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Filters
Published in Solomon Musikant, Optical Materials, 2020
The interference filter depends on multilayer dielectric-metal stacks to control the transmission or reflection of particular bandpasses by means of constructive and destructive interference. The design of such stacks is beyond the scope of this volume but is well covered by Dobrowolski (1978) and in other texts.
Impact of co-doping concentration in copolymer network liquid crystals
Published in Liquid Crystals, 2019
Fatemeh Jahanbakhsh, Alexander Lorenz
To investigate the electro-optical properties in the samples, thinner test cells were assembled. The procedure of test cell-fabrication was comparable to the procedure for SEM samples. However, ITO coated glass substrates were used and thinner spacer films were applied. The cell gap measured was ≈ 6.3 μm. The ITO coated test cells were filled with the samples (A, B, C, D, E and F) and exposed to UV light for 15 min. Subsequently, these samples were investigated in a polarised optical microscope (Leica DM/Lp, crossed polarisers) equipped with a photodiode detector (PDD), connected to a digital storage oscilloscope (Tektronix TBS-1102b). The test cells were electrically addressed with a.c.-electrical signals (square wave, 1 kHz) generated with a waveform generator (PM 5193) and amplified (KH 7602M). Various interference filters were tested, and it was found that a red wavelength (661.5 nm) was suitable to record electro-optic response curves in all samples. Thus, experiments were conducted with an interference filter (red wavelength). In order to record electro-optic response curves, various voltages were applied. Threshold voltage and switching times for a 90% answer were extracted from the recorded electro-optic response curves.
Super-resolution pupil filtering for visual performance enhancement using adaptive optics
Published in Journal of Modern Optics, 2018
Lina Zhao, Yun Dai, Junlei Zhao, Xiaojun Zhou
The visual testing channel is highlighted by a green dashed rectangle box. The visual stimuli for visual testing were generated by Matlab 2011b and Psychtoolbox extensions on another computer, and projected by an OLED display (EMA-100110, eMagin Corporation). The OLED display emitted at 540 nm (green light) with a bandwidth of 70 nm. It had a resolution of 800 × 600 pixels and a maximum refresh rate of 75 Hz. An interference filter (550nm ± 5 nm) was placed in front of the OLED display. The OLED display and interference filter were fixed on a stepping motor for adjusting the chromatic focus shift between the HS infrared light source and the green stimulus. A gamma correction setting was used to calibrate the OLED display for its luminance nonlinearity. An objective lens (L3) and a reflecting mirror (M5) were used to form an image of the stimulus on the retina. Static aberrations introduced by BS2, BS3, M5 and L3 may have slightly deteriorated the contrast level of the display. As such, they were calibrated and pre-corrected.
Current Profile Reconstruction Using Motional Stark Effect Polarimeter Data on HL-2A Tokamak
Published in Fusion Science and Technology, 2020
W. J. Chen, D. L. Yu, L. W. Yan, B. S. Yuan, X. X. He, L. Liu, Y. L. Wei, N. Zhang, X. F. He, H. Wu, Z. B. Shi, Y. Liu, Q. W. Yang
Light is transmitted by the fiber array to the real-time filter monochrometer in the laboratory, where the light is filtered by a narrow-band interference filter and imaged onto an avalanche photodiode (APD) chip, as shown in Fig. 3a. The MSE polarimeter observes the σ component of the Doppler-shifted Dα line DE. With a magnetic field of 1.3 T and beam energy of 40 keV, the Doppler shift of DE is 2.88 nm at R = 1.7 m, and the Stark splitting width Δλs is nearly 0.17 nm. The full-width at half-maximum (FWHM) of the interference filter is 0.15 ± 0.05 nm at an angle of incidence of 0 deg. In combination with the spectra and filter used, the maximum polarization fraction is only nearly 33%. However, because of variation of the beam energy Eb during a discharge that makes the Doppler-shifted emission variable, sometimes the spectral line drifts out of the filter transmission region. As a result, the SNR becomes poor. In order to obtain a good SNR and accurate MSE measurement angle, the monochrometer is designed to precisely fast tilt filter guided by beam energy Eb in real time during a discharge. The flowchart of the real-time monochrometer is illustrated in Fig. 3b. Beam energy Eb is collected and converted to an analog signal of −5 to 5 V. Then, it is transferred to a controller to precisely guide a rotator to tilt the filter. The relationship γfilter= f (Eb) needs to be carefully calibrated in the laboratory. This real-time filter monochrometer system can largely improve the accuracy of the MSE measurement angle.19