High energy photon colliders (γγ,γe) are based on e-e-linear colliders where high energy photons are produced using Compton scattering of laser light on high energy electrons just before the interaction point. This paper is a part of the Technical Design Report of the linear collider TESLA.1Physics program, possible parameters and some technical aspects of the photon collider at TESLA are discussed.

We demonstrate a double chirped-pulse-amplification (CPA) Ti: sapphire laser system that includes two CPA stages with intermediate nonlinear temporal pulse filtering. The method makes it possible to reduce substantially the background of amplified spontaneous emission (ASE), including prepulses and postpulses. An ASE temporal contrast of 10(10) was demonstrated at 20 mJ of output energy and 50-fs pulse duration. The demonstrated scheme is applicable to petawatt power-level laser systems.

Hot-electron confinement can build up fields capable of accelerating ions up to MeV energies when an ultrashort 35-fs laser pulse at ∼2×1018 W/cm2 interacts with a small spherical target. Singly charged ions with different masses have similar energies. A simple phenomenological model describes how ultrashort and less-energy-consumptive pulses drive ions to MeV energies. The energetic and spatial-emission characteristics of protons, deuterons and oxygen ions released from water and heavy-water droplets of ∼15 μm in size was determined for this interaction scenario.

A nonlinear filter using rotation of the polarization ellipse in air is investigated. Scheme to enhance the temporal contrast is developed for a double-CPA multi-terawatt Ti:sapphire laser. It supports an energy level of millijoule and has a high efficiency. The method allows suppression of the ASE pedestal, pre- and post-pulses by 3 orders of magnitude and also steepens the pulse front. For the physical interpretation of the results, numerical simulation of the filtering is performed.

By pumping with a cw diode-pumped Nd:YAG laser operating at 946nm laser operation of a new Yb-doped phosphate glass with 440mW cw output power and a slope efficiency of 48% with respect to the absorbed pump power was achieved at room temperature.