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Ask RP Photonics for advice concerning any method of pulse compression, or the selection of the most suitable method in a particular situation. RP Photonics has the powerful RP ProPulse modeling software for simulating various kinds of pulse compression.
Definition: linear or nonlinear techniques for reducing the durations of optical pulses
There is variety of methods for temporally compressing (shortening) optical pulses, i.e., to reduce the pulse duration, typically starting in the picosecond or femtosecond region, i.e., already in the regime of ultrashort pulses. These methods can be grouped into two categories:
- Linear pulse compression: When pulses are chirped, their duration can be reduced by removing (or at least reducing) this chirp, i.e., by flattening the spectral phase. Dechirping can be accomplished by sending the pulses through an optical element with a suitable amount of chromatic dispersion (→ dispersion compensation), e.g. a grating compressor, a prism pair, an optical fiber, or a chirped mirror. The smallest possible pulse duration is then set by the optical bandwidth of the pulses, which is not modified by dispersive (linear) compression. In the ideal case, bandwidth-limited pulses are obtained.
- Nonlinear pulse compression: in a first step, the optical bandwidth is increased, typically with a nonlinear interaction such as self-phase modulation. In most cases, this leads to chirped pulses, often with a duration which is even larger than the original pulse duration. Thereafter, the pulse duration can be strongly reduced by linear (dispersive) compression (see above), which removes or at least decreases the chirp.
Methods for Nonlinear Pulse Compression
Nonlinear pulse compression can be done with quite different configurations of optical elements, and with methods which are based on different physical principles. Some examples are:
- Originally unchirped pulses can be spectrally broadened by propagation in a normally dispersive optical fiber and then dispersively compressed e.g. with a prism pair, a grating pair, chirped mirrors, a fiber Bragg grating, or a fiber with anomalous dispersion [2] . The used fibers may be standard optical fibers, photonic crystal fibers, or hollow fibers (for extremely broad spectra). It is possible e.g. to start with picosecond pulses from a mode-locked Nd:YAG laser and get to pulse durations far below 1 ps, or to generate few-cycle pulses starting from pulses with e.g. 50 fs duration.
- For high intensity femtosecond pulses, the spectral broadening can be done in a gas-filled hollow fiber, where most of the optical power propagates in the gas, where self-phase modulation occurs. Subsequent dispersive compression can be done e.g. with double-chirped mirrors. This method is suitable e.g. for compressing 20-fs pulses with millijoule energies down to a few femtoseconds.
- When high intensity few-cycle femtosecond pulses are injected into a gas jet, high harmonic generation can occur, and under certain circumstances pulse durations of a few hundred attoseconds (→ attosecond pulses) are achieved.
- In higher-order soliton compression, a pulse with an energy far above the fundamental soliton energy is injected into a fiber with anomalous dispersion. After a certain propagation distance, a strongly compressed pulse can be obtained, but the choice of propagation distance can be critical.
- In adiabatic soliton compression, a soliton pulse is compressed during propagation in a fiber the anomalous dispersion of which gets weaker and weaker along the propagation direction. Alternatively, the pulse energy can be increased by amplification in a doped fiber with constant dispersion properties.
- In a fiber amplifier with normal dispersion, self-similar parabolic pulses experience spectral broadening while a good pulse quality is preserved.
- Pulse compression can also occur during nonlinear frequency conversion [4,11,17]. Under certain circumstances, frequency doublers or optical parametric oscillators can emit pulses which are much shorter than the pump pulses.
Which one of these methods is most suitable depends on a number of circumstances, including the initial and required pulse duration, the pulse energy, the demands on pulse quality, etc.
Pulse compression setups can be analyzed and optimized using pulse propagation modeling.
Bibliography
| [1] | C. V. Shank et al., "Compression of femtosecond optical pulses", Appl. Phys. Lett. 40, 761 (1982) |
| [2] | W. J. Tomlinson, R. H. Stolen, and C. V. Shank, "Compression of optical pulses chirped by self-phase modulation in fibers", J. Opt. Soc. Am. B 1 (2), 139 (1984) |
| [3] | R. L. Fork et al., "Compression of optical pulses to six femtoseconds by using cubic phase compensation", Opt. Lett. 12 (7), 483 (1987) |
| [4] | A. Stabinis et al., "Effective sum frequency pulse compression in nonlinear crsytals", Opt. Commun. 86, 301 (1991) |
| [5] | S. V. Chernikov et al., "Soliton pulse compression in dispersion-decreasing fiber", Opt. Lett. 18 (7), 476 (1993) |
| [6] | S. V. Chernikov et al., "Comblike dispersion-profiled fiber for soliton pulse train generation", Opt. Lett. 19 (8), 539 (1994) |
| [7] | A. Baltuka et al., "Optical pulse compression to 5 fs at a 1-MHz repetition rate", Opt. Lett. 22 (2), 102 (1997) |
| [8] | M. D. Pelusi et al., "Higher order soliton pulse compression in dispersion-decreasing optical fibers", IEEE J. Quantum Electron. 33 (8), 1430 (1997) |
| [9] | M. Nisoli et al., "Compression of high-energy laser pulses below 5 fs", Opt. Lett. 22 (8), 522 (1997) |
| [10] | Y. Matsui et al., "Generation of 20-fs optical pulses from a gain-switched laser diode by a four-stage soliton compression technique", IEEE Photon. Technol. Lett. 11 (10), 1217 (1999) |
| [11] | J. Biegert and J.-C. Diels, "Compression of pulses of a few optical cycles through harmonic generation", J. Opt. Soc. Am. B 18 (8), 1218 (2001) |
| [12] | C.-M. Chen and P. L. Kelley, "Nonlinear pulse compression in optical fibers: scaling laws and numerical analysis", J. Opt. Soc. Am. B 19 (9), 1961 (2002) |
| [13] | B. Schenkel et al., "Generation of 3.8-fs pulses from adaptive compression of a cascaded hollow fiber supercontinuum", Opt. Lett. 28 (20), 1987 (2003) |
| [14] | A. Couairon et al., "Pulse self-compression to single-cycle limit by filamentation in a gas with a pressure gradient", Opt. Lett. 30 (19), 2657 (2005) |
| [15] | B. Schenkel, R. Paschotta, and U. Keller, "Pulse compression with supercontinuum generation in microstructure fibers", J. Opt. Soc. Am. B 22 (3), 687 (2005) |
| [16] | G. Steinmeyer and G. Stibenz, "Generation of sub-4-fs pulses via compression of a white-light continuum using only chirped mirrors", Appl. Phys. B 82, 175 (2006) |
| [17] | J. Moses and F. K. Wise, "Soliton compression in quadratic media: high-energy few-cycle pulses with a frequency-doubling crystal", Opt. Lett. 31 (12), 1881 (2006) |
| [18] | C. P. Hauri et al., "Intense self-compressed, self-phase-stabilized few-cycle pulses at 2 μm from an optical filament", Opt. Lett. 32 (7), 868 (2007) |
| [19] | R. E. Kennedy et al., "High-peak-power femtosecond pulse compression with polarization-maintaining ytterbium-doped fiber amplification", Opt. Lett. 32 (10), 1199 (2007) |
See also: pulses, spectral phase, pulse propagation modeling, pulse duration, dispersion compensation, nonlinearities, self-phase modulation, adiabatic soliton compression
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