Francesco Maccarrone

Light-induced ejection of alkali atoms in polysiloxane coated cells

SummaryAn intense laser-induced fluorescence of sodium and of other alkali atoms (K, Rb) at room and lower temperatures has been observed in polysiloxanecoated cells, producing a vapor density of the metal which is much higher than that corresponding to the thermal equilibrium between the vapor and the condensed phase. This enhancement is attributed to the light-induced ejection of atoms absorbed by the polysiloxane coating. The atomic density of the vapor can be manipulated by changing either the laser power or frequency. The dependence of the atomic density on these and other parameters as well as its time-dependent behavior are studied experimentally. A tentative interpretation of the phenomenon is discussed in terms of the properties of solutions of the alkali metals in several solvents.

Light-pressure bistability at microwave frequencies

Evidence of bistability induced by radiation pressure in a system operating at millimeter bandwidth is presented. The transmittance of a microwave cavity equipped with a movable mirror becomes bistable under the variation of two control parameters: the incident field intensity and the incident field frequency. Good agreement between theory and experiment has been achieved.

Absorptive optical bistability at microwave frequencies

SummaryIntrinsic absorptive bistability and hysteresis cycles in a steady-state regime are obtained at microwave frequencies. A theory is presented which takes into account the Gaussian shape of the fundamental mode excited into the resonator and is compared with the experimental results.RiassuntoSono state osservate la bistabilità assorbitiva intrinseca e l’isteresi nel caso stazionario, operando alle frequenze delle microonde. Si presenta una teoria che tiene conto della forma gaussiana del modo fondamentale eccitato nel risuonatore e che è confrontata con i risultati sperimentali.РезюмеНа микроволновых пастотах наблюдаются внутренняя абсорбционная бистабильность и гистерезисные циклы в стационарном режиме. Предлагается теория, которая учитывает гауссову форму основной моды, возбужденноц в резонаторе, и которая сравнивается с экспериментальными резулстатами.

Circular plate capacitor with different discs

In this paper, we write a system of integral equations for a capacitor composed of two discs of different radii, generalizing Love’s equation for equal discs. We compute the complete asymptotic form of the capacitance matrix for both large and small distances obtaining a generalization of Kirchhoff’s formula for the latter case.

Measuring light speed with a modulated laser diode

The time of flight (TOF) of a light pulse travelling back and forth and optical path length measurements are used to estimate the velocity of light. The light pulse has a duration of 10 ns, and is obtained from a suitably modified CW commercial laser diode. The TOF is read with a digital oscilloscope connected to two fast sensors, detecting the signals at the switch-on of a laser diode and at the arrival of the light pulse reflected from a plane mirror placed at a known distance.

Measuring the refractive index of water with a pulsed laser diode

In a previous paper published in this journal (Ronzani et al 2008 Eur. J. Phys. 29 957), an estimate of the light speed in air, obtained by measuring the time of flight of a pulsed laser beam, was reported. Using the same method and apparatus, we have improved the measure of the light speed in air, by increasing the data sample, and measured the light speed in water, obtaining an estimate of the water refractive index equal to n = 1.323 (0.016), at the wavelength of 665 nm.

Hall Effect in a Moving Liquid.

A simple experiment, suitable for performing in an undergraduate physics laboratory, illustrates electromagnetic induction through the water entering into a cylindrical rubber tube by detecting the voltage developed across the tube in the direction transverse both to the flow velocity and to the magnetic field. The apparatus is a very simple example of an electromagnetic flowmeter, a device which is commonly used both in industrial and physiological techniques. The phenomenology observed is similar to that of the Hall effect in the absence of an electric current in the direction of motion of the carriers. The experimental results show a dependence on the intensity of the magnetic field and on the carrier velocity, in good agreement with the theory. Discussion of the system, based on classical electromagnetism, indicates that the effect depends only on the flow rate, and is independent both of the velocity profile and of the electrical conductivity of the medium.

Width of OB Switching Time Distribution

In the OB experiments the commutation between the lower and upper branches of the bistability cycle (or viceversa) occurs within a time dependent on the relaxation rates of the cavity and of the absorbing medium. For an OB operation near the hysteresis region,the critical slowing- down phenomenon takes place and the commutation occurs with a time very long compared to the relaxation rates of the system. If a control parameter is modified by a step-function, the monitored output power of the bistable system reaches a new equibrium state after a delay time τD. A complete description of the transient regime is obtained only through a statistical analysis, where the intrinsic fluctuations and the external noise are included. Such a statistical analysis of the delay time in an optical bistability experiment has been recently presented for sodium atoms in an optical cavity [1].