太赫兹宽带相位变换器 THz Board-band Phase Transformers

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太赫兹宽带相位变换器
THz Board-band Phase Transformers

THz monochromatic waveplates can be used only at single wavelength since phase retardation strongly depends on the wavelength. Sometimes it's necessary to have nearly constant retardation at the specified wavelength range. For that case we have developed THz broad-band phase transformers.

Basic methods of broad-band phase transformers calculation are well-known. However, they are not suitable for the case if measuring system has high resolution. So we have modified the methods to take into account interference effect. Broad-band phase transformers consist of several specially oriented crystal quartz plates. The plates are stacked together and fixed into a holder. According to Jones formalism system of several retardation plates is optically equal to system containing only two elements: so called “retarder” and “rotator” (please see Fig.1). Retarder provides required phase shift (usually π or π/2). Rotator turns the polarization plane at angle ω.

Fig.1. Broad-band phase transformer in terms of Jones formalism
and its position relative to polarizer and analyzer.

There are two types of broad-band phase transformers:

1) ω is not 0º and it depends on the wavelength. We call it “achromatic polarization converter” (APC). Example of ω behavior is below.

Fig.2.a) Angle ω of the APC L/4@60-300 um.

2) ω is about 0º and it is constant within the operating wavelength range. In this case it is usual “achromatic waveplate” (AWP) and its operating principle is the same as of monochromatic waveplate. 

Fig.2.b) Angle ω of the AWP L/4@60-95 um.