Femtosecond micro-machining use laser pulses of 10-15 seconds to fundamentally change materials through the interaction of the pulse with the material.  The femtosecond oscillator produces a continuous train of pulses. Selectivity of pulses can be achieved by introducing a pulse picker. Using optical modulators, one can also alter the temporal and spatial character of a light beam. 

As most of us know, the current trend of technology is moving toward compactness and miniaturization. It is necessary to achieve higher resolutions in fabrication. However, the smallest spot size that can be achieved by a focusing lens is given by the diffraction-limited spot size. This is given by the Rayleigh criterion D = 0.61 λ/ N.A., where λ is the incident light wavelength and N.A. is the numerical aperture of the optic. Lowering the wavelength helps to improve the spatial resolution of the final fabricated structure.

Diffractive optics are known to possess high damage thresholds in comparison to refractive optics. Also, the collection of extreme wavelengths with ionizing properties (such as x-rays and cosmic waves) is done using diffractive optics as the EM wave no longer has to pass through the material, thereby reducing the chances of damage through absorption. Diffractive optics is of growing interest since it can achieve any optic function with no constraint on the shape of the optical element.

The facility has been involved in the fabrication of gratings, micron-sized lens arrays, Fresnel zone plates, and photon sieves. 

1. Rodrigues VR, Thomas J, Santhosh C, Ramachandran H, Mathur D. Microfabrication of Fresnel zone plates by laser induced solid ablation. Journal of Optics. 2016 May 18;18(7):075403.

2. Rodrigues VR, Dharmadhikari JA, Dharmadhikari AK, Chidangil S, Mathur D, Ramachandran H. Direct femtosecond laser fabricated photon sieve. OSA Continuum. 2019 Apr 15;2(4):1328-41.