The development of high-temperature photodetectors can be beneficial for numerous applications, such as aerospace engineering, military defence and harsh-environments robotics. However, current high-temperature photodetectors are characterized by low photoresponsivity (<10 A/W) due to the poor optical sensitivity of commonly used heat-resistant materials. Here, we report the realization of h-BN-encapsulated graphite/WSe2 photodetectors which can endure temperatures up to 700 °C in air (1000 °C in vacuum) and exhibit unconventional negative photoconductivity (NPC) at high temperatures. Operated in NPC mode, the devices show a photoresponsivity up to 2.2 × 10⁶ A/W, which is ~5 orders of magnitude higher than that of state-of-the-art high-temperature photodetectors. Furthermore, our devices demonstrate good flexibility, making it highly adaptive to various shaped surfaces. Our approach can be extended to other 2D materials and may stimulate further developments of 2D optoelectronic devices operating in harsh environments.

The simultaneous and independent measurements of in-plane and out-of-plane displacements are significant issues to be solved in research. Here a novel system to realize single-spot two-dimensional (2D) displacement measurement of a noncooperative target is reported. The performance of the system is tested in the displacement measurement of an aluminum target with a rough surface. 2D random movement and 2D movement with different parameters of Lissajous figures are measured by the system. The ranges of the 2D displacement measurement reach 500 μm and the accuracies reach the submicron scale. The resolutions of the two dimensions are all better than 5 nm. The measurement system is based on laser heterodyne self-mixing interferometry with frequency multiplexing, which has advantages such as noncontact, nondestruction, nanometer-scale resolution and high sensitivity. The method is promising to be applied in 2D deformation tests of materials, 2D rotor vibration measurement, 2D positioning of particles, thermal expansion coefficient measurement, and other applications.

Frequency-swept interferometry (FSI) is a powerful ranging method with high precision and immunity to ambient light. However, the stand-off distance of the current FSI-based ranging system for noncooperative targets is relatively short because the weak echo power cannot provide the needed signal-to-noise ratio (SNR). Here, we report a ranging method that combines FSI and the laser feedback technique. Compared with conventional FSI, the interference between the weak echo signal and the local oscillator occurs in the laser cavity, which enhances the signal spontaneously and then provides an improved SNR. In the experiments, the detection limit of the echo power is less than 0.1 fW, with a 1 mW probe beam. Based on the enhancement from the laser feedback technique, the system can detect a noncooperative target that is up to hundreds of meters away in space without extra optical amplifiers. On the other hand, a large stand-off distance makes the system sensitive to environmental disturbance, which degrades the ranging precision. To address this issue, an interferometry-based compensation device, which is also sensitive to weak echoes from noncooperative targets, is proposed to monitor the optical-path-length drifts and ensure accurate beat frequency recognition. Moreover, the device can record distance changes during the integration time of ranging and track a moving target precisely with improved temporal resolution. Owing to the high sensitivity and the validity of the compensation approach, the standard deviation in 10 measurements is better than 0.07 mm when targeting an aluminum sheet at approximately 152 m. Generally, with a large range, high relative precision, and low photon consumption, the novel technical scheme for laser ranging demonstrates new capabilities that promise to enable a wide range of applications, such as large equipment assembly and noncooperative-target tracking.

The response of the microchip solid-state Nd:YAG laser, which is subjected to external frequency-shifted feedback, is experimentally and theoretically analysed. The continuous weak response of the laser to the phase and amplitude of the feedback light is achieved by controlling the feedback power level, and this system can be used to achieve contact-free measurement of displacement, vibration, liquid evaporation and thermal expansion with nanometre accuracy in common room conditions without precise environmental control. Furthermore, a strong response, including chaotic harmonic and parametric oscillation, is observed, and the spectrum of this response, as examined by a frequency-stabilised Nd:YAG laser, indicates laser spectral linewidth broadening.

We present a novel method using $\mathrm{Nd}\text{:}{\mathrm{YVO}}_4$ laser with a waveplate in the external cavity to generate two orthogonally polarized signals with stable and adjustable phase difference. The phase difference is observed in the presence of external interference, and it is determined by the phase retardation of the waveplate. A model based on birefringent external-interference effect is proposed to theoretically explain the phase difference phenomenon, and the arithmetic solution of the relation between the phase difference and the phase retardation of waveplate is given. The simulated results accord with the experimental phenomena. This Letter provides the possibility for the measurement of phase retardation and also offers guidance to the design of interferometers based on fringe counting technique.