Apertureless near-field/far-field CW two-photon microscope for biological and material imaging and spectroscopic applications

Nowak, Derek; Lawrence, A. J.; Sánchez, Erik J.

doi:10.1364/ao.49.006766

Cited by 10 publications

(8 citation statements)

References 42 publications

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“…Fig 12 was obtained with the Del Mar Photonics Trestles-50 Ti:Sapphire configured in CW mode. The power levels needed were similar to the diode laser used in our previous publication [11], demonstrating near-field imaging in this configuration. The CW TPE power levels can be utilized on the metal probe without any noticeable damage to the imaging quality throughout an image.…”

Section: Near-field Fluorescence Imagingmentioning

confidence: 76%

“…Currently the costs of a pulsed laser system are vastly greater than that of continuous wave (CW) diode laser systems. We previously demonstrated the use of a CW diode laser used with near-field imaging [11]. It has been determined the CW source can provide similar TPE response from the sample compared to the pulsed source.…”

Section: Nonlinear Far-field Diffraction Limited Imagingmentioning

confidence: 99%

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A low cost non-linear fluorescence near-field/far-field microscope

Nowak

Lawrence

Sánchez

2011

2011 11th IEEE International Conference on Nanotechnology

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Presented is a microscope design that employs two-photon non-linear excitation to allow the imaging of the fluorescence from almost any visible fluorophore at resolutions below 30 nm without changing filters or excitation wavelength. The ability of the microscope to image samples at atmospheric pressure, room temperature, and in solution makes it a very promising tool for the biological and materials science communities. The microscope demonstrates the ability to image topographical, far-field and near-field optical responses from the sample of interest. A single computer, simple custom control circuits, field programmable gate array (FPGA) data acquisition, and a simplified custom optical system are used. This versatility enables the end user to custom-design experiments from confocal far-field single molecule imaging to high resolution scanning probe microscopy imaging. Demonstrated is the far-field, topographic and near-field imaging using two-photon excitation of Bovine Pulmonary Artery Endothelial (BPAE) cells and J-aggregates (PVS Poly vinyl Sulfate) and PIC (Pseudo-Isocyanine) dye.

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Section: Near-field Fluorescence Imagingmentioning

confidence: 76%

Section: Nonlinear Far-field Diffraction Limited Imagingmentioning

confidence: 99%

A low cost non-linear fluorescence near-field/far-field microscope

Nowak

Lawrence

Sánchez

2011

2011 11th IEEE International Conference on Nanotechnology

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“…This is useful www.crt-journal.org for other techniques to be utilized such as Raman due to heat conduction away from the smaller end tip apex. The experimentally determined fluorescence resolution which has been achieved with this type of tip so far is on the order 20-30 nm [11][12][13]. Future methods of tip quality determination could involve scanning the tip with respect to the sample.…”

Section: Discussionmentioning

confidence: 99%

“…The near-field probe is located at the point of focus for the laser illumination through an infinity-corrected objective lens (Olympus 1.4 NA, 60x). The feedback setup for maintaining the probe-sample distance spacing was based on a typical tuning fork based scanning probe setup described elsewhere in detail [11][12][13]. The normal method for obtaining an image involves scanning the sample using a closed loop scanning piezo XY translation Fig.…”

Section: Methodsmentioning

confidence: 99%

Enhanced image contrast with delocalized near‐field excitation

Sánchez

Dunham

Nowak

et al. 2014

Crystal Research and Technology

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For Tip Enhanced Near-field Optical Microscopy (TENOM) utilizing detection of fluorescence or Raman emission, signal to noise amplification is highly desirable for higher resolution imaging. This goal may be achieved by amplifying the signal produced by the probe at the sample through a highly resonant geometry and/or by filtering out the unwanted signal of the excitation source through the addition of an aperture in the collection optical pathway. Making highly resonant tip geometries via nanofabrication can be a difficult process, while the aperture method is a much easier method. With this technique, even tips with undesirably low resonance can be utilized for imaging. We demonstrate the concept through the use of a low field enhancement probe by showing the spatial separation of the excitation and field enhancement locations. We also are able to predict this effect using finite difference time domain modeling of the potential geometries for a desired wavelength.

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“…Ultimately the best geometries should have a surface plasmon resonance with the wavelength of excitation light used. This talk will present our latest results [3,4,5] and important considerations for problems encountered in the making and design of these probes.…”

mentioning

confidence: 99%

Sub-Diffraction Optical Probe Design Considerations

et al. 2011

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Scanning Near-field Optical Microscopy (SNOM) employs many different forms of optical probes to achieve sub-diffraction limited imaging. The first commonly used probes utilized optical fibers pulled or etched to a small end diameter. This technique has successfully demonstrated better than 100 nm spatial optical resolution. These original near-field probes utilized a coating of Aluminum on the sidewalls to achieve field confinement (with coating while rotating), making a decent probe that achieved below 50 nm was a needle in a haystack situation.The fabrication process had problems with; irreproducible coatings, leading to light leakage or coatings blocking the light, insensitive scanning surface interaction mechanisms, or taper issues leading to low throughput. To overcome these issues a probe design, which involved illumination of sharp metals with optimal polarization was developed to achieve higher topography and optical spatial resolution. This technique has been termed Tip Enhanced Nearfield Scanning Optical Microscopy (TENOM). TENOM also allows for the use of multi-photon excitation laser sources, aiding in the suppression of far-field background signal. Fabrication of these probes requires the use of nano-manipulation systems to achieve the correct shape. Systems such as dual-beam focused ion beams (FIB) were making their way into the university research environment at the right time.Before the FIB capabilities, the hit and miss nature of probe fabrication slowed progress. In addition, without the use of a field emission scanning electron microscope (FESEM) to inspect the probes there was no reliable method for verifying light confinement. In addition to the TENOM probes relying on the FIB, fiber probes have benefitted greatly from these fabrication systems. With proper milling (FIB) and inspection (FESEM), fiber probes can be very reproducible.Although the TENOM probes demonstrate higher optical and topographical resolution than fiber probes, in general the fiber probes with proper modification can achieve similar results. Utilizing numerical modeling for electromagnetic interactions on the nanoscale, we have modeled many promising designs that could be very useful in near-field applications. We utilize Fresnel equations and finite difference time domain (FDTD) to optimize probe designs. With the help of the dual beam FIB, we have been able to create these probes.TENOM probes have issues as well, which prevent their use by many researchers seeking to use a sub diffraction imaging process. The biggest problem is what geometry to make. A geometry that generates a large localized field enhancement is ideal. Larger enhancement factors, increase the signal to noise ratio, effectively suppressing the far-field background contribution in the image. In terms of fluorescence imaging quenching can be an added a problem for fluorescence systems, which have the chromophores within 10 nm of the probe, tip. There are some fixes for this issue, which involve scanning at a higher distance over the sample, or SiO 2 coat...

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Apertureless near-field/far-field CW two-photon microscope for biological and material imaging and spectroscopic applications

Cited by 10 publications

References 42 publications

A low cost non-linear fluorescence near-field/far-field microscope

A low cost non-linear fluorescence near-field/far-field microscope

Enhanced image contrast with delocalized near‐field excitation

Sub-Diffraction Optical Probe Design Considerations

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