Spatially and temporally polarization shaped laser pulses for two-photon excited fluorescence
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Spatially and temporally polarization shaped laser pulses for two-photon excited fluorescence Marek B. Hild, Robin Gottschalk, Karsten Heyne, and Albrecht Lindingera Institut f¨ ur Experimentalphysik, Freie Universit¨ at Berlin, Arnimallee 14, 14195 Berlin, Germany Received 20 June 2020 / Received in final form 28 August 2020 / Accepted 3 September 2020 Published online 6 October 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. We present simultaneous spatial and temporal polarization pulse shaping for two-photon excited fluorescence of dyes. A temporal pulse shaper and a subsequent spatial pulse shaper are used to generate laterally and axially tailored two-photon excited fluorescence profiles. The induced fluorescence is recorded for different polarization directions by utilizing the anisotropy of the dyes embedded in glycerol. We achieve an increased fluorescence contrast between different dyes by employing specific polarization shaped laser pulses and by taking polarization dependent emission into account. This versatile pulse shaping method is prospective for novel biophotonic imaging.
1 Introduction In recent years laser pulse shaping received increasing attention due to its capability to control molecular processes and various applications emerged [1–7]. Particularly, closed-loop optimizations were successfully performed for discrimination of different molecules [8–10]. An important field of activity for tailored pulses is multiphoton excited fluorescence, where intrapulse interference is used to selectively excite different species [11], which is employed in multiphoton excited three-dimensional imaging of tissue [12]. In order to increase the shaping capabilities, additionally the modulation of the polarization was included into laser pulse shaping [13,14]. Another pulse shaping direction is the modification of the spatial laser profile by utilizing focussing lenses and a two dimensional liquid crystal array assembled to a spatial light shaper [15]. Spatial phase modulation of the liquid crystals yields well defined tailored beam profiles in the focal plane. Such beam profiles were employed for microstructuring [16], beam focussing in tissue [17], and high resolved spatial imaging [18]. For performing topical deep tissue imaging it is relevant to conduct axially resolved two-photon excited fluorescence measurements by modifying the focal depth employing specific spatial phase pattern. As a next step, combined temporal and spatial laser pulse shaping was developed since it allows for modifying photo-induced processes, both temporally and spatially. Such tailored pulses were explored in initial experiments [19–21], yet the shaping properties were limited in these studies and particularly no polarization shaping was included. Here, we perform simultaneous temporal and spatial polarization pulse shaping for two-photon excited a
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fluorescence of molecu
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