Sažetak
Femtosecond laser micromachining is a technique used for the modification of various
materials both on the surface and under the surface. In our laboratory, we have utilized this
technique to modify different materials such as metals, ceramics, teeth, and polymers. Binary
computer-generated holograms (CGH) can be written in transparent materials. While CGH
computation is a well-researched field, challenges arise in their production and application
due to high production costs and the need for specialized machinery. Holograms are mostly
manufactured in the graphic industry, where they serve as security features in printed
documents, among other uses.
We have successfully created holograms using a direct laser writing method with 120 fs pulses
at 800 nm and a repetition rate of 1 kHz at the Institute of Physics in Zagreb, utilizing the
Spectra-Physics Spitfire amplifier to generate femtosecond pulses from the Spectra-Physics
Tsunami laser. We selected polycarbonate as our material of choice. The two-axis stage
system from Micos was computer-controlled simultaneously with the laser. By tightly
focusing the laser beam, an optical breakdown can occur within the bulk of the transparent
material through multi-photon absorption. This absorption takes place in a confined space,
resulting in permanent material modifications.
For a comparison I will also show reconstruction of the same CGH using other techniques:
hologram generated with liquid crystal mask, Computer-to-Plate Process, Computer-to-Film
Process and Monochrome Offset Printing.
Ključne riječi
Femtosecond laser, engraving, holograms