Nobuhisa Ishii

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.

Parametric amplification of few-cycle carrier-envelope phase-stable pulses at 2.1 μm

We demonstrate an optical parametric chirped-pulse amplifier producing infrared 20 fs (3-optical-cycle) pulses with a stable carrier-envelope phase. The amplifier is seeded with self-phase-stabilized pulses obtained by optical rectification of the output of an ultrabroadband Ti:sapphire oscillator. Energies of -80 microJ with a well-suppressed background of parametric superfluorescence and up to 400 microJ with a superfluorescence background are obtained from a two-stage parametric amplifier based on periodically poled LiNbO3 and LiTaO3 crystals. The parametric amplifier is pumped by an optically synchronized 1 kHz, 30 ps, 1053 nm Nd:YLF amplifier seeded by the same Ti:sapphire oscillator.

Soliton-based pump-seed synchronization for few-cycle OPCPA

We demonstrate a significant simplification of the scheme for few-cycle Optical Parametric Chirped Pulse Amplification (OPCPA) which results in the elimination of a picoseconds master oscillator and electronic synchronization loops. A fraction of a broadband seed pulse centered at 760 nm from a 70-MHz Ti:sapphire oscillator was frequency-shifted in a photonic crystal fiber to enable synchronized seeding of a picoseconds Nd:YAG pump laser. The seed radiation at 1064 nm is produced in the soliton regime which makes it inherently more intense and stable in comparison with other methods of frequency conversion. The remaining fraction of the Ti:sapphire output is amplified with a FWHM bandwidth of 250 nm in a single timing-jitter-free OPCPA stage. Our work opens up the exciting possibility to use sub-picoseconds pump pulses from highly efficient Yb-based amplifiers for jitter-less parametric amplification of carrier-envelope phase stabilized pulses from Ti:sapphire oscillators.

Generation of carrier-envelope-phase-stable 2-cycle 740-μJ pulses at 2.1-μm carrier wavelength

We produce carrier-envelope-phase-stable 15.7-fs (2-cycle) 740-μJ pulses at the 2.1-μm carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 49-ps 11-mJ Nd:YLF laser. A novel seed pulse spectral shaping method is used to ascertain the true amplified seed energy and the parametric superfluorescence levels.

Seeding of an eleven femtosecond optical parametric chirped pulse amplifier and its Nd/sup 3+/ picosecond pump laser from a single broadband Ti:Sapphire oscillator

We demonstrate direct simultaneous seeding of a few-cycle optical parametric chirped pulse amplifier (OPCPA) in the 700-1000-nm spectral range, and of a Nd:YLF amplifier emitting 30-ps pulses at 1053 nm by use of a chirped-mirror 6-fs Ti:sapphire oscillator. This approach of employing a single master oscillator to drive two power amplifiers simplifies the pump laser design and is applied to eliminate the timing jitter between the seed and the pump pulses in the OPCPA chain. We show that 10 mJ fundamental picosecond pump pulses with the intensity contrast in excess of 10/sup 4/ relative to the nanosecond Q-switched background can be achieved with the seed intensity available in the edge of the oscillator spectrum around 1053 nm. Cross-correlation measurements between the picosecond pump and femtosecond oscillator pulses reveal no traceable timing jitter between the OPCPA pump and seed pulses. The estimated long-term jitter of 0.3 ps is attributed to the thermal expansion of the cavity of the Nd:YLF regenerative amplifier.

All-optical pump-seed synchronization for few-cycle OPCPA

We suggest and experimentally verify a simple method for timing-jitter-free synchronization of the seed and pump pulses in an optical parametric chirped-pulse amplifier. A fraction of a broadband seed pulse centered at 800 nm was frequency-shifted in a photonic crystal fiber to enable synchronized seeding of a picosecond Nd:YAG pump laser.

Optical Synchronization for OPCPA Chains

We demonstrate two types of all-optical synchronization of two lasers based on dissimilar gain materials, that significantly simplify the scheme for optical parametric chirped-pulse amplification (OPCPA). Both methods lead to negligible timing jitter between the OPCPA seed and pump and eliminate one master oscillator and all synchronization electronics. In the first approach, a fraction of a broadband Ti:sapphire seed oscillator centered at 760 nm is frequency shifted in a photonic crystal fiber to enable synchronized seeding of a picosecond Nd:YAG pump laser. The seed radiation at 1064 nm is produced in the soliton regime which makes it inherently more intense and stable in comparison with other methods of frequency conversion. In the second approach, we further simplify the setup by employing direct optical seeding of a Nd: YLF amplifier from the NIR wing of our Ti: sapphire oscillator. Our work opens up the exciting possibility to use sub-picosecond pump pulse from highly efficient Yb-based amplifiers for jitterless parametric amplification of carrier-envelope phase stabilized pulses from Ti:sapphire oscillators.

Infrared Optical Parametric Chirped Pulse Amplifier for High Harmonic Generation

Rapid advances in high-field physics achieved in recent years, most notably generation of isolated soft X-ray attosecond pulses, owe their success to the development of driver lasers with specific pulse properties. The latter include ultrahigh peak intensity, quasi-monocycle duration, and reliable control over the carrier-envelope phase (CEP) [1],[2]. Although the driver lasers currently employed in this research field operate nearly exclusively in the wavelength region of the Ti:sapphire gain (i.e. around 0.8 µm), a switching over to a longer, infrared (IR) wavelength would offer significant advantages. Because of the λ 2 scaling of the ponderomotive energy, the intensity of IR pulses needed to attain emission at a given X-ray photon energy could be substantially lowered in comparison with the 0.8-µm case [3]–[5]. This is expected to be extraordinarily helpful for up-scaling the X-ray frequency, decreasing the duration of X-ray attosecond pulses by at least a factor of λ 3/2, and suppressing undesired target preionization before the interaction with the strongest half-cycle of the laser pulse. From the standpoint of laser technology, the longer duration of the IR optical period reduces the number of cycles for a given pulse envelope and, therefore, relaxes the demand to the amplifier gain bandwidth, which in the case of 5-fs 0.8-µm pulses typically reaches the extreme > 100 THz.

Passively synchronized multimillijoule optical parametric chirped pulse amplifier with a positive-dispersion sub-10-fs pulse compression

Multimillijoule few-cycle pulses supported by a broadband stretcher and a low-loss compressor are demonstrated. The seed of the non-collinear optical parametric amplifier and of the Nd:YAG pump laser is derived from a single Ti:sapphire oscillator.

Toward a terawatt few-optical-cycle driver laser for attosecond spectroscopy

We discuss routes towards developing an ultra-high peak power phase-stable source of few-cycle laser pulses suitable for driving a wide range of strong-field applications. Experiments with a phase-stable 0.1-TW 5-fs system based on a Ti:sapphire amplifier and the progress in construction of a 1-TW few-cycle optical parametric amplifier are presented.