From measurements of the degree of polarization of the molecular fluorescence, it is shown that one can determine the coefficients of the first three even-ordered Legendre polynomials in the expansion of the spatial distribution of J vectors (MJ population), n(θ)=1 + a2P2(cosθ) + a4P4(cosθ), where θ is the angle between the angular momentum vector J of the molecule and the beam direction. This method is applied to determine the alignment of Na2 molecules in a supersonic nozzle beam generated by expansion of sodium vapor through a converging nozzle (throat diameter = 0.375 mm and channel length = 0.750 mm) with stagnation temperature (oven temperature) up to ∼1015°K, corresponding to stagnation pressures (oven pressures) up to ∼155 torr. The 4880 Å line of a cw argon-ion laser is used to excite the transition (ν″=3, J″=43 → ν′=6, J′=43) in the B 1Πu−X 1Σg+ band system of Na2 molecules and the degree of polarization of a single line of the resulting fluorescence series (Q series) is measured as a function of (1) stagnation pressure p0 and (2) the angle θ0 between the electric vector of the exciting laser light and the molecular beam direction. A decrease in the degree of polarization from its isotropic value of 0.50 for θ0=0 to a value of 0.44 at a stagnation pressure of 155 torr is found, showing increasing alignment of dimer molecules with their angular momenta preferentially pointing perpendicular to the beam direction. At the stagnation pressure of 155 torr the coefficients of the Legendre polynomials are found to be a2=−0.203±0.006 and a4=−0.14±0.03. For this distribution the ratio of molecules with angular momentum J parallel and perpendicular to the beam axis is ∼2:3. Classical models involving the nonreactive collisions between hard spheres (atoms) and ellipsoids of revolution (molecules) and the chemical exchange between atoms and dimers predict the production of alignment in qualitative agreement with experiment.

By spectroscopically analyzing the white light and laser-induced fluorescence excited in a nozzle beam of Na 2 molecules, we have measured the population distribution of the (v,J) levels of the ground state. The Na2 molecules are produced in nozzle beams with various stagnation pressures (50-240 torr) of alkali metal and with nozzles of different throat diameters (0.12-0.50 mm). We find at a stagnation pressure of 50 torr and a nozzle diameter of 0.5 mm a Boltzmann distribution characterized by a vibrational temperature of 153±5'K and a rotational temperature of 55 ± 10'K. Beams under different stagnation conditions have essentially the same internal state distribution. Studies of K2 dimers produced in a nozzle beam with various stagnation pressures (20-300 torr) and a 0.25 mm nozzle throat diameter also show cooling in both vibrational and rotational modes. A search is made for atomic fluorescence arising from the photodissociation of dimers in high vibrational levels of the ground state. No evidence is found for the presence of vibrationally-excited dimers in the nozzle beam.

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SUMMARYCode-spread and conventional CDMA systems are discussed and compared for varying interleaver sizes. Results are evaluated in terms of BER versus E b /N o . It is observed that the code-spread systems give better performance. It is also observed that performance of both the systems improves significantly with an increase in the interleaver size.