Short Focal Length Lens Research Articles

Theory and experiment of two-photon $lquot$direct$rquot$ interference for type-II spontaneous parametric down-conversion with an ultrafast pulse laser pump

Fourth-order spatial interference of entangled photon pairs generated in the process of spontaneous parametric down-conversion pumped by a femtosecond pulse laser has been performed for the first time. In theory, it takes into account the transverse correlation between the two photons and is used to calculate the dependence of the visibility of the interference pattern obtained in Young’s double-slit experiment. In this experiment, a short focal length lens and two narrow band interference filters were adopted to eliminate the effects of the broadband pump laser and improve the visibility of the interference pattern under the condition of nearly collinear light and degenerate phase matching.

Tomographic imaging of foam

The morphology of three-dimensional foams is of interest to physicists, engineers, and mathematicians. It is desired to image the 3-dimensional structure of the foam. Many different techniques have been used to image the foam, including magnetic resonance imaging, and short-focal length lenses. We use a camera and apply tomographic algorithms to accurately image a set of bubbles. We correct for the distortion of a curved plexiglas container using ray-tracing.

7071 Endoscopy without air insufflation.

Background: Most gastrointestinal endoscopy is performed with inflation with air to distend the viscus. For some applications and the development of new endoscopic methods airless endoscopy is likely to become important. Little is known about the efficacy and limitations of airless gastrointestinal endoscopy. Methods: A variety of experimental airless endoscopes were constructed. These included: 1. short focal length lens of a) curved shape, b) conical shape were mounted on the tip. 2.Wire cage fronted endoscope. 3. Transparent balloon fronted airless endoscope: balloon filled with a) clear gas, b) clear water. 4.Water immersed endoscope. Lighting was transmitted either through the lens, cage, balloon, water or by mounting the light source coaxially adjacent to the lens or optics. These experimental endoscopies were tested in post mortem and live oesophagus, stomach, small bowel and colon. Results: Reasonably good quality video images were obtained using all these experimental endoscopes in airless endoscopy of the GI tract. Short focal length lenses required careful focussing to optimise image quality. Reflections from the cage were diminished by using a non-reflecting paint. Mucus adherence was occasionally a problem but mucus was often wiped off as the endoscope moved. Movement of the endoscope allowed assessment of whether the mucus was adherent to the lens or tissue. Gas and water filled transparent balloons gave moderately good views but were unreliable and not robust. Tissue laying on the lenses sometimes impaired the view although this was less of a problem in live supported bowel. Practically, it was difficult to maintain water in the GI tract for immersion endoscopy. Curved shape short focal length lenses gave the best images overall. Conclusion: Despite some limitations airless endoscopy was able to give high quality images of the small bowel and oesophagus. Better than expected views could also be obtained in the stomach and large bowel but were limited by the diameter of the viscus. Problems with illumination with internal reflection were encountered and resolved. Background: Most gastrointestinal endoscopy is performed with inflation with air to distend the viscus. For some applications and the development of new endoscopic methods airless endoscopy is likely to become important. Little is known about the efficacy and limitations of airless gastrointestinal endoscopy. Methods: A variety of experimental airless endoscopes were constructed. These included: 1. short focal length lens of a) curved shape, b) conical shape were mounted on the tip. 2.Wire cage fronted endoscope. 3. Transparent balloon fronted airless endoscope: balloon filled with a) clear gas, b) clear water. 4.Water immersed endoscope. Lighting was transmitted either through the lens, cage, balloon, water or by mounting the light source coaxially adjacent to the lens or optics. These experimental endoscopies were tested in post mortem and live oesophagus, stomach, small bowel and colon. Results: Reasonably good quality video images were obtained using all these experimental endoscopes in airless endoscopy of the GI tract. Short focal length lenses required careful focussing to optimise image quality. Reflections from the cage were diminished by using a non-reflecting paint. Mucus adherence was occasionally a problem but mucus was often wiped off as the endoscope moved. Movement of the endoscope allowed assessment of whether the mucus was adherent to the lens or tissue. Gas and water filled transparent balloons gave moderately good views but were unreliable and not robust. Tissue laying on the lenses sometimes impaired the view although this was less of a problem in live supported bowel. Practically, it was difficult to maintain water in the GI tract for immersion endoscopy. Curved shape short focal length lenses gave the best images overall. Conclusion: Despite some limitations airless endoscopy was able to give high quality images of the small bowel and oesophagus. Better than expected views could also be obtained in the stomach and large bowel but were limited by the diameter of the viscus. Problems with illumination with internal reflection were encountered and resolved.

4467 Wireless endoscopy.

Background: Miniaturization of electronic components might allow the development of a new type of wireless endoscopy. Advances in complementary metal oxide silicon (CMOS) technology allow high quality video images to be transmitted with much lower power consumption than with charge coupled devices (CCDs). Small bowel endoscopy is currently limited by problems of discomfort and failure to advance far into the small-bowel. Aim: To develop and test wireless capsule endoscopy. Methods: Using a CMOS imaging chip, miniature processor, white light emitting diode (LED) light source, short focal length lens, miniature transmitter and antenna powered by silver oxide batteries, a wireless capsule endoscope (Given Imaging) was constructed measuring 11 x 33 mm. Results: The video images were transmitted using a radio-frequency signal (approx. 410 MHz) at a rate of two frames per second to an array of aerials attached to the body which allowed image capture and were also used to calculate the position of the capsule in the body. The images were stored on a portable recorder carried on a belt and subsequently downloaded for analysis. The system allowed more than 5 hours of recording of images from the gastrointestinal tract. Live transmission of good quality video images were obtained for 6 hour periods in dogs. With ethical committee approval the first human volunteer studies were performed. The capsule was easily swallowed and caused no discomfort whatsoever. The capsule, propelled by peristalsis, successfully transmitted video images from the whole of the small bowel and reached the cecum in under 2 hours. The image window remained clear through out the whole of the transmissions. Trigonometric analysis of signal strength allowed continuous monitoring of anatomic endoscope position. Clear video images of the human small bowel were recorded from the pylorus to cecum. Conclusion: This study reports the development of a new type of endoscopy which for the first time allows painless endoscopic imaging of the whole of the small bowel for prolonged periods. Its development, testing and first application in man is described. Background: Miniaturization of electronic components might allow the development of a new type of wireless endoscopy. Advances in complementary metal oxide silicon (CMOS) technology allow high quality video images to be transmitted with much lower power consumption than with charge coupled devices (CCDs). Small bowel endoscopy is currently limited by problems of discomfort and failure to advance far into the small-bowel. Aim: To develop and test wireless capsule endoscopy. Methods: Using a CMOS imaging chip, miniature processor, white light emitting diode (LED) light source, short focal length lens, miniature transmitter and antenna powered by silver oxide batteries, a wireless capsule endoscope (Given Imaging) was constructed measuring 11 x 33 mm. Results: The video images were transmitted using a radio-frequency signal (approx. 410 MHz) at a rate of two frames per second to an array of aerials attached to the body which allowed image capture and were also used to calculate the position of the capsule in the body. The images were stored on a portable recorder carried on a belt and subsequently downloaded for analysis. The system allowed more than 5 hours of recording of images from the gastrointestinal tract. Live transmission of good quality video images were obtained for 6 hour periods in dogs. With ethical committee approval the first human volunteer studies were performed. The capsule was easily swallowed and caused no discomfort whatsoever. The capsule, propelled by peristalsis, successfully transmitted video images from the whole of the small bowel and reached the cecum in under 2 hours. The image window remained clear through out the whole of the transmissions. Trigonometric analysis of signal strength allowed continuous monitoring of anatomic endoscope position. Clear video images of the human small bowel were recorded from the pylorus to cecum. Conclusion: This study reports the development of a new type of endoscopy which for the first time allows painless endoscopic imaging of the whole of the small bowel for prolonged periods. Its development, testing and first application in man is described.

Reflective grating interferometer for measuring the focal length of a lens by digital moiré effect

A new technique is proposed, based on digital moiré effects, for measuring the focal length of a lens. The test lens is illuminated by a variable pitch interference pattern produced by an interferometer which makes use of a reflective diffraction grating. Moiré fringes are generated by digitally adding the magnified images produced by the lens on the original interference pattern. The focal length of the lens can be determined by counting the number of moiré fringes. This technique is suitable for measuring both long and short focal length lenses. The focal lengths of both positive and negative lenses were experimentally measured.

The role of field-emission SEM in biology in the 21st century

To predict how field emission SEM (FESEM) will be applied to biological investigation in the transition to the 21st century requires some recapitulation of how dramatically changes have occurred in the last half of the 20th century. Although, initially developed in the 1930s by Knoll and later, von Ardenne, the commercial production of instruments in the 1960s was brought about chiefly due to contributions in secondary (SE) and backscatter (BS) electron detector design from the Cambridge group led by Oatley. Continued instrumentation development over the next three decades led to numerous improvements, i.e. new lanthanum hexaboride emitters, advances in specimen preparation, and was culminated in the late 1980s, by the commercial development of a high resolution SEM possessing short focal length lenses together with a cold field emission electron gun, resulting in electron probes with diameters of 3nm at 1.5 keV and 0.5nm at 30 keV.From the perspective of a biologist using FESEM for both structural and immunocytochemical studies, I would like to suggest changes in both instrumentation and methodology that would be of great practical value today, and would hopefully be surpassed by standard features in new instruments available at the turn of the century.

High-Resolution stereo imaging of frozen-hydrated biological samples by Cryo-SEM

The introduction of cryo-techniques to SEM allowed the biologist to examine frozen-hydrated specimens at low temperatures on a cryo-stage in the SEM. The problems associated with conventional cryo-SEM included ice crystal formation caused by low cooling rate, poor resolution, limited magnification (<10 kX), specimen contamination, beam damage and charging. Recently, the effectiveness of this technique has been improved because a number of new cryo-preparation instruments have become commercially available. The high pressure freezer permits cryo-fixation of large biological specimens (diameter up to about 1mm) without ice crystal artifacts. Cryo-coating units permit fine-grain metal coating of fractured specimens. In addition, microscopes combining a short focal length lens with a fieldemission (FE) source permit high resolution imaging at low beam voltage (Vo). However, for high resolution cryo-SEM, especially for producing stereo pictures, the artifacts caused by electron irradiation remain a critical problem.The purpose of this work was to evaluate the extent to which beam damage varies with Vo, and to determine the most appropriate Vo for stereo imaging.

Low-voltage high-resolution SEM of biological samples

There are three reasons for the recent upsurge of interest in using the SEM at a beam voltage (Vo) around 1 kV (LVSEM). The most common one arises from applications in the semiconductor industry and emphasizes the reduction in charging artifacts and in subsurface beam damage obtainable at low VoThe second reason derives from the belief that, given instrumentation capable of producing a sufficiently small probe, the increased contrast in the topographic component of the secondary electron signal will permit an important improvement in real topographic spatial resolution.The third reason is that recent developments in instrumentation have shown that by coupling a cold field-emission source with a short focal length lens, it is indeed possible to obtain small probe diameters at low voltage. Although they are considerably larger than probes obtained at higher voltage, they are nonetheless smaller than the smallest topographical feature yet imaged in the secondary electron (SE) mode. (Fig 1)

Scanning electron beam method for examining surfaces in a short focal length magnetic lens

A new scanning electron microscope method for examining the surface of bulk samples is described that uses a short focal length (1 mm), low aberration, magnetic electron lens. The minimum beam size produced by the lens is 2–3 times smaller than the minimum beam size in a conventional secondary electron scanning electron microscope. The new method, in which backscattered electrons are detected with silicon diodes located inside the pole-piece gap of the lens, allows large area samples such as silicon integrated circuit wafers to be examined, despite the constricted sample region of the lens. The new method also makes it possible to use this type of short focal length lens for electron beam lithography, because it allows alignment marks on the wafers to be detected while the wafers are immersed in the lens. A 1 mm focal length lens produces a beam current density that is more than 20 times higher than that produced by the longer focal length lenses used in conventional electron beam lithography systems.

Scanning Eye Movements in A Heteropod Mollusc

ABSTRACT The eyes of the heteropod molluscs are unusually large and complex, compared with those of other gastropods (Hesse, 1900). They have a basic design not unlike fish eyes, with a large spherical lens of short focal length that forms an image on a retina of highly ciliated photoreceptors (Dilly, 1969). Perhaps the strangest feature of the eyes is the shape of the retina. It is not a hemispherical cup as in fish, cephalopods and alciopid worms, but a long narrow ribbon only a few receptors wide (6 in Pterotrachea coronata, only 3 in Oxygyrus). The ribbon is several hundred receptors long and in some species it is straight whilst in others it is curved into a horseshoe configuration. In either case this means that the field of view of the eye is a narrow strip of space a few degrees high and 80–180° long. Most of the surroundings are therefore not seen by the animal at any given time. In this paper I show that the problem of the narrow field of view is solved in one heteropod species at least by systematic scanning movements of the eyes, in which each retina ‘sweeps’ through a 90° arc.

Development Mechanism of Laser Spark in High Pressure Argon Gases

High pressure argon gas up to 70 atm. was irradiated by a Q-switched ruby laser. The dynamical behavior of the laser induced plasma was observed, and the development mechanism of the plasma towards the focusing lens was studied. Two different development mechanisms could be observed under the same experimental conditions; a breakdown wave and a radiation supported shock wave. At high pressure with a lens of long focal length, only a breakdown wave could be obtained, while at low pressure with a lens of short focal length, a radiation supported shock wave was predominant.

Optical Digital Recording

An optical information storage system based on direct binary bit imaging is described. The recorded bit diameters are about one micron, and a density of about 5 x 107 bits/cm2 has been demonstrated. Color television program material has been encoded in a differential PCM format, recorded and played back in real time. The system uses a stationary rec-ord, and a scanned optical aperture that is smaller than usual for these bit densities. The present work has been directed toward a low cost video player/recorder for home use. Optical digital recording is a technique for high density storage of binary information. Each information bit is stored as a discrete, direct image in contrast to the more usual holo graphic transform images. By the use of short focal length lenses and a mechanical scanner a data density of 5 x 1 07 bits per square centimeter and data rates of 3 x 107 bits per second have been demonstrated. For comparison, the information on a typical reel of computer tape (2600 ft at 1600 BPI) could be stored in roughly one square inch on this optical record. This technology was developed for several applications. The first, consumer prerecorded TV, is reported here. This choice was made because a video record would require the highest densities and the simplest, lowest cost player of all the applications considered. In effect, the results of this work would help define those applications that are commercially feasible. Color TV material has been successfully re corded in real time and played back with basically no degredation of the signal. The luminance bandwidth is 3.5 MHz plus the .6 MHz color components. The playback device is simple and probably inexpensive in quantity. Holographic data storage techniques were not used for this work because the inherent advantages of holographic systems can be had with properly designed direct bit systems, while the playback equipment for direct systems appears less expensive. Scanner In contrast to much previous work, the record element is held stationary during re

Factors affecting the detection of slope instability with air photographs in an area near Sevenoaks, Kent

Summary Twenty-six sets of air photographs were used to test the best photographic conditions for detecting landslips, mainly old periglacial solifluction movement, along a ten mile stretch of sloping ground. A total of 141 old landslip features were detected and many varied in clarity on the different photographs, some being hard or impossible to detect on foot without the aid of air photographs. The repeated images of the same landslips on different sets of photographs produced a total of 2 715 photo-features for statistical studies. Analysis of the results showed that the best technical photographic conditions for detecting such features are the use of infra red colour film, stereoscopic photography with a short focal length lens, a nominal photographic scale of about 1:5 000, and a sun angle that casts local but not very extensive shadows. It is considered that automatic dodging can both enhance and suppress vital information on images, and that the best seasons for photography are likely to be spring and late summer to early autumn.

Portable Multi-Media Rear-Screen Presentations

A portable multi-media rear-screen presentation was created for promotional purposes and has been shown to potential customers at luncheons serving about 250 guests. A 74- by 14-ft (22.5- by 4.3-m) rear-projection screen was constructed, to display 14 images of different sizes and shapes, projected by 16 Carousel slide projectors and one 16mm arc projector. The 14-minute presentation was programed on four Spindler & Sauppe Quadra Ques, used in tandem with a 4-track TEAC stereo tape unit. Three Spindler dissolve units and a variety of short focal length lenses were used. A special portable scaffolding was built to hold the series of projection units. The equipment was transported throughout the United States in a Dodge van and was set up in six hours by two projectionists.

A Spherical-Aberration Corrector Using Electrontransparent Conducting Foils

One of the problems associated with building any aberration-corrected electron microscope objective lens lies in the difficulty of obtaining a sufficiently short focal length. A number of systems have focal lengths in the 1cm. range, and these are more suitable for microprobe work. If the focal length can be made short enough, the chromatic aberration probably does not need to be corrected, and the design is much simplified. A corrector device which can be used with a conventional magnetic objective lens of short focal length (Fig. 1) must either have dimensions comparable to the bore and gap of that lens, or have very large magnetic or electric field gradients. A successful approach theoretically has been to use quadrupoleoctopole corrector units, although these suffer from very large fifth order aberrations and a limited field of view.

A 100 KV Transmission Scanning Microscope

A 100 kv transmission scanning microscope is now being constructed which should have a point resolution of 2.5 to 3 Å. The design of this microscope is similar to the design of our existing 30 kv 5 Å microscope, but there are several significant changes which are based upon some difficulties and sources of inflexibility of that microscope.A field emission electron gun of our usual design will be used as the source of electrons, the only difference being that the spacing between the anodes has been increased from 2 to 3 cm. The electron beam will then pass through a condenser lens which will produce a parallel beam of electrons. This parallel beam will then be focused onto the specimen by means of a short focal length lens (approximately 1 mm focal length). The reason for using a condenser lens to produce the parallel beam of electrons is that in the future a quadrupole-octupole correction system will be installed in this section of the microscope in order to attempt to correct the spherical aberrations of the objective lens and thereby improve its resolution.

A Combined Conventional and Scanning Electron Microscope

In electron optical instrumentation, it would be generally desirable to have a lens with a short focal length. Both spherical and chromatical aberration decreases with focal length and this will result in a better resolution and image brightness. This consideration has been taken into account in the design of conventional electron microscopes, and the focal length of the objective lens of such instrumentation ranges from a few millimeters to a fraction of a millimeter. A short focal length lens requires that the specimen be located in a magnetic field i.e., within the pole piece gap. This results in (a) a limitation in the size of the specimen and (b) a restriction, to use the microscope to nonmagnetic specimens only.

Multiple Collinear Laser-produced Sparks in Gases

THERE has been much interest in the recently reported1–4 ionization and breakdown in gases induced by the focused output (∼ 20 MW) of Q-switched lasers. A puzzling feature of the phenomenon is the occurrence5,6 of distinct collinear regions of intense ionization along the laser beam axis near the focal point of the short focal length lenses commonly used in this work. There seems to be no satisfactory explanation of the mechanism producing these quite distinct regions. Considerations based on the development of a radiation supported shock wave7 or travelling ionization waves8 seem to be more appropriate to the later stages of breakdown when the local ionized regions coalesce to form a long spark which appears to be moving. The separate regions of ionization suggest that the spatial distribution of the electric field needed for ionization and created by the focused laser beam has regions of maximum and minimum intensities along the beam axis.

Some Novel Projected Motion Picture Presentations

MANY of us remember Lyman H. Howe who toured this country for several years, with his famous travel pictures. He began before the birth of the Nickelodeon and continued to be a success for a number of years after our present movie palaces became established. Let us analyze his methods. Most of his subjects were photographed with short focal length lenses. He then brought his audience right into the scene by making his projected picture nearly large enough to fill the average stage opening. It appears that this, together with especially good projection for that time, was the greatest factor of his continued success. The above is cited merely to show that motion pictures of greatly enlarged dimensions are really nothing new.

An Accessory Lens for Observing Interference Figures of Small Mineral Grains

As long ago as i88o Bertrand' discovered that in the bubbles which are found so frequently in the Canada balsam between the mineral section and the cover-glass, there may be seen an interference figure of the mineral lying below it. The bubble acts as a lens of short focal length and takes the place of the objective, while the ocular and objective combined act as do the Bertrand lens and the ocular in the usual method of observing interference figures. Later, Schroeder van der Kolk' carried this method a step farther. He placed a drop of glycerine upon the cover-glass of the slide to be examined and stirred it rapidly with a thin rod so that it became filled with small bubbles. Over this he placed a coverglass and, between crossed nicols and with a medium-power objective, he depressed the tube a very little below the focal plane and found in each bubble a small interference figure. To avoid the necessity each time of preparing anew a glycerine foam, Schroeder van der Kolk used the following simple device: He placed a drop of Canada balsam on an object-glass and, if necessary, cooked it. After producing foam by rapid stirring, he placed a cover-glass upon it and the instrument was completed. To use it he placed it, cover-glass downward, upon the rock section and shoved it into such positions that bubbles appeared over the desired spots. In using this method, the present writer found that he could not produce bubbles in well-cooked balsam. If undercooked, the gum would squeeze out at the sides and stick to the rock slice under examination and the bubbles would become distorted from their