Aleem M. Siddiqui

High-energy, kHz-repetition-rate, ps cryogenic Yb:YAG chirped-pulse amplifier

We demonstrate amplification of picosecond laser pulses to 40?mJ at a 2?kHz pulse repetition frequency (PRF) from a two-stage cryogenic chirped-pulse Yb:YAG amplifier, composed of a regenerative amplifier (RGA) and a two-pass booster amplifier. The RGA produces 8.2mJ of energy at 2kHz PRF and 13.2mJ at 1kHz PRF with excellent energy stability (approximately 0.3% rms) and beam quality (M(2)<1.1). Pulse stretching and compression are achieved by using a chirped fiber Bragg grating and a multilayer dielectric grating pair, respectively. Compressed 15?ps pulses from the RGA are obtained with a throughput efficiency of approximately 80% (approximately 6.5 mJ for 2kHz). The booster amplifier further amplifies the pulses to 40mJ at 2kHz PRF, and approximately 32 mJ, approximately 15 ps pulses are expected after compression. The amplifier chain seeded from a femtosecond Yb-fiber laser enables the optical self-synchronization between signal and pump in optical parametric chirped-pulse amplifier applications.

Generation of 287 W, 5.5 ps pulses at 78 MHz repetition rate from a cryogenically cooled Yb:YAG amplifier seeded by a fiber chirped-pulse amplification system

We generate linearly polarized, 287 W average-power, 5.5 ps pulses using a cryogenically cooled Yb:YAG amplifier at a repetition rate of 78 MHz. An optical-to-optical efficiency of 41% is obtained at 700 W pump power. A 6 W, 0.4 nm bandwidth picosecond seed source at 1029 nm wavelength is constructed using a chirped-pulse fiber amplification chain based on chirped volume Bragg gratings. The combination of a fiber amplifier system and a cryogenically cooled Yb:YAG amplifier results in good spatial beam quality at large average power. Low nonlinear phase accumulation as small as 5.1 x 10(-3) rad in the bulk Yb:YAG amplifier supports power scalability to a > 10 kW level without being affected by self-phase modulation. This amplification system is well suited for pumping high-power high-repetition-rate optical parametric chirped-pulse amplifiers.

Generation of <7 fs pulses at 800 nm from a blue-pumped optical parametric amplifier at degeneracy

Optical Parametric Amplifiers (OPAs), thanks to their broad phase matching bandwidths, allow for the dramatic shortening of the duration of the driving pulse. In particular, OPAs pumped by the fundamental frequency (FF) or the second harmonic (SH) of Ti:sapphire and seeded by white-light continuum (WLC) enable the generation of few-optical-cycle pulses in a wide spectral range, from the visible [1] to the near-IR [2]. However the important spectral range around 800 nm has not yet been covered. In fact the WLC produced from an 800-nm driving pulse presents a highly structured amplitude and phase profile around the pump frequency. Previous attempts of amplification at 800 nm of a supercontinuum generated in a photonic crystal fiber resulted in ultra-broadband spectra, which were however not compressed due to the strong chirp on the seed pulses [3]. In this work we report on a two-stage approach for the generation of few-optical-cycle pulses at 800 nm; (i) a FF-pumped near-IR OPA produces pulses at 1.3 µm, which are used to generate a WLC with smooth spectral amplitude and phase characteristics around 800 nm; (ii) this WLC is amplified in a broadband SH-pumped OPA around degeneracy. The pulses are compressed to nearly transform-limited 6.8 fs duration by chirped mirrors.

130-W picosecond green laser based on a frequency-doubled hybrid cryogenic Yb:YAG amplifier

130-W average-power picosecond green laser pulses at 514.5 nm are generated from a frequency-doubled hybrid cryogenic Yb:YAG laser. A second-harmonic conversion efficiency of 54% is achieved with a 15-mm-long noncritically phase-matched lithium triborate (LBO) crystal from a 240-W 8-ps 78-MHz pulse train at 1029 nm. The high-average-power hybrid laser system consists of a picosecond fiber chirped-pulse amplification seed source and a cryogenically-cooled double-pass Yb:YAG amplifier. The M(2) value of 2.7, measured at 77 W of second-harmonic power, demonstrates a good focusing quality. A thermal analysis shows that the longitudinal temperature gradient can be the main limiting factor in the second-harmonic efficiency. To our best knowledge, this is the highest-average-power green laser source generating picosecond pulses.

Diode-pumped, high-average-power femtosecond Cr3+ :LiCAF laser.

We demonstrate a high-average-power continuous wave (cw) and cw mode-locked Cr3+ :LiCAF laser pumped by broad-area laser diodes. In cw lasing experiments, up to 580 mW of output was obtained with 4.35 W of incident pump. A semiconductor saturable absorber mirror was used to initiate stable, self-starting, mode locking. In the cw mode-locked regime, the Cr3+ :LiCAF laser produced nearly transform-limited, 67 fs long pulses near 800 nm with an average output power of 300 mW. The pulse repetition rate was 120 MHz, with a pulse energy of 2.5 nJ.

Performance scaling via passive pulse shaping in cavity-enhanced optical parametric chirped-pulse amplification

We show that an enhancement cavity seeded at the full repetition rate of the pump laser can automatically reshape small-signal gain across the interacting pulses in an optical parametric chirped-pulse amplifier for close-to-optimal operation, significantly increasing both the gain bandwidth and the conversion efficiency, in addition to boosting gain for high-repetition-rate amplification. Applied to a degenerate amplifier, the technique can provide an octave-spanning gain bandwidth.

Demonstration of a cavity-enhanced optical parametric chirped-pulse amplification system

The use of a low finesse enhancement cavity resonant with a low average power (<1 W) and a high repetition rate (78 MHz) pump source is shown to achieve 55% conversion efficiency into signal and idler from the coupled pump in an optical parametric process, whereas an equivalent amount of pump power in a single-pass configuration leads to negligible conversion. Careful comparison of the intracavity conversion process to the single-pass case is performed to assess the underlying impedance matching that yields the high conversion results.

Optimized 2-micron Optical Parametric Chirped Pulse Amplifier for High Harmonic Generation

An optical parametric chirped pulse amplification system producing high-energy, few-cycle pulses at 2.0-mm wavelength for high harmonic generation is demonstrated. Simultaneous optimization of conversion efficiency, bandwidth and signal-to-noise ratio is obtained.

2-micron optical parametric chirped pulse amplifier for long-wavelength driven high harmonic generation

An optical parametric chirped pulse amplification system producing high-energy, few-cycle pulses at 2.0-mum wavelength with low superfluorescence noise background for high harmonic generation in gas jets is demonstrated.

Demonstration of phase matching bandwidth extension in cavity-enhanced optical parametric chirped pulse amplification

Repetition rate scaling of optical parametric chirped-pulse amplification (OPCPA) systems, while highly desirable for increased photon flux, requires average pump power scaling as well to maintain pump peak intensities. Alternatively, we have proposed cavity-enhanced OPCPA (C-OPCPA) [1] to boost nonlinear drive using moderate average power sources. In C-OPCPA, pump pulses are coherently combined in a low finesse enhancement cavity transparent to signal and idler containing an OPA crystal in which a signal is amplified. If the pump has a narrow bandwidth (BW) and the seed is sufficiently chirped, the cavity passively shapes the intra-cavity pump profile in the time domain to attain more optimal conversion and increased BW, overcoming limitations set by the bell-shaped pump intensity profile and the time-varying wave-vector mismatch of the interacting pulses. We previously simulated octave-spanning gain [1] showing the potential of this system.