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P. Bianchini et al.
7.4 Summary and Future Perspectives
Among nonlinear optical approaches, pump–probe methods allow the resolving and
monitoring of chemical and atomic ultrafast processes, which occur on a picosecond
(or lower) timescale; no other mediators are required, for example, fluorescence.
Such ability is of interest in the microscopy field. The standard optical microscope
often uses fluorescence, and it relies on the photo-physical properties of fluorescent
molecules to obtain the desired contrast and spatial resolution. A label-free approach
is highly desirable since the labeling procedure can be invasive, and fluorescence
can degrade and photo-bleach. The direct imaging of the molecules of interest using
pump–probe methods allows gathering insights about molecular organization and
interaction, while it does not exclude the simultaneous use of the fluorescence. It is
worth noting that when the absorption process is saturable, super-resolution can also
be achieved following the general RESOLFT concept.
Among nanomaterials, recentlygraphene has started to be intensively studied for
the development of novel electronic and optoelectronic devices. Owing to its particular linear electronic band structure, graphene shows a wavelength-independent,
broadband optical absorption in the NIR, together with a large third-order susceptibility χ
(3) . This characteristic makes pump–probe spectroscopy and microscopy
ideal techniques to explore carrier dynamics in all its different graphene forms, for
example, few-layer epitaxial graphene, single- and multi-layer exfoliated graphene,
graphene suspensions, and graphene oxide. Interestingly, since its absorption property in the NIR is saturable and allows super-resolution imaging, it is opening a
new envisaging way to study it. Nevertheless, since transient saturable absorption
is not a unique property of graphene, many other materials could be studied using
absorption-based super-resolution imaging approaches.
Acknowledgments The authors thank Kseniya Korobchevskaya, Colin Sheppard, Amira El Merhie, Silvia Dante, Antonio Esaù Del Rio Castillo, Camilla Coletti (Fondazione Istituto Italiano di
Tecnologia, Genova, Italy), and Fumihiro Dake (Nikon Corporation, Yokohama, Japan) for the scientific discussion; Eileen Sheppard for proofreading the chapter and the Nikon Imaging Center at
the Fondazione Istituto Italiano di Tecnologia for help with light microscopy. This work was partially funded by the European Community’s Seventh Framework Programme (FP7/20012-2015)
under grant agreement no. 280804 in the LANIR project framework.
References
1. R.W. Boyd, Nonlinear Optics (2003)
2. P. Bianchini, A. Diaspro, Three-dimensional (3D) backward and forward second harmonic
generation (SHG) microscopy of biological tissues. J. Biophotonics 1(6), 443–450 (2008)
3. W.R. Zipfel, R.M. Williams, W.W. Webb, Nonlinear magic: multiphoton microscopy in the
biosciences. Nat. Biotechnol. 21(11), 1369–77 (2003)
4. H. Chen, H. Wang, M.N. Slipchenko, Y. Jung, Y. Shi, J. Zhu, K.K. Buhman, J.-X. Cheng, A
multimodal platform for nonlinear optical microscopy and microspectroscopy. Opt. Express
17(3), 1282–1290 (2009)
P. Bianchini et al.
7.4 Summary and Future Perspectives
Among nonlinear optical approaches, pump–probe methods allow the resolving and
monitoring of chemical and atomic ultrafast processes, which occur on a picosecond
(or lower) timescale; no other mediators are required, for example, fluorescence.
Such ability is of interest in the microscopy field. The standard optical microscope
often uses fluorescence, and it relies on the photo-physical properties of fluorescent
molecules to obtain the desired contrast and spatial resolution. A label-free approach
is highly desirable since the labeling procedure can be invasive, and fluorescence
can degrade and photo-bleach. The direct imaging of the molecules of interest using
pump–probe methods allows gathering insights about molecular organization and
interaction, while it does not exclude the simultaneous use of the fluorescence. It is
worth noting that when the absorption process is saturable, super-resolution can also
be achieved following the general RESOLFT concept.
Among nanomaterials, recentlygraphene has started to be intensively studied for
the development of novel electronic and optoelectronic devices. Owing to its particular linear electronic band structure, graphene shows a wavelength-independent,
broadband optical absorption in the NIR, together with a large third-order susceptibility χ
(3) . This characteristic makes pump–probe spectroscopy and microscopy
ideal techniques to explore carrier dynamics in all its different graphene forms, for
example, few-layer epitaxial graphene, single- and multi-layer exfoliated graphene,
graphene suspensions, and graphene oxide. Interestingly, since its absorption property in the NIR is saturable and allows super-resolution imaging, it is opening a
new envisaging way to study it. Nevertheless, since transient saturable absorption
is not a unique property of graphene, many other materials could be studied using
absorption-based super-resolution imaging approaches.
Acknowledgments The authors thank Kseniya Korobchevskaya, Colin Sheppard, Amira El Merhie, Silvia Dante, Antonio Esaù Del Rio Castillo, Camilla Coletti (Fondazione Istituto Italiano di
Tecnologia, Genova, Italy), and Fumihiro Dake (Nikon Corporation, Yokohama, Japan) for the scientific discussion; Eileen Sheppard for proofreading the chapter and the Nikon Imaging Center at
the Fondazione Istituto Italiano di Tecnologia for help with light microscopy. This work was partially funded by the European Community’s Seventh Framework Programme (FP7/20012-2015)
under grant agreement no. 280804 in the LANIR project framework.
References
1. R.W. Boyd, Nonlinear Optics (2003)
2. P. Bianchini, A. Diaspro, Three-dimensional (3D) backward and forward second harmonic
generation (SHG) microscopy of biological tissues. J. Biophotonics 1(6), 443–450 (2008)
3. W.R. Zipfel, R.M. Williams, W.W. Webb, Nonlinear magic: multiphoton microscopy in the
biosciences. Nat. Biotechnol. 21(11), 1369–77 (2003)
4. H. Chen, H. Wang, M.N. Slipchenko, Y. Jung, Y. Shi, J. Zhu, K.K. Buhman, J.-X. Cheng, A
multimodal platform for nonlinear optical microscopy and microspectroscopy. Opt. Express
17(3), 1282–1290 (2009)