多波长测量技术

给出了3种多波长测量技术的应用实例，采用多波长二极管激光器干涉仪测量表面轮廓，3个二极管激光器分别发射780nm、823nm和825nm3种近红外光波，可以得到2个近似15μm和29μm的合成波长，激光二极管的注入电流用1MHz左右的3种不同频率调制，以获得干涉仪的相位调制，这3个干涉信号用1个光电检测器和锁相放大器检测，采用同样的干涉仪，仅用2种波长进行了圆度偏差测量，论述了相移干涉测量技术，其试件的长度表示为光源波长的倍数，如果只使用1种波长，则要求确切知道整数干涉级；而使用多种波长，如532nm、633nm和780nm时，可得到几个独立的长度，此时整数衍射级不同，可以通过“精确小数法”计算得到，PTB精密干涉仪长度测量不确定度很小，其单值性范围约0.6mm，因此其近似的长度估算足以满足超精密长度测量的要求。

Multi-Wavelength Measurement Techniques

In this paper, three experimental examples are given for applications of the multi-wavelength measurement technique. A multi-wavelength diode laser interferometer for the measurement of surface profiles has been developed. With three diode lasers emitting in the near infrared (780 nm, 823 nm, and 825 nm) synthetic wavelengths of approximately. 15 μm and 290 μm could be achieved. The injection current of the laser diodes is modulated with different frequencies around 1 MHz which leads to a modulation of the wavelength and therefore the interferometer phase. The three interferometer signals are detected by lock-in amplifiers using only one photo detector. In the second example the same interferometer is used for the measurement of roundness deviations. For this application only two wavelengths were used. The third example describes phase shifting interferometry, where the length of a material sample is expressed as a multiple of the wavelength used as light source. Using only one wavelength would require the exact knowledge of the integer interference orders. The use of different wavelengths, i.e. 532 nm, 633 nm and 780 nm, results in independent lengths, where the integer orders can be varied. It is shown in which way the number of variations can be reduced drastically. Considering a measurement example at PTB's Precision Interferometer, the uncertainty of the individual length measurement is small enough so that the range of unambiguity is about 0.6 mm, i.e. a rough estimate of the length is sufficient for ultra precise length measurements.