Stable single frequency output around 943 nm was obtained from a quasi-continuous wave (qcw) diode-pumped, $Q$-switched Nd:GSAG laser. The $Q$-switched Nd:GSAG laser was injection seeded with a single mode laser diode. Its frequency was stabilized by an active-control loop specially designed for a strong qcw pump. The spectral linewidth of the Nd:GASG laser was 41 MHz and the frequency stability was 10 MHz. The single-frequency-pulsed laser generated 32 mJ pulse energy at 10 Hz repetition rate. When the repetition rate was increased to 100 Hz, 5.6 mJ pulse energy was obtained by a thermal dynamic stable resonator. By tuning the seed laser, the wavelength of the pulsed Nd:GASG laser can be continuously varied from 942.1 to 943.1 nm.

Thin layer broadband porous Cr absorber with 93% absorption in whole visible range was fabricated on a free-standing polyimide film by wet-etching.

Metamaterial absorbers exhibit high absorption and flexible tuning ability has been widely applied in energy harvesting, radiative cooling, and radar cross-section reduction. In this paper, an ultra-broadband microwave metamaterial absorber containing a lossy meta-dielectric layer was proposed. The lossy layer was a PLA meta-layer with resistive ink coating on the sidewall of the periodic structure. Through tuning the thickness and height of the resistive ink coating on the side wall, the effective impedance of the absorber was modified to match the air impedance. It could enhance the absorption in an ultrabroad microwave frequency band. Simulation results showed that over 90% absorptivity was obtained in an ultra-broad frequency range from 4.4 to 60 GHz, with a relative absorption bandwidth of 173%. Moreover, within the entire absorption band, the absorptivity was uniform, and the peak fluctuation was only 0.053. In addition, the absorber was insensitive to the wave incident angle. Even under a big oblique incident angle of 45°, the average absorptivity was still 95% and the absorption band shifted only 0.5 GHz. Detailed investigations revealed that the resistive ink coating on the PLA middle meta-layer significantly enhanced absorption within the frequency range from 20 to 60 GHz and maintained high absorption at wide incidence angles. It proved that the middle meta-layer effectively broadened the absorption band and made the absorptivity insensitive to the wave incidence angles. The experimental results of the fabricated prototype absorber effectively verified our design. We believe it has good potential in inflight vehicle stealth.

A robust micro-electro-mechanical systems (MEMS) infrared thin film transducer of an ultra-large-scale array was proposed and fabricated on a 4-inch silicon wafer. The silicon substrate and micro cavities were introduced. This novel transducer had excellent mechanical stability, time response, and state-of-the-art pixel scale. It could bear a load of 1700 g and its load pressure was improved by more than 5.24 times and time constant decreased by 50.7% compared to the traditional soft infrared thin film transducer. The array scale of its pixels exceeded 2k × 2k. The simulation and measured results of the transient temperature and radiation intensity were well consistent. Illuminated by a 532 nm laser with a frequency of 50 Hz and 50% duty cycle, the thermal decay time of the proposed transducer was 6.0 ms. A knife-edge image was utilized for spatial resolution test and the full width at half maximum (FWHM) of the proposed transducer was 24% smaller than the traditional soft one. High-resolution infrared images were generated using the proposed robust transducer. These results proved that the robust transducer was promising in infrared image generation.

A radio-frequency intensity-modulated light source at 532 nm was built for underwater ranging. The maximum output power at 532 nm was 2.56 W, the highest efficiency from the fundamental to second harmonic generation was 22.6%. The watt level 532 nm light source was applied in underwater ranging experiments. Frequency domain reflectometry was applied to retrieve the distances of the objects to the transmitter in a water tank. When the modulation frequency was tuned from 10 MHz to 200 MHz, we obtained ranging accuracy better than 5 cm and ranging resolution smaller than 0.5 cm at 8.6 attenuation length. Two objects spacing by 0.8 m could be resolved simultaneously. The attenuation length at which the object could be detected was limited by the sensitivity of the silicon photodetector. Moreover, we did not use the full bandwidth of the modulation since the lock-in amplifier adopted for data processing had a bandwidth of 200 MHz. Both ranging distance and resolution can be improved if a photomultiplier tube and a high-speed data sampling board were used. Nevertheless, the experimental results showed that the watt level, broadband intensity modulated light source has great potential in underwater detection in terms of ranging accuracy and resolution.

Composite thin film absorbers show superior performance and have a wide range of applications. Obtaining a broadband composite thin film absorber is a challenge. In this work, we proposed a modeling of a broadband microwave composite thin film absorber based on the impedance matching theory and equivalent circuit model of the square loop. The unit cell of the absorber was composed of metal square loops with high magnetic conductivity deposited on the polyethylene substrate, and an FR-4 (epoxy glass cloth) substrate was the spacer substrate layer. The simulation results show that the absorptivity of the absorber reached more than 90% in the frequency range of 8.7–18 GHz for TE and TM waves under normal incidence. The thickness of the designed absorber was 2.05 mm (0.059 λ_max, λ_max corresponds to the maximum absorption wavelength). The simulation results show that the energy distribution in the proposed absorber was mainly localized in the top metal FSS layer due to the ohmic loss of metal, and the dielectric loss played a small role in the absorption of the absorber. Our work provides a design approach to improve the efficiency of optoelectronic devices and thermal detectors and has application prospects in radar and aircraft stealth applications.