Scanning optical microscopy

Microscopy using a scanning approach is reviewed, with numerous references to previous work, as at 1987, before the confocal laser scanning microscope was widely available commercially. The advantages of microscope imaging using a scanning technique are described. The principles of confocal microscopy are introduced. Use of Bessel beam illumination in a confocal microscope is discussed. This combination can increase spatial resolution while retaining some confocal optical sectioning. The advantages of imaging using a scanning method with a point source are detailed. For example, differential phase contrast may be performed to obtain phase information. Use of a point source allows different types of spectroscopy to be performed in a spatially resolved fashion. An advantage of point-source systems for such applications is that imaging, performed with the incident radiation, is separated from wavelength selection and analysis of the emitted radiation, thus simplifying system design and resulting in superior performance. Use of a point source to excite carriers in a semiconducting sample allows the electronic properties of materials and devices to be investigated. Advantages of object scanning, rather than beam scanning, are discussed. Advantages of using a laser source are described, including the use of the heterodyne technique as a synthetic confocal pinhole, and nonlinear microscopy such as two-photon fluorescence and CARS (coherent anti-Stokes Raman spectroscopy). It should be noted that 1987, as well as being before commercial confocal microscopes were widely available, was before the special properties of Bessel beams were appreciated, and before two photon fluorescence microscopy was first experimentally demonstrated.