Linear and Nonlinear Spectroscopy by a Common-Path Birefringent Interferometer

Abstract

We introduce a passive common-path interferometer to replace Michelson interferometers in Fourier transform spectroscopy. Our device exploits birefringence to introduce a highly accurate delay between two orthogonal polarization components by continuously varying the material thickness. Thanks to its inherent delay stability and reproducibility, it can be used even for short wavelengths (down to ~200nm) without the need for any active control or position tracking. We first demonstrate its performances in linear spectroscopy, by implementing a spectrometer and a spectrophotometer. We then extend its use to nonlinear spectroscopy and, in combination with lock-in detection at MHz modulation frequencies, illustrate its application to pump-probe spectroscopy with high sensitivity (ΔT⁄T<3·10-6 in 1-s integration time) and broad spectral coverage (>500nm) and to broadband stimulated Raman scattering microscopy in the CH stretching\ud region

Time-domain measurement of optical activity by an ultrastable common-path interferometer

“…For a Michelson interferometer the optical frequencies ω are linearly proportional to f x ; for the CPI this relationship slightly deviates from linearity due to the aforementioned frequency dependence of the birefringence Δnω of commonly used materials. This effect has been discussed previously [21][22][23][24][25][26][27]; see also Fig. 2(b) in Ref.…”

“…The broadband illumination is sent to a first polarizer P 1 (extinction ratio > 10 5 ), with transmission axis tilted from the vertical direction by a small angle γ. After the polarizer, the light passes the birefringent CPI, which is a simplified version of the Translating-Wedge-based Identical pulses eNcoding System (TWINS) [21,22]. TWINS is composed of two blocks of a birefringent material, A and B, with optical axes (see blue arrow and dots in Fig.…”

Stokes shift microscopy by excitation and emission imaging

“…1(b)). In addition, emission spectra are obtained by placing a birefringent based interferometer [32,33] in front of the complementary metal oxide semiconductor (CMOS) camera. For ideal polarization of the entrance light, the interferometer throughput is close to 100% and therefore higher than for standard dispersion based spectrographs.…”

“…At such long exposure times it is likely that thermal drift would lead to image distortions. [27,32,33]. B) Measurement procedure for excitation spectra based on scanning the excitation wavelength.…”

Vibrational phase imaging by stimulated Raman scattering via polarization-division interferometry

“…A 6-mm thick birefringent YVO 4 plate is inserted in the Stokes beam to generate a LO which is anticipated by ~4ps [27]. After the sample, the delay between Stokes and LO is canceled with interferometric precision by a pair of YVO 4 wedges (apex angle 10°), whose insertion can be finely tuned via a mechanical motor [28,31]. The use of a wedge pair is crucial, as it would be very difficult to find two plates with precisely matched thickness.…”