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D
D*
D* 是探测器的检测能力，表示当 1 W 的辐射能量入射到探测器上时的信噪比。由于 D* 由 1 cm2 的受光面和 1 Hz 的噪声带宽归一化，因此它与光敏元件的大小和形状无关。在下面的公式中，S 为信号，N 为噪声，P 为入射能（单位为 W/cm2），A 为受光面积（单位为 cm2），Δf 为噪声带宽（单位为 Hz）。D* 值越高，探测器越好。$$ D^{*}=\frac{S/N \cdot \sqrt{\triangle f\ }}{P\cdot \sqrt{A\ }}$$ $$ D^{*}=\frac{ \sqrt{A\ } }{NEP}$$
Dark count - 暗计数
这是探测器在没有光的情况下每秒产生的计数。
Dark current - 暗电流
向光电二极管施加反向电压时流过的小电流，即使在暗态下也会出现。此电流称为暗电流。向光电二极管（PIN 光电二极管等）施加反向电压时，暗电流产生的噪声占主导地位。
Dark resistance - 暗电阻
这是光导器件在暗态下的电阻。
DBR (distributed Bragg reflector) - DBR（分布式布拉格反射器）
这是一种包含衍射光栅的反射器，该衍射光栅的周期为 λ/2n（λ：真空中的波长，n：介质的折射率），在发光器件（如 LED 和半导体激光器）中的发光区域外部形成，用于选择性地反射波长为 λ 的光。在 VCSEL（垂直腔面发射激光器）中，在适当的距离处形成 DBR 层作为发光层的上层和下层，这只会在特定波长下产生谐振，因此激光光束可在垂直于表面的方向上发射。在一些 LED 中，在发光层下方形成一个 DBR 层以增加光量。
Diffraction grating - 衍射光栅
设计为利用光衍射获得光谱的光学元件。反射衍射光栅通常在其表面形成大量沟槽，并利用与光栅表面反射的光束干涉而产生的衍射图像。
Double-heterostructure - 双异质结构
一种结构，其中低带隙能量半导体材料夹在高带隙能量半导体材料之间。由于载流子被限制在低带隙区域（发射区域），因此载流子密度增加可允许有效的电子孔再结合。
Drift - Lamps - 漂移 - 光源
漂移是指输出在很长一段时间内的变化。它可能是由于阴极的热电放电特性变化、气压变化、窗口上的污垢或光源的电压引起的。它以每小时的变化量表示。
Drift - Photomultiplier tubes - 漂移 - 光电倍增管
在长时间连续操作光电倍增管后，即使操作条件并未改变，光电倍增管的阳极输出电流也可能随着时间推移而略有变化。在阳极电流的波动中，相对较短时间内的变化称为“漂移”，而长时间（例如 103 至 104 小时或更长时间）内的变化称为寿命特性。漂移主要是由重电子轰击对最后一个倍增器电极的损害造成的。因此，最好使用较低的阳极电流。当稳定性最重要时，建议将平均阳极电流保持在最大值以下 100 倍。
Dynamic range - 动态范围
术语“动态范围”是指测量器件或探测器能够准确测量信号的范围。动态范围是可以检测到的最大信号等级与最小信号等级（探测限）之比。
对于 CCD，动态范围为饱和电荷量（最大阱容）除以读出噪声。由于探测限取决于暗散粒噪声和读出噪声，因此动态范围随操作条件（如工作温度和电荷积分时间）变化。
在 CCD 充分冷却的操作条件下确定动态范围，这样可以忽略暗散粒噪声。由于探测限上限由最大阱容决定，因此动态范围 (DR) 的公式为：$$DR = \frac{最大阱容}{读出噪声}$$或$$ 20\ log \biggl( \frac{最大阱容}{读出噪声} \biggr)\ [dB]$$
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