Abstract
Recent advances of ultrafast spectroscopy allow the capture of an entire ultrafast signal waveform in a single probe shot, which greatly reduces the measurement time and opens the door for the spectroscopy of unrepeatable phenomena. However, most single-shot detection schemes rely on two-dimensional detectors, which limit the repetition rate of the measurement and can hinder real-time visualization and manipulation of signal waveforms. Here, we demonstrate a new method to circumvent these difficulties and to greatly simplify the detection setup by using a long, single-mode optical fiber and a fast photodiode. Initially, a probe pulse is linearly chirped (the optical frequency varies linearly across the pulse in time), and the temporal profile of an ultrafast signal is then encoded in the probe spectrum. The probe pulse and encoded temporal dynamics are further chirped to nanosecond time scales using the dispersion in the optical fiber, thus, slowing down the ultrafast signal to time scales easily recorded with fast detectors and high-bandwidth electronics. We apply this method to three distinct ultrafast experiments: investigating the power dependence of the Kerr signal in LiNbO3, observing an irreversible transmission change of a phase change material, and capturing terahertz waveforms.
Highlights
Traditional ultrafast pump-probe measurements can require thousands to millions of laser shots to record a single time-dependent signal trace, which can make ultrafast measurements exceptionally time-consuming, and exclude the possibility of studying irreversible phenomena in many systems
After passing the ultrafast probe pulse through a high dispersion SF11 glass rod in order to pre-chirp it, the probe pulse is transmitted through a sample of interest, and subsequently directed to the input facet of a long fiber to further stretch each pulse into the nanosecond range
We demonstrate in this paper the power of this novel single-shot detection scheme in three spectroscopic experiments: the observation and fast acquisition of pump-power dependent Kerr waveforms in ferroelectric LiNbO3, the measurement of the onset of a permanent photo-induced phase change in a chalcogenide alloy film, and the fast acquisition of THz waveforms via electro-optic sampling
Summary
In the Kerr and GST experiments, the output of a Ti:sapphire amplifier with 40-fs pulse duration, 1-kHz repetition rate, 1.4-mJ output power and 800-nm center wavelength is used. The polarization rotated signal or the transmitted probe pulses were input into a 3-km-long single-mode fiber (Nufern, 780-OCT), and the intensity profile was recorded using a 1-GHz photodiode (ThorLabs DET02AFC) and a 12.5-GHz real-time oscilloscope (Tektronics DPO71254C). The probe pulses were pre-stretched to approximately 2 ps by passing through a 150 mm SF11 glass rod, and focused collinearly with the THz pulses to a 300 μm thick (110) GaP electro-optic crystal. After passing through a quarter-waveplate oriented at 45 degrees to the initial probe polarization, and a polarizer, the probe beam was focused and input into a 3-km single-mode optical fiber from Mitsubishi (Optiflex FSFC2/9S-S-V/1–3 K). The pump/probe wavelength was selected to ensure significant stretching in the single mode optical fiber resulting in a probe intensity profile of a few ns duration. The relative delay between pump and probe was changed, and the data compared to electro-optic traces recorded using a conventional stage scan technique with ~100 fs 800 nm probe pulses
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