Migdall A L, Frenkel A, Kelleher D E
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
J Res Natl Inst Stand Technol. 1993 Nov-Dec;98(6):691-697. doi: 10.6028/jres.098.045.
We have set up a novel direct detection system to measure filter transmittances over an attenuation range of at least 5 decades, with relative combined standard uncertainties as low as 0.5% (1) per decade, in the 9 m to 11 m spectral region. This system, using an apparatus originally designed for a heterodyne measurement of transmittance, achieves higher accuracy at the expense of a reduced dynamic range. This independent measurement of transmittance allows verification of the heterodyne technique. Our system uses a source modulated at 30 MHz and a specially constructed high dynamic range and high accuracy lock-in amplifier capable of operation at the modulation frequency. The high modulation frequency and narrow bandwidth of the system allow thermal background radiation to be suppressed and high accuracy to be achieved. We correct for the non-ideal natures of the detector and attenuators. In particular, the detector position is scanned to reduce the effect of its spatial nonuniformity and the deflection of the transmitted beam caused by the nonparallel surfaces of the filter. We discuss the sources of systematic errors and the methodology to reduce their contribution.
我们建立了一种新型直接检测系统，用于在9米至11米光谱区域测量至少5个数量级衰减范围内的滤光片透过率，每十年相对合成标准不确定度低至0.5% (1)。该系统使用最初设计用于外差式透过率测量的设备，以牺牲动态范围减小为代价实现了更高的精度。这种透过率的独立测量允许对外差技术进行验证。我们的系统使用30 MHz调制的光源和能够在调制频率下运行的特殊构造的高动态范围和高精度锁相放大器。系统的高调制频率和窄带宽允许抑制热背景辐射并实现高精度。我们对探测器和衰减器的非理想特性进行了校正。特别是，扫描探测器位置以减少其空间不均匀性以及滤光片非平行表面引起的透射光束偏转的影响。我们讨论了系统误差的来源以及减少其影响的方法。
