We report on experiments using a near-infrared Ti:Sapphire laser system based on a 85 MHz, sub-15 fs resonator. In the
negative photoresist SU-8 multiphoton polymerization of 3D structures resulted in a minimum line width of
approximately 80 nm at aspect ratios in excess of 50:1. The second part of our contribution deals with sub-wavelength
nanostructuring and laser-annealing of thin indium-tin-oxide (ITO) films. The ablation experiments allowed for the
generation of cuts of sub-100 nm width in periodic and single cut arrangements. Annealing resulted in a different phase
of ITO which is more resistive against etching in HCl at room temperature. The dependence of cuts on scan parameters
that affect the ITO film properties was investigated.
Ultrabroad band 12 femtosecond near infrared laser pulses at transient TW/cm2 intensities and low picojoule pulse
energies (mean powers < 20 mW at 85 MHz repetition rate) have been used to perform material nanoprocessing based on
multiphoton ionization and plasma formation. Cut sizes of
sub-wavelength, sub-100 nm which is far beyond the Abbe
diffraction limit have been realized without any collateral damage effect in silicon wafers, photoresists, glass, polymers,
metals, and biological targets. Multiphoton sub-15fs microscopes may become novel non-invasive 3D tools for highly
precise nanoprocessing of inorganic and organic targets as well as two-photon 3D imaging.
A near infrared sub-15 femtosecond laser scanning microscope was employed for structuring of bulk colored glass and
polymethylmethacrylate (PMMA). The 400-mW Ti-Sapphire laser operates at 85 MHz with an M-shaped emission
spectrum with maxima at 770 nm and 827 nm. Using a high numerical aperture objective light intensity of about
7 TW/cm2 at the focal plane can be reached. For PMMA a mean power of less than 17 mW, which corresponds to a pulse
energy of 0.2 nJ, was sufficient for ablating material. Holes of a diameter of less than 170 nm were produced. Two-photon
fluorescence measurements, which can be performed with the same microscope, reveal an extension of the focus
length in the specimen, which is most likely caused by self-focusing effects. By applying the same power, the refractive
index of the glass could be changed. Islands at the glass surface of a size of less than 100 nm have been produced.
Laser-assisted surgery based on multiphoton absorption of NIR laser light has great potential for high precision surgery
at various depths within the cells and tissues. Clinical applications include refractive surgery (fs-LASIK). The non-contact
laser method also supports contamination-free cell nanosurgery.
Here we apply femtosecond laser scanning microscopes for sub-100 nm surgery of human cells and metaphase
chromosomes. A mode-locked 85 MHz Ti:Sapphire laser with an M-shaped ultrabroad band spectrum (maxima: 770
nm/830 nm) with an in situ pulse duration at the target ranging from 12 femtoseconds up to 3 picoseconds was
employed. The effects of laser nanoprocessing in cells and chromosomes have been quantified by atomic force
microscopy (AFM) and electron microscopy. These studies demonstrate the potential of extreme ultrashort femtosecond
laser pulses at low mean milliwatt powers for sub-100 nm surgery.
A compact ultra-broadband femtosecond laser scanning microscope with 12 femtoseconds pulse width at the focal plane
of a high NA objective has been employed in material nanoprocessing. The laser works at 85 MHz with an M-shaped
emission spectrum with maxima at 770 nm and 827 nm. Different motorized setups based on the introduction of chirped
mirrors, flint glass wedges, and glass blocks have been realized to vary the in situ pulse length from 12 femtoseconds up
to 3 picoseconds. Nanoprocessing was performed in silica, photoresists, glass, polymers, and biological structures. Mean
powers as low as 2 mW were sufficient to realize plasma-mediated cutting effects in human chromosomes with sub-80
nm cut width. Using a mean power of 7-9 mW, transient nanoholes were "drilled" in the cellular membrane for targeted
transfection of stem cells and the introduction of μRNA probes. Region of interest (ROI) scanning have been used for
optical cleaning of human adult stem cell populations and blood cell suspensions. 3D two-photon nanolithography based
on the ultrabroad band laser pulses was realized with the photoresist SU-8. Multiphoton sub-20fs microscopes may
become novel non-invasive 3D tools for highly precise nanoprocessing of inorganic and organic targets.
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