Using a fast dual-wavelength imaging ellipsometric system to measure the flow thickness profile of an oil thin film

An instantaneous polarization phase-shifting interferometric system with stroboscopic illumination by using a photoelastic modulator

“…It is commonly known that two or more wavelengths interferometry can increase the dynamic range of an interferometric measurement, and we have been employed this stroboscopic illumination technique for the two-wavelength imaging ellipsometric measurement. 37) © 2019 The Japan Society of Applied Physics 122002-5…”

“…The characteristic of the fixed frequency is sometimes incompatible with some applications, such as the polarimetric imaging system, which desires a high-speed camera and short exposure time in the scale of microseconds or less. The practical approach to overcome the difficulty of high modulation frequency of the PEM was to employ stroboscopic illumination by synchronizing the light source with the PEM modulation, [34][35][36][37] where the camera sequentially integrates the flux of one quarter modulation periods to obtain four images. By adopting this approach, 35) the deduced phase map was associated with the ratio of the linear combination of the four time-intensity integration images that are related to the amplitude and phase of the sinusoidal signal.…”

Photoelastic Modulated Imaging Ellipsometry

“…The frequency drift of PEMs and image recovery were taken more effort on calibration and measurement [22][23][24][25]. We adopted a simple approach by just changing the manner of light illumination from continuous mode to pulse mode, which coordinates with the reference signal of the PEM modulator, known as the stroboscopic illumination technique [14][15][16][17][18]. Stroboscopic effect is a result of temporal aliasing that occurs when continuous motion is represented by a series of short samples.…”

“…However, a few seconds are required to reach resonance equilibrium and stabilize the modulator, while there is a change in the modulation amplitude for different wavelength; this procedure significantly reduced the measurement speed for the multi-wavelength measurement. Here, we developed an equivalent phase retardation technique that may help prevent the above disadvantage of PEM for multi-wavelength measurement [17]. In general, the half-wave modulation Figure 6.…”

“…In order to remove the chromatism limits of this system, we adopted an equivalent phase retardation technique that used dual wavelength ellipsometric measurement to extend the imaging ellipsometry technique without any adjustment of the photoelastic modulator or the optical configuration. Moreover, the image acquisition time for one set of ellipsometric parameters for dual-wavelength measurement remained virtually unchanged [17]. This technique was also applied in Mueller matrix imaging system; we introduced a hybrid phase modulation technique to evaluate the optical polarization characteristics of the specimens [18].…”