16 fs, 350 nJ pulses at 5 MHz repetition rate delivered by chirped pulse compression in fibers

Abstract

We demonstrate a simple approach for broadening and compression of intense pulses at megahertz repetition rates by self-phase modulation in nonlinear photonic crystal fibers. In order to avoid damage by self-focusing, we positively chirp the input pulses, which allows coupling of significantly more energy into the fiber, while maintaining the same spectral bandwidth and compression as compared to the Fourier-limited case at lower energy. Using a commercial long-cavity Ti:sapphire oscillator with 55 fs, 400 nJ pulses at 5 MHz, we generate 16 fs, 350 nJ pulses, which is a factor of 4 more energy than possible with unchirped input pulses. Self-phase-modulated spectra supporting 11 fs duration are also shown with 350 nJ pulse energy. Excellent stability is recorded over at least 1 h.

Conversion of chirp in fiber compression

“…Similarly to our earlier measurements (see Fig. 3 of [6]), we again observe an increase in energy for longer pulses.…”

“…The latter approach is particularly promising for upscaling the pulse energy because the nonlinear broadening mechanisms in the fiber scale with the pulse's peak intensity, whereas damaging effects caused by self-focusing scale with the peak power. Experiments show that chirped pulses at higher energy can provide the same amount of broadening as short pulses of lower energy [6]. Positive chirp was applied to generate 350 nJ, 16 fs pulses at a repetition rate of 5.1 MHz in this way [6].…”

“…Experiments show that chirped pulses at higher energy can provide the same amount of broadening as short pulses of lower energy [6]. Positive chirp was applied to generate 350 nJ, 16 fs pulses at a repetition rate of 5.1 MHz in this way [6]. Negatively chirped input can also result in some improvements [1], although the fiber's dispersion tends to compress the propagating pulses in a nondesired way.…”

“…In practice, the reduction of chirp observed here allows for compressing the spectrally broadened intense pulses by ultrabroadband dispersive multilayer mirrors of quite moderate dispersion. Spectral broadening and pulse compression in fibers can be extended to significantly higher pulse energies by (1) using large-mode-area photonic crystal fibers [1][2][3][4][5][6] in combination with (2) chirping the input pulses [6,1]. The latter approach is particularly promising for upscaling the pulse energy because the nonlinear broadening mechanisms in the fiber scale with the pulse's peak intensity, whereas damaging effects caused by self-focusing scale with the peak power.…”

Pulse compression with large-mode-area photonic crystal fibres

“…The large mode area prohibits optical damage at the fiber entrance and fiber guiding allows sufficient nonlinearity for pulse compression at the same time, as indicated by supercontinuum (SC) generation experiments. The potential offered by LMA PCFs was shown recently in compression experiments with relatively long and/or heavily chirped pulses [11], based on the principle of chirped-pulse supercontinuum generation [12]. It was also possible to perform efficient and energy scalable compression with transform limited input [13].…”