Setup used to determine the dispersion and resolving power of the VPH grating in double pass. Overall, the optical layout is very similar to the setup in Fig. A.1. The only difference is that the linear polarizer has been removed and with the help of the fold mirror, the VPH is placed in double pass. The beamsplitter that is used to inject light into the spectrum analyzer is now used in the second pass to re-direct the spectrum to a near-infrared (NIR) detector to image the resulting spectrum.