Pulses circularly polarized

Recently, an interesting correlation between the laser pulse polarization and the ellipticity of the electron beam profile has been observed [71]. However, no major influence of laser polarization on the efficiency of the electron acceleration processes has been observed so far, nor this influence has been predicted by theory and simulations, differently from the proton acceleration. For proton acceleration, a great improvement on bunch charge and quality are expected by using circularly polarized laser pulses focused on thin foils at ultra-high intensities [72-74]. 

Consider the case when the external field is a monochromatic circularly polarized pulse, E(f) = Aexp(-iojf), where A is a slowly varying envelope function. For this pulse the phase angle of dE/df is rotated by r/2 from the direction of E. From Eqs. (5.17) and (5.18) we then find... 

While ionization by linearly polarized fields has been well studied, there is only one report of ionization by a circularly polarized field, the ionization of Na by an 8.5 GHz field.36 In the experiment Na atoms in an atomic beam pass through a Fabry-Perot microwave cavity, where they are excited to a Rydberg state using two pulsed tunable dye lasers tuned to the 3s — 3p and 3p —> Rydberg transitions at 5890 A and —4140 A respectively. The atoms are excited to the Rydberg states in the presence of the circularly polarized microwave field which is turned off 1 fis after the laser pulses. Immediately afterwards a pulsed field is applied to the atoms to drive any ions produced by microwave ionization to a microchannel plate detector. To measure the ionization threshold field the ion current is measured as the microwave power is varied. 

For the specific case of differential circularly polarized emission, starting with time-dependent perturbation theory, one obtains the following relationship between the time-dependent experimental observable, AI(X, ), the excited state population, Nn, and the differential transition probability, AW = WLeft - Wpjght, following an excitation pulse of polarization, k, at time t = 0... 

When a circularly polarized probe pulse is introduced at a time delay of At after the pump laser pulse, new features with a pair of straight distributions running parallel to the horizontal and vertical axes emerge [29], as... 

Photoderacemization is the simplest case of direct asymmetric photoreactions induced by cpl. The enantiomers are interconverted, and the mixture becomes optically active. Reaction scheme 2 is a modification of Scheme 1 ground state racemization is excluded. The enantiomerization step R S was observed directly by Metcalf et al. [9] by means of the time-resolved circularly polarized luminescence of europium-tris(bipicolinate). By means of a cpl laser pulse, a difference in the excited state population is created, and the decay of circular... 

A schematic setup of the photo-elasticity technique is given in Fig. 2. Two sheets of a circular polarizer were placed on both sides of the specimen. An Innova Sabre argon-ion pulsed laser... 

Impulse Noise Analysis Results. ANITA-lite measured about 130,000 distinct events, with an approximate rate of 5 events per minute. Fig. 6 shows examples of the major classes of impulsive noise encountered. The vast majority of triggered events are due to local payload interference such as switching noise from the Support Instrument Package. The duration of this class of events exceeds several hundred nanoseconds and a few events exhibit circular polarization for a portion of the pulse. The bottom two panes show an example of a synthetic pulse injected into the data stream to simulate a true signal event. The pulse is coherent and aligned across all channels. Preliminary studies of event selection procedures were conducted. They yield no passing events, while 97% of simulated Askaryan-induced impulses with amplitude 5<7 above noise survive (Miocinovic et al., 2004). 

The transmitter power needs to be adjusted to provide pulses short enough to obtain nonselective 180° pulses. In applications requiring large coils, resonators can be constructed which are fed with the sine and the cosine component of the rf signal [Hou2]. By using such circularly polarized excitation a factor of two is saved in the rf power in comparison to linearly polarized excitation [Glol]. 

Fig. 10 Femtosecond-pulse laser treatment of polyimide. r=150 fs, 1=800 nm. Squared diameters of the modified areas of polyimide in dependence on the maximum laser flu-ence for circularly polarized light. Solid symbols focusing with/= 25 mm lens, right axis. Hollow symbols focusing with/=60 mm lens, left axis [18]...

Fig. 23 Scanning electron microscope pictures of femtosecond pulse laser-ablated poly-imide. r=150 fs, 2=800 nm, -F0=L3 J crrT2, N= 50, circular polarization, (a) Total aspect, (b) detail [18]...

Barth et al. performed a quantum simulation of laser-driven electron dynamics in Mg porphyrin, which is an aromatic molecule of symmetry [14]. The results of their simulation showed that n electrons of Mg porphyrin can be rotated around its aromatic ring by an ultrashort circularly polarized UV laser pulse propagating along its C4 axis. The rotation direction of n electrons is predetermined in a laboratory frame by that of the polarization plane of the circularly polarized laser pulse, that is, by photon angular momentum. 

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