Gain induced stability of active plane-parallel resonators

It has been observed for a plane-parallel resonator with a saturated medium that under certain conditions confined beams mainly concentrated near the axis are present. The experiments have been done with a sealed-off plane-parallel CO2 laser of one meter length and with an internal diameter of 20 mm. Without gain variations such a system is unstable because of thermal defocussing by the heated gas. But due to sufficiently high gain variations the beam converges nevertheless. Since the gain variation increases with decreasing reflectivity confined beams near the optical axis are only observed at sufficiently low reflectivity. The experiments were done with a totally reflecting mirror and an outcoupling mirror having a reflectivity of, respectively, 90%, 80%, 50%, and 36%. For the high reflectivities the outcoupled beam is mainly concentrated near the edge with irregular density distributions. For the low reflectivity the beam is more or less radially symmetric, concentrated near the axis having decreasing intensity with the distance from the axis.\ud \ud The behaviour can be understood by an analysis in which the constant and quadratic term of the complex propagation constant near the optical axis due to gain variations, dispersion and heat effects are taken into account

On the saturation effects and start jump of Gaussian modes in oscillators

The present paper deals with the interaction of a Gaussian mode with a homogeneous and an inhomogeneous laser transition. The interaction of the beam with the medium in a laser is treated by taking into account the spatial distribution of both radiation and gain. The intensity characteristics are very different from those obtained for a one-dimensional interaction of a plane wave with a saturating medium. In the presence of a small-signal gain profile the threshold condition requires much higher inversion densities along the optic axis than by ignoring this profile. For gas lasers, for instance, having a small-signal gain profile that is approximately described by a zero-order Bessel function, the threshold inversion density can be about 50 percent higher. For high-power systems the saturation of the medium by the Gaussian intensity distribution results in a considerable amount of radial radiation transport. For homogeneous transitions this amount is about equal to the stimulated emission and for inhomogeneous transitions it is about half of it, independent of the beamwidth. Further, it is found that if one slowly passes the threshold condition for laser action, the intensity jumps from zero to a certain value and vice versa. This effect has also been verified experimentally

Construction and operation of high power gas lasers

In the present paper some typical gas laser construction and their performances will be described. Aspects of transition selective systems and high pressure operation will be treated

An improved discharge technique for excimer lasers

The further development of discharge excimer lasers depends upon a better degree of control over the discharge stability. A problem is the large difference between the breakdown and steady-state voltage which requires a time dependent impedance of the power circuit. Further the large attachment rates of halogens like HCl, causing electric field disturbances require a short rise time of the applied current pulse. A large effort has been expended towards this goal by researchers since the early development of discharge excimer lasers

Subnanosecond pulse measurements of 10.6 μm radiation with tellurium

Subnanosecond infrared pulses have been measured by noncollinear secondharmonic generation in tellurium. The method is very practical because due to the high refractive index the fine tuning of the phase matching is easily obtained by rotating the crystal around the optic axis

The effect of radial radiation transport on intensity characteristics and oscillation frequency of homogeneously broadened lasers

In the present treatment of performance characteristics of laser systems, having homogeneous line broadening, a radial gain profile is taken into account. It will be shown that such a profile, which may be induced by the laser beam itself, changes the curvature of the phase front, so that additional radiation transport in the radial direction takes place. It turns out that for many practical systems the radial radiation transport can be comparable to the radiation gained directly from the medium and therefore may not be neglected. Furthermore, it will be shown how the additional radial radiation transport affects the oscillating frequency. Conditions are deduced in which mode competition leads to the survival of the mode having highest radiation intensity. This is not the one closest to the line center as found in systems where radial radiation transport is not taken into account. Treating this problem we approximate medium parameters by a quadratic profile so that the modes have a Gaussian structure. The oscillation frequency, determined on one side by the dispersion of the active medium and on the other side by the spontaneous decay of the upper level, is discussed. The frequency shift is not very sensitive to changes of mirror reflectivity but increases considerably with increasing thermal effects. Numerical calculations show, for instance, that for a semiconfocal system a frequency shift close to 0.5 in units of normalized frequency can be predicted

Status of the "TEU-FEL" project

The free-electron laser of the TEU-FEL project will be realized in two phases. In phase I the FEL will be driven by a 6 MeV photoelectric linac. In phase II the linac will be used as an injector for a 25 MeV race-track microtron. Information is presented on some technical details and the status of the different subsystems

Developments of the TEUFEL injector racetrack microtron

In this paper we report on developments of the 25 MeV racetrack microtron (RTM) that will be the electron source for the second phase of the TEUFEL project, to generate radiation of 10 µm in a 2.5 cm period hybrid undulator. The theoretical understanding of this unconventional, azimuthally varying field type of RTM has been extended. A comparison of analytically calculated orbit stability with that based on measured data will be presented; orbit calculations using measured field data show the designed performance. Construction and tuning of the 1300 MHz, 2.2 MV microwave cavity have been completed, and signal level measurements have been performed. The overall assembly of the microtron is nearing completion. At present a vacuum pressure better than 5 × 10-7 Torr is achieved