G. Brederlow

The asterix III pulsed high-power iodine laser

A system description and first results of the Asterix III high-power iodine laser built at IPP Garching are given. This laser is designed to yield an output energy of 1 kJ in about 1 ns. Until now pulses with output energies up to 300 J and pulse lengths ranging from 1 to 3 ns have been obtained.

Advanced iodine laser concepts

The essential features of an advanced iodine laser are outlined. These are governed primarily by the proper choice of the stored inversion density of an amplifier and also by the means to enhance the energy extraction efficiency to values in excess of 50 percent. With these measures an amplifier chain with output energies in the kJ range and overall system efficiencies of almost 0.2 percent can be designed. This value is twice as high as that now achieved. As the laser-fusion experiments require a greater pulse duration variability than hitherto obtained, an oscillator pumped by an excimer laser is developed, allowing chain output pulse durations in the range from some 100 ps to several ns. The frequency conversion of iodine laser light by nonlinear interaction in crystals is also investigated.

The pulsed high power iodine laser Asterix III

Three-dB couplers or power dividers are expected to be important components in optical waveguide amplitude modulators or switches which operate by interferring two phase-shifted guided waves.’ The conventional 3-dB coupler operates by maintaining a degree of velocity synchronism between two coupled waveguides over a coupling length L. Fabrication tolerances posea difficult problem in construction of such a coupler, since the necessary length L for 50-50 power division between the coupled guides depends on the coupling constant. Also the degree of synchronism must be maintained over the coupling length L. We propose a novel device which allows 50-50 power division between two coupled waveguides with reduced fabrication tolerances. It requires a degree of mode synchronism only at a single point, and the exact length of the coupler is not

Status of the Asterix IV iodine laser

After a description of the design and layout of the 2 kJ/5 TW single beam Asterix IV iodine laser the steps necessary for obtaining a laser beam intensity profile as homogeneous as possible are reported. These steps are: providing a homogeneous inversion density profile in the amplifiers by an appropriate flashlamp-reflector geometry and by compensating the edge enhancement caused by the image relaying system by suitable soft apertures. The paper concludes with a description of the results obtained by the laser system with the end-amplifier not in operation. The full system will become operational at the end of 1990.

Terawatt Iodine Laser

In this paper the high power iodine laser ASTERIX III is described. It is a single beam system designed to yield an output power in the 1 Terawatt range (energy about 1 kJ, pulse duration about or less than 1 ns). It will be used for plasma production with power densities on the target surface expected in the range between 1017 to 1018 W/cm2.

Laser−plasma research at MPQ

The ASTERIX iodine laser delivers after frequency tripling to λ = 0.44-μm laser pulses with energies up to 500 J at a pulse duration of 300 ps for target experiments. Experimental investigations of radiative transfer in low- and high-Z materials are reported.

Scalability and Prospects of the Iodine Laser

With the continuing use of the ASTERIX III system for laser plasma experiments, experience in the handling of a large iodine laser is accumulating. In view of the favourable performance of this laser, it is thus appropriate to discuss its scalability to a new generation of large-scale iodine laser systems for research applications (scientific break-even). Such lasers should not only provide higher output energy and power, but also include additional features such as pulse lengths longer than those hitherto obtained (up to several ns) and possibly pulse shaping. Moreover, a better overall efficiency than that realized so far is also desirable. These questions are dealt with in the first two sections of this chapter.

Beam Quality and Losses

There are a variety of mechanisms which change the refractive index of the medium in which the pulse propagates. These changes in the refractive index may lead to a distortion of the wave-front of the pulse, thereby increasing the energy losses of the beam and deteriorating its focusibility. Three different types of mechanisms can be distinguished according to their source and their characteristic time scale.

The ASTERIX III System

The realization of a high power iodine laser will now be illustrated by describing the layout of the single-beam ASTERIX III laser, built at the Max-Planck-Institut fur Quantenoptik, Garching [6.1–4]. This laser has been in routine use for laser plasma research since 1978 and has already demonstrated that it meets the requirements of high-quality target experiments. The ASTERIX III laser is presently capable of delivering an output power higher than 1 TW at an energy level of up to 300 J and pulse lengths ranging from 180 to 360 ps. Its present overall efficiency (defined as the laser output energy over the electrical energy stored in the capacitor banks) is 0.08%.

Design and Layout of an Iodine Laser System

The preceding chapters have been devoted to the physical principles of the iodine laser, the generation and amplification of short pulses, and the scaling laws of a single amplifier stage. This chapter now deals with the technical aspects and possible versions of an iodine laser system such as can be built at present for its main field of application, namely laser fusion research.