Recently we built a polarization shaper, as shown in the figure on the left, which can modulate the phase, amplitude and polarization of mid-IR light independently. Two identical beams are sent through the shaper along different paths such that their frequency-dependent amplitudes and phases can be programmed independently. The polarization is then rotated by 90° for one of the two beams, which are then recombined on a wire-grid polarizer so that they propagate collinearly.
This polarization shaper is capable of producing pulses with a wide variety of polarization profiles. We expect that polarization shaping will find use in discriminating between degenerate modes that have different transition dipole directions, such as the amide I normal modes of peptides and protein secondary structures, or in eliminating diagonal peaks in 2D IR spectra to make it easier to extract cross-peaks.