The worlds most powerful sub-10fs laser system

Taranis X is a highly innovative laser development project, upgrading Queen’s University Belfast’s (QUB’s) Taranis laser to a Joule-class femtosecond laser system. For this upgrade, the high quality picosecond output of Taranis will be used to pump a high energy optical parametric chirped-pulse amplifier (OPCPA) system. Taranis X will deliver high energy pulses at 10 fs pulse duration for discovering new frontiers in laser-plasma interaction research – reaching unprecedented power with laser pulses whose duration is at the physical limit for near-infraed laser pulses.

Optical parametric chirped-pulse amplification:

Optical parametric amplification (OPA) is a nonlinear amplifier concept. The energy of an intense laser pulse (pump pulse) is down-converted to a signal and an idler pulse using a nonlinear optical crystal. In contrast to conventional lasers, no population inversion and thus no energy storage within the medium is required for the amplification. As the photon energy difference is carried away by the idler radiation, no quantum defect exists. Furthermore, non-collinear phase-matching in OPA offers a large amplification bandwidth. The concept of optical parametric chirped-pulse amplification (OPCPA) combines the laser chirped-pulse amplification (CPA) scheme with OPA (Fig. 1). With this powerful combination, the advantages of both methods are merged. Pulses with only a few optical cycles can be amplified to very high pulse energies. Achieving very short pulses requires a large frequency bandwidth – and that can be achieved by combining the intense picosecond pulses of Taranis with OPA technology

Major advantages of OPCPA:

Gain bandwidth: The amplification of a full optical octave is possible in a single amplification stage , using non-collinear phase-matching in a sufficiently short crystal, pumped at sufficiently high intensity. The amplification bandwidth is limited by phase-matching. With pumping at multiple wavelengths, even more than one optical octave is possible.

Single-pass gain: A high single-pass gain of G > 106 can be achieved with only a few mm of nonlinear crystal. This relaxes the design complexity of the ampli- fier stages, whereas conventional laser amplifiers require multi-pass or regenerative amplifiers.

• Power scaling: Owing to the instantaneous nature of the nonlinear parametric response, no energy storage within the medium is required for amplification. Con-sequently, the absorption of photons is reduced by several orders of magnitude. This enables unprecedented average powers and repetition rates, limited only by the residual absorption of signal, idler and pump pulses.

• Spectral tunability: The amplified bandwidth and central frequency can be adjusted by several degrees of freedom, for example by varying the phase-matching angle or the temperature.

Major challenges:

• Pump laser requirements: A high energy, ultrashort laser system is required for pumping. The pump-to-signal conversion efficiency is around 10%. The high inten-sities needed for driving the broadband nonlinear amplification require picosecond pulse durations, provided by rare-earth doped solid state lasers.

• Dispersion management: The temporal stretching and compression scheme of the broadband pulses needs to be carefully designed with focus on the dispersion and nonlinear effects in the optical elements in the beam path. Taranis-X employs advanced chirped mirror technology to compress the ultrashort pulse.

Schematic of the Taranis X layout. The high energy picosecond beam amplifies the few cycle pulse from the low energy front end.
Front End Layout of Taranis X. Ultrabroadband pulses are generated using white-light generation and amplified in a high repetition rate OPA amplifier.
Layout of the 16 bounce chirped mirror compressor with 100mm diameter chirped mirrors
Principle of chirped mirrors. Dielectric layers with varying thickness are designed to reflect different wavelengths at different depths into the layer stack – producing a well defined delay and leading to pulse compression.