Nanosecond pulse miniaturized lasers are widely used in laser detectors and target designators, among other applications. In most practical applications, lasers must remain insensitive to shock, vibration, and large temperature variations and have a small volume, light weight, and low power consumption. Cross-Porro prism resonators can effectively reduce the misalignment caused by vibration and exhibit high anti-detuning characteristics. Locally and internationally, many methods, such as multiwavelength matching and long-range absorption, are usually used to enable the laser to work in a wide temperature range; this wide range reduces the dependence of the semiconductor-pumped laser on its accurate temperature control. In this study, we used single-wavelength pump sources with a spectral width of 6.8 nm to end pump a segmented doped Nd∶YAG slab and a combined crossed-Porro prism resonator to achieve a compact laser with good beam quality, anti-detuning characteristics, and a wide temperature range. The work presented in this study can provide a new reference for the design of lasers operating over a wide temperature range.

First, the influence of different spectral widths (2, 4, 6, 8, and 10 nm) on the absorption efficiency of a gain medium with 30 mm length and atomic fraction 1.0% of doping Nd was numerically analyzed. The results show that pump light with a spectral width of 6 nm increases the absorption efficiency of the slad by more than 75% in a continuous and wide temperature range (Fig.2). The polarization coupling output characteristics of the crossed-Porro prism resonator were then calculated theoretically (Fig.3). Next, to prevent end-face heat accumulation caused by the end-pumped slab structure, the distribution characteristics of the absorption flux of 805 nm pump light in the segmented bonding slab were simulated (Fig.6), and the results show that the segmented bonding slab can effectively homogenize the pump light distribution. According to the theoretical analysis, a laser with wide-temperature operation based on a conduction-cooled end-pumped slab (CCEPS) combined with a crossed-Porro prism resonator configuration was designed. The laser can operate over a wide temperature range using a broad-spectrum, single-wavelength pump source to end pump the segmented bonding slab (Fig.4). The central wavelength of the pump source used in the experiment was 805.8 nm at 60 ℃, and the spectral width was 6.8 nm (Fig.11), which is favorable for laser operation in a wide temperature range. The crossed-Porro prism resonator used in the experiment comprises two orthogonal Porro prisms: a half-wave plate and polarization beam splitter (PBS) that can realize a polarization coupling output. The slab size was designed to be 3 mm×3 mm×39.9 mm, which is formed by bonding five segments of crystals with a cutting angle of 45° (Fig.5), which is conducive to improving laser beam quality.

The laser system achieves a maximum output pulse energy of 49.82 mJ (Fig. 8) with a pulse width of 8.11 ns at a repetition rate of 20 Hz (Fig.9). The spot diameter and divergence angle of the output laser are approximately 2.12 mm and 2 mrad, respectively. The peak power reaches 6.14 MW with energy instability within -1.5%?+1.5%. The experimental results show that the laser could operate over a wide temperature range of 15?70 ℃ (Fig.10). The relationship between the pump wavelength and temperature can be obtained from the spectrum of the pump source at different temperatures; hence, the absorption efficiency curve of the slab to the pump light at different temperatures and the curve of the output energy with temperature can be linked. When the wavelength of the pump source changes in the range of 791.6 to 818.1 nm (26.5 nm), the absorption efficiency of the slab can reach more than 78.7%, and the partial absorption efficiency curve of 793.9 to 808.5 nm (14.6 nm) is consistent with the measured change of the output energy in the temperature range of 15 to 70 ℃ (Fig.12). When the design of the pump source is further optimized, the central wavelength of the pump source with a broad spectrum is set to 806 nm at 25 ℃. The temperature-insensitive range of the laser is nearly double that of the experiment’s temperature range.

In this study, a wide-temperature-operating CCEPS laser combined with a crossed-Porro prism resonator is designed. The laser is compact, has good anti-detuning characteristics, and can operate over a wide temperature range using single-wavelength pump sources with a 6.8 nm spectrum width to end pump the segmented bonding slab. This design reduces the complexity of the pump source without complex wavelength matching of the pump light and does not require a crystal length that is too long. Related parameters are analyzed theoretically, including the influence of pump light with a broad spectrum on the absorption efficiency of the gain medium, polarization coupling output characteristics of the crossed-Porro prism resonator, and distribution characteristics of the pump light absorption flux in segmented bonding crystals. The results show that the laser can operate in a wide temperature range of 15?70 ℃. When the design of the pump source is further optimized, the central wavelength of the pump source with a broad spectrum is set to 806 nm at 25 ℃, and the temperature-insensitive range of the laser can nearly be double that of the test temperature range in this experiment. The work presented in this paper provides a valuable reference for the design of thermally insensitive lasers.