Dawn Vitek

Temporally focused femtosecond laser pulses for low numerical aperture micromachining through optically transparent materials

Temporal focusing of spatially chirped femtosecond laser pulses overcomes previous limitations for ablating high aspect ratio features with low numerical aperture (NA) beams. Simultaneous spatial and temporal focusing reduces nonlinear interactions, such as self-focusing, prior to the focal plane so that deep (~1 mm) features with parallel sidewalls are ablated at high material removal rates (25 µm3 per 80 µJ pulse) at 0.04-0.05 NA. This technique is applied to the fabrication of microfluidic devices by ablation through the back surface of thick (6 mm) fused silica substrates. It is also used to ablate bone under aqueous immersion to produce craniotomies.

Simultaneous spatial and temporal focusing for tissue ablation

Simultaneous spatial and temporal focusing (SSTF) of femtosecond pulses was originally conceived as a novel method for increasing the field-of-view in multiphoton imaging applications. Multiphoton imaging with SSTF deviated from traditional nonlinear systems in that it enabled the use of low numerical aperture beams to be used to increase the field-of-view, but retain the axial sectioning of a high numerical aperture beam. In this manner efficiency gains in the imaging process were achieved without compromising axial resolution [1,2].

Utilising Ultrafast Lasers for Multiphoton Biomedical Imaging

This chapter covers the benefits and applications of ultrafast laser scanning microscopes from a biomedical perspective. The basic architecture of a laser microscope is discussed, including how to design a laser scanning system with lateral and axial control. Also investigated is the design of custom collection optics for optimizing the detection of emitted photons and maximizing that emitted fluorescence in the presence of photobleaching. In addition, this chapter addresses three techniques novel to the biomedical community. The first is the technique of temporal focusing and its application toward wide-field imaging and micromachining. Also investigated is the concept of photon counting in multiphoton microscopy and how this approach to imaging has become practical for everyday use. Finally, several different methods are revealed for implementing spectral imaging with a multiphoton microscope platform.

Polymer micro-molding of femtosecond laser micromachined substrates

Micro-molding can be used for the cost-effective fabrication of elements such as active or passive components in MEMS devices, hydrophobic surfaces, cell-growth scaffolds or optical components such micro-lens arrays and gratings. This method is also particularly interesting for examining high-aspect ratio laser-machined structures fabricated in glass material. Thanks to this technique, surfaces not accessible with common imaging techniques can be observed on their molded negative structure with very high fidelity. As an illustration, we issue the use of the PDMS molding technique to analyze the quality of high aspect ratio holes and channels structures. Furthermore, we show preliminary results on the molding of a novel type of complex structures formed in glass using temporal and spatial beam shaping.

Spatially chirped pulses for high aspect ratio micromachining by femtosecond laser ablation

We demonstrate that spatially chirped femtosecond laser pulses overcome previous limitations for the machining of high-aspect ratio features with low numerical aperture beams in optically transparent materials.

Highly localized plasma formation in air using space-time cusing of mJ ultrafast pulses

Space-time focusing of spatially-chirped Ti:Sapphire laser pulses is used to generate a plasma in air axially localized to 28× less than the confocal parameter, suppressing filamentation on the way to the focus.

Intuitive analysis of space-time focusing with double-ABCD calculation

We analyze the structure of space-time focusing of spatially-chirped pulses using a technique where each frequency component of the beam follows its own Gaussian beamlet that in turn travels as a ray through the system.

Remote Focusing Differential Multiphoton Microscopy: Application to Neuronal Imaging

We apply remote focusing to multi-focal multiphoton microscopy by simultaneously imaging multiple focal planes of Drosophila melanogaster olfactory neurons. This technology permits imaging the entire volume of the antennal lobe in a single scan.

Differential Multiphoton Microscopy

High-speed nonlinear imaging systems capable of dynamically imaging differences in depth, excitation polarization, excitation wavelength, beam shape, and pulse shape with single element detection are presented for the first time.