Editing Confocal microscopy (section)

== Techniques used for horizontal scanning ==
{{refimprove section|date = October 2024}}
[[File:Diatom chain.jpg|thumb|upright=2| This projection of multiple confocal images, taken at the [[European Molecular Biology Laboratory|EMBL]] light microscopy facility, shows a group of [[diatom]]s with cyan cell walls, red chloroplasts, blue DNA, and green membranes and organelles]]

Four types of confocal microscopes are commercially available:

'''Confocal laser scanning microscopes''' use multiple mirrors (typically 2 or 3 scanning linearly along the x- and the y- axes) to scan the laser across the sample and "descan" the image across a fixed pinhole and detector. This process is usually slow and does not work for live imaging, but can be useful to create high-resolution representative images of [[Fixation (histology)|fixed]] samples.

'''Spinning-disk''' ([[Nipkow disk]]) confocal microscopes use a series of moving pinholes on a disc to scan spots of light. Since a series of pinholes scans an area in parallel, each pinhole is allowed to hover over a specific area for a longer amount of time thereby reducing the excitation energy needed to illuminate a sample when compared to laser scanning microscopes. Decreased excitation energy reduces [[phototoxicity]] and [[photobleaching]] of a sample often making it the preferred system for imaging live cells or organisms.

'''Microlens enhanced''' or '''dual spinning-disk''' confocal microscopes work under the same principles as spinning-disk confocal microscopes except a second spinning-disk containing micro-lenses is placed before the spinning-disk containing the pinholes. Every pinhole has an associated microlens. The micro-lenses act to capture a broad band of light and focus it into each pinhole significantly increasing the amount of light directed into each pinhole and reducing the amount of light blocked by the spinning-disk. Microlens enhanced confocal microscopes are therefore significantly more sensitive than standard spinning-disk systems. [[Yokogawa Electric]] invented this technology in 1992.<ref>{{cite patent|country=US|number=5162941|pubdate=1992-11-10|title=Confocal microscope|assign1=[[Wayne_State_University|The Board of Governors of Wayne State University]]|inventor1-last=Favro|inventor1-first=Lawrence D.|inventor2-last=Thomas|inventor2-first=Robert L.|inventor3-last=Kuo|inventor3-first=Pao-Kuang|inventor4-last=Chen|inventor4-first=Li}}</ref>

'''Programmable array microscopes (PAM)''' use an electronically controlled [[spatial light modulator]] (SLM) that produces a set of moving pinholes. The SLM is a device containing an array of pixels with some property ([[Opacity (optics)|opacity]], [[reflectivity]] or [[optical rotation]]) of the individual pixels that can be adjusted electronically. The SLM contains [[microelectromechanical systems|microelectromechanical mirror]]s or [[liquid crystal]] components. The image is usually acquired by a [[charge-coupled device]] (CCD) camera.

Each of these classes of confocal microscope have particular advantages and disadvantages. Most systems are either optimized for recording speed (i.e. video capture) or high spatial resolution. Confocal laser scanning microscopes can have a programmable sampling density and very high resolutions while Nipkow and PAM use a fixed sampling density defined by the camera's resolution. Imaging [[frame rate]]s are typically slower for single point laser scanning systems than spinning-disk or PAM systems. Commercial spinning-disk confocal microscopes achieve frame rates of over 50 per second<ref name="Nanofocus">{{cite web | title=Data Sheet of NanoFocus ''µsurf'' spinning-disk confocal white light microscope | url=http://www.nanofocus.com/products/usurf/usurf-explorer/ | access-date=2013-08-14 | archive-url=https://web.archive.org/web/20140120120344/http://www.nanofocus.com/products/usurf/usurf-explorer/ | archive-date=2014-01-20 | url-status=dead }}</ref> – a desirable feature for dynamic observations such as live cell imaging.

In practice, Nipkow and PAM allow multiple pinholes scanning the same area in parallel<ref name="Sensofar">{{cite web | title=Data Sheet of Sensofar 'PLu neox' Dual technology sensor head combining confocal and Interferometry techniques, as well as Spectroscopic Reflectometry| url=http://www.sensofar.com/products/products_neox.html}}</ref> as long as the pinholes are sufficiently far apart.

Cutting-edge development of confocal laser scanning microscopy now allows better than standard video rate (60 frames per second) imaging by using multiple microelectromechanical scanning mirrors.

Confocal [[X-ray fluorescence]] imaging is a newer technique that allows control over depth, in addition to horizontal and vertical aiming, for example, when analyzing buried layers in a painting.<ref>{{cite journal | title=Confocal X-ray Fluorescence Imaging and XRF Tomography for Three Dimensional Trace Element Microanalysis | author=Vincze L | journal = Microscopy and Microanalysis | volume=11 | issue=Supplement 2 | year=2005 | doi=10.1017/S1431927605503167 | doi-access=free }}</ref>