Real-Time Time–Frequency Imaging of Ultrashort Laser Pulses Using an Echelon Mirror

Abstract

We demonstrate real-time time-frequency imaging for the autocorrelation traces of ultrashort laser pulses using an echelon mirror fabricated on a Ni block with 500 steps; the echelon mirror is employed to generate spatially encoded time delays for the probe pulses. By using the frequency-resolved optical gating (FROG) technique with the echelon mirror, the time-frequency images of ultrashort laser pulses were successfully mapped in real-time. The chirp characteristics of the laser pulses were also evaluated with the phase-retrieval procedure on a single-shot basis. Our technique provides significant advantages over conventional autocorrelation and FROG techniques, such as single-shot detection of time-frequency images, a small spot size at a nonlinear crystal, chirp-free characteristics of echelon mirrors, and ultrafast measurement capabilities by simply replacing the nonlinear crystal with samples. Hence, we believe that it becomes a powerful spectroscopic tool for monitoring ultrashort laser pulses and for investigating ultrafast dynamics of materials.

Singleshot and high-sensitivity detection of terahertz waveforms using phase-offset electro-optic sampling and an echelon mirror

“…Therefore, the spot size of the pump pulse can be as small as the diffraction spot. The spot size can also be calculated by the wavelength dispersion of the diffraction [12].…”

Broadband pump–probe imaging spectroscopy applicable to ultrafast single-shot events

“…To address these limitations, a number of spectroscopic techniques based on single-shot detection have been proposed. [6][7][8][9][10][11][12][13][14] Single-shot techniques are usually realized by manipulating the probe pulse to produce a spatially encoded time delay, but this presents some experimental difficulties: in the dual-echelon technique, only the temporal profiles of the transient signals can be obtained, [6][7][8] whereas in pumpprobe imaging spectroscopy, a large spot size at the sample is needed to detect transient signals having a wide temporal range. [9][10][11] Thus, none of these techniques can measure transient signals with wide temporal and spectral ranges.…”

“…We recently proposed a time-frequency two-dimensional (2D) pump-probe imaging spectroscopy with an echelon mirror based on single-shot detection in an effort to remove these constraints. [12][13][14] One of the technical merits of our imaging spectroscopy is the adjustability of the echelon mirror; it can be designed with a desirable step-width and step-height, which enables us to observe various transient phenomena of interest with a suitable time resolution, overall time delay, and spectral bandwidth. In past works, we applied this method to the visualization of phonon-polariton oscillations in ferroelectric crystals, 12) an autocorrelation system, 13) and terahertz wave detection.…”

“…[12][13][14] One of the technical merits of our imaging spectroscopy is the adjustability of the echelon mirror; it can be designed with a desirable step-width and step-height, which enables us to observe various transient phenomena of interest with a suitable time resolution, overall time delay, and spectral bandwidth. In past works, we applied this method to the visualization of phonon-polariton oscillations in ferroelectric crystals, 12) an autocorrelation system, 13) and terahertz wave detection. 14) Here, we design an echelon mirror applicable to wider spectral and temporal ranges of 420-630 nm and a few tens of picoseconds, respectively, and demonstrate broadband single-shot pumpprobe spectroscopy.…”

“…The white light is then directed toward the reflective echelon mirror with 500 steps at a step width and height of 80 and 10 µm, respectively. The echelon mirror is fabricated on a nickel block using a precise micromachining technique and has a surface roughness of <0.2 µm, 13) which results in minimal spatiotemporal modi- fication of the probe beam. The echelon mirror is used to produce multiple probe beamlets.…”