An experiment about amplification without population inversion is discussed. The used configuration is a combination of a V and a Λ system. With a short (ns) laser pulse a coherent superposition is made, that is used afterwards as the lower state of an amplification scheme. Typical values for the gain factor and the output energy are four and hundreds of fJ, respectively.

We report the observation of light amplification without population inversion. A linear superposition of an m=1 and an m=-1 magnetic substate is populated coherently. Absorption from this superposition to a higher state is canceled by interference of channels, a so-called dark resonance. An inverse transition is used for amplification of light. The temporal behavior of the amplified pulse and the gain are studied as a function of the energy splitting due to a magnetic field. In a vapor of cadmium-112 gain factors of up to 4.3 are observed.

The radiative lifetimes of the levels in the 3d(9)4s(1D)4p configuration of Cu I are measured. The levels are excited from the metastable 3d(9)4s(2)2D3/2,5/2 levels. The metastable Cu atoms are generated in a pulsed hollow cathode discharge. The levels investigated are populated with a 35-ps laser pulse at wavelengths around 220 nm. The laser induced fluorescence signal is detected. The lifetime of the 3d(9)4s(3D)4p4D1/2 level is also determined by direct excitation from the ground state. A comparison with calculated literature values is given.

The hyperfine structure sub-levels of the 5s5p3P1 state of cadmium are populated coherently with a 35 ps light pulse. The coherence is detected in a second excitation step resulting in a modulation of the ionization probability. A third light pulse ionizes the atom. Differences in the H.F.S. of the odd isotopes are used to selectively enhance the ionization of one isotope. In a magnetic field the Zeeman splitting of the hyperfine structure causes an additional modulation. Measurements and a theoretical interpretation are given.

Coherence between the magnetic sub-levels of the 5s5p3P1 level of cadmium is induced by excitation. A second excitation step and photo-ionization are used to detect the coherence and perturbations by the nuclear angular momentum. The ionization probability of even isotopes is suppressed with respect to the odd isotopes by a factor 59.

A commercial copper vapour laser has been modified to operate at wavelengths of 303.6 nm and 306.3 nm. The laser transition at 578 nm was suppressed, in order to enhance the competing U.V. transitions. The time averaged U.V. output power level is a few mW's at an electrical input power of up to 4.5 kW. The duration of the pulses is 68 ns.

The branching ratios of transitions between the 6s 2S1/2, 7s 2S1/2, 6p 2P1/2,3/2, 5d 2D3/2,5/2 and 6d 2D3/2,5/2 levels in the spectrum of Ba II have been measured. The accuracy of oscillator strengths have been improved in respect to literature values.

The authors investigated the 3s2ns 2S, 3s2nd 2D and the 3s2nf 2F series in aluminium. These high levels were populated by three-photon two-step excitations using the 3s24p 2P3/2 as the intermediate state. They determined the positions of the series members accurately for n values between 28 and 60. The 2S and the 2F series are not perturbed. The quantum defect of the 2S series is confirmed to be 1.728 (2), the quantum defect of the 2F series is 0.041 (2). The perturbation of the 2D series is demonstrated by the variation of the quantum defect over the series, and by the fine structure (FS) of the 2D levels which is measured for n(37. The large positive splitting is shown to be explained by taking into account the fine structure of the 3s3p2 2D perturber. Using simple arguments the percentage of admixture of 3s3p2 2D to the 3s2nd 2D series can be determined while the FS of the perturber is estimated to be 20.5 cm-1.

L'abondance solaire en cadmium est determinee a partir des probabilites de transition de la raie Cd I a 5085.823 A.

Level positions of members betweenn=25 andn=45 of the2S Rydberg series in Ga I were measured with high accuracy. The quantum defect of this series turns out to be constant over the region observed, indicating an unperturbed series. The value of the quantum defect is 2.791(2). The fine structure in the2D series was measured by using direct excitation. A qualitative explanation is given.

Natural radiative lifetimes have been measured of the2P,2D,2F and4D5/2 terms in the 3 d9 4s(3D) 4p structure of copper I. A pulsed hollow cathode was used to generate 3d9 4s22D metastable atoms. From these metastable levels the states investigated were populated by a pulsed dye laser pumped by a Nd:YAG laser. A comparison with theoretical and experimental literature values is given.