Guiding of 10 μm laser pulses by use of hollow waveguides

Guiding of intense 10 μm laser light over many Rayleigh ranges is important in many advanced accelerator schemes. We have carried out such guiding experiments using both evacuated and gas-filled tubes of different materials. The CO2 laser pulse length was typically 200ps (FWHM) and the CO2 laser peak power was up to 100GW. A maximum energy transmission of 15% was obtained when a 2 cm long, 1mm diameter, evacuated stainless steel waveguide was used. This dropped to about 8% when 180 mTorr of hydrogen was added to the waveguide. At the peak intensity of 5x10 W/cm at the waveguide entrance, we expect the formation of a fully ionized plasma throughout the waveguide. The implications of the study to acceleration experiments will be discussed.