Optical system for measuring the spectral retardance function in an extended range

Abstract

Background: Optical retarders are key elements for the control of the state of polarization of light, and their wavelength dependance is of great importance in a number of applications. Methods: We apply a well-known technique for determinig the spectral retardance by measuring the transmission spectra between crossed or parallel polarizers. But we we develop an optical system to perform this measurement in a wide spectral range covering the visible (VIS) and near infrared (NIR) spectrum in the range from 400 to 1600 nm. Results: As a result we can measure the spectral retardance of different retarders and easily identify the kind of reterder (multiple order, zero-order, achromatic). We show results with tunable liquid-crystal retarders as well, where the technique is applied to determine the spectral retardance as a function of the applied voltage. Finally, the accuracy of the technique is verified by the generation of a birefringent spectral filter. Conclusions: A technique to measure the spectral retardance of a linear retarder in a wide spectral range is applied to identify different types of retarders, and provide an accurate description of the spectral polarization conversion properties of these elements.

Solc filters in a reflective geometry

“…where f l ( ) is the spectral retardance of the quartz retarder (the factor 2 is due to the double pass through the retarder, and the additional π term is the retardance due to the FR-QWR). Since the retardance of the multiple-order retarder varies rapidly with wavelength, typically as f=kΔn•d, the spectrum in figure 2(b) displays the characteristic oscillatory pattern [24]. We verified that the second quartz retarder exhibits equivalent oscillatory spectrum, thus providing identical spectral retardance.…”

“…Since the retardance of the multiple-order retarder varies rapidly with wavelength, typically as f =kΔnˑd, the spectrum in Fig. 2(b) displays the characteristic oscillatory pattern [24]. We verified that the second quartz retarder exhibits equivalent oscillatory spectrum, thus providing identical spectral retardance.…”

Wavefront phase calculation of optical vector beams using phase shifting interferometry

“…For that purpose, the input polarizer in the system was oriented at 45º while the output polarizer was oriented crossed, oriented at -45º. This configuration has been used extensively to measure the retardance of linear retarders [36] which can be derived directly from intensity measurements. If both SLMs display the same amplitude and a uniform phase pattern, in Eq (10) we can consider the amplitude terms as constant, α(x, y) = 0; and therefore, the intensity is given directly proportional to (1+cos(δ j )).…”

Synthesis, Mesomorphism and the Optical Properties of Alkyl-deuterated Nematogenic 4-[(2,6-Difluorophenyl)ethynyl]biphenyls

“…LC-tunable filters were successfully demonstrated in research labs and some industrial environments to have a great potential in agriculture, process inspection, remote sensing and medical diagnosis for spectral and polarization imaging (SPI) and hyperspectral imaging (HSI). For those applications, the interest is usually in the near-infrared window (750–1300 nm), which is covered with LC devices, enhancing the functionality of optical imaging systems [ 39 , 40 , 41 , 42 , 43 , 44 ]. LCs can also be applied in optical systems based on a LCoS-SLM, that acts as a waveplate with a programmable spectra retardance function in the visible and NIR wavelength [ 45 , 46 ].…”