Figure 3
Detection of the differential optical response between LCP and RCP irradiation.
In the discrete CPL modulation setup depicted in Fig. 1b, the BD divides an incident LP beam into horizontal LP (HLP) and vertical LP (VLP) components. The HLP and VLP beams are alternately blocked by a chopper blade, which provide light beams that are discretely modulated between two mutually orthogonal linear polarizations (as shown in (a), where the red and blue lines represent the HLP and VLP intensities, respectively). The modulated HLP beam and the VLP beam are recombined into a single beam with the same optical axis by BD2 and then converted by a quarter waveplate (1/4 WP) to LCP and RCP light, respectively. The LCP and RCP intensities vary as shown in (b), where the orange and green lines represent the LCP and RCP intensities, respectively. The circular-polarization modulated beam transmitted through the sample is detected by a photodetector. If the sample is CD active, then it yields difference in the detected signal intensities between LCPn and RCPn, as shown in (c). The differential optical intensity between LCPn and RCPn (ILCP − IRCP) is obtained via lock-in detection.
