Acousto-optic replication of ultrashort laser pulses

Precisely controlled sequences of ultrashort laser pulses are required in various scientific and engineering applications. We developed a phase-only acousto-optic pulse shaping method for replication of ultrashort laser pulses in a TW laser system. A sequence of several Fourier-transform-limited pulses is generated from a single femtosecond laser pulse by means of applying a piecewise linear phase modulation over the whole emission spectrum. Analysis demonstrates that the main factor which limits maximum delay between the pulse replicas is spectral resolution of the acousto-optic dispersive delay line used for pulse shaping. In experiments with a Cr:forsterite laser system, we obtained delays from 0.3 to 3.5 ps between two replicas of 190 fs transform-limited pulses at the central wavelength of laser emission, 1230 nm.

Figure 1

Three types of transmission function $\tilde{H}\left(\omega \right)$ corresponding to different pulse replication methods: top – mask function, middle – absolute value, bottom – phase; (a) direct phase and amplitude modulation, (b) phase-only MICS method, (c) chirped pulse modulation. The example shown is for $N=2$ pulses at the output sequence.

Figure 2

Single replica pulse response of the MICS method for $N=3$; $p$ is the satellite number, equivalent to the principal maximum order of a diffraction grating.

Figure 3

Experimental setup.

Figure 4

Autocorrelation function of a pulse with satellites at various widths of the comb teeth.

Figure 5

Autocorrelation function of $N=2$ replicas with various delay $\mathrm{\Delta }\tau$ from 0.3 to 0.6 ps. The width of the comb teeth is $4\delta \lambda =0.96$ nm, $Q=52$.

Figure 6

Output spectra for $N=2$ replicas with the delay $\mathrm{\Delta }\tau =0.6$ ps. The reference spectrum was obtained using direct phase-and-amplitude modulation.

Figure 7

Autocorrelation function of $N=3$ replicas with equal intervals of $\mathrm{\Delta }\tau =0.6$ ps. The width of the comb teeth is $2\delta \lambda =0.48$ nm, $Q=69$.