  Moving the detection wavelength in vibrational sum-frequency generation
(VSFG) spectroscopy to the near-infrared (> 700 nm) can potentially enable the
study of molecular interfaces absorbing in the visible and give access to
buried bio-interfaces at minimal absorption, reduced scattering, and negligible
autofluorescence. Here, we employ an ultra-narrow bandpass thin-film optical
interference filter on 180-fs, 1.03-$\mu$m laser pulses to generate an
upconversion beam yielding a spectral resolution of 5 cm$^{-1}$ and VSFG
wavelengths between 890 and 980 nm for molecular vibrations in the fingerprint
region. We demonstrate that the beam rejected by the filter can be utilized for
driving a supercontinuum-seeded near-infrared optical parametric amplifier
serving as the front-end of a broadband LiGaS$_{2}$-based mid-infrared
amplifier. Benchmark data on a phospholipid monolayer at the air-water
interface acquired using the resulting VSFG spectrometer show the possibility
of achieving high resolution and signal-to-noise ratio at short acquisition
times. The scheme can also be utilized in other types of vibrational
spectroscopy that derive their spectral resolution from bandpass-filtering of
femtosecond near-infrared laser pulses, such as stimulated Raman scattering
(SRS) and coherent anti-Stokes Raman scattering (CARS) spectroscopy.
