Extended depth-of-focus femtosecond laser pulses for flexible micromachining.

We present a simple and efficient method for extending depth-of-focus of intense femtosecond (fs) pulses with a flat and thin multilevel diffractive lens (MDL). The MDL focuses fs-pulses at a desired distance, which remains invariant over an extended range of propagation distances, several times beyond that of a traditional lens. We have presented the results of strongly focused fs-pulses with different extended depth-of-focus obtained by two different MDLs. Further, we have shown laser filamentation with long plasma channels. We have also performed laser marking/machining in glass material with approximately constant spatial resolution over an EDOF. These findings can be exploited for high-throughput compact in-line fs-micromachining, potentially useful in micro-optics, microfluidics, and nanosurgery.