Μm Focal Length Research Articles

Laser-Driven Electron Lensing in Silicon Microstructures.

We demonstrate a laser-driven, tunable electron lens fabricated in monolithic silicon. The lens consists of an array of silicon pillars pumped symmetrically by two 300fs, 1.95 μm wavelength, nJ-class laser pulses from an optical parametric amplifier. The optical near field of the pillar structure focuses electrons in the plane perpendicular to the pillar axes. With 100±10 MV/m incident laser fields, the lens focal length is measured to be 50±4 μm, which corresponds to an equivalent quadrupole focusing gradient B^{'} of 1.4±0.1 MT/m. By varying the incident laser field strength, the lens can be tuned from a 21±2 μm focal length (B^{'}>3.3 MT/m) to focal lengths on the centimeter scale.

The novel hybrid metal-graphene metasurfaces for broadband focusing and beam-steering in farfield at the terahertz frequencies

A hybrid metal-graphene metasurface was proposed and researched in terahertz (THz) frequencies. It is found that these hybrid structure metasurfaces give rise to a larger phase variation in comparison to bare graphene metasurface. Based on the analysis of electric field of the hybrid structures, it implies that due to the enhanced localized electric field and the Fabry-Perot resonance cause the phase increasing quadratically with the improvement of the graphene Fermi energy (EF) in hybrid metal-graphene structures. By designing different metal sizes and modulating EF, the structure shows up to 295° of smooth phase modulation at the frequency of 4.5 THz. Based on the phase profile design, a reflection-type focusing metasurface with near 1000 μm focal length in a broadband frequency range from 4 to 4.8 THz and 1-bit dynamically tunable coding metasurface to steer the reflected THz waves into multiple beams in farfield were both demonstrated successively. Moreover, the degree of freedom for beam-steering of 2-bit coding metasurfaces was enhanced and the process of manipulation was also qualitatively interpreted by the convolution principle. This work may supply a potentially effective method to instruct the design of desirable metasurfaces with multi-function in the modulation of electromagnetic waves.

Design and application of high polarized purity metasurface lens

Dealing with potential applications of metasurface in lens technologies, we propose a focusing metasurface with high polarized purity based on anisotropic elements, and then put it into application of high gain antenna with high polarized purity. Firstly, we design a metasurface cell with the polarization filtering characteristic, which is capable of transmitting the x-polarized waves efficiently while reflecting the y-polarized waves completely. By changing the metallic patch size, we can modulate the phase shift for the x-polarized transmitting waves. Then by imposing a hyperboloidal phase profile onto the surface, we design a metasurface lens with 105 mm105 mm in size, 2121 in cell number, and 30 mm in focal length. According to the principle of reversibility of light path, the spherical waves emitted from the patch antenna can be converted into plane waves by the focusing metasurface lens, which is used to improve the antenna gain. As for the experiment, we tend to obtain the metasurface lens impinged by differently polarized waves in order to study the lens response to differently polarized waves. The results show that the metasurface acts as a lens when impinged by the x-polarized waves but serves as a reflector when illuminated by the y-polarized waves. That is to say, the y-polarized waves are mostly filtered out while the x-polarized waves are efficiently transmitted and focused, which is in good accordance with the designed principle. Assuming that a patch antenna emits the x/y-polarized waves at the focal point, we obtain not only the antenna gain improved remarkably but also polarized isolation above 25 dB in the operating bandwidth of the designed metasurface. The results of the antenna application give a further proof of the designed lens which eventually contributes to the high gain and high polarized purity of the lens antenna.

High-reflectivity high-contrast grating focusing reflector on silicon-on-insulator wafer**Project supported by the National Natural Science Foundation of China (Grant Nos. 61274044, 61574019 and 61020106007), the National Basic Research Program of China (Grant No. 2010CB327600), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20130005130001), the Natural Science Foundation of Beijing, China (Grant No. 4132069), the

A high-contrast grating (HCG) focusing reflector providing phase front control of reflected light and high reflectivity is proposed and fabricated. Basic design rules to engineer this category of structures are given in detail. A 1550 nm TM polarized incident light of 11.86 mm in focal length and 0.8320 in reflectivity is obtained in experiment. The wavelength dependence of the fabricated HCGs from 1530 nm to 1580 nm is also tested. The test results show that the focal length is in the range of 11.81–12 mm, which is close to the designed focal length of 15 mm. The reflectivity is almost above 0.56 within a bandwidth of 50 nm. At a distance of 11.86 mm, the light is focused to a round spot with the highest concentration, which is much smaller than the size of the incident beam. The FWHM of the reflected light beam decreases to 120 nm, and the intensity increases to 1.18.

Ultraprecision Machining-based Micro-Hybrid lens design for micro scanning devices

This paper presents design of a refractive-diffractive hybrid lens for use in micro optical scanning systems. To achieve the target focal length with minimized aberration, the refractive lens was optimally designed with consideration of reducing transverse ray aberration. The diffractive efficiency was calculated in terms of depth and period of the Fresnel pattern via rigorous coupled wave-analysis (RCWA). The geometry of the V-shaped diamond tools limits the depth of Fresnel edge of the diffractive lens due to the interference, which eventually determines the whole size of the lens. In this study, two types of hybrid lenses for micro scanning system were compared and designed in consideration of optical performance and machining limit. Therefore, the designed diffractive lens was optimized for 300 μm focal length with minimum aberration. The depth of Fresnel edge and the diameter was determined to be 0.94μm and 423.4μm within the machining limit, respectively. The lens base mold was fabricated using a 5-axis ultraprecision machine, and the lens was imprinted through a hot embossing process. The measured focal length and the calculated NA are 336μm and 0.63 respectively. Lastly, Imaging tests and diffractive efficiency are measured to evaluate the optical performance of the micro-hybrid lens.

Integrated wide-angle scanner based on translating a curved mirror of acylindrical shape

A wide angle microscanning architecture is presented in which the angular deflection is achieved by displacing the principle axis of a curved silicon micromirror of acylindrical shape, with respect to the incident beam optical axis. The micromirror curvature is designed to overcome the possible deformation of the scanned beam spot size during scanning. In the presented architecture, the optical axis of the beam lays in-plane with respect to the substrate opening the door for a completely integrated and self-aligned miniaturized scanner. A micro-optical bench scanning device, based on translating a 200 μm focal length micromirror by an electrostatic comb-drive actuator, is implemented on a silicon chip. The microelectromechanical system has a resonance frequency of 329 Hz and a quality factor of 22. A single-mode optical fiber is used as the optical source and inserted into a micromachined groove fabricated and lithographically aligned with the microbench. Optical deflection angles up to 110 degrees are demonstrated.

Development of micro-objective lens array for large field-of-view multi-optical probe confocal microscopy

We describe multi-optical probe confocal microscopy using a micro-objective lens array for large areal inspection. A microlens array with 100 µm focal length, 80 µm diameter and 90 µm pitch was designed and fabricated with an array size of 10 × 10. In order to produce the high-fidelity microlens array, a UV imprinting process was employed, and a UV transparent mold for the imprinting process was manufactured by replicating a reflow lens master. A blocking filter between the microlenses was introduced to minimize crosstalk and stray light noise for high resolution and high contrast imaging. The developed system is characterized by a 1 mm × 1 mm field of view with a nano-stage with 100 µm travel length. The lateral resolution was measured to be 0.79 µm. The method can be used for various applications such as the inspection of electric devices including display panels and large-area printed circuits with a high resolution.

長焦点距離集光光学系を用いた高出力ファイバレーザ溶接時のレーザ誘起プルームの影響

High power fiber lasers of high beam quality have been developed, and remote welding with a high-power fiber laser has been expected to be one of new high-speed welding procedures in automobile industries. In particular a long-focal-distance focusing optics is beneficial to the welding of a wide area. However, features and effects of a laser-induced plume in such welding process are not fully understood. Therefore, the study was undertaken to investigate weld penetration characteristics with or without removal of a laser-induced plume, to clarify welding phenomena and to develop a stable welding procedure in 4 kW high-power fiber laser welding of a 1.5 mm-thick zinc-coated steel sheet using the focusing optics with a lens of 1,250 mm in focal length. The welds obtained at the focal position without removal of the plume were so unstable that the full penetrations were changed to partial penetrations during laser welding. To fundamentally understand the remote welding phenomena, refractive-index distribution above the laser-irradiated area was visualized by the Michelson interference method. The observation results of fringe patters through a high-speed video camera demonstrated that the incident laser beam was defocused and refracted by a wide formation range and complicated behavior of small refractive-index values derived from the high-temperature metal vapor of the plume, leading to the formation of an unstable penetration weld. It was also confirmed that the removal of the laser-induced plume and the corresponding widespread field of low refractive-index values by using a fan was essential to the stable production of fully-penetrated welds in the high-power fiber laser remote welding with the long-focal-distance focusing optics.

Optical focusing of plasmonic Fresnel zone plate-based metallic structure covered with a dielectric layer

By modulating the zone width of a plasmonic Fresnel zone plate, consisting of metallic nanostructures covered with a dielectric layer, the authors demonstrated numerically that a focused beam can be achieved with higher intensity and smaller spot size than the diffraction-limited conventional Fresnel zone plate. Rigorous electromagnetic simulation predicts a full width at half maximum of 162nm (equivalent to an effective numerical aperture of 1.30) at 0.5μm focal length, using 405nm wavelength illumination. This sub-diffraction-limit focusing has potential in applications such as maskless nanolithography, high resolution scanning optical microscopy, optical data storage, and optical antenna. This focusing capability is related to extraordinary optical transmission, which is explained by the complex propagation constant in the zones afforded by higher refractive index dielectric layer and surface plasmons.

SU‐GG‐J‐133: MR Guided Focused Ultrasound (MRgFU) for Cance Therapy

Purpose: The purpose of this work was to commission and to evaluate the role of MR guided high intensity focused ultrasound (MRgHIFU) in cancer therapy in ex vivo and in vivo. Method and Materials: An InSightec ExAblate 2000 HIFU system with a 1.5T GE MR scanner (MRgHIFU) is approved by FDA for the treatment of uterus fibroids clinically and being investigated in our department for treating bone metastases, prostate and breast cancers under local IRB approval. The phased array transducer is housed in a sealed bath and connected to a motion system. The focal region is cigar shaped, about 2mm in diameter and 10mm in focal length. Extensive experiments have been carried out on phantoms and excised tissues to determine optimal ultrasound parameters including the acoustic power output, frequency and exposure duration. We also performed in vivo studies on feasibility of enhancement of drug delivery for both chemotherapy and gene therapy using an animal model. Both MR T2‐weight MR image and proton resonance frequency shift MR images were used for treatment planning and monitoring the effect of the treatment in real time. Results: Phantom studies demonstrated that MRgHIFU could provide adequate temperature elevation for tissue ablation; acoustic power >10W leading to temperature elevation (ΔT) > 7 °C. At a lower acoustic power (5 W) we could keep ΔT < 4 °C, which is adequate for drug enhancement. The results were served for animal studies. Tissue damage was achieved at predetermined region in excised tissue through MR real‐time guidance. Our preliminary results showed increased drug concentrations in MRgHIFU treated mice than the control group. Conclusion: MRgHIFU may have a great potential as a safe, noninvasive treatment modality for cancer therapy including tumor ablation, enhancement of drug livery and boost treatment for hypoxic tumors in combination with radiotherapy.

Studies on the light permeance characteristic of a Fresnel lens group applied in high concentration solar energy

A key point to limit wide applications of solar energy is the exploitation cost. With the advantages of compact volume, less weight, small focal length and low cost Fresnel lenses are suitable for solar radiation concentration and system modularization. The optical efficiency of transmitted solar radiation is improved compared to thick ordinary lenses and the solar tracking accuracy required by a Fresnel lens group is lower than for other reflection schemes. In this study, a modular device composed of a two-stage Fresnel lens is presented and its performance is investigated. Based on the analysis of rays passing through the wedge structure of the lens, the optical efficiency is obtained under different incidental angles. Facular point image qualities of a Fresnel lens are compared using simulation results. As for the Fresnel lens 100 mm in diameter, 220 mm in focal length, when the incident angle is kept within 1°, the focal point will not move out of the receiver domain with the dimensions of 10 mm × 10 mm and the relationship between incident angle against receiver dimension is obtained. Optical efficiency measurements have been carried out on a practical Fresnel lens group which includes another Fresnel lens 30 mm in diameter with the small-size secondary lenses integrated into an intermediate panel combined with the first Fresnel lens plane to improve the performance of the integral battery system at high concentration ratio. According to experimental studies, the positions of the focal spot varying with the incident angles of solar radiation are recorded continuously. It has been found that 50–60% of the collected solar radiation can pass through the Fresnel lens group under a condition of over 1000 suns, and the deviation range of the focal spot fundamentally agrees with the result of the simulation.

TH-C-M100J-09: MR Guided Focused Ultrasound (MRgFU) For The Treatmentment of Prostate Cancer: A Feasibility Study of Increasing Cellular Uptake of AS-MDM2 in Vivo

Purpose: MDM2 is an oncogene and overexpressed in 30–40% of prostate cancer. Antisense MDM2 oligonucleotide (AS‐MDM2) inhibits MDM2 expression, and enhances the effects of radiation and chemotherapy on prostate cancer. The purpose of this study is to investigate the feasibility of increasing the cellular uptake of AS‐MDM2 using MR guided High Intensity Focused Ultrasound (MRgFU). Materials and Methods: A HIFU system (InSightec ExAblate 2000) and a 1.5T MR scanner(GE) were used for this study. Human prostate cancer cells LNCaP 105, were grown orthotopically in the prostates of 11 nude mice. Extensive experiments were performed to determine the optimal MR parameters for target delineation and the optimal ultrasound parameters for animal treatment studies using an acoustic phantom. The mice bearing implanted prostate tumors (61±22mm3) were treated under general anesthesia using pulsed focused ultrasound with the output acoustic power of 4W, pulse width of 100msec and either 300 or 900 pulses in one sonication. The focal region is cigar shaped, about 2mm in diameter and 10mm in focal length. The focal peak was set within the target under the MR guidance. Two to four sonications were used to cover the whole tumor. Immediately after the treatment 0.1ml of AS‐MDM2, dissolved in PBS, was given by tail vein injection at doses 25mg/kg. After 24hr, the animals were sacrificed and tumors were removed. The expression levels of p53 proteins were analyzed by immunohistochemical staining. Results: Our preliminary results showed that the animals tolerated well the HIFU treatment. With 300 pulses per site in each sonication blood cell extravasation on H&E staining and an increase in p53 expression (5.0±2.4%) in the treatedtumor bearing LNCaP cells were observed as compared to the control group (1.3 ± 0.5%). Conclusion: MRgFU can be used an alternative treatment modality for prostate cancertreatment.

Optimal Design for Nonperiodic Fine Grating Structure Controlled by Proximity Correction with Electron-Beam Lithography

We describe a method for designing nonperiodic fine grating structures such as a small F-number diffractive cylindrical lens, to be fabricated by direct-writing electron-beam lithography. The design is based on a resist development simulator for estimating a proximity effect of electron dose and the finite difference time domain (FDTD) method for simulating an electromagnetic field. The surface profile and electron dose distribution are simultaneously optimized to obtain the high diffraction efficiency. For the design of a diffractive lens of 50 µm width and 25 µm focal length, the calculated diffraction efficiency is 49% for 650-nm-wavelength light, which is slightly lower than that of a diffractive lens profile optimized by electromagnetic analysis without restrictions on fabrication limits.

Microelectron field emitter array with focus lenses for multielectron beam lithography based on silicon on insulator wafer

We report on a device concept, results of fabrication, and characterization of a monolithic electron field emitter array with focus lenses for multielectron beam lithography and high-density nano data storage. An array of individually addressable emitters of various materials was patterned on oxidized etch pits of a silicon on insulator (SOI) wafer. Si active layer of the SOI with gate hole array that self-aligned with the emitters was used as a common gate electrode. An array of cylindrical holes formed at the Si base of the SOI was used as a common lens electrode. For a single Pt emitter with gate hole of 2 μm diameter, the emission current started at a gate voltage Vgate=90 V and reached to 1.2 μA current and 0.84 mW beam power at Vgate=300 V and anode voltage Vanod=0.7 kV. The emission current was found to be stable with a fluctuation smaller than 10%/h. The emitter-gate and emitter-lens leak currents were found to be less then 1% compared with the emission current. The focusing characteristic of the device was experimentally confirmed by observing emission patterns on a phosphor anode screen. A simulation work using a finite-element method has shown that the emitted electron beam with emission cone angle within 15° can be focused at a spot of 40 nm diameter and 200 μm focal length at a lens voltage Vlens=−6 V.

Miniature low voltage beam systems producable by combined lithographies

The project of a miniaturized vacuum microelectronic 100 GHz switch is described. It implies the development of a field emission electron gun as well as the investigation of miniaturized lenses and deflectors. Electrostatic elements are designed and developed for this application. Connector pads and wiring pattern are created by conventional electron beam lithography and a lift-off or etching process. Wire and other 3-dimensional structures are grown using electron beam induced deposition. This additive lithography allows to form electrodes and resistors of a preset conductivity. The scanning electron microscope features positioning the structures with nm precision. An unconventional lithography system is used that is capable of controlling the pixel dwell time within a shape with different time functions. With this special function 3-dimensional structures can be generated like free standing square shaped electrodes. The switch is built by computer controlled additive lithography avoiding assembly from parts. Lenses of micrometer dimensions were investigated with numerical electron optics programs computing the 3-dimensional potential and field distribution. From the extracted axial field distribution the electron optic characteristic parameters, like focal length, chromatic and spherical aberration, were calculated for various lens excitations. The analysis reveals that miniaturized optics for low energy electrons, as low as 30 eV, are diffraction limited. For a lens with 2 μm focal length, a chromatic aberration disc of 1 nm contributes to 12 nm diffraction disc. The spherical aberration blurs the probe by 0.02 nm, assuming an aperture of 0.01 rad. Employing hydrogen ions at 100 V, a probe diameter of 0.3 nm generated by chromatic aberration is possible. Miniaturized electron optical probe forming systems and imaging systems can be constructed with those lenses. Its application as lithography systems with massive parallel beams can be forseen.

Gallium phosphide microlenses by mass transport

Arrays of high quality refractive microlenses have been formed in GaP substrates by mesa etching followed by a heat treatment in which the multistep mesas were smoothed due to surface energy minimization. A smooth lens surface and an accurately controlled lens profile have been obtained. Microlenses of 130 μm diameter and 200 μm focal length have been used to collimate the outputs of GaInAsP/InP and GaAs/GaAlAs diode lasers and have yielded a nearly diffraction-limited beam divergence of 0.68°.

Interferometric testing with computer-generated holograms: aberration balancing method and error analysis

When testing aspheric surfaces with a computer-generated hologram, some problems should be considered. In this paper, first, we compare two types of hologram: Lohmann and interference. The phase error in the Lohmann type hologram is estimated, and a method of compensating the error is described. Second, we discuss the relation between the shape of the required wavefront and the number of resolution cells of the hologram. Since testing smaller f number optical elements increases the required number of resolution cells of the hologram, we propose the aberration balancing method to reduce the number of resolution cells. The optimum values of the defocus aberration are calculated. Especially, it is shown that the number of resolution cells in the hologram is capable of being reduced to 25%. Third, we discuss the error due to incorrect hologram size and due to misalignment of the optical system when the aberration balancing method is applied. Finally, an experimental example for testing an aspheric mirror 150 mm in diameter and 300 mm in focal length is given.

An Infrared Radiation Thermometer for Normal Temperature Region

An infrared radiation thermometer for measuring surface temperature of targets in a normal temperature region has been developed.The construction, operating mechanism and specification of this instrument and some data obtaind by it are described in this paper.Two types of measuring head based on different optical systems have been designed and constructed. One is a reflection type using Cassegrain mirrors, and the other a refraction type.The refraction type contains a germanium objective lens (40mm in focal length, f/1.4) coated on both surfaces with thin films of ZnS (nt=2.5μ), and two kinds of optical band pass filters limited the sensitive region of the instrument in wavelength between 8 and 12μ.A thermister bolometer as the infrared detector is installed in its compartment which is held at a definite temperature around 30°C by the temperature controlling system and serves as the reference radiant source for the detector.The measuring radiation temperature range extenss from-70°C to +90°C, especially normal temperature region (10°C-45°C) is most sensitive. Minimum detectable temperature difference is within 0.2deg. at 30°C.Temperature measurement of a target is affected by its emmisivity and the temperature of the objective lens. Some considerations for probable errors caused by them and the practical correction methods have been discussed.

The spectrum of Comet 1948 l.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The spectrum of Comet 1948 l. Jose, Paul D. Abstract The first spectrogram of Comet 1948 1 was obtained at the McDonald Observatory on Xovember 14, at 12h9m UT. The comet was extremely bright and could easily be photographed with the quartz prisms and the 500 mm camera giving a dispersion of about 50 A/mm at ~4O0O. The spectrum was guided accurately so that the nucleus of the comet which had a stellar appearance could be kept in the same place on the slit throughout the exposure. The continuous spectrum of the nucleus is very strong and the absorption lines of the solar spectrum are prominent. The emission features of the comet are relatively faint. We distinguish the very prominent bands of CN and those of C2. In addition there are many of the other bands which are usually found in comets but a detailed study of this spectrum has not yet been undertaken. The group of lines in the vicinity of X4050 which Herzberg has identified with the molecule C112 is present but is rather weak on this plate. I would like to call attention especially to a group of lines in the vicinity of ~43O0. This is the band of CH designated as A 1A H x2ll. This is usually a complex band showing several branches. The strongest line is at ~43I3 belonging to the Q branch of the band. This group of lines is blended on this spectrogram but it is clearly visible. Just to the violet of it we see another line or group of lines with a wave length of about ~43O4. This line would correspond to the R branch of the band and it is usually second in intensity in cometary spectra. Still further to the violet we see another emission feature at a wave length of about X4296. This too should be a group of lines belonging to the R branch. It seems to me that the middle line at ~43O4 has a slightly different distribution of intensity along the slit than do the other two lines. I would like to ask you to remember this feature so that you can compare it with the next spectrogram which was taken on Xovember 17. This plate was obtained with the quartz prisms and a camera having a focal length of 180 mm. The dispersion is thus very much smaller than on the preceding spectrogram and it is difficult to say very much about the distribution in the line at ~4304. However, the spectrogram is interesting because it is very much stronger and it seems to show a strengthening of the emission features relative to the continuous spectra of the nucleus. Xext, we come to a spectrogram which was taken on Xovember 19 at 12L5m UT. This plate was obtained using a pair of glass prisms with a camera of 180 mm in focal length. The dispersion is somewhat smaller than that used for the first plate but it is about twice that used for the spectrogram on Xovember 17. The definition is particularly fine on this spectrogram and I would like here to stress especially the unsymmetrical distribution of the intensity along the slit as shown by the line at X4304. You will notice that it extends almost wholly towards one side of the nucleus and differs in this respect very greatly from most of the other lines including those which belong' to the same band. The feature to which I have called attention is undoubtedly real and is interesting in connection with the fact that during the exposure the slit was held in the parallel as is usually done for stellar exposures. This means that the tail of the comet extended to one side of the nucleus almost exactly along the slit so that we have here a distinction between the direction along the tail of the comet and away from it. This spectrogram shows many very fine features in the visual and red regions. These have not yet been measured but I hope that I shall have the pleasure of cooperating with Dr. P. Swings in the discussion of this material. McDonald Observatory, Fort Davis, Ten. Publication: The Astronomical Journal Pub Date: April 1949 DOI: 10.1086/106220 Bibcode: 1949AJ.....54..130J full text sources ADS |