Microlens System Research Articles

Fibre-end micro-lens system for endoscopic erbium-laser surgery applications

A sapphire micro-lens system in combination with a zirconium-fluoride (ZrF4) fibre has been designed and constructed as a surgical tool for focusing Er:YAG-laser radiation. It both refocuses the laser radiation transmitted through a 350 µm core fibre to a spot diameter of 570 µm at a working distance of 7.6 mm, and protects the distal fibre end from damage. An accurate and uncomplicated visualization of the focus position of the erbium-laser beam is realized by coupling a HeNe aiming laser into the cladding of the fibre. In vitro cutting experiments reveal the high cutting precision with minimal thermal damage of the surrounding tissue and the high damage resistance of the system. It may render the use of the erbium laser possible in a wide range of endoscopic applications.

Magnetic microlens focusing of electron beams

Recently, field emission sources in combination with either magnetic or electrostatic microlenses have been predicted to produce electron beams with high brightness and low aberrations. The key advantage to such systems is the short focal length and thus small coefficients of spherical and chromatic aberration. In addition, by using either small apertures or extremely sharp emission sources, the emission angle can be made small and thus the effect of the aberrations reduced further. We present here our initial results on building a magnetic microlens system. The unique feature of this work is the use of permanent magnets as the sole focusing elements in the lens, resulting in an extremely simple and inexpensive system.It has been shown that the aberrations in a focused electron beam can be reduced by selectively scaling the column dimensions. The focused spot sized is limited by the spherical aberrations,and the chromatic aberrations

Electron optical properties and aberrations of a miniaturized electron beam system

Based on dimensional analysis, a configuration of a microlens system for focusing an electron beam can be obtained by the dimensional scaling down from a conventional lens. An electrostatic microlens system consisting of two planar microsize apertures has been investigated. For this microlens, the spherical and chromatical aberrations, the astigmatism due to elliptic distortion, and the displacement due to misalignment have been calculated in detail. The resolution has been derived by a general formula, and thus has been evaluated numerically. The computational results have shown that the miniaturized microlens system proposed in the present article possesses remarkably small aberrations and ultrahigh resolution in the low voltage operation, and will be likely applicable for some practical uses.

Morse theory and gravitational microlensing

Morse theory is used to rigorously obtain counting formulas and lower bounds for the total number of images of a background point source, not on a caustic, undergoing lensing by a single-plane microlens system having compact bodies plus either subcritical or supercritical continuously distributed matter. An image-counting formula is also found for the case when external shear is added. In addition, it is proven that a microlens system consisting of k lens planes will generate N = 2M− + Πki=1(1 − gi) images of a background point source not on a caustic, where M− is the total number of critical points of odd index of the time-delay map and gi is the number of stars on the ith lens plane. Morse theoretic tools also yield that the smallest value N can have is Πi=1k(1+gi).

Electron optical performance of a scanning tunneling microscope controlled field emission microlens system

Use of a scanning tunneling microscope (STM) controlled field emission tip in conjunction with microlenses has been explored to form an exceptionally high brightness electron source and low aberration beam forming system at the low-keV energy range. In its basic configuration, the STM feedback principle is used for precision x, y, and z alignment of tip to microlens to form a self-aligned field emission (SAFE) microsource. The microlenses can be made using microfabrication techniques on silicon or other suitable substrates with dimensions reduced by approximately three orders of magnitude from those of conventional lenses. As the lens aberrations generally scale with lens dimensions, such lenses can be designed to have negligible aberrations thus allowing exceptionally high brightness and resolution to be achieved. This paper discusses the electron optical performance of such a microsource and its applications with other microlenses as beam forming systems.