Broadband high resolution sum frequency generation spectrometer for molecular vibrational spectroscopy at interfaces

Abstract

Broadband Sum Frequency Generation (BB-SFG) spectrometer is a complete solution for femtosecond vibrational spectroscopy designed and manufactured by EKSPLA. System produces optically coupled femtosecond broadband midinfrared pulse covering the spectral range of the molecular "fingerprint" region and narrowband visible pulse which are directed to the sample to produce sum frequency signal. Ultrashort pulses of high intensity allow to get better signal to noise ratio using lower pulse energy thus reducing the possibility of sample modification. It is especially important for aqueous and biological samples. Single measurement can cover up to 800 cm-1 bandwidth which shortens the measurement time and lets obtaining spectrum of the same sample state at the beginning and at the end of measurement, which can be different in case of scanning. The design of BB-SFG helps to overcome the main shortcoming of common broadband SFG spectrometers: a complex and energy inefficient narrowband visible pulse channel formation. We use a single all-fiber mode-locked oscillator to generate ultrashort pulses for both broadband femtosecond mid-IR and narrowband picosecond visible channels. Up to 10 μJ energy tunable broadband (>300 cm^-1) pulses in 2.5-10 μm spectral range are mixed at the sample with less than 2 cm^-1 bandwidth visible (532 nm) picosecond pulses in order to produce SFG signal at kHz repetition rates. Real-time spectral scanning technique allows even broader simultaneous spectral acquisition.