We irradiate the surface of pure fused silica with few-cycle pulses (duration < 10 fs, central wavelength at 800 nm, repetition of 400 kHz and a pulse energy of ca. 1 µJ) focused at a quasi grating incidence and observe a permanent densification in the irradiated region. A translation of the sample in the direction of the laser results in the direct writing of surface waveguides. The eigen modes of such structures exhibit a pronounced sensitivity to the refractive index of the immediate environment which we exploit to demonstrate direct refractive index sensing as well as plasmonic sensing.
The recent development of sources able to deliver laser pulses with a duration of a few optical cycles has created many opportunities for fundamental research. Few-cycle laser pulse sources are now commercially available and are able to deliver energetic pulses (tens of micro-joules) at a MHz repetition rate. With such an extremely short pulse duration (<10 fs FWHM at 800 nm), the amount of energy required to reach the breakdown threshold in dielectrics is minimal, thus suggesting that few-cycle laser pulses are a very promising tool for reducing the heat affected zone and therefore the amount of thermo-induced stress during and after irradiation in transparent materials. In this article, the potential relevance of few-cycle laser pulses for microprocessing fused silica is examined. In particular, we demonstrate the fabrication of optical microstructures in the volume as well as on the surface of undoped fused silica.
A high power, high repetition rate optical parametric chirped pulse amplification (OPCPA) system is presented. The OPCPA delivers Carrier-Envelope Phase (CEP)-stable 7 fs pulses, with up to 0.19mJ of energy, with a total compressed average power of 19 W. The system is being currently integrated in an attosecond pumpprobe beamline capable of combining attosecond pulses in the extreme ultraviolet (XUV) with synchronized few-cycle pulses in the near infrared (NIR). The main motivation for this development is to perform pump-probe experiments with attosecond time resolution, in which electrons and ions produced during photo-ionization are detected in coincidence utilizing a reaction microscope.
The potential of few-cycle pulses for bulk microprocessing of fused silica in tight focusing conditions is explored.
Few-cycle pulses emitted from a non-collinear optical parametric amplifier (NOPA) delivering sub-7 fs laser
pulses at a repetition rate of 400 kHz with a pulse energy up to 10 μJ are focused in the bulk of fused silica
sample. The focusing apparatus is a high numerical aperture (NA = 0.5), all-reflective microscope objective.
The characterization of the photoinduced microstructures in spatial light interference microscopy reveals that
few-cycle pulses offer an unprecedented flexibility for producing Type I structures, characterized by a uniform
refractive index (higher than the refractive index of the pristine bulk) and the absence of damage in the vicinity of
the microprocessing region.
The table-top generation of high average power coherent soft x-ray radiation in a compact set up is of high interest for numerous applications. We have demonstrated the generation of bright soft x-ray laser pulses at 100 Hz repetition rate with record-high average power from compact plasma amplifiers excited by an ultrafast diode-pumped solid state laser. Results of compact λ=18.9nm Ni-like Mo and λ=13.9nm Ni-like Ag lasers operating at 100 Hz repetition rate are discussed.
We discuss recent advances in the development of high repetition rate table-soft soft x-ray lasers resulting from
research conducted at Colorado State University. Advancing saturated table-top lasers to shorter wavelengths we report
the operation of gain-saturated sub-10 nm table-top lasers at 1 Hz repetition rate. We also present experimental results
that show that injection-seeding of solid-target soft x-ray plasma amplifiers reduces the far field divergence by an order
of magnitude and to allow for control of the far-field beam characteristics by tailoring the divergence of the seed. We
finally discuss progress towards the development of high repetition rate compact all-diode-pumped soft x-ray lasers. We
have operated the front end of the diode-pumped soft-ray laser driver at 100Hz repetition rate, obtaining sub-5 ps optical
laser pulses of 100 mJ energy.
We present a complete systematic study on the effect of assist beam energy on SiO2/HfO2 quarter wave stacks deposited
by dual ion beam sputter (DIBS) deposition. Increasing assist beam energy results in lower surface roughness and
reduced micro-crystallinity. The coatings also show reduced mechanical stress. The improvements in the structural
properties are accompanied by a reduction in the absorption loss and an increase in the laser resistance to damage at 1
μm.
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