Broadening of the satellites of the Hg green line $\ensuremath{\lambda}5461$ was observed when the light passed between the plates of a Kerr cell on which was impressed a varying E.M.F. having a frequency of 2\ifmmode\times\else\texttimes\fi{}${10}^{7}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. The E.M.F. was obtained by superposing the output of a vacuum tube oscillator upon a steady potential of about 7000 volts. The maximum oscillator voltage was about 5000 volts. With this voltage the fine structure of the Hg green line became so diffuse that two satellites having a separation of 0.045A were scarcely resolved by the Lummer-plate. The broadening was observed to increase rapidly with the oscillator voltage. The observed effect is predicted by the classical electromagnetic theory and the quantum theories of dispersion of Kramers-Heisenburg, Schr\"odinger, and Dirac. The high frequency voltage effects a rapid variation of the refractive index of the nitrobenzene in the Kerr cell which in turn produces a corresponding variation in optical path, giving the source a virtual velocity, and thereby producing a Doppler effect. The magnitude of the observed boradening is in agreement with the predictions of theory.
Broadening of the satellites of the Hg green line \ensuremathλ5461 was observed when the light passed between the plates of a Kerr cell on which was impressed a varying E.M.F. having a frequency of 2\ifmmode\times\else\texttimes\fi{}107sec\ensuremath−1. The E.M.F. was obtained by superposing the output of a vacuum tube oscillator upon a steady potential of about 7000 volts. The maximum oscillator voltage was about 5000 volts. With this voltage the fine structure of the Hg green line became so diffuse that two satellites having a separation of 0.045A were scarcely resolved by the Lummer-plate. The broadening was observed to increase rapidly with the oscillator voltage. The observed effect is predicted by the classical electromagnetic theory and the quantum theories of dispersion of Kramers-Heisenburg, Schr"odinger, and Dirac. The high frequency voltage effects a rapid variation of the refractive index of the nitrobenzene in the Kerr cell which in turn produces a corresponding variation in optical path, giving the source a virtual velocity, and thereby producing a Doppler effect. The magnitude of the observed boradening is in agreement with the predictions of theory.
The Doppler frequency shift of an optical wave can be made, not only by moving media, but by a moving boundary in a stationary medium. Especially, the reflected wave by the boundary is shifted by a large amount of the frequency, as the velocity of the boundary approaches the one of the light. The moving boundary in a stationary medium can be produced in a liquid, in nitro-benzene (C_6H_5NO_2) for example, by a high voltage pulse, transmitted along a strip line which is installed in a cell filled with the liquid. This paper describes, theoretically and experimentally, the Doppler frequency shift of a He-Ne laser by the moving boundary. The frequency of the light transmitted to the end of the cell is shifted by about 15MHz. The shifted frequency of the reflected light by the boundary has not, however, been observed yet, because the variation of the refractive index of the medium is too little. From the results of this paper the large amount of the frequency shift of the laser is highly expected if the medium with the large kerr constant is discovered in the near future.
Introduction One of the most impressive accomplishments of wave optics is its success in providing a coherent and succinct description of the interactions between electromagnetic waves and matter (gases, solids, etc.). Maxwell's equations, which describe the propagation of light, and the Laplace–Lorentz equations, which describe the source terms of light, allow one to take into account the phenomena of refraction, diffusion, and diffraction of light by dense media. It is amazing – to say the least – that such a theory can account for the complex interactions of an electromagnetic wave with an immense ensemble of atoms (each approximated in terms of individual harmonic oscillators), by means of a simple optical index n op . Such an achievement is reminiscent and, indeed, on par with the level of concision achieved by the concept of effective mass in representing the interaction of a conduction electron with a crystalline lattice. In the description of all these effects, an electromagnetic wave with (angular) frequency ω forces free carriers into oscillatory motion at the same frequency, leading to radiative re-emission at this same frequency. This behaviour is a natural by-product of the linear equations we have employed up until now. In this chapter, we will see that non-linear media (i.e. materials whose response to external excitations contains non-linear terms), may by used to perform frequency conversion as evidenced, for example, by second harmonic light generation or optical parametric oscillations.
The group velocity at which light pulses propagate through a dispersive material system is very different from the vacuum speed of light c, One refers to light as being "slow" for v g << c (Boyd & Gauthier, 2009) or "fast" for v g > c or v g <0 (Stenner et al, 2003 ).For v g <0, the pulse envelope appears to travel backward in the material (Gehring et al, 2006), and hence it is sometimes referred to as "backward light."The subject of slow light has caused keen interest in the past decade or more, and it is possible to control the group velocity of light pulses in the dispersive materials.Interest in slow and fast light dates back to the early days of the 20th century.Sommerfeld and Brillouin (Sommerfeld & Brillouin, 1960) were intrigued by the fact that theory predicts that v g can exceed c, which leads to apparent inconsistencies with Einstein's special theory of relativity.Experimental investigations of extreme propagation velocities were performed soon after the invention of the laser (Faxvog and et al, 1970).In 1999, Harris's group research work greatly stimulated researchers' interests, which showed that light could be slowed down to 17m/s.The result was obtained in ultra cold atom clouds with the use of electromagnetically induced transparency (EIT), which induces transparency in a material while allowing it to retain strong linear and nonlinear optical properties (Hau et al, 1999).Slow light can also be obtained through the use of the optical response of hot atomic vapors (Philips et al, 2001).These early research works require hard conditions and the slow light cannot operate in room temperature.Recently, researchers found ways to realize slow light operating in room temperature and solid-state materials, which are more suited for many practical applications, namely slow light via stimulated Brillouin scattering(SBS), slow light via coherent population oscillations (CPO), tunable time delays based on group velocity dispersion or conversion/ dispersion(C/D), slow light in fiber Bragg gratings and so on.In this chapter, we describe some of the physical mechanisms that can be used to induce slow and fast light effects in room-temperature solids (Bigelow et al, 2003) and some of the exotic propagation effects that can thereby be observed.We also survey some applications of slow and fast light within the fields of quantum electronics and photonics. Fundamentals of slow and fast lightSlow and fast light refer to the group velocity of a light wave.The group velocity is the velocity most closely related to the velocity at which the peak of a light pulse moves through an optical dispersive material (Milonni, 2005), and is given by the standard result www.intechopen.comRecent Progress in Optical Fiber Research 82where n is the refractive (phase) index and ω is the angular frequency of the carrier wave of the light field.One refers to light as being slow light for v g << c, fast light for for v g > c, and backwards light for v g <0 or v g is negative.Extreme values of the group velocity invariably rely on the dominance of the second contribution to the group index of Equation ( 1).This contribution of course results from the frequency dependence of the refractive index, and for this reason extreme values of the group velocity are usually associated with the resonant or near-resonant response of material systems.According to this theory, slow light is expected in the wings of an absorption line and fast light is expected near line center, and the spatial dispersion, that is, the non-locality in space of the medium response, is another mechanism that can lead to slow light, as has been predicted (Kocharovskaya et al,2001) and observed (Strekalov et al, 2001).We catalogue the main methods to realize slow light in room temperature solid, namely slow light via stimulated Brillouin scattering(SBS), slow light via coherent population oscillations (CPO), tunable time delays based on group velocity dispersion or conversion/ dispersion(C/D), slow light in fiber Bragg gratings and so on.We will describe CPO and SBS slow light in more details.
The two-level atom can, for good reason, be considered the basic material structure for the study of quantum optics [1]. The two-level atom has played a fundamental role in studies of physical processes, including self-induced transparency (SIT), photon echoes, optical nutation, saturation spectroscopy, and, most recently, slow- and fast-light research. This latter field has recently been the subject of great activity, as researchers have learned how to utilize various physical processes to exert control over the velocity of propagation of light pulses through material systems [2]. This interest stems both from the intellectual intrigue in situations in which the velocity of light can be speeded up or slowed down by many orders of magnitude and the promise that such techniques might be useful for applications in fields such as telecommunications and optical computing [3‐6]. Most of the recent work in this field has made use of the process of electromagnetically induced transparency (EIT) to induce a narrow transparency region in an otherwise highly absorbing optical material [7, 8]. The rapid variation of the refractive index n associated with this transparency window then leads to a strong modification of the group velocity n g in accordance with the standard relation
A detailed theory of the frequency dependence of the electro-optical Kerr effect of an atom in the region of absorption lines is presented and applied to the particular case of 2 P←2 S doublets of sodium and lithium vapours. Doppler broadening is taken into account. With electric dipole matrix elements derived from the Coulomb approximation for both discrete and continuum states, the molar Kerr constant, m K(32 P←32 S), of atomic sodium vapour in the D-line absorption region is calculated to ±30 per cent; the calculations indicate that m K in the vicinity of the D2 line (32 P 3/2←32 S 1/2) should be very much greater than near the D1 line (32 P 1/2←32 S 1/2) in qualitative agreement with the experiments of Kopfermann and Ladenburg Qualitative consideration is also given to dispersion of magnetic birefringence; in contrast with electric birefringence strong dispersion is expected near both lines of alkali metal 2 P←2 S doublets.
Abstract A method of determining directly the mean lives of excited atoms was described in detail in a previous paper. This method employs a Kerr cell operated by a high frequency oscillator which is also used to run a Geissler tube. With the electrical arrangement used, a minimum of light should pass through the Kerr cell system if light were emitted instantaneously. Owing to the finite time that the atoms remain in the excited state, there is a lag between the current in the discharge tube and the emission of light. By increasing the distance that the light travels before reaching the cell a point may be found where a maximum of light passes the cell, from which the lag may be determined. This is directly connected with the mean life of the state. In the previous paper results for neon were given and the present paper deals with the application of this method to hydrogen. Fig. 1 shows the electrical arrangement used. This is essentially the same as that used for neon, except that a cathode ray oscillograph is used to determine the phase difference between the potential on the Kerr cell and the current in the discharge tube. Thus the deflector plates Px give deflections proportional to the voltage on the Kerr cell K. C. while the plates Py give deflections proportional to the voltage on C2 and therefore in phase quadrature with the current through the discharge tube. L1C1 is a tuned circuit which picks up energy from the oscillator and by tuning this, the oscillograph figure may be made a straight line. When this is so the current through the discharge tube is 90° out of phase with the voltage on the Kerr cell. L2C2 forms a series tuned circuit of low impedance, and the variable condenser C7 gives a means of making the two deflections equal. The oscillograph can be set for linearity within an accuracy of ½° which is of the same order as the accuracy of the experiment. A correction has to be applied for the time that the electrons take to travel between the plates of the oscillograph. Thus when the same oscillating voltage is applied to the two pairs of plates, the oscillograph figure is not a straight line, but shows an apparent phase difference, owing to the fact that one pair of plates acts on the electron beam sooner than the other pair. With the oscillograph used, this time was 1⋅5 . 10-9 secs, or at a wave-length of 60 metres a phase angle of 2⋅7°. This must be added to the observed lag.