Broadband pump-probe spectroscopy at 20-MHz modulation frequency

Abstract

We introduce an innovative high-sensitivity broadband pump-probe spectroscopy system, based on Fourier-transform detection, operating at 20-MHz modulation frequency. A common-mode interferometer employing birefringent wedges creates two phase-locked delayed replicas of the broadband probe pulse, interfering at a single photodetector. A single-channel lock-in amplifier demodulates the interferogram, whose Fourier transform provides the differential transmission spectrum. Our approach combines broad spectral coverage with high sensitivity, due to high-frequency modulation and detection. We demonstrate its performances by measuring two-dimensional differential transmission maps of a carbon nanotubes sample, simultaneously acquiring the signal over the entire 950-1350 nm range with 2.7·10^-6 rms noise over 1.5 s integration time.

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.…”

“…In addition, time-domain detection enables modulation of an actinic pump pulse at high repetition rates, up to the MHz range, as demonstrated in Refs. [25,26]. Demodulation of the signal as a function of pump-probe delay T and PDI delay τ should allow extracting the pump-induced differential chiral IG ΔI chi τ, T , from which the transient OA spectra can be obtained by FT, with much higher sensitivity than the linear measurements reported here.…”

Linear and Nonlinear Spectroscopy by a Common-Path Birefringent Interferometer

“…We then apply the TWINS interferometer to broadband nonlinear spectroscopy, in the pump-probe [24] and SRS [23] configurations. Since both techniques use the same experimental approach to extract the differential signal, for the sake of clarity we will explain it in detail for the pump-probe case.…”

“…TWINS can be used to build a compact FT spectrometer also at wavelength ranges, such as visible or UV, where pathlength stabilization in classical Michelson interferometers becomes technically too demanding. In addition, TWINS can be used in nonlinear spectroscopy for time-domain FT detection of broadband differential signals, exploiting sensitive modulation transfer schemes with high-frequency modulation and synchronous detection with lock-in amplifiers [23], [24]. This approach exploits the linearity of the FT operator, which allows one to obtain the differential spectrum as the FT of the delay-dependent demodulated signal.…”

Fourier transform spectroscopy in the vibrational fingerprint region with a birefringent interferometer

“…TWINS has the advantages of being inherently stable, compact and potentially low cost, and we have proved its applicability to a number of spectroscopic methods, including 2DES in the visible [18] and the UV [19], 2DIR spectroscopy [20], FT spectroscopy [16], broadband pump-probe spectroscopy [21] and stimulated Raman scattering spectroscopy [22]. So far two birefringent materials have been used for TWINS, alpha barium borate (α-BBO) and lithium niobate (LiNbO 3 ).…”