Hybrid chirped-pulse amplification

Spectral shaping of an OPCPA preamplifier for a sub-20-fs multi-PW laser

We developed an OPCPA preamplifier with an actively shaped output spectrum to obtain a sub-20-fs-duration pulse for a 4-PW laser. The active spectral shaping was facilitated by controlling the temporal profile of a pump pulse in the OPCPA preamplifier. By optimizing the output spectrum of the OPCPA to compensate for the gain-depletion effect in the 4-PW laser, a final laser pulse with a broad spectrum of 101-nm in width (FWHM), resulting in a short pulse duration of 17 fs, was achieved.

Combined Yb/Nd driver for optical parametric chirped pulse amplifiers

We report on the developed front-end/pump system for optical parametric chirped pulse amplifiers. The system is based on a dual output fiber oscillator/power amplifier which seeds and assures all-optical synchronization of femtosecond Yb and picosecond Nd laser amplifiers operating at a central wavelength of 1030 nm and 1064 nm, respectively. At the central wavelength of 1030 nm, the fiber oscillator generates partially stretched 4 ps pulses with the spectrum supporting a <120 fs pulse duration and pulse energy of 0.45 nJ. The energy of generated 1064 nm pulses is 0.15 nJ, which is sufficient for the efficient seeding of high-contrast Nd:YVO chirped pulse regenerative amplifier/post amplifier systems generating 9 mJ pulses compressible to 16 ps duration. The power amplification stages, based on Nd:YAG crystals, provide 62 mJ pulses compressible to 20 ps pulse duration at a repetition rate of 1 kHz. Further energy scaling currently is prevented by limited dimensions of the diffraction gratings, which, because of the fast progress in MLD grating manufacturing technologies is only a temporary obstacle.

Finite-difference time-domain methods to analyze ytterbium-doped Q-switched fiber lasers

Q-switched lasers are widely used in material processing, laser ranging, medicine, and nonlinear optics--in particular, Q-switched lasers in optical fibers are important since they cannot only generate high peak powers but can also concentrate high peak powers in small areas. In this paper, we present new finite-difference time-domain methods that analyze the dynamics of Q-switched fiber lasers, which are more flexible and robust than previous methods. We extend the method to analyze fiber ring lasers and compare the results with our experiments.

Long-cavity passively mode-locked fiber ring laser with high-energy rectangular-shape pulses in anomalous dispersion regime

We report on a long-cavity passively mode-locked fiber laser in the anomalous dispersion regime. The nonlinear polarization rotation technique is employed to achieve mode locking. The output pulse from the fiber laser has a rectangular shape and a corresponding gaussian-shape spectral profile. Stable mode-locked pulses at a repetition rate of 278 kHz with single pulse energy as high as 715 nJ are obtained under equal bidirectional pumping power of 500 mW in cavity. The experimental results demonstrate that the passively mode-locked fiber laser operating in the anomalous regime can also realize a high-energy pulse, which is different from the conventional low-energy soliton pulse.

High energy cw-diode pumped Nd:YVO4 regenerative amplifier with efficient second harmonic generation

We report on a 888 nm diode-pumped Nd:YVO4 regenerative amplifier with up to 33.7 W output power with a repetition-rate of 20 kHz and an adjustable pulse duration between 217 ps and 1 ns. This setup allowed for efficient second harmonic generation with an efficiency of up to 79%.

Multi-terawatt chirped pulse optical parametric amplifier with a time-shear power amplification stage

We report on a compact and simple, broadband optical parametric chirped pulse amplifier system that amplifies femtosecond pulses directly from a titanium sapphire oscillator up to 2 TW power. Our system relies on a new technique - time shear - that improves the time overlap between the seed and pump pulses and, thus, improves the efficiency of the power amplification stage pumped with a ns laser. Parametric amplification was achieved in two stages: a multipass, noncollinear geometry preamplifier with a single beta-barium borate crystal, and a power booster stage incorporating three beta-barium borate crystals in the new time-shear design. Both stages were pumped with pulses from a commercial 10 Hz frequency doubled ns Nd:YAG laser. The system delivers 49 mJ pulses with a temporal width of 23 fs and its overall conversion efficiency after pulse compression is 10%.

Generation of sub-three-cycle, 16 TW light pulses by using noncollinear optical parametric chirped-pulse amplification

We present a two-stage noncollinear optical parametric chirped-pulse amplification system that generates 7.9 fs pulses containing 130 mJ of energy at an 805 nm central wavelength and 10 Hz repetition rate. These 16 TW light pulses are compressed to within 5% of their Fourier limit and are carefully characterized by the use of home-built pulse diagnostics. The contrast ratio before the main pulse has been measured as 10(-4), 10(-8), and 10(-11) at t=-3.3 ps, t=-5 ps, and t=-30 ps, respectively. This source allows for experiments in a regime of relativistic light-matter interactions and attosecond science.

Tunable flat-top nanosecond fiber laser oscillator and 280 W average power nanosecond Yb-doped fiber amplifier

We demonstrate a nanosecond fiber laser with tunable central wavelengths and narrow spectral bandwidths suitable for high-power amplification. Spectrally narrowband flat-top nanosecond pulses were generated at the fundamental repetition rate of 1.9 MHz in an Yb-doped fiber laser, which could be tuned in central wavelength from 1033 to 1053 nm by changing the nonlinear polarization rotation in the fiber laser cavity. In particular, such flat-top nanosecond pulses could be tuned around 1030 nm to match the gain bandwidth of ytterbium-doped double-clad fibers or 1053 nm to match the maximum gain in Nd-doped phosphate glass. The pulse duration could be changed from 1 to 15 ns by varying the pump power or laser polarization evolution in the cavity. By using an ytterbium-doped single-mode fiber preamplifier and a two-stage large-mode-area Yb-doped double-clad-fiber power amplifier, 280-W average power with pulse duration of 3 ns was obtained at 1034 nm.

High-energy, diode-pumped, picosecond Yb:YAG chirped-pulse regenerative amplifier for pumping optical parametric chirped-pulse amplification

A diode-pumped, cryogenic-cooled Yb:YAG regenerative amplifier utilizing gain-narrowing has been developed. A 1.2-ns chirped-seed pulse was simultaneously amplified and compressed in the regenerative amplifier, which generated a 35-ps pulse with ~8-mJ of energy without a pulse compressor. Second-harmonics of the amplified pulse was used to pump picosecond two-color optical parametric amplification.

Optical parametric chirped-pulse amplifier and spatiotemporal shaping for a petawatt laser

We present a degenerate noncollinear optical parametric chirped-pulse amplifier pumped by a high-energy, diode-pumped Nd:Glass regenerative amplifier delivering monomode pulses at 527 nm. The spatial mode shaping of the pump pulses is achieved with a diffractive laser cavity element, and temporal pulse shaping makes use of an electro-optic modulator and an arbitrary electrical waveform generator. Amplification at gain saturation achieves tailoring of the signal pulses. Numerical simulations with Miró software are presented and compared with experimental measurements.

Engineering of multicolor spatial solitons with chirped-period quasi-phase-matching gratings in optical parametric amplification

We demonstrate the excitation of solitons in a parametric amplifier with enhanced signal content through the use of a chirped-period quasi-phase-matching grating. This technique affords a low soliton threshold at the input end of a parametric amplifier, and the subsequent transformation to a desired soliton that exists at nonzero wave-vector mismatch through the use of a linearly chirped quasi-phase-matching grating. This approach has an advantage over direct excitation of solitons at nonzero wave-vector mismatch in uniform nonlinear materials and holds potential for improving the efficiency and mode quality of high-gain parametric amplifiers.

Generation of high-contrast millijoule pulses by optical parametric chirped-pulse amplification in periodically poled KTiOPO4

A new high-contrast, high-gain optical parametric chirped-pulse amplifier (OPCPA) architecture is demonstrated in periodically poled KTiOPO4 (PPKTP). This architecture overcomes parametric fluorescence contrast limitations of the OPCPA in periodically poled materials. The scheme is based on two passes of a single relay-imaged pump pulse and a free-propagating signal pulse through a 1.5 mm x 5 mm x 7.5 mm PPKTP crystal. The output energy of 1.2 mJ is generated at a center wavelength of 1053 nm by 24 mJ of pump energy. A prepulse contrast level of > 3 x 10(7) was measured with > 10(6) saturated gain in the amplifier. Amplified pulses were compressed to 200 fs. This simple and versatile concept requires only a modest pump energy from a commercial pump laser and represents a possible high-contrast front end for high-energy Nd:glass-based petawatt-class lasers.

Multimillijoule chirped parametric amplification of few-cycle pulses

The concept of optical parametric chirped-pulse amplification is applied to attain pulses with energies up to 8 mJ and a bandwidth of more than 100 THz. Stretched broadband seed pulses from a Ti:sapphire oscillator are amplified in a multistage noncollinear type I phase-matched beta-barium borate parametric amplifier by use of an independent picosecond laser with lock-to-clock repetition rate synchronization. Partial compression of amplified pulses is demonstrated down to a 10-fs duration with a down-chirped pulse stretcher and a nearly lossless compressor comprising bulk material and positive-dispersion chirped mirrors.

High-conversion-efficiency optical parametric chirped-pulse amplification system using spatiotemporally shaped pump pulses

High-conversion-efficiency, high-stability optical parametric chirped-pulse amplification is demonstrated with a spatiotemporally shaped pump laser system. Broadband 5-mJ pulses are produced at a 5-Hz repetition rate with a pump-to-signal conversion efficiency of 29% and energy stability better than 2% rms. To our knowledge this is the highest conversion efficiency and stability achieved in an optical parametric chirped-pulse amplification system.