ubl
Photothermal Single Particle Detection in Theory & Experiments
2013-10-28
[Electronic ed.]
prv
Universitätsbibliothek Leipzig
Universitätsbibliothek Leipzig, Leipzig
Fakultät für Physik und Geowissenschaften
Prof. Dr. Frank Cichos
male
Herdecke
The dissertation presents theoretical and experimental studies on the physical origin of the signal in photothermal microscopy of single particles. This noninvasive optical far field microscopy scheme allows the imaging and detection of single absorbing nanoparticles. Based on a heat-induced pertur- bation in the refractive index in the embedding medium of the nanoscopic absorber, a corresponding probe beam modification is measured and quantified. The method is well established and has been applied since its first demonstration in 2002 to the imaging and characterization of various absorbing particle species, such as quantum dots, single molecules and nanoparticles of different shapes.
The extensive theoretical developments presented in this thesis provide the first quantitative assess- ment of the signal and at the same time enlarge its phenomenology and thereby its potential. On the basis of several approximation schemes to the Maxwell equations, which fundamentally gov- ern the interaction of light with inhomogeneities, several complementing models are devised which describe the photothermal signal both qualitatively and quantitatively. In succession an interdepen- dent and self-consistent set of theoretical descriptions is given and allows important experimental consequences to be drawn. In consequence, the photothermal signal is shown to correspond to the action of a nanoscopic (thermal) lens, represented by the spherically symmetric refractive index pro- file n(r) which accompanies the thermal expansion of the absorber’s environment. The achieved quantification allows the direct measurement of absorption cross-sections of nanoparticles. Further, a qualitatively new phenomenology of the signal is unraveled and experimentally demonstrated. The separate roles of the probing and the heating beams in photothermal microscopy is dismantled and the influence of their relative alignment shown to allow for a controlled adjustment of the effective detection volume. For the first time, both positive and negative signals are demonstrated to occur and to be the characteristic signature of the lens-like action on the probe beam. The detection of the probe beam’s modification is also shown to sensitively depend on the aperture used in the detection chan- nel, and a signal optimization is shown to be feasible. Also, a generalization of the detectable signal via the use of a quadrant photodiode is achieved. Specifically, measuring the far field beam deflec- tion the result of the beam passing the lens off-center manifests in a laterally split detection volume. Hereby, finally each classical photothermal spectroscopic techniques has been shown to possess its microscopic counterpart. Central to the understanding of this generalized and new phenomenology is a scalar wave-optical model which draws an analogy between the scattering of a massive particle wave-packet by a Coulomb potential and the deflection of a focused beam by a photonic potential connected with the thermal lens.
The significance of the findings is demonstrated by its methodological implications on photother- mal correlation spectroscopy in which the diffusion dynamics of absorbing colloidal particles can be studied. The unique split focal detection volumes are shown to allow the sensitive measurement of a deterministic velocity field. Finally, the method is supplemented by a newly introduced sta- tistical analysis method which is capable of characterizing samples containing a heterogeneous size distribution.
530
Photothermische Mikroskopie, Transmissions-Mikroskopie, Interferenz-Mikroskopie, Gold Nanopartikel, Thermische Linse
Photothermal microscopy, Transmission Microscopy, Interference microscopy, thermal lens, Mie scattering, gold nanoparticles, Photothermal correlation spectroscopy
>1
4.5.3 Lessons to be learned from plane-wave scattering by thermal lenses
4.6 What is a lens? And is n(r) a lens?
5 Methodological Applications of the Results
5.1 Generalized photothermal correlation spectroscopy (incl. twin-PhoCS)
5.2 Photothermal signal distribution analysis (PhoSDA)
6 Summary and Outlook
6.1 Summary of the results
6.2 Outlook
7 Appendix
7.1 Material parameters
7.2 Calculation parameters
7.3 Interactive simulation scripts (Processing)
7.4 Vectorial scattering in the BORN-approximation
7.5 Details regarding the scattering framework
7.5.1 Connection between Gmn,TE,TM of Ref.1 and gmn,TE,TM in the GLMT
7.5.2 Off-axis BSCs including aberration (single interface)
7.5.3 Details on the incidence power Pinc
7.5.4 Details on the incidence power Pinc for arbitrary beams
7.5.5 Explicit expressions for the spherical field components of Es,i and Hs,i
7.5.6 Note on the time-dependence and the corresponding sign-conventions in M
7.5.7 Recurrence relation for Pn and tn
7.5.8 Gaussian beam shape coefficients: Off-axis
7.5.9 Multilayered Scatterer
7.5.10 POYNTING-vector and energy flow fields
7.5.11 Convergence
7.5.12 Further evaluations in the GLMT framework
7.5.13 Diffraction model: Comparison of angular PT signal pattern to the GLMT
7.6 Details on geometrical optics models
7.6.1 Geometrical optics: Exact solution r(f) for |bx|<1
7.6.2 Correspondences in photonic and partile RUTHERFORD scattering
7.6.3 On the difference in the definition of optical energy
7.6.4 Ray-opticsphotothermalsignal
7.6.5 Thick lens raytracing and the equivalent lens shape for a given aberration
7.7 Thermal lens around a wire of radius R
7.8 Twin-PhoCS: Graphic illustration of the CCF integrand
Curriculum Vitae
Publications
Declaration
Acknowledgements
List of Tables
List of Figures
Bibliography]]>
urn:nbn:de:bsz:15-qucosa-126286
Universität Leipzig
dgg
Universität Leipzig, Leipzig
Markus
Selmke
1986-04-14
aut
Frank
Cichos
Prof. Dr.
dgs
rev
Dieter
Braun
Prof. Dr.
rev
eng
2013-05-17
2013-07-10
born digital
Markus Selmke
01713239048
markus.selmke@gmx.de
doctoral_thesis