Surface processing of PMMA and metal nano-particle resist by sub-micrometer focusing of coherent extreme ultraviolet high-order harmonics pulses
To achieve a higher resolution in laser materials processing, minimizing both the focal spot size of the laser beam and the heat-affected zone near the focal spot is essential. The heat-affected zone can be naturally suppressed by reducing the pulse duration of irradiating pulses, whereas the focal spot size can shrink by using shorter laser wavelength, and focusing optics with low F-number and aberrations. In this article, through high harmonic generation of near-IR femtosecond laser pulses, the authors fully utilize the benefits of short wavelength and pulse duration of generated ultrafast XUV laser pulses. Moreover, by using an ellipsoidal mirror, both spherical and chromatic aberrations from the focusing optics are simultaneously minimized. These efforts eventually lead to sub-micrometer focusing of ultrafast XUV laser pulses, and this capability can be potentially useful for ultrafine laser materials processing.