Observation of reflectance fluctuations in metals

Abstract

Through the study of the power spectra of a monochromatic light beam reflected by metallic mirrors, fluctuations in their reflectance is observed. The power spectra were obtained down to a factor 10 −6 below the Standard Quantum Limit, with a dynamic range of 10 5 in the frequency and power, using methods we developed. The properties of the spectra are investigated and their dependence on the material is analyzed. The physics underlying the phenomenon is also discussed. These fluctuations provide a new window into the degrees of freedom responsible for the reflection process in metals.

Observing random walks of atoms in buffer gas through resonant light absorption

“…On the microscopic scale, perhaps the most well known example is the Brownian motion of particles, which is optically visible [1][2][3]. Even on a smaller scale, the thermal motions of the atoms are visible through surface fluctuations of liquids [4][5][6], high power interferometry measurements on mirrors [7] and complex materials [8]. In gases, the ballistic thermal motion of atoms and molecules lead to the transit time broadening of the resonant widths [9] and the free streaming of atoms can be observed through their transit noise in light [10].…”

“…where · · · denotes averaging, and the relative statistical error here is 1/ √ N , with N being the number of averagings [8]. This statistical reduction can reduce any uncorrelated noise, including shot noise, to any desired level, in principle.…”

Thermal interface fluctuations of liquids and viscoelastic materials

“…Taking the correlation of independent measurements here is crucial, since without it, the shot-noise is not reduced. This principle for reducing the shot-noise has been used to achieve factors of 10 −3 to 10 −5 reduction, in the measurements of surface thermal fluctuations of fluids [19,20], spontaneous noise in atomic vapor [21,22], and reflectance fluctuations [23].…”

“…where P (q, ω) is the spectral function for the interface fluctuations, and w is the beam spot radius, and q denotes the wave number [19,25]. Since the observed inclination of the surface is averaged within the beam spot, fluctuations with shorter wavelengths are effectively cutoff by a Gaussian factor.…”

“…The theory of thermal fluctuations of interfaces was worked out from first principles some time ago [11][12][13][14][15], yet it had not been possible to experimentally examine their behavior in detail. In this work, the fluctuations are observed using light reflection, with the interface effectively acting as an optical lever [16][17][18][19], so that the method does not rely on the existence of waves that act as gratings. This allows us to measure properties of thermal fluctuations of previously inaccessible interfaces with precision, over a wide frequency range, including those involving highly viscous materials.…”