Reflection Of Wave Packets Research Articles

Ellipsometry and transient reflectivity near the excitonic resonance in CdSe.

We report two experiments. The first is an accurate measurement of the phase of the light reflected by a CdSe crystal in the excitonic region. The second is a direct measurement of the time delay experienced by a reflected wave packet in the same frequency range. We show that it is necessary to take into account the existence of an exciton-free surface layer to satisfactorily fit the experimental results. The very fast variation of phase near the longitudinal exciton frequency, larger than \ensuremath{\pi} over 0.3 meV, and the very large delay of 12 ps observed under the same conditions are attributed to multiple reflections inside the exciton-free layer in a frequency range where the layer acts as an antireflecting Fabry-P\'erot plate.

Branch conversion at surfaces of superfluid3He

We study the reflection of wave packets of quasiparticles from surfaces of a superfluid Fermi liquid. The reflection process is accompanied by changes in the internal structure of the wave packet. One finds particle-hole conversion (Andreev reflection), and a changed magnetization of the wave packet. The latter effect is a special consequence of triplet pairing and is related to the spontaneously broken spin-orbit symmetry. A particularly striking example is a non-magnetic wave packet that is split by the surface into two magnetic ones moving in different directions.

Reflection of ion acoustic soliton from the sheath around a negatively biased grid

Experimental observations on the partial reflection of ion acoustic solitary waves from sharp density gradients, produced by a negatively biased grid immersed in the plasma, are presented. Reflection occurs where the density gradient scale size is of the same order as the width of the soliton. The reflected wave packet apppears to be highly dispersive and travels with subsonic velocity.

Interaction of electromagnetic waves with a moving ionization front

The problem of an electromagnetic wave packet, incident on a relativistically moving plane ionization or recombination front in a stationary gas, is considered. The frequency of the reflected wave packet is found to obey the usual double Doppler shift relation. However, the reflection coefficients and the physics can differ significantly from the case of reflection from moving material objects. In the unmagnetized case, the ratio of the energy in the reflected wave packet to that in the incident wave packet is found to be εr*/εi*=ωi*/ωr* for an oncoming overdense ionization front, for which ωi*<ωr* (where ωi* and ωr* are the incident and reflected wave frequencies in the laboratory frame). For an oncoming ionization front in the presence of an applied magnetic field normal to the front, εr*/εi* can considerably exceed ωi*/ωr*. For a retreating recombination front (ωi*≳ωr*), in the overdense unmagnetized case, εr*/εi*=ωr*/ωi*. These results have important implications for the production of sub-millimeter wavelength pulses by upshifted reflection from a relativistically moving ionization front.

Position-operator method for evaluating the shift of a totally reflected electron

A method based on expectation values of a position operator is developed for evaluating the spatial shift of a polarized Dirac electron undergoing total reflection. Longitudinal and transverse components of the shift, as well as the associated time delay, are obtained by considering the differences in the expectation values for the physically reflected wave packet and a purely geometrically reflected wave packet. For a number of position operators, this method is used to calculate the mean shift arising from a single reflection of an electron from a step-function potential. Eigenpolarization states are determined by means of a localization form-invariance argument. For these states, results obtained employing the Newton-Wigner position operator are shown to be identical to those obtained using the phase-shift analysis method. A comparison calculation giving different results is made using the current-flux method. The current-flux results are shown to be inconsistent with conservation of total angular momentum normal to the reflecting boundary.

Note on the Transmission and Reflection of Wave Packets by Potential Barriers

In previous studies, by the methods of wave mechanics, of one-dimensional motion of particles in cases in which there are intervals in which the value of the potential energy function $V(x)$ exceeds the value of the total energy $E$, attention has been confined to wave functions of the form $f(x, E)\mathrm{exp}(\ensuremath{-}\frac{2\ensuremath{\pi}\mathrm{iEt}}{h})$. In the present note wave packets are considered, instead of these trains of waves.The function $V(x)$ is taken as follows: ${V(x),=0 \mathrm{for} xl0 \mathrm{and}\mathrm{for} xga,}{={V}_{0}g0 \mathrm{for} 0lxla.}$ A wave function is set up which initially represents a wave packet moving toward the point $x=0$ from the left. The separation of the incident packet into a reflected packet and a transmitted packet is studied. It is found that the transmitted packet appears at the point $x=a$ at about the time at which the incident packet reaches the point $x=0$, so that there is no appreciable delay in the transmission of the packet through the barrier.