The objective lens is the most important optical component of a microscope, which uses light to create the first image of the object being tested. Therefore, it directly affects and affects the quality of the image and various optical technical parameters, and is the primary standard for measuring the quality of a microscope.

Normally, any frequency of electromagnetic radiation or light cannot pass through holes smaller than the radiation's wavelength. A cook can see food in a microwave oven because visible light waves are smaller than the holes in the oven door's grating. But microwaves, with wavelengths larger than the holes, cannot escape to injure the cook.

That shows high-frequency terahertz signals can be switched on and off to carry data in the digital code of ones and zeroes, and that it someday may be possible to build superfast switches to carry terahertz data at terahertz speeds. That is 1,000 times faster than gigahertz fiber optic lines that carry data as near-infrared and visible light, and 10,000 times faster than microwaves that carry cordless and cell phone conversations.

To visualize their discovery, imagine shining a flashlight through a kitchen colander, and that holes make up 20 percent of the colander's surface. Only 20 percent of the light will pass through the colander. But when the Utah researchers shined far-infrared radiation through holes punched in a thin steel foil or film, almost all of the radiation passed through the film if the holes were arranged in semi-regular patterns known as "quasicrystals" or "quasicrystal approximates."

Objectiveback focal plane

The new study was conducted by Nahata and principal author Z. Valy Vardeny, a distinguished professor of physics at the University of Utah, along with Tatsunosuke Matsui, a postdoctoral researcher in physics, and Amit Agrawal, a doctoral student in electrical and computer engineering.

Microscopic objective is an aberration cancelling system. This means that for a pair of conjugate points on the axis, when the aberration is eliminated and the sine condition is achieved, each objective only has two such aberration cancellations. Therefore, any change in the calculated position of the object and image results in an increase in aberration. On the rotator installed at the lower end of the lens barrel, there are generally 3-4 objective lenses, among which the shortest one engraved with the "10 ×" symbol is a low magnification lens, the longer one engraved with the "40 ×" symbol is a high magnification lens, and the longest one engraved with the "100 ×" symbol is an oil lens. In addition, a circle of different colors is often added to the high magnification lens and the oil lens to show the difference.

Objective lens

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Until now, such efficient transmission of far-infrared light was achieved only when crystal patterns were used, but unwanted frequencies also were transmitted. In the new study, the researchers could select the wavelength of far-infrared light transmitted through the holes and, by tilting the films, they could switch the transmission on and off.

"We found a way to manipulate a form of infrared radiation that is not now used for communications so that, in the future, it may be possible to use it for high-speed, short-range communication between computers and other devices," says Ajay Nahata, an associate professor of electrical and computer engineering.

The study in the March 29, 2007, issue of the journal Nature also shows the feasibility of building devices that emit and detect specific frequencies of far-infrared light -- also known as terahertz radiation -- to spot chemical or biological warfare agents such as anthrax bacteria and to make images of packages or people to find concealed weapons and plastic explosives, Nahata adds.

Sound, like light and heat, can be made to focus. What is spoken at normal volume into the focal point of the reflector can be picked up in a second ...

Modern technology uses many frequencies of electromagnetic radiation for communication, including radio waves, TV signals, microwaves and visible light. Now, a University of Utah study shows how far-infrared light -- the last unexploited part of the electromagnetic spectrum -- could be harnessed to build much faster wireless communications and to detect concealed explosives and biological weapons.

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(Crystals have repeating patterns over a short distance, such as the ordered pattern of carbon atoms in diamond. Quasicrystals have less structure, but display a pattern over a larger area. Quasicrystal approximates -- a term coined by Vardeny and Nahata -- also have patterns, but less so than quasicrystals. Crystals, quasicrystals and approximates all can bend or break up light or other electromagnetic waves.)

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Near-infrared radiation and some visible light now are used for fiber optic phone and data lines. But terahertz or far-infrared radiation -- on the spectrum between microwaves and mid-infrared radiation -- is not now used for communication.

The spectrum of electromagnetic radiation ranges from short to long wavelengths (or from high to low frequency): gamma rays, X-rays, ultraviolet rays, visible light (violet, blue, green, yellow, orange and red), infrared rays (including radiant heat), microwaves, FM radio waves, television, short wave and AM radio.

Aligning focus is not only used in microscopy, but also when observing images clearly with a certain magnification objective, and when switching to another magnification objective, the imaging should be basically clear, and the center deviation of the image should also be within a certain range, that is, the degree of axis alignment. The quality of confocal performance and the degree of alignment are important indicators of microscope quality, which are related to the quality of the objective lens itself and the accuracy of the objective lens converter.

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The aberration related to a wide beam of light is spherical aberration, coma aberration, and positional chromatic aberration; The aberrations related to the field of view are astigmatism, field curvature, distortion, and magnification aberration.

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The study used stainless steel film about three-quarters the thickness of a human hair. Different patterns of holes were punched in the film. The holes were one-quarter to one-half millimeter in diameter (about one-hundredth to one-fiftieth of an inch). That is smaller than the roughly 1-millimeter wavelength of far-infrared light.

The study was funded as part of a three-year, $250,000 grant from the U.S. Army Research Office and by $100,000 from the Synergy program, operated by the University of Utah's vice president for research to promote interdisciplinary research.

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Microscopic objective and eyepiece differ in their involvement in imaging. Objective is the most complex and important part of a microscope, operating in a wide beam of light (with a large aperture), but these beams have a smaller inclination angle to the optical axis (with a smaller field of view); The eyepiece works in a narrow beam of light, but its inclination angle is large (with a large field of view). When calculating the objective and eyepiece, there is a significant difference in eliminating aberration.

No one has built terahertz switches, but Nahata says the new study shows it is possible to use terahertz radiation to carry data and thus may be possible to create terahertz-speed switches for superfast wireless communication over short distances, such as between a cellular phone and headsets, a wireless mouse and a computer, and a PDA (personal digital assistant) and a computer.

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Study co-author Agrawal used a computer to design patterns of holes that he expected would allow "resonance" or "anomalous transmission," meaning all the far-infrared light passes through the holes in the metal films. The researchers projected terahertz or far-infrared light onto the metal films with punched patterns. They found certain frequencies of the far-infrared radiation were completely transmitted through the films with crystal, quasicrystal and quasicrystal-approximate patterns -- even though the terahertz radiation has wavelengths larger than the holes.

Microscope

The structure of the objective lens is complex and precise, usually composed of a combination of lenses, with each lens spaced at a certain distance to reduce the difference. Each group of lenses is made by bonding one or several lenses with different materials and parameters. There are many specific requirements for the objective lens, such as axial alignment and alignment. The modern microscope objective has reached a high level of perfection, with its numerical aperture approaching its limit, and the difference between the resolution at the center of the field of view and the theoretical value is negligible. However, the possibility of further increasing the field of view of the microscope objective and improving the imaging quality of the field edge still exists, and this research work is still ongoing to this day.

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Vardeny adds: "Industry is starving for more electromagnetic frequencies," yet terahertz frequencies are unexplored. They are too high for electronics and there are technical obstacles in generating, manipulating and detecting terahertz radiation.

"Terahertz is a new region of the spectrum for communications" because the rest of the spectrum is crowded with communication and broadcasting signals, says Nahata.

Vardeny says such efficient transmission occurs because the far-infrared light not only goes through the holes, but also moves electrons in the metal film, generating "surface plasma waves" that launch all the far-infrared radiation through the holes.

For electromagnetic radiation to transmit data, the signal must be turned on and off to rapidly create the binary code of ones and zeroes. Modern optical and electronic switches cannot do that fast enough to handle signals with terahertz frequencies (1,000 billion waves per second), but can handle gigahertz signals (1 billion waves per second).