A multichannel photodetection system for the use in ultra-fast spectroscopy is presented. The system consists of pairs of photodiode-arrays combined with amplifier circuits and a gated analogue-to-digital converter. It allows real single-pulse analysis at repetition rates well above 1 kHz, gating in the submicrosecond regime and a sensitivity high enough to allow one to perform multichannel experiments at weak light energies.

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The development of CO2-lasers tends to high power devices with an average power of ten kilowatt and more. In the same way as laser power is raised, the thermal load on the output coupling window increases. So it is necessary to investigate either materials for high power solid state windows or gasdynamic windows as we did. Preliminary investigations with a supersonic free -vortex aerodynamic window proved both, a good optical quality and fluidmechanical sealing of a simulated laser cavity. Basing upon these results an experimental prototype was designed. To minimize the flow rate needed for the maintaining of the sealing gas jet, the aperture area is chosen very small, 5mm x 5mm. The outcoupled laser beam is focused through this opening by means of two asphere mirrors. The sealing properties and optical quality were demonstrated by operating the prototype mounted at a 5 kW CO3-One particularity is the active controlling of the gas flow in the aerodynamic window by adjusting part of the diffuser. So it is possible to vary the achievable cavity pressure and to adapt it to the actual pressure level in the laser.