Stephen G. Lipson

Comparison between sensitivities of phase and intensity detection in surface plasmon resonance

We have experimentally and theoretically compared intensity and phase measurements of surface plasmon resonance, in order to check the widely claimed superiority of the phase method. Both experiment and theory show a slightly higher sensitivity for intensity detection. Simulations confirm that this result is generally true for a wide range of resonance conditions. The basic reason is that phase measurements must be performed by measuring light intensities in some way, and therefore both modes of operation are limited in similar ways by photon statistics. Sensitivity can only be improved by using larger light intensities.

Adjustable spiral phase plate

A spiral phase retarder phi(r, theta) = mtheta has been constructed with use of a deformed cracked plexiglass plate. By changing the degree of deformation, the retarder can be adjusted for use at any wavelength, and the value of the phase step 2pim at theta = 2pi can be chosen.

Modulation transfer function of a lens measured with a random target method

We measured the modulation transfer function (MTF) of a lens in the visible region using a random test target generated on a computer screen. This is a simple method to determine the entire MTF curve in one measurement. The lens was obscured by several masks so that the measurements could be compared with the theoretically calculated MTF. Excellent agreement was obtained. Measurement noise was reduced by use of a large number of targets generated on the screen.

Fourier fringe analysis with improved spatial resolution

The spatial resolution of the phase image derived from the interferogram by Fourier fringe analysis is limited by the necessity to isolate a first order in the Fourier plane. By use of the two complementary outputs of the interferometer, it is possible to eliminate the zero order and thus to improve the spatial resolution by a factor of approximately 2. The theory of this improvement is presented and confirmed experimentally.

Enhanced Interferometric Identification of Spectra in Habitable Extrasolar Planets

An Earth-like extrasolar planet emits light that is many orders of magnitude fainter than that of the parent star. We propose a method of identifying bio-signature spectral lines in light of known extrasolar planets based on Fourier spectroscopy in the infrared, using an off-center part of a Fourier interferogram only. This results in superior sensitivity to narrower molecular-type spectral bands, which are expected in the planet spectrum but are absent in the parent star. We support this idea by numerical simulations that include photon and thermal noise, and show it to be feasible at a luminosity ratio of 10?6 for a Sun-like parent star in the infrared. We also carried out a laboratory experiment to illustrate the method. The results suggest that this method should be applicable to real planet searches.

NMR, optical, and plastic flow experiments in bcc3He —4 He mixture crystals — in pursuit of a vacancy fluid

We describe experiments on the properties of bcc3He —4 He solid mixtures on the melting curve between 0.5K and 1.9K. In this paper we focus on effects related to the presence of thermal vacancies. First, we used NMR to image the3He distribution within the solid in equilibrium with the superfluid, as well as its T1 and t2. The most surprising result was that above about 1K, vacancy related motion of3He atoms in the solid becomes faster than in the liquid. To check the macroscopic aspects of this motion, we used the vibrating wire technique to look at plastic flow of the bcc solid phase, by moving the wire through the crystal. The temperature dependence of the plastic flow velocity indicates that the vacancy population in the bcc solid behaves like a viscous fluid. The extent to which the vacancy population causes the solid to have liquid like properties is best demonstrated through optical observations of the distillation of3He atoms out of the crystal, which takes place via formation of fluid bubbles within the solid, which then percolate into the liquid, creating a vivid impression of boiling.

New 3-5 μ wavelength range hyperspectral imager for ground and airborne use based on a single element interferometer

Spectral imagers rely mainly on two techniques for collection of spectral information: gratings and interferometers. The former type needs cooling of the optics to avoid background signals which significantly limit the dynamic range of the measurement. The latter type, in its present commercial configurations, is not suitable for pushbroom operation in an airborne situation. A recent spectral imager configuration based on a shearing interferometer has been shown to be suitable for pushbroom operation without the need for cooling the optics. In this paper we describe the planned implementation of such a spectral imager for the 3-5 μ range, where the interferometer is a specially designed single prism. The advantages of this interferometer configuration are: i) compact optics, ii) high S/N ratio in the 3-5 μ range with small optical collection diameter, and iii) enhanced mechanical stability. The instrument yields a spectrum for 320x240 pixels of the image with a spectral resolution of better than 50 cm-1. The spectrum is calibrated in units of Watt/(steradian.cm2.cm-1). If used in an airborne pushbroom mode it provides a swath width of 240 pixels in a ~6.9 degree transverse field of view. If used in a horizon scanning configuration, it has a vertical field of ~6.9° and a horizontal field up to 300 degrees. The IFOV is 0.5 milliradians. In this paper the major instrument design considerations are presented. The instrument is being constructed and we will give more details on actual performance and examples of measurement results in a future paper, as we gain more experience. An 8-12 μ range version is also planned for the near future.

Experimental Validation Of Atmospheric Transmittance Codes

This review describes the present computer codes used to predict atmospheric transmittance. Since these codes are based on modeling of the optical properties of the atmosphere, there is a constant need to validate them in long-path atmospheric transmittance measurements. These measurements and their results will be described here.

A high resolution magneto-optical system for imaging of individual magnetic flux quanta

A high-resolution magneto-optical imaging system is described. In this system magneto-optical Kerr effect is utilized for resolving individual flux quanta in a type II superconductor. Using an ultra thin EuSe indicator a spatial resolution of 0.8 microm is achieved.

The residual resistivity of very dilute iron impurities in copper, and their precipitation by oxidation

The residual resistance of high-purity copper can be greatly reduced if the metal is annealed in oxygen at a temperature just below its melting point. The effect is well known and has been used in many low-temperature investigations of the electronic properties of pure copper. We have carried out electrical and magnetic measurements which confirm that the effect is due to oxidation of residual Fe impurities in the copper, but in addition the formation of macroscopic particles of Fe3O4 is a necessary condition for success of the method. The macroscopic precipitation was discovered at Fe impurity levels down to 1 ppm. As a result of freezing out the contribution of Fe to the residual resistance, a minimum figure can be deduced for the resistivity contribution of free Fe impurities, and this figure is not in agreement with values deduced in earlier works. Resistance measurements were made with a superconducting galvanometer and magnetic measurements by the Faraday method.