Lockerbie N A, Tokmakov K V
SUPA (Scottish Universities Physics Alliance) Department of Physics, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, United Kingdom.
Rev Sci Instrum. 2016 Jul;87(7):075002. doi: 10.1063/1.4955471.
The background to this work was a prototype shadow sensor, which was designed for retro-fitting to an advanced LIGO (Laser Interferometer Gravitational wave Observatory) test-mass/mirror suspension, in which a 40 kg test-mass/mirror is suspended by four approximately 600 mm long by 0.4 mm diameter fused-silica suspension fibres. The shadow sensor comprised a LED source of Near InfraRed (NIR) radiation, and a "tall-thin" rectangular silicon photodiode detector, which together were to bracket the fibre under test. The photodiode was positioned so as to be sensitive (primarily) to transverse "Violin-Mode" vibrations of such a fibre, via the oscillatory movement of the shadow cast by the fibre, as this moved across the face of the detector. In this prototype shadow sensing system the photodiode was interfaced to a purpose-built transimpedance amplifier, this having both AC and DC outputs. A quasi-static calibration was made of the sensor's DC responsivity, i.e., incremental rate of change of output voltage versus fibre position, by slowly scanning a fused-silica fibre sample transversely through the illuminating beam. The work reported here concerns the determination of the sensor's more important AC (Violin-Mode) responsivity. Recognition of the correspondence between direct AC modulation of the source, and actual Violin-Mode signals, and of the transformative role of the AC/DC gain ratio for the amplifier, at any modulation frequency, f, resulted in the construction of the AC/DC calibration source described here. A method for determining in practice the transimpedance AC/DC gain ratio of the photodiode and amplifier, using this source, is illustrated by a specific numerical example, and the gain ratio for the prototype sensing system is reported over the frequency range 1 Hz-300 kHz. In fact, a maximum DC responsivity of 1.26 kV.m(-1) was measured using the prototype photodiode sensor and amplifier discussed here. Therefore, the measured AC/DC transimpedance gain ratio of 922.5 for this sensor, at 500 Hz, translated into a maximum Violin-Mode (AC) responsivity of (1.16 ± 0.05) MV m(-1), at that frequency.
这项工作的背景是一个原型阴影传感器，它被设计用于改装到先进的激光干涉引力波天文台（LIGO）的测试质量/镜子悬架上，在该悬架中，一个40千克的测试质量/镜子由四根约600毫米长、直径0.4毫米的熔融石英悬架纤维悬挂。阴影传感器包括一个近红外（NIR）辐射的发光二极管光源和一个“细长”的矩形硅光电二极管探测器，它们共同将被测纤维夹在中间。光电二极管的位置设置成使其（主要）对这种纤维的横向“小提琴模式”振动敏感，通过纤维投射的阴影的振荡运动，因为阴影在探测器表面移动。在这个原型阴影传感系统中，光电二极管连接到一个特制的跨阻放大器，该放大器有交流和直流输出。通过缓慢地横向扫描一根熔融石英纤维样品穿过照明光束，对传感器的直流响应度进行了准静态校准，即输出电压相对于纤维位置的增量变化率。这里报告的工作涉及传感器更重要的交流（小提琴模式）响应度的测定。认识到光源的直接交流调制与实际小提琴模式信号之间的对应关系，以及在任何调制频率f下放大器的交流/直流增益比的转换作用，导致了这里所述的交流/直流校准源的构建。通过一个具体的数值例子说明了一种使用该源在实际中确定光电二极管和放大器的跨阻交流/直流增益比的方法，并报告了原型传感系统在1赫兹至300千赫兹频率范围内的增益比。实际上，使用这里讨论的原型光电二极管传感器和放大器测量到的最大直流响应度为1.26千伏·米⁻¹。因此，该传感器在500赫兹时测得的交流/直流跨阻增益比为922.5，在该频率下转化为最大小提琴模式（交流）响应度为（1.16±0.05）兆伏·米⁻¹。
