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.

Single-shot time-frequency imaging spectroscopy using an echelon mirror

“…2(b), we could easily obtain the second-and thirdorder derivatives of the chirp profiles as −1.39 × 10 4 fs 2 and 1.89 × 10 5 fs 3 for the NC pulses, 3.13 × 10 2 fs 2 and 5.16 × 10 5 fs 3 for the nearly Fourier TL pulses, and 2.35 × 10 4 fs 2 and 4.78 × 10 5 fs 3 for the PC pulses. These values were also numerically confirmed by the calculation from the geometrical configuration of the built-in compressor [16,20]. The value of the second-order derivative for the nearly Fourier TL pulse is 2 orders of magnitude smaller than those of the NC and PC pulses, although it is not ideally 0.…”

“…Very recently, we successfully evaluated the intensity and phase profiles of ultrashort laser pulses using the second harmonic generation (SHG) FROG apparatus with an echelon mirror [16]. However, because of the nature of the second-order correlation between probe and gate pulses, the chirp direction of the laser pulse (either the PC or NC pulse) is not determined straightforwardly.…”

“…Here, the echelon mirror acts as a spatially encoded time delay optic but not as a spectral-resolved reflective grating. The detail of the echelon mirror is described elsewhere [16,17].As a light source, we used a conventional Ti:sapphire regenerative amplifier system with pulse duration, center wavelength, and repetition rate of ∼130 fs, 800 nm, and 1 kHz, respectively. The output of the regenerative amplifier system is divided into probe and gate pulses by a beam splitter (BS); the probe pulse is expanded to a diameter of ∼2 cm to cover a whole area of the echelon mirror with almost homogeneous intensity, while the gate pulse goes through an optical delay stage to tune the time delay between the probe and gate pulses.…”

“…Here, the echelon mirror acts as a spatially encoded time delay optic but not as a spectral-resolved reflective grating. The detail of the echelon mirror is described elsewhere [16,17].…”

Control of Phonon Polariton Propagation in LiNbO3 Single Crystals

“…Due to the strong optical anisotropy of refractive indices between extraordinary and ordinary lights, we could precisely control the generated E-mode terahertz phonon polariton propagation, which was difficult in the A-mode phonon polaritons: that is, the double pulse excitation can control the direction of the phonon polariton propagations. To visualize the phonon polariton propagations, we utilized the single-shot time-frequency two-dimensional (2D) mapping spectroscopy using an echelon mirror [6][7]. The single-shot technique designed for the investigation of irreversible phenomena in materials is also useful for such a complicated experiment like the double-pump and single-probe measurement demonstrated here, because it dramatically reduces the time required for a complete set of experiments with good signal-to-noise ratio.…”