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High-Acquisition-Rate Single-Shot Pump-Probe Measurements Using Time-Stretching Method

View Article: PubMed Central - PubMed

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.

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Fast acquisition of pump and single-shot probe data on the phase change material GST.(a) Intensity profiles of the probe pulses (left) and the normalized transmission change (−ΔI/I) (middle). The right-most trace indicates the pump intensity simultaneously monitored using the same oscilloscope. The slices of the ultrafast waveforms are shown in red (frame 400 in the amorphous phase) and blue (frame 150 in the crystalline phase) at the right side of the figure. The blue and orange dashed lines show the crystalline-to-amorphous phase change and the relaxation dynamics in the amorphous phase, respectively, which are taken from the data in refs 4 and 29. (b) The transmission change at 1 ps (top), pump (middle), and probe (bottom) intensities as a function of the frame number. Solid lines in the figures indicate the average of 10 frames around. Since the measurement was made at 500 Hz, the horizontal axis corresponds to the time of the measurement.
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f3: Fast acquisition of pump and single-shot probe data on the phase change material GST.(a) Intensity profiles of the probe pulses (left) and the normalized transmission change (−ΔI/I) (middle). The right-most trace indicates the pump intensity simultaneously monitored using the same oscilloscope. The slices of the ultrafast waveforms are shown in red (frame 400 in the amorphous phase) and blue (frame 150 in the crystalline phase) at the right side of the figure. The blue and orange dashed lines show the crystalline-to-amorphous phase change and the relaxation dynamics in the amorphous phase, respectively, which are taken from the data in refs 4 and 29. (b) The transmission change at 1 ps (top), pump (middle), and probe (bottom) intensities as a function of the frame number. Solid lines in the figures indicate the average of 10 frames around. Since the measurement was made at 500 Hz, the horizontal axis corresponds to the time of the measurement.

Mentions: Perhaps the most useful advantage of this high-repetition rate single-shot measurement is the ability to study irreversible phenomena. To demonstrate this capability using the setup shown in Fig. 1, we examine the ultrafast laser-induced amorphization in the phase change material Ge2Sb2Te5 (GST), a famous material for optical storage devices262728. The laser induced crystalline to amorphous phase change induces relatively high contrast in the optical constant, yet the ultrafast dynamics are less studied due to the difficulty in the measurement of the irreversible phase change4. Here the amplitude of transmitted probe light is monitored as the pump fluence is increased from 5.3 mJ/cm2 to 10.8 mJ/cm2, crossing the phase change threshold. Figure 3a shows the observed probe profiles as a function of time (the left panel), and transmission change calculated by the pulses with and without the pump pulse (−ΔI(t)/I(t) – the right panel). Again, the vertical axis in this figure corresponds to the time of the measurement (as the pump fluence is increased), and each frame is captured at 500 Hz acquisition rate.


High-Acquisition-Rate Single-Shot Pump-Probe Measurements Using Time-Stretching Method
Fast acquisition of pump and single-shot probe data on the phase change material GST.(a) Intensity profiles of the probe pulses (left) and the normalized transmission change (−ΔI/I) (middle). The right-most trace indicates the pump intensity simultaneously monitored using the same oscilloscope. The slices of the ultrafast waveforms are shown in red (frame 400 in the amorphous phase) and blue (frame 150 in the crystalline phase) at the right side of the figure. The blue and orange dashed lines show the crystalline-to-amorphous phase change and the relaxation dynamics in the amorphous phase, respectively, which are taken from the data in refs 4 and 29. (b) The transmission change at 1 ps (top), pump (middle), and probe (bottom) intensities as a function of the frame number. Solid lines in the figures indicate the average of 10 frames around. Since the measurement was made at 500 Hz, the horizontal axis corresponds to the time of the measurement.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5120281&req=5

f3: Fast acquisition of pump and single-shot probe data on the phase change material GST.(a) Intensity profiles of the probe pulses (left) and the normalized transmission change (−ΔI/I) (middle). The right-most trace indicates the pump intensity simultaneously monitored using the same oscilloscope. The slices of the ultrafast waveforms are shown in red (frame 400 in the amorphous phase) and blue (frame 150 in the crystalline phase) at the right side of the figure. The blue and orange dashed lines show the crystalline-to-amorphous phase change and the relaxation dynamics in the amorphous phase, respectively, which are taken from the data in refs 4 and 29. (b) The transmission change at 1 ps (top), pump (middle), and probe (bottom) intensities as a function of the frame number. Solid lines in the figures indicate the average of 10 frames around. Since the measurement was made at 500 Hz, the horizontal axis corresponds to the time of the measurement.
Mentions: Perhaps the most useful advantage of this high-repetition rate single-shot measurement is the ability to study irreversible phenomena. To demonstrate this capability using the setup shown in Fig. 1, we examine the ultrafast laser-induced amorphization in the phase change material Ge2Sb2Te5 (GST), a famous material for optical storage devices262728. The laser induced crystalline to amorphous phase change induces relatively high contrast in the optical constant, yet the ultrafast dynamics are less studied due to the difficulty in the measurement of the irreversible phase change4. Here the amplitude of transmitted probe light is monitored as the pump fluence is increased from 5.3 mJ/cm2 to 10.8 mJ/cm2, crossing the phase change threshold. Figure 3a shows the observed probe profiles as a function of time (the left panel), and transmission change calculated by the pulses with and without the pump pulse (−ΔI(t)/I(t) – the right panel). Again, the vertical axis in this figure corresponds to the time of the measurement (as the pump fluence is increased), and each frame is captured at 500 Hz acquisition rate.

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus