A novel laser system with optical parameters that fill the gap between Q-switched and modelocked lasers has been developed. It consists of a high gain hybrid fiber-bulk amplifier seeded by a low power SESAM Q-switched oscillator. The mW level output power of the seed oscillator is preamplified by a single mode fiber which is limited by SRS effects. The final amplification stage is realized by a longitudinal pumped Nd:YVO4 crystal in a double pass setup. This MOPA configuration delivers sub-300ps pulses at repetition rates up to 1 MHz with an output power exceeding 60W. Nonlinear frequency conversion to 532nm and 355nm is achieved with efficiencies of >75% and >45%, respectively. Due to the high peak power, high repetition rate and high beam quality of this system, applications formerly only addressable at lower pulse repetition frequencies or with complex modelocked laser systems are now possible with high speed and lower cost of ownership. Application results that take benefit from these new laser parameters will be shown. Furthermore, the reduction of the pulse duration to sub-100ps and power scaling to output powers <100W by the use of the Innoslab concept are being presented.
Behavior of micromachined membrane deformable mirrors under continuous laser load has been investigated experimentally and theoretically. It was shown that load-induced variation of the membrane temperature and mechanical tension result in addition thermal deformation of the deformable mirror figure. Modeling the membrane tension and thermal deformation as functions of beam diameter, optical power and mirror design parameters, we found that the thermal resistance of the mirror substrate is critical for high- power operation. According to our estimations an optically- designed membrane mirror with 99.8 percent reflectivity can be safely loaded with up to 500W of optical power in a 10mm- diameter beam. This model was compared with experimental data obtained for micro-machined membrane deformable mirrors with five different types of reflective coatings loaded with up to 70W beam with power density of up to 20W/mm<SUP>2</SUP>. We also demonstrated operation of a multilayer membrane mirror in a stable resonator of a diode-pumped YAG:Nd laser with output power of up to 4.5W.
For fiber coupling and end-pumping of solid-state lasers, the astigmatic beam emitted from high power diode lasers has to be transformed into a beam with rotational symmetry. In this paper we present the result of beam transformation of a high power laser diode stack. The transformation optics consists of rotated cylindrical lenses, originally used in generating twisted beams from coherent and partially coherent fields. The astigmatic beam emitted from a 500 W 2D laser diode stack is transformed into a rotationally symmetric beam. The symmetrized beam has equal beam widths, equal beam divergences in x,y-directions and the same waist positions.
Hermite-Gaussian, Laguerre-Gaussian and complex Hermite- Gaussian modes are solutions of the paraxial wave equation. Using an astigmatic optical system each type of beams can be transformed into the others. This allows a generation of complex Hermite-Gaussian modes with twist whose propagation behavior is investigated in detail.
A major problem using laser diodes for longitudinal pumping of solid state lasers is the poor beam quality and the non symmetric beam profile of the diodes as the astigmatic beam emitted from the array of diodes exhibits a limited focusability in the direction of the slow axis of the diodes. To overcome this problem an optic which turns the astigmatic beam of a stacked diode array into a radially symmetric (stigmatic) beam has been designed. This symmetric beam is then focused into an axially water cooled disk laser to serve as a longitudinal pump source. Up to now different laser crystals have been investigated as laser source. Using Yb:YAG an output power of 60 W in qcw operation has been realized whereas Nd:YVO<SUB>4</SUB> delivers a qcw power of 113 W. The optical to optical efficiencies are 18% and 32.3% respectively.
In this article we describe an efficient method of the compensation of thermally induced birefringence in high power Nd:YAG rod lasers. Losses at a resonator internal polarizer due to depolarization in the rods are reduced, and a polarized cw laser with an output power of 300 W is realized. Resonators with a small stability range and therefore beam quality near the diffraction limit are introduced. To improve the variability and stability of such resonators an adaptive high reflecting mirror is used as resonator mirror. The maximum average output power of the resonator with adaptive mirror is 145 W at a beam quality of M<SUP>2</SUP> equalsV 2.