A fixed wavelength optical parametric amplifier laser was constructed to create nanosecond pulsed light at 1527 nm for eye-safe range gated active short-wave infrared (SWIR) imaging. The laser pulse is generated using a Nd:YAG operating at 1064 nm to pump a potassium titanyle arsenate crystal in a single-pass geometry, resulting in ≈85 mJ at up to 28 Hz at 1527 nm with a pulse duration of ∼8 ns. The SWIR imager can be gated in as short as a 70-ns window (active time) with time steps as small as 5 ns (e.g., 0 to 70 ns and 5 to 75 ns). This allows for significant weather penetration by reducing the contribution from back-scattered photons reaching the receiver from scattering along the path prior to the imaging target. In addition, by converting to 1527 from 1064 nm, the maximum permissible exposure limit for eye-safety is ≈4 orders of magnitude larger, allowing for higher fluences without risk of injury. NEXRAD weather data along the line-of-sight were utilized to facilitate atmospheric propagation modeling via MODTRAN to retrieve an estimate of the path transmittance during testing. The integrated system herein is shown to extend imaging ranges with improvement factors of ≈2.5–3.1 × during periods of rain. An image of a water tower at a 10-km range was generated with visibilities between 3 and 4 km during testing.

中文翻译：

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距离选通的主动短波红外成像可穿透雨水

构造了固定波长的光参量放大器激光器，以产生1527 nm的纳秒脉冲光，用于人眼安全范围选通的有源短波红外（SWIR）成像。激光脉冲是通过在1064 nm处工作的Nd：YAG产生的，以单次通过的方式泵浦钛酸钽砷酸钾晶体，在1527 nm处高达28 Hz时≈85mJ，脉冲持续时间约为8 ns。SWIR成像器可以在70 ns的窗口（激活时间）之内以短至5 ns（例如0到70 ns和5到75 ns）的时间步长进行门控。通过减少来自后向散射光子到达接收器的贡献，以及由于沿着成像目标之前的路径进行散射，可以实现显着的天气穿透。另外，通过从1064 nm转换为1527，眼睛安全的最大允许暴露极限要大≈4个数量级，从而可以实现更高的通量而无受伤危险。沿视线的NEXRAD气象数据被用于通过MODTRAN进行大气传播建模，以获取测试过程中路径透射率的估计值。此处显示的集成系统可在下雨期间以约2.5-3.1×的改善因子扩展成像范围。在测试过程中，生成了10公里范围内水塔的图像，可见性在3-4 km之间。此处显示的集成系统可在下雨期间以约2.5-3.1×的改善因子扩展成像范围。在测试过程中，生成了10公里范围内水塔的图像，可见性在3-4 km之间。此处显示的集成系统可在下雨期间以约2.5-3.1×的改善因子扩展成像范围。在测试过程中，生成了10公里范围内水塔的图像，可见性在3-4 km之间。