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22 October 2004 Microfabrication of optical elements with femtosecond Ti:sapphire laser oscillator
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We demonstrate experimentally fabrication of optical elements with femtosecond pulses. The laser source we adopted is a low power Ti: sapphire laser oscillator, with a central wavelength of 790 nm and pulse duration of 100 fs. Positive-photoresist-film-coated glass substrate acts as the sacrificial material. Due to the extreme high intensity of the tightly focused femtosecond laser beam, nonlinear processing occurred between photoresist and the laser pulses, which enable the sub-micron feature processing. In the experiments, we use a translational stage that is controlled by a computer to accurately move for fabrication of optical elements with high precision. Various gratings and phase plates are fabricated by this method. The obtained gratings patterns are checked with a conventional optical microscopy. The fabricating widths and depths are measured with the Taylor Hobson equipment. With the same method, photomask for microelectronics can also be fabricated. From the experimental results, we see that a high processing precision and the feature size exceeding the diffraction limit can be achieved with this method. This technique can be applied to the fields of microoptics and microelectronics. The mechanism between femtosecond laser and photoresist is also investigated. The processing mechanics is considered as laser ablation and nonlinear two-photon absorption phenomenon. Fabrication of optical elements with femtosecond laser reflects a new trend for fabrication of microoptical elements.
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Xiaohui Sun, Changhe Zhou, Liren Liu, and Bingkun Yu "Microfabrication of optical elements with femtosecond Ti:sapphire laser oscillator", Proc. SPIE 5524, Novel Optical Systems Design and Optimization VII, (22 October 2004);

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