Andrew James Lawrence

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

We present the development of a versatile spectroscopic imaging tool to allow for imaging with single-molecule sensitivity and high spatial resolution. The microscope allows for near-field and subdiffraction-limited far-field imaging by integrating a shear-force microscope on top of a custom inverted microscope design. The instrument has the ability to image in ambient conditions with optical resolutions on the order of tens of nanometers in the near field. A single low-cost computer controls the microscope with a field programmable gate array data acquisition card. High spatial resolution imaging is achieved with an inexpensive CW multiphoton excitation source, using an apertureless probe and simplified optical pathways. The high-resolution, combined with high collection efficiency and single-molecule sensitive optical capabilities of the microscope, are demonstrated with a low-cost CW laser source as well as a mode-locked laser source.

Field programmable gate array based reconfigurable scanning probe/optical microscope

The increasing popularity of nanometrology and nanospectroscopy has pushed researchers to develop complex new analytical systems. This paper describes the development of a platform on which to build a microscopy tool that will allow for flexibility of customization to suit research needs. The novelty of the described system lies in its versatility of capabilities. So far, one version of this microscope has allowed for successful near-field and far-field fluorescence imaging with single molecule detection sensitivity. This system is easily adapted for reflection, polarization (Kerr magneto-optical (MO)), Raman, super-resolution techniques, and other novel scanning probe imaging and spectroscopic designs. While collecting a variety of forms of optical images, the system can simultaneously monitor topographic information of a sample with an integrated tuning fork based shear force system. The instrument has the ability to image at room temperature and atmospheric pressure or under liquid. The core of the design is a field programmable gate array (FPGA) data acquisition card and a single, low cost computer to control the microscope with analog control circuitry using off-the-shelf available components. A detailed description of electronics, mechanical requirements, and software algorithms as well as examples of some different forms of the microscope developed so far are discussed.

Tip-enhanced probe design for nanometrology

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 spatial optical resolution better than 100 nm. These original near-field probes utilized a coating of aluminum on the sidewalls to achieve field confinement. The fabrication process had problems with irreproducible coatings (leading to blockage or leakage of 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 topographic and optical spatial resolution. This technique has been termed tip enhanced near-field scanning optical microscopy (TENOM). Although this technique overcomes many of the issues with using fibers, it introduces other issues. This work will cover how one overcome some of the issues with metal probes as well as presenting show our latest results.

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

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.

Technical Considerations for Improving Near-Field Enhancement Optical Microscopy

Tip enhanced near-field optical microscope probes are used to image spectroscopic samples with special resolutions below the diffraction limit [1]. Transmission electron microscopes (TEM) play a major role in material development in order to elucidate structural information on a nanometer scale. However large samples and electron conduction experiments within a TEM can be very challenging. With spectroscopic techniques such as Raman or Fluorescence one also has the ability to gain information on structure, but typically on the level of the diffraction limit (λ/2). We developed a nonlinear tip enhanced method of utilizing field enhancement in order to image on the levels far below the diffraction limit [2]. Many factors must be matched perfectly to achieve a high level of field enhancement; one particular important aspect of the field enhancement process involves a well designed probe tip. The proper fabrication of this tip requires the use of a focused ion beam (FIB) system as well as a finite difference time domain (FDTD) modeling.