High Power Laser System with Built-In Dynamic Beam Shaping Capabilities – Mr Jiho Han
Traditionally, a laser beam shaping problem is defined as redistribution of the intensity profile into another more desirable profile. Attempt goes as far back as when Frieden (1965) discussed a method for obtaining a top hat beam profile. Top hat beam profiles are still very useful today for applications such as laser machining, laser surface hardening, tattoo removal, keratectomy, and tissue welding. Today, beam shaping method are much generalised, and holography is able to arbitrarily transform a beam shape into another.
In addition, today, there exist dynamic beam shaping solutions such as Spatial Light Modulators (SLMs) or deformable mirror arrays. However, SLMs have a fairly modest power handling capabilities at around 15W/cm2 (Norton et al. 2010). Deformable mirrors can have up to 400W/cm2 of power handling capacities, but the degrees of freedom available for modulation are severely limited at around 10-100.
Therefore, it would seem that currently, high fidelity dynamic beam shaping and high power handling capabilities are incompatible. In this work, we focus on beam shaping, but the incompatibility between throughput and resolution is evident in other contexts: scanning a focussed laser beam offers high resolution while defocussed beam offers high through put, but the two incompatible!
If the dynamic beam shaping capabilities of Spatial Light Modulators (SLMs) could be made compatible with today’s high power lasers, we may be able to process a 2D area through single exposure to a shaped high power laser beam, instead of relying on scanning. Process throughput would then be scaled with available average power rather than scanning speeds. The types of laser process that may benefit from this include laser material process (marking/engraving/machining), lithography, and selective laser melting for 3D printing.
The currently perused concept is to take a low power beam, shape it, and then pass it through an appropriately designed optical amplifier.
Somewhat of a literal translation of such an approach, using bulk amplifiers have been demonstrated in the past, but would usually suffer from generic issues of single pass bulk amplifiers, such as low gains, poor energy efficiency, and non-linearity. This project focus is on a design for an optical amplifier that can offer compatibility between high powers and high resolutions.
This research is supervised by Prof Bill O’Neill at the Institute for Manufacturing, University of Cambridge.