Dieter Roess

Giant Pulse Shortening by Resonator Transients

A method for giant pulse shortening by oscillator transients is proposed, where giant pulses are used to pump a secondary laser oscillator with suitable absorption bands. Further shortening is possible by combination with a saturated amplifier, which too is pumped by the primary pulse. Materials of high transition probability are favorable for this scheme; ruby‐YAG:Nd3+ seems well suited.

Exfocal Pumping of Optical Masers in Elliptical Mirrors

An efficiency near unity can be achieved in optical pumping devices for lasers, where unabsorbed light is refocused at the light source, leading to multiple passes of pumping energy through source and laser. In properly dimensioned elliptical mirrors this can, in principle, be done by placing source and laser outside of the focal points. Furthermore, in these “exfocal” elliptical designs the light density of the source is transformed into the laser at a ratio of 1:1, resulting in very low-threshold energies. The lowest value observed for ruby lasers up to 7.6 cm in length was 50 W-sec at room temperature in a rotational-ellipsoidal mirror where the axis of source and laser are oriented in the rotational axis of the ellipsom, while their lengths are equal to the distance between focus and wall. Alternative designs are exfocal elliptical and circular cylinders. In exfocal ellipsoids the pump light distribution is of exactly rotational symmetry which leads to symmetrical absorption of pumping light in the laser. As a result, quasi-periodic relaxation oscillations of 5000-μsec duration and a component of continuous emission have been observed at room temperature with 300 W-sec pumping energy.

Analysis of a Room‐Temperature cw Ruby Laser of 10‐mm Resonator Length: The Ruby Laser as a Thermal Lens

A nominally plane‐parallel ruby laser of 10‐mm length was investigated in continuous operation in an ellipsoidal pumping system under water cooling. The laser emits pure transverse modes of low order. The zero‐order mode can be described by Gaussian distributions; it corresponds approximately to the mode of a confocal resonator of 9‐cm radius of curvature. The resonator curvature is induced by a thermal curvature of the ruby end faces and by a bulk thermal lens effect.The axial‐mode frequencies and the emission‐center frequency shift to smaller values with increasing pump power as a consequence of the increasing ruby temperature in cw operation. The relaxation pulses of single axial modes do not overlap in this short laser, and the interaction of different axial modes can be observed in the emission of one mode. Consequences of the observed thermal curvature for the transverse mode selection of cw and pulsed crystal lasers are discussed.A nominally plane‐parallel ruby laser of 10‐mm length was investigated in continuous operation in an ellipsoidal pumping system under water cooling. The laser emits pure transverse modes of low order. The zero‐order mode can be described by Gaussian distributions; it corresponds approximately to the mode of a confocal resonator of 9‐cm radius of curvature. The resonator curvature is induced by a thermal curvature of the ruby end faces and by a bulk thermal lens effect.The axial‐mode frequencies and the emission‐center frequency shift to smaller values with increasing pump power as a consequence of the increasing ruby temperature in cw operation. The relaxation pulses of single axial modes do not overlap in this short laser, and the interaction of different axial modes can be observed in the emission of one mode. Consequences of the observed thermal curvature for the transverse mode selection of cw and pulsed crystal lasers are discussed.

Influence of Pump‐Induced Material Inhomogeneities on Giant Pulse Evolution

In a giant‐pulse laser rod an inhomogeneous excess inversion across the rod diameter will lead to a non‐uniform growth rate of the photon avalanche, when the transverse modes are not tightly coupled. For a model inversion distribution the resulting giant‐pulse elongation is calculated. The radial time dispersion can be compensated by a radius‐dependent resonator feedback or by transverse mode coupling. The influence of thermal resonator curvature on the decoupling of transverse modes is discussed.