrasts of the image show that there exists an optimum optical depth (∼0.8) of the weakly scattering medium for DPG imaging through a specific turbid medium.