Quarter wave plate

Current–voltage characteristics of OFETs were measured inside a vacuum chamber, using a Keithley 4200-SCS semiconductor parametric analyzer. To investigate photocurrent of phototransistor devices, laser instrument (CNI laser, maximum power of 5 mW) was used to generate monochromatic light. For testing the spectral photoresponse, monochromatic light was produced using a 300 W Xenon lamp and Oriel Cornerstone 130 monochromator with dual gratings. In all, 280 μm slits were used for bandwidth of 3.7 nm. The CPL illumination was generated through a linear polarizer and a quarter-wave plate (Thorlabs). To confirm the quality of circular polarization of the light, we tested the intensity independence of the light passing through the quartz as the degree between the transmission axis of the linear polarizer and the fast axis of the quarter-wave plate changed. Also, we rotated the degree to avoid elliptical polarization by confirming that the intensity of light splits into two orthogonal linear polarization state using beam splitter (Thorlabs). All corrections were conducted by placing the Si photodetector in the same position with the samples.

The ultrafast pump-probe measurements are conducted by employing a commercial TA spectrometer (Ultrafast Systems, USA). The 800 nm output pulse laser (1 kHz repetition rate, ~100 fs pulse width) from a Ti:sapphire regenerative amplifier (Spectra-Physics Spitfire) is split into two paths. One beam goes through a mechanical delay stage to pump a CaF₂ or sapphire crystal to generate a light continuum to serve as the probe pulse. The second beam is sent to an optical parametric amplifier (Spectra-Physics TOPAS) to generate pump pulses (260–2000 nm). The circularly polarized pump and probe beams are obtained by using quarter-wave plates purchased from Thorlabs. The pump and probe pulses are non-collinearly focused on samples with a beam size of about 100 and 50 μm, respectively, by using parabolic mirrors. A mechanical chopper with a synchronized readout of a CMOS detector is used for acquisitions of probe spectra with and without pump-induced changes, enabling the measurement of a differential transmission. The spectra resolution is ~1.0 nm across the detecting range. For each TA spectrum, three scans are performed to ensure the repeatability for the obtained results. The steady-state and ultrafast optical spectra at low temperatures are conducted by using a commercial cryostat (Cryo Industries of America, INC.).

A femtosecond laser pulse with a repetition rate of 500 Hz, a central wavelength of 800 nm, pulse width of 100 fs, and pulse energy of 2 mJ was generated by a titanium‐sapphire laser amplifier (Spectra‐physics) in the pump–probe experiment. The output laser was then split into two beams, and the stronger pulse was sent to the TOPAS system to generate a pump pulse, which was then chopped to 250 Hz. The other beam, the probe beam, was produced by focusing the weaker part on a sapphire slab to generate a wide band of white light. The two pulses are then focused through convex lenses and overlapped onto the sample. The sample was placed in the variable temperature device (Advanced Research Systems). The circular polarization of the pump and probe pulses were controlled by two sets of wideband Glan Polarizers and quarter‐wave plates (310–1100 nm, Thorlabs). The time delay between the pump and probe pulse was controlled by a mechanical delay line stage (DL325, Newport). Finally, the differential transmission probe signal was recorded by a spectrometer (AvaSpec‐ULS2048CL‐EVO Avantes). A chirp program was used to compensate the group velocity dispersion of the TA spectra.

We built a monochromatic polariscope as the experimental setup for photoelastography. The experiment was performed in 2D because this method is more commonly used and more friendly to computational power during the imaging post-processing. It consisted of 2 linear polarizers, 2 quarter waveplates (Thorlabs, Germany), an LED light source (λ = 630 nm) and 1 CCD camera. Normal force was placed perpendicularly onto the implant to mimic the biting force. The forces ranged from 20, 30, 40 over 50, 60, 70 to 80 N. The photographic records obtained from each load application were stored in an image database. A visualization of the intensity of the stresses (fringe order: 0, 1/2, 1, 3/2, 2, 5/2, etc. in the different regions of each model was performed. We validated the mechanical force distribution around the implant through the 2D photoelastic experiments on bone mimicking tissue phantom. The phantom was constructed with castable aliphatic polyurethanes (BJB Enterprise Co., US). The finished PU material has an average density of 1050 kg/m³ and a Young’s moduli of 820.42 MPa (determined by DIN-ISO 527 universal mechanical test). The PU liquid mixture were casted into a thin mold, where the half implant was folded. This simulates the geometry, where the dental implant is coupled into the jaw.