Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye. There are three well-known branches of microscopy: optical, electron, and scanning probe microscopy, along with the emerging field of X-ray microscopy.
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Light is a type of electromagnetic radiation, and other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.
Holography is a technique that enables a wavefront to be recorded and later reconstructed. It is best known as a method of generating three-dimensional images, and has a wide range of other uses, including data storage, microscopy, and interferometry. In principle, it is possible to make a hologram for any type of wave.
Stereoscopy is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word stereoscopy derives from Greek στερεός (stereos) 'firm, solid', and σκοπέω (skopeō) 'to look, to see'. Any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of stereo images which could be viewed using a stereoscope.
Security printing is the field of the printing industry that deals with the printing of items such as banknotes, cheques, passports, tamper-evident labels, security tapes, product authentication, stock certificates, postage stamps and identity cards. The main goal of security printing is to prevent forgery, tampering, or counterfeiting. More recently many of the techniques used to protect these high-value documents have become more available to commercial printers, whether they are using the more traditional offset and flexographic presses or the newer digital platforms. Businesses are protecting their lesser-value documents such as transcripts, coupons and prescription pads by incorporating some of the features listed below to ensure that they cannot be forged or that alteration of the data cannot occur undetected.
A 3D display is a display device capable of conveying depth to the viewer. Many 3D displays are stereoscopic displays, which produce a basic 3D effect by means of stereopsis, but can cause eye strain and visual fatigue. Newer 3D displays such as holographic and light field displays produce a more realistic 3D effect by combining stereopsis and accurate focal length for the displayed content. Newer 3D displays in this manner cause less visual fatigue than classical stereoscopic displays.
Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser scanning confocal microscopy (LSCM), is an optical imaging technique for increasing optical resolution and contrast of a micrograph by means of using a spatial pinhole to block out-of-focus light in image formation. Capturing multiple two-dimensional images at different depths in a sample enables the reconstruction of three-dimensional structures within an object. This technique is used extensively in the scientific and industrial communities and typical applications are in life sciences, semiconductor inspection and materials science.
Photoacoustic imaging or optoacoustic imaging is a biomedical imaging modality based on the photoacoustic effect. Non-ionizing laser pulses are delivered into biological tissues and part of the energy will be absorbed and converted into heat, leading to transient thermoelastic expansion and thus wideband ultrasonic emission. The generated ultrasonic waves are detected by ultrasonic transducers and then analyzed to produce images. It is known that optical absorption is closely associated with physiological properties, such as hemoglobin concentration and oxygen saturation. As a result, the magnitude of the ultrasonic emission, which is proportional to the local energy deposition, reveals physiologically specific optical absorption contrast. 2D or 3D images of the targeted areas can then be formed.
Holographic data storage is a potential technology in the area of high-capacity data storage. While magnetic and optical data storage devices rely on individual bits being stored as distinct magnetic or optical changes on the surface of the recording medium, holographic data storage records information throughout the volume of the medium and is capable of recording multiple images in the same area utilizing light at different angles.
A parallax barrier is a device placed in front of an image source, such as a liquid crystal display, to allow it to show a stereoscopic or multiscopic image without the need for the viewer to wear 3D glasses. Placed in front of the normal LCD, it consists of an opaque layer with a series of precisely spaced slits, allowing each eye to see a different set of pixels, so creating a sense of depth through parallax in an effect similar to what lenticular printing produces for printed products and lenticular lenses for other displays. A disadvantage of the method in its simplest form is that the viewer must be positioned in a well-defined spot to experience the 3D effect. However, recent versions of this technology have addressed this issue by using face-tracking to adjust the relative positions of the pixels and barrier slits according to the location of the user's eyes, allowing the user to experience the 3D from a wide range of positions. Another disadvantage is that the horizontal pixel count viewable by each eye is halved, reducing the overall horizontal resolution of the image.
Terahertz tomography is a class of tomography where sectional imaging is done by terahertz radiation. Terahertz radiation is electromagnetic radiation with a frequency between 0.1 and 10 THz; it falls between radio waves and light waves on the spectrum; it encompasses portions of the millimeter waves and infrared wavelengths. Because of its high frequency and short wavelength, terahertz wave has a high signal-to-noise ratio in the time domain spectrum. Tomography using terahertz radiation can image samples that are opaque in the visible and near-infrared regions of the spectrum. Terahertz wave three-dimensional (3D) imaging technology has developed rapidly since its first successful application in 1997, and a series of new 3D imaging technologies have been proposed successively.
Computer-generated holography (CGH) is a technique that uses computer algorithms to generate holograms. It involves generating holographic interference patterns. A computer-generated hologram can be displayed on a dynamic holographic display, or it can be printed onto a mask or film using lithography. When a hologram is printed onto a mask or film, it is then illuminated by a coherent light source to display the holographic images.
3D optical data storage is any form of optical data storage in which information can be recorded or read with three-dimensional resolution.
A laser beam profiler captures, displays, and records the spatial intensity profile of a laser beam at a particular plane transverse to the beam propagation path. Since there are many types of lasers—ultraviolet, visible, infrared, continuous wave, pulsed, high-power, low-power—there is an assortment of instrumentation for measuring laser beam profiles. No single laser beam profiler can handle every power level, pulse duration, repetition rate, wavelength, and beam size.
A holographic display is a type of 3D display that utilizes light diffraction to display a three-dimensional image to the viewer. Holographic displays are distinguished from other forms of 3D displays in that they do not require the viewer to wear any special glasses or use external equipment to be able to see the image, and do not cause the vergence-accommodation conflict.
Digital holographic microscopy (DHM) is digital holography applied to microscopy. Digital holographic microscopy distinguishes itself from other microscopy methods by not recording the projected image of the object. Instead, the light wave front information originating from the object is digitally recorded as a hologram, from which a computer calculates the object image by using a numerical reconstruction algorithm. The image forming lens in traditional microscopy is thus replaced by a computer algorithm. Other closely related microscopy methods to digital holographic microscopy are interferometric microscopy, optical coherence tomography and diffraction phase microscopy. Common to all methods is the use of a reference wave front to obtain amplitude (intensity) and phase information. The information is recorded on a digital image sensor or by a photodetector from which an image of the object is created (reconstructed) by a computer. In traditional microscopy, which do not use a reference wave front, only intensity information is recorded and essential information about the object is lost.
Holographic optical element (HOE) is an optical component (mirror, lens, directional diffuser, etc.) that produces holographic images using principles of diffraction. HOE is most commonly used in transparent displays, 3D imaging, and certain scanning technologies. The shape and structure of the HOE is dependent on the piece of hardware it is needed for, and the coupled wave theory is a common tool used to calculate the diffraction efficiency or grating volume that helps with the design of an HOE. Early concepts of the holographic optical element can be traced back to the mid-1900s, coinciding closely with the start of holography coined by Dennis Gabor. The application of 3D visualization and displays is ultimately the end goal of the HOE; however, the cost and complexity of the device has hindered the rapid development toward full 3D visualization. The HOE is also used in the development of augmented reality(AR) by companies such as Google with Google Glass or in research universities that look to utilize HOEs to create 3D imaging without the use of eye-wear or head-wear. Furthermore, the ability of the HOE to allow for transparent displays have caught the attention of the US military in its development of better head-up displays (HUD) which is used to display crucial information for aircraft pilots.
An optical variable device or optically variable device (OVD) is an iridescent or non-iridescent security feature that exhibits different information, such as movement or colour changes, depending on the viewing and/or lighting conditions. The particular changes of appearance when rotating and tilting are reversible, predictable and reproducible. OVDs cannot be photocopied or scanned, nor can they be accurately replicated or reproduced. OVDs are often used as security devices and anti-counterfeiting measures on banknotes, government-issued identification documents, or credit cards. OVDs can be created through a combination of printing and embossing.
Optical holography is a technique which enables an optical wavefront to be recorded and later re-constructed. Holography is best known as a method of generating three-dimensional images but it also has a wide range of other applications.
A diffractive optically variable image device (DOVID) is a type of optical variable device; a security feature based on visual effects created by diffraction. DOVIDs are incorporated in government-issued documents of value to increase their counterfeit resistance. Brand protection is another application of DOVIDs. DOVIDs contain micro- or nanostructures in the form of diffractive gratings. Due to these structures, they exhibit optically variable effects such as dynamic chromatic, holographic, and kinematic effects, two- or three-dimensional images or color-changing effects, which ideally are easily recognized, but are difficult to reproduce. Well known examples of DOVIDs are holograms such as 2D or 3D or 2D/3D holograms based on mask illumination, dot matrix or e-beam origination technology and Kinegrams.
