Laser Beam Amplification by Homogenous Pumping of an Amplification Medium

Abstract

Apparatus and method for the amplification of a laser beam by pumping a homogenous composite source beam through an amplification medium. A slab crystalline active medium is side-pumped via a pump module having a laser diode bar and an optical assembly. The optical assembly has a fast axis collimator and a lens in the fast axis and an array of slow axis collimators and the lens in the slow axis. The lenses are spaced so that the individual source beams from the emitters are: imaged upon a first facet of the amplification medium; have a beam waist at or near the first facet; are sized to fill the first facet; substantially overlap on the first facet; and are directed so that peripheral source beams undergo total internal reflection on entering the amplification medium. Embodiments of multiple laser diode bars and optical assemblies are described together with double side pumping arrangements.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to an apparatus and method for the amplification of a laser beam by pumping a homogenous composite source beam through an amplification medium.[0002]Lasers with pulse widths of less than 10 ps offer new processing capabilities in micro-machining industrial applications. However, the processing speeds enabling mass manufacture require pulse repetition frequencies of between 100 kHz to 10 MHz, adjustable to an optimal frequency with average powers in excess of 100 W. Typically, such combinations are not achievable with most laser architectures as the maximum pulse energy is limited by non-linear effects and damage to the laser crystal. Thin disk laser oscillators have achieved powers approaching 150 W, being at the lower end of the power range required, but at fixed pulse repetition frequencies of between 3.50 MHz and 60 MHz, being above the required range, and they cannot easily be adjusted to an optimal frequency for a s...

AI Technical Summary

Benefits of technology

The patent describes a way to create a powerful and uniform beam of light using a new optical system. This system involves combining multiple laser beams in a way that creates a Gaussian-like gain profile along one axis and a top hat profile along another axis, resulting in better and more complete pumping. The system is also more compact, making it easier to create and use. Additionally, the pump beams are arranged off-axis from the optical assemblies to prevent interference from other pump beams.

Problems solved by technology

However, the processing speeds enabling mass manufacture require pulse repetition frequencies of between 100 kHz to 10 MHz, adjustable to an optimal frequency with average powers in excess of 100 W. Typically, such combinations are not achievable with most laser architectures as the maximum pulse energy is limited by non-linear effects and damage to the laser crystal.

Thin disk laser oscillators have achieved powers approaching 150 W, being at the lower end of the power range required, but at fixed pulse repetition frequencies of between 3.50 MHz and 60 MHz, being above the required range, and they cannot easily be adjusted to an optimal frequency for a specific process whilst maintaining the average power.

In 4 level laser systems such as Nd: YAG, thermally generated refractive index profiles can lead to beam steering, modal distortion and depolarisation.

Whereas some of these effects can be reduced by the choice of crystal geometry, such as a thin slab or planar waveguide, they cannot be eliminated entirely.

Additionally, in quasi 3 level systems, such as Yb: YAG, a finite lower laser level population at room temperature can lead to unwanted absorbing regions if the crystal is not uniformly pumped.

A disadvantage of this arrangement is that the gain in the active region is limited and thus complex regenerative amplifiers are required for MOPA's.

The main disadvantages of this approach are the complexity of the components and the large footprint of the device which is, typically, 500 mm by 500 mm.

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