Ultra-short pulse laser (UPL) industry is counting on high power P sources (100W class) to increase the throughput of a wide variety of industrial fabrication process. Nevertheless, this poses the challenge to overcome heat accumulation phenomena observed when P exceeds few tens of Watts compromising the machining quality. Novel beam engineering strategies are required to tackle this issue and guarantee high throughput with the high, distinctive, UPL machining quality. Here a study is reported on a variety of laser processes carried out with 100W class femtosecond lasers following two possible beam engineering strategies i.e. beam scanning with high speed (both a 100 m/s polygon scanner head and a 2D, 20 m/s fast, galvo-head) and parallel processing with multiple beams (obtained with both a DOE and an SLM head). Results show that by increasing P from few to 100 W also the throughput increases by nearly a factor 10 for micro-cutting (with galvo head and DOE) and even higher for surface texturing (with polygon scanner) while the machining quality is kept unchanged. Furthermore, we optimised the use of an SLM head for precise micro drilling of matrix holes showing the benefit of this technological approach in term of throughput. A full characterisation of the results carried out via optic and electronic microscopy will be also reported. We believe that all these results further increase the USP laser technology effectiveness level which is primed for industrial applications.
Recent studies showed that the excitation spectral window lying between 1.6 and 1.8 μm is optimal for in-depth three-photon microscopy of intact tissues due to the reduced scattering and absorption in this wavelength range. Hence, millimeter penetration depth imaging in a living mouse brain has been demonstrated, demonstrating a major potential for neurosciences.
Further improvements of this approach, towards much higher imaging frame rates (up to 15-20 s/frame in previous achievements) requires the development of advanced molecular optical probes specifically designed for three-photon excited fluorescence in the 1.6 -1.8 μm spectral range.
In order to achieve large three-photon brightness at 1700 nm, novel molecular-based fluorescent nanoparticles which combine strong absorption in the green-yellow region, remarkable stability and photostability in aqueous and biological conditions have been designed using a bottom-up route. Due to the multipolar nature of the dedicated dyes subunits, these nanoparticles show large nonlinear absorption in the NIR region.
These new dyes have been experimentally characterized through the measurement of their three-photon action cross-section, fluorescence spectra and lifetimes using a monolithically integrated high repetition rate all-fiber femtosecond laser based on soliton self-frequency shift providing 9 nJ, 75 fs pulses at 1700 nm. The main result is that their brightness could be several orders of magnitude larger than the one of Texas Red in the 1700 nm excitation window.
Ongoing experiments involving the use of these new dyes for in vivo cerebral angiography on a mouse model will be presented and the route towards three-photon endomicroscopy will be discussed.
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