Guenter Hollemann

High-power laser projection displays

In this paper recent research on high-power laser displays for large display applications is reported. We discuss our compact high-power red-green-blue laser system for use as a light source based on a passively mode-locked solid-state laser with an optical parametric oscillator and sum- frequency mixing with very high efficiency and 19 W of white light. Concepts for power scaling to 35 W of white laser light are presented. A direct laser beam scanning technology is described which results in high resolution displays. Multi channel concepts as required in flight simulator applications are discussed. The laser light is modulated at 32 MHz using acousto-optic modulators with 75% diffraction efficiency. A high contrast ratio of 1:150,000 is achieved and has been successfully tested in novel planetarium applications. We also present performance and lifetime data of initial commercial laser display systems in the field.

Near-diffraction-limited diode-pumped thin-disk Nd:YVO 4 laser

Room temperature operation of a Nd:YVO4 thin disk laser with excellent beam quality is reported. Pumping by a fiber coupled diode laser with 10 W at the fiber end yields a continuous wave output power of 4.4 W at 1064 nm. The corresponding total optical efficiency is 44% and the average slope efficiency is 46%. For higher pump powers, a maximum output power of 13.7 W was achieved in a near diffraction limited beam.

Pulsed Yb:YAG thin disk laser with 100 W at 515 nm

Pulsed lasers with high average output power in the green spectral range are of interest for laser annealing applications. In this paper an efficient pulsed diode-pumped Yb:YAG thin disk laser with intracavity frequency doubling is presented. The Yb:YAG laser crystal disk has a thickness of 180 &mgr;m and a diameter of 10 mm and is pumped by a laser diode stack at a wavelength of 938 nm. The disk is soldered to a water-cooled Cu-W heat sink and exhibits a nearly perfect spherical surface. The folded resonator is dynamically stable with a beam factor of M2 = 5 and which is matched to the requirements of the application. Acousto-optical and electro-optical switches are investigated to operate the laser in the cavity-dumping mode. An average output power of 150 W at 515 nm is achieved. The diode-to-green efficiency is about 28%. A critically phase matched LBO crystal is used for intracavity second harmonic generation. We show that stable pulsing is obtained from 10 kHz to 150 kHz. The pulse-width can be varied from 200 ns to 700 ns by control of the low-loss period of the switching element. The experimental results are compared with theoretical modeling of the system and first application results are discussed.

High-power cw diode-pumped Nd:YAG rod lasers for industrial applications

The use of a cw diode-pumped Nd:YAG rod laser for industrial applications is investigated. The laser is pumped by water cooled high-power laser diode bars in a star-shaped transverse pumping configuration. An output power of 75 W is achieved with 240 W of pumping power, corresponding to 40% slope efficiency. Thermal lensing and birefringence of a laser rod with a diameter of 4 mm is investigated. High fundamental transverse mode and second harmonic efficiency is reported. A simple scalable concept for lasers with 10 W to 100 W output power is presented.

4.6-mJ-diffraction limited solid-state laser for industrial micromaterials processing

A novel Nd:YAG micro slab laser amplifier is presented and experimental results for Q-switched operation are discussed. The laser crystals are directly pumped by conduction cooled laser diodes with an ISO/FDIS 17526 extrapolated standard lifetime above 30,000 h. The diffraction limited cw output power of the amplifier is 50 W. In pulsed operation, the laser shows a pulse energy of 4.65 mJ and a pulse length of 12 ns FWHM at a pulse repetition rate of 6 kHz. Beam quality has been measured to be M2 = 1.1. The beam pointing stability was 10 μrad and the pulse-to-pulse stability was 1.5% rms in a linear-polarised beam.