講演情報
[22p-13M-11]Background-free Mid-infrared Spectroscopy via Upconverted Sub-cycle Pulses
〇Neil Irvin Cabello1, Shinta Ozawa1, Yue Zhao2, Takao Fuji1 (1.Toyota Tech. Inst., 2.Muroran Inst. Tech.)
キーワード：
ultrafast optics、nonlinear optics、mid-infrared
In this work, we present a background-free, single-shot mid-infrared (MIR) absorption spectroscopy based on nonlinear effects. The background signal is temporally separated from the detected absorption signal i.e. the MIR free-induction decay, which consequently lessens the dynamic range requirements for the detector. Since the MIR signal is upconverted to the visible range, silicon-based CCD detectors capable of multi-channel detection can be employed for broadband and rapid acquisition, with no need for performing signal post-processing. This makes obtaining single-shot, broadband MIR transmission spectroscopy in real time possible. The excitation is provided by an ultrafast Ti:sapphire multipass amplifier laser (Femtopower CompactPro) with central wavelength of 800 nm, repetition rate of 1 kHz and maximum pulse energy of 1 mJ. The main beam was split into two using a 70:30 beam splitter. The 70% beam was passed through a Treacy compressor and then used to generate the MIR pulse by two-color filamentation, while the 30% beam was introduced to a Fabry-Perot resonator, mechanically delayed and passed through another Treacy compressor to generate the gate pulses. These two beams were made collinear and overlapped onto a 200 nm-thick silicon membrane for upconversion via four-wave mixing. To demonstrate the capability of the system, we obtained signal from varying concentrations of glucose samples. We were able to obtain absorption signal to up to ~50 mM glucose, which is not detectable in a conventional Fourier transform infrared spectrometer.