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Jahng, Junghoon,Potma, Eric O.,Lee, Eun Seong American Chemical Society 2018 ANALYTICAL CHEMISTRY - Vol.90 No.18
<P>We investigate the tip-enhanced thermal expansion force for nanoscale chemical imaging and spectroscopy in the tip-sample junction. It is found, both theoretically and experimentally, that the tip-enhanced absorption of the near-field at the tip followed by sample expansion shows characteristic behaviors with respect to the sample thickness and the incident laser pulse width. The van der Waals interaction plays a major role in exerting a force on the tip from the thermally expanded sample. The force behavior of the photoinduced force microscope (PiFM) is compared with that of the existing photothermal-induced resonance technique (PTIR) to unravel the ambiguous thermal expansion force mechanism. The present study opens up new opportunities for enhancing the performance of optical nanoscopy and spectroscopy such as chemical imaging of nanobiomaterials and the local field mapping of photonic devices, including surface polaritons on van der Waals materials with the assistance of the thermal expansion of a functionalized tip.</P> [FIG OMISSION]</BR>
Quantitative analysis of sideband coupling in photoinduced force microscopy
Jahng, Junghoon,Kim, Bongsu,Lee, Eun Seong,Potma, Eric Olaf American Physical Society 2016 Physical Review B Vol.94 No.19
<P>We present a theoretical and experimental analysis of the cantilever motions detected in photoinduced force microscopy (PiFM) using the sideband coupling detection scheme. In sideband coupling, the cantilever dynamics are probed at a combination frequency of a fundamental mechanical eigenmode and the modulation frequency of the laser beam. Using this detection mode, we develop a method for reconstructing the modulated photoinduced force gradient from experimental parameters in a quantitative manner. We show evidence, both theoretically and experimentally, that the sideband coupling detection mode provides PiFM images with superior contrast compared to images obtained when detecting the cantilever motions directly at the laser modulation frequency.</P>
Eigenmodes of a quartz tuning fork and their application to photoinduced force microscopy
Kim, Bongsu,Jahng, Junghoon,Khan, Ryan Muhammad,Park, Sung,Potma, Eric O. American Physical Society 2017 Physical Review B Vol.95 No.7
<P>We examine the mechanical eigenmodes of a quartz tuning fork (QTF) for the purpose of facilitating its use as a probe for multifrequency atomic force microscopy (AFM). We perform simulations based on the three-dimensional finite element method and compare the observed motions of the beams with experimentally measured resonance frequencies of two QTF systems. The comparison enabled us to assign the first seven asymmetric eigenmodes of the QTF. We also find that a modified version of single beam theory can be used to guide the assignment of mechanical eigenmodes of QTFs. The usefulness of the QTF for multifrequency AFM measurements is demonstrated through photoinduced force microscopy measurements. By using the QTF in different configurations, we show that the vectorial components of the photoinduced force can be independently assessed and that lateral forces can be probed in true noncontact mode.</P>
Biological imaging with coherent Raman scattering microscopy: a tutorial
Alfonso-Garcí,a, Alba,Mittal, Richa,Lee, Eun Seong,Potma, Eric O. SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS 2014 JOURNAL OF BIOMEDICAL OPTICS Vol.19 No.7
<P>Coherent Raman scattering (CRS) microscopy is gaining acceptance as a valuable addition to the imaging toolset of biological researchers. Optimal use of this label-free imaging technique benefits from a basic understanding of the physical principles and technical merits of the CRS microscope. This tutorial offers qualitative explanations of the principles behind CRS microscopy and provides information about the applicability of this nonlinear optical imaging approach for biological research.</P>
Visualizing surface plasmon polaritons by their gradient force.
Jahng, Junghoon,Ladani, Faezeh Tork,Khan, Ryan Muhammad,Li, Xiaowei,Lee, Eun Seong,Potma, Eric Olaf Optical Society of America 2015 Optics letters Vol.40 No.21
<P>A new method is presented for visualizing the electric field distributions associated with propagating surface-plasmon-polariton (SPP) modes directly in the near-field. The method is based on detecting the photo-induced gradient force exerted by the evanescent field onto a sharp and polarizable tip. Using a photo-induced force microscope (PiFM), images of propagating SPPs are obtained on flat gold surfaces.</P>