Kluczynski P, Axner O
Department of Experimental Physics, Umeå University, SE-901 87 Umeå, Sweden.
Appl Opt. 1999 Sep 20;38(27):5803-15. doi: 10.1364/ao.38.005803.
A theoretical description of the wavelength-modulation (WM) spectrometry technique is given. The formalism is based on Fourier analysis and can therefore correctly handle arbitrary large frequency-modulation amplitudes. It can also deal with associated intensity modulations as well as wavelength-dependent transmission effects. It elucidates clearly how various Fourier components of these entities combine with those of the line-shape function to yield separately the final analytical and background nf WM signals. Explicit expressions are given for the 2f and the 4f signals. It is shown, among other things, that the 4f technique in general gives rise to smaller background signals (and therefore larger signal-to-background ratios) than does the 2f technique when the background is dominated by etalon effects from short cavities and that a finite intensity modulation necessarily leads to an out-of-phase nf WM signal. The formalism is also able to elucidate clearly that a linear intensity modulation is not sufficient to cause any 2f background residual-amplitude-modulation signals (as was the general consensus until recently in the literature) but that 2f background signals instead can exist only in systems with either wavelength-dependent transmission or a laser with nonlinear intensity modulation.
给出了波长调制（WM）光谱技术的理论描述。该形式基于傅里叶分析，因此能够正确处理任意大的频率调制幅度。它还可以处理相关的强度调制以及与波长相关的传输效应。它清楚地阐明了这些实体的各种傅里叶分量如何与线形函数的分量相结合，以分别产生最终的分析性和背景性WM信号。给出了二次谐波（2f）和四次谐波（4f）信号的显式表达式。结果表明，当背景由短腔的标准具效应主导时，一般来说，4f技术产生的背景信号比2f技术小（因此信背比更大），并且有限的强度调制必然导致异相的WM信号。该形式还能够清楚地阐明，线性强度调制不足以产生任何2f背景残余幅度调制信号（直到最近文献中的普遍共识），但2f背景信号反而只能存在于具有与波长相关的传输或具有非线性强度调制的激光器的系统中。
