Conical Lens Research Articles

Single-beam optical bottle for cold atoms using a conical lens

We report a new method to generate an optical dipole potential with a null intensity region surrounded in all directions by light walls. This is achieved with a simple scheme based on a conical lens. Applications to optical trapping of neutral atoms are discussed.

Production of an extended plasma column in vacuumby irradiating a target by a quasi-Bessel beam

A technique of focusing the heating radiation wasinvestigated, which makes it possible to produce an extended(under laboratory conditions, up to 1 m and over) plasmacolumn and enables an easy output of VUV radiation. A planesolid-state target in vacuum was arranged along the caustic ofa conic lens (axicon), which focused the laser beam. An analytic dependence, which describes the spatial intensity distribution of the heating radiation in the case of a nontransparent, partially reflecting target, was derived and experimentally verified. Experiments on the irradiation of an aluminiumtarget in vacuum with a 5-J, 5-ns pulse of a neodymium-glasslaser were performed. A plasma column up to 30 mm in lengthand no greater than 10 μm in diameter was formed. A ratherintense plasma radiation was recorded in the VUV range.

A Time-Resolved Low-Angle Light Scattering Apparatus. Application to Phase Separation Problems in Polymer Systems

A time-resolved small-angle light scattering apparatus equipped with azimuthal integration by means of a conical lens or software analysis of scattering patterns detected with a CCD camera was developed. Averaging allows a significant reduction of the signal-to-noise ratio of scattered light and makes this technique suitable for investigation of phase separation kinetics. Examples of applications to time evolution of phase separation in concentrated statistical copolymer solutions and dissolution of phase-separated domains in polymer blends are given.

Formation of an extended homogeneous optical channel in a nonlinear medium with focusing of the laser radiation by an axicon

It is shown theoretically that, when a laser beam is focused by an axicon (a conical lens) in a Kerr-type nonlinear medium with nondissipative saturation of a square-root nonlinearity, an extended homogeneous optical channel may form and its length may be comparable with the length of the axicon caustic.

Conical lens for atom focusing

Light reflected from a conical mirror produces an intensity gradient that can be used to focus atoms to a single spot. Within the Raman-Nath approximation the position of the focal plane, peak atomic density, and spot size have been determined for a range of field strengths. Theoretical estimates of the field strength needed to focus atoms using a conical lens are found to be three to four orders of magnitude lower than that needed for focusing atoms using standing-wave fields.

Calculation of toroidal and conical electrostatic fields for angle resolved electron energy analysis

Abstract An analytical perturbation method is discussed for the calculation of electrostatic fields, which simplifies considerably the design of electron-optical elements of spectrometers for a simultaneous angle and energy analysis of wide electron beams––polar-toroidal condensers and conical lenses. Comparison of this method with numerical computation demonstrates the high accuracy of the anlytical field representation. Methods for the elimination of beam deflection in conical lenses are proposed.

Field distribution and electron optical properties of electrostatic conical slit lenses

Properties of electrostatic lenses for focusing hollow charged particle beams are investigated based on an analytical representation of the field potential. These lenses are of use in devices for analysis of the angular distributions of characteristics in wide charged particle beams.

Matching of single-mode fibre to laser diode by microlenses at 1.5 µm wavelength

A theoretical and experimental comparison at 1.5 µm wavelength is made of the coupling efficiency between a laser diode and a single-mode fibre, on the end face of which a matching conical or hemispherical lens is formed. The same analysis applied to a hyperbolic microlens also gives good agreement with a recently published experimental result for this alternative matching lens.

Apodization of diffractionless beams

Coatings with graded transmission, placed near the rims of conical lenses and perhaps other axicons, provide apodization that removes the axial intensity variations in Bessel-type optical beams.

New computer-controlled dual stage SEM—model DS-700

The dual stage electron-optical column design of the DS-700 provides a unique combination of high resolution and flexible sample handling. The top stage accomodates a sample between the polepieces of a low aberration immersion objective lens, while the bottom stage accepts large samples below a conical second objective lens. This column configuration has been described elsewhere, and is therefore not the subject of this paper.A completely new digital electronic system with computer control of all operating parameters has been developed. A combined keyboard and menue control system has been adopted. Commonly used functions are assigned to a simple operating panel, with discrete functions which may be set and easily changed. Secondary functions are addressed using a menue display. In this manner, rapid simple operation is realized, while still providing extreme flexibility.A single high quality TV monitor displays real time and processed images. It is also used to display menues, various operating parameters, and vacuum system status.

Development of a digital SEM

A newly developed digital scanning electron microscope, the JSM-6300, has the following features: Equipped with a narrower conical objective lens (OL), it allows high resolution images to be obtained easily at a short working distance (WD) and a large specimen tilt angle. In addition, it is provided with automatic functions and digital image processing functions for ease of operation.Conical C-F lens: The newly developed conical C-F objective lens, having low aberration characteristics over a wide WD range, allows a large-diameter (3-inch) specimen to be tilted up to 60° at short WD, and provides images with low magnifications starting at 10*. On the bottom of the lens, a p n junction type detector is provided to detect backscattered electrons (BE) from the specimen. As the narrower conical 0L increases the secondary electron (SE) detector's field intensity on the specimen surface, high SE image quality is obtained.

Production and uses of diffractionless beams

It is proposed to obtain intense optical fields, whose form shows little change in size over long paths, through the use of either conical lenses or spherical lenses showing spherical aberration together with a single projecting lens. The conical lens is shown to produce fields whose transverse structure is given by a zero-order Bessel function J0, while the spherical aberrating lens produces (real or virtual) J0-like transverse structures, provided that the central portion of the aberrating lens is occluded. In all cases projection gives a J0 real-image optical structure. Intensity, size of the transverse structure, and range considerations are developed, and some aspects of optimization are discussed. A negative aberrating lens gives a long range of nearly constant size in the image field, and a universal expression is presented to describe the image size as a function of image distance for this case. Projection with an aberrating projection lens is shown to improve the constancy of the final J0 pattern size dramatically. Typical photographic results are included for beams generated by using a low-power He–Ne laser. Brief considerations of practical uses of diffractionless beams are presented.

Simple laser setup for continuous laser spark generation

The continuous extended laser spark (CELS) is an optical breakdown in a gas arising at the axis of a ‘‘diffraction‐free’’ beam at the caustic of a conical lens (axicon). It looks like a long (10–15 cm) continuous plasma string. In this article a setup for the CELS generation and investigation is described. It consists of a powerful Nd‐glass laser, an axicon mounted in a discharge chamber, and diagnostic apparatus. CELSs were obtained in air, xenon, argon, helium, and carbon dioxide under pressures of 0.02 to 1 atm. It is proved that the simple laser with unstable cavity can be successfully used for CELS formation. This laser is highly reliable in operation and relatively cheap. It can be recommended for different scientific and technological applications.

Asymptotic methods applied to electrostatic field calculations for ion optical systems

An approximate analytical method of electrostatic field calculation for ion optical systems with a narrow interelectrode gap is developed. It is applied for field potential calculation of a coaxial conical lens, a cylindrical deflector terminated by additional electrodes as well as for evaluation of the toroidal energy analyzer fringing field.

Optics of conical electrostatic analysing and focusing systems

Abstract Energy analysis and focusing of hollow beams of charged particles may be performed with the aid of conical electrode structures. Two analyser geometries and two lens designs are described and the behaviour of some typical configurations is studied numerically. Some advantages of conical lenses over round lenses of more conventional design are indicated.

Dual Stage SEM with thermal field-emission gun

Resolution improvement is an on-going goal in scanning electron microscope development. High resolution is required at both high and low accelerating voltages in a wide field of applications, including, but not exclusive to, semiconductors and new materials development. Two approaches which result in improved resolution through-out the operating voltage range of the SEM are 1) the adoption of low aberration objective lenses, and 2) the use of high brightness electron sources.The DS-130F SEM which is described here uses a high brightness thermal field emission gun (TFEG) in conjunction with a modified DS-130 column. The electron optical configuration is quite unique, as it includes two independent stages. The top stage places the sample within a high field strength low aberration objective lens, resulting in ultra high resolution on samples up to 18 x 8 mm. The bottom stage accommodates 6” samples and uses a second dedicated conical objective lens allowing a short working distance to be maintained on tilted samples.

Thermal-diffusivity measurements by the converging-thermal-wave technique

A converging-thermal-wave technique is described for the measurement of thermal diffusivity in bulk or thin-sheet materials. An annular-shaped area is heated by a pulsed laser beam focused on the material's surface through a combination of spherical and conical lenses, and the surface temperature is monitored by an infrared detector focused on the center of the annulus. The converging action of the thermal flux results in a high amplitude of the detected signal with little overheating of the irradiated material. An analysis of such a technique is presented, as well as some experimental results obtained on heterogeneous materials. Several aspects relevant to the practical implementation of such a technique in an industrial environment, such as the effect of surface losses and different noise sources, are discussed.

Microlens for coupling a semiconductor laser to a single-mode fiber

Simple conical microlenses are fabricated on the end of a vapor-axial-deposition single-mode fiber to increase the coupling efficiency between the laser diode and the single-mode fiber. The lowest coupling loss, 3 dB, has been achieved by using a 1.3-microm InGaAsP buried-heterostructure laser diode and a single-mode fiber. Experimental results on coupling efficiency and the loss penalty due to lateral misalignment are also reported. This conical lens is easy to manufacture and reproduce.

Azimuthal integration of scattered light intensity using a conical lens

A simple optical scheme using a conical lens to perform azimuthal integration of light collected in a light scattering experiment is described. A substantial increase in the signal-to-noise ratio of the scattered light intensity is achieved. The scheme is particularly useful in nonequilibrium experiments such as spinodal decomposition, where the angular distribution of scattered light varies slowly in time and is peaked in the forward direction.

Complex Amplitude Distribution Transmitted by a Conical Lens

The method of the transmission function is used to determine the complex amplitude distribution transmitted by a conical lens illuminated by a plane or spherical wave. We study the transmission function of the conical lens and determine the focal curve which coincides with that obtained by the ray-tracing method.