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Fig. 1: BlueCut microjoule laser

Fig. 2: Volume grating for mid-IR applications (image courtesy: Prof. Robert R. Thomson, Heriot Watt University)

Fig. 3: Photonic lantern used in astronomical telescopes (image courtesy: Prof. Robert R. Thomson, Heriot Watt University)

Fig. 4: 3-D micro lens array (image courtesy: Prof. Robert R. Thomson, Heriot Watt University)

Authors: Dr. Klaus Hartinger, Menlo Systems

Fields of Application

With femtosecond laser pulses it is possible to machine materials even if they are transparent at the laser wavelength being used. The highly non-linear nature of the interaction between sample and pulse is the key to precise and clean machining of a wide array of materials with one and the same tool.

The BlueCut - a fiber-based micro-Joule femtosecond laser

The BlueCut is an ideally suited solution for ultrafast laser inscription. It’s a stable, robust and compact laser. It is easily integrated into the laser writing setup and provides energy tuning, synchronization to scanner or stage movement via a TTL interface, and a simple and intuitive graphical user interface out of the box. Extremely productive processes are possible due to the high repetition rate. This is combined with high reliability and low cost-of-ownership. (Fig. 1)

KEY FEATURES

• Wavelength 1030 nm
• Pulse energy >10 μJ
• Pulse duration 400 fs
• Up to 10 MHz repetition rate
• Integrated AOM for external gating and energy tuning

Manufacturing optical elements - utilizing new spectral ranges of light more efficiently

Using ultrafast laser inscription, a technique which locally modifies the index of refraction of a transparent material, volume gratings were fabricated in Gallium Lanthanum Sulphide (GLS) glass. With the BlueCut this technique uniquely enables the fabrication of volume phase gratings directly in a material which transmitts all the way from 500 nm to 10 um. The gratings are designed for highly efficient diffraction from the near- to mid-infrared wavelength range. (Fig. 2)

The photonic dicer - improving the performance of astronomical instruments

This optical element consists of a pair of waveguides which were inscribed using the BlueCut laser. Designed for near-infrared astronomical applications, it offers a fully integrated alternative to contemporary fiber-based approaches and enables the multimode stellar light collected by a telescope to be reformatted efficiently. This can help minimize the length of the pseudo-slit as well as reduce detector noise in future astronomical instruments. (Fig. 3)

Integrated optical elements - novel processing techniques open up new applications

Using the focus spot from the BlueCut femtosecond laser source as an essentially unrestricted “tool-path”, it is possible to directly write the surface of a lenslet in three dimensions within the volume of a transparent material. The lenses can then be etched and a high surface quality can be achieved by using an oxy-natural gas flame to polish the roughness caused by etching. The shape and position of each lenslet can be tailored to match the spatial positioning of a two-dimensional array of multimode fibers, which can be monolithically integrated with the micro-lens array (Fig. 4).