New adjustment technique for time coincidence of femtosecond laser pulses using third harmonic generation in air and its application to holograph encoding system

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Abstract
The third harmonic generation of light (266 nm) is enhanced, sensitively depending on the time delay between a pair of pulses split from a single 800 nm femtosecond laser pulse, when they are focused and collided in air. This finding offers a convenient and widely applicable technique to detect temporal and spatial overlapping of two femtosecond pulses. This technique has several advantages over the conventional sum frequency generation method using nonlinear optical crystals, since it obviates the need for expensive crystals, free from phase matching, and elimination of temporal walk off. By applying it to “a holographic encoding system using an interference femtosecond laser pulse,” a periodic fringe spacing is minimized to ∼430 nm by extending the colliding angle between two-pulse beams up to ∼160 °C.