In situ and real time monitoring of two-photon polymerization using broadband coherent anti-Stokes Raman scattering microscopy

ArticleinOptics Express 18(18):19219-31 · August 2010with15 Reads
DOI: 10.1364/OE.18.019219 · Source: PubMed
We demonstrate in situ and real time characterization of two-photon polymerization (TPP) by means of broadband coherent anti-Stokes Raman scattering (CARS) microscopy. The same experimental setup based on one femtosecond oscillator is used to perform both TPP and broadband CARS microscopy. We performed in situ imaging with chemical specificity of three-dimensional microstructures fabricated by TPP, and successfully followed the writing process in real time. Broadband CARS microscopy allowed discerning between polymerized and unpolymerized material. Imaging with good vibrational contrast is achieved without causing any damage to the microstructures or undesired polymerization within the sample.
    • "In the case of STED microscopy the time-gated detection allows to obtain spatial resolution comparable to more complex and costly STED microscopy implementations based on pulsed lasers. Finally, changes in the degree of conversion of the polymerization process have been indicated to influence the mechanical strength and the refractive index of the photoresist [18,19]. We believe that variation of the latter two parameters should not affect the signal in STED microscopy since fluorescence is exclusively determined by the organic dye. "
    [Show abstract] [Hide abstract] ABSTRACT: The development of optical fabrication tools such as direct laser writing (DLW) lithography provides an unprecedented ability to rapidly generate arbitrary structures with control down to the nanoscale. Key to the further advance of these strategies is the development of simple and straightforward methods to monitor or characterize the fabricated structures. Here, we use a two-beam approach based on the reversible saturable optical fluorescence transition (RESOLFT) concept that enables the fabrication as well as the rapid characterization of nanometer-sized DLW lithography structures since both steps can be performed in the same experimental system. Our two-step approach uses two-beam DLW lithography based on the triplet state absorption (TSA) mechanism to polymerize a resist containing isopropyl thioxanthone (ITX) as the photoinitiator and Chromeo 488 carboxylic acid derivative as a fluorescent reporter, and then stimulated emission depletion (STED) microscopy to rapidly characterize the size and morphology of the polymerized structures after the development of the sample. Our results show photopolymerized lines with a linewidth of ~90 nm whose size was properly determined with STED microscopy.
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    • "Furthermore, the traditional techniques used to visualize such microstructures lack three-dimensional imaging capabilities [29][30][31]and require physical sectioning or external contrast agents [27,[32][33][34][35][36][37]. While near-field imaging [38] and vibrational spectroscopy [39][40][41]have been utilized to characterize photopolymerized microstructures, such techniques are not easily accessible due to the requirements of multiple laser sources and cumbersome instrumentation. Thus, there is an obvious need for simple and nondestructive characterization tools for photopolymerized structures. "
    [Show abstract] [Hide abstract] ABSTRACT: We demonstrate the capability of polarized third-harmonic generation (THG) for high contrast imaging of three-dimensional microstructures fabricated by photopolymerization. Using circular polarization of fundamental light, background-free optically-sectioned THG images were obtained from laser-written photopolymerized microstructures. The technique has great potential for simple and noninvasive characterization of photopolymerized devices, which typically show poor contrast in conventional light microscopy.
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    • "However, this approach requires high intensity laser systems, including a kHz amplifier and optical parametric amplifier. The more efficient approach to achieve a large Raman frequency range (> 2000 cm −1 ) from an unamplified and high repetition-rate source (> 100 MHz) is to use SC generated in nonlinear fibers89101112131415161718192021 . This has been implemented in frequency domain twocolor CARS, with degenerate pump and probe excitations driven by the narrowband source and the Stokes induced by the continuum [8]. "
    [Show abstract] [Hide abstract] ABSTRACT: We demonstrate the use of a photonic crystal fiber (PCF) as a compact three-color fs laser system operating at 76 MHz, limited only by the repetition rate of the pump laser. The system is suitable for background-free time-resolved four-wave mixing measurements, which arguably reach fundamental limits in signal detectivity. We give a detailed characterization of the near transform-limited multi-color pulses that are extracted from the PCF, and prove the system through time-resolved coherent anti-Stokes Raman scattering measurements in bipyridyl ethylene and styrene.
    Full-text · Article · Sep 2015
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