Polarization and intensity spectra have been obtained for excited-state magnesium (3s3p 1P1) - rare gas optical collisions. The magnesium was excited by a linearly polarized laser tuned to the 3s21s0 → 3s3p 1P1 atomic transition at 285 nm. A second linearly polarized laser was tuned near the 3s3p 1P1 → 3s5s 1S0 transition at 571 nm (experiment A) and near the 3s3p 1P1 → 3s4d 1D2 transition at 553 nm (experiment B). The polarization vector of the second laser was oriented either parallel or perpendicular to the polarization direction of the first laser. The absorption of nonresonant light from the second laser, possible only during a collision, was monitored by cascade fluorescence from the 3s21S0 ← 3s4p 1P1 transition at 203 nm. For each detuning of the second laser from resonance, the degree of linear polarization and the intensity were measured. For experiment A, argon and neon were used as rare gases. For experiment B, argon was the rare gas used. For experiment B, fluorescence from the 3s3p 1P1 ← 3s5s 1S0 transition, and the 3s3p3Pj ← 3s5s 3S1 transition at 333 nm were also measured in an attempt to observe the region of inelastic transitions in the molecular states. No inelastic branching was observed in this experiment.
An anomalous resonant dip of two-photon ionisation with 3s3p 1 P as an intermediate state and a stimulated emission by the 3s4s 3 S-3s3p 3 P transition, at 518.37 nm following the pulsed laser excitation near the 3s 2 1 S-3s3p 1 P resonance at 285.21 nm in magnesium vapour are observed and studied. The mechanism of the ionisation dip is attributed to formation and predissociation of the A 1 Sigma + u Mg 2 dimer, which transfer the population from the laser-pumped 3s3p 1 P level to 3s3p 3 P levels. Re-excitation of the produced 3s3p 3 P atoms and the subsequent radiative processes are presumed to explain the generation of stimulated emission. A theoretical model is employed to interpret the experimental phenomena.
We have measured the lifetime of the
3P1 metastable state of Mg and obtained a value of 2.2 \ifmmode\pm\else\textpm\fi{} 0.2 msec. The level was excited with a dye laser tuned to the intercombination line ($3s3p^{3}P_{1}\ensuremath{\leftrightarrow}3{s}^{2}^{1}S_{0}$). In addition to the
3P1 state, the
3P2 and
3P0 levels were populated by mixing collisions owing to the presence of an inert buffer gas. The populations of all three metastable levels were monitored as a function of time by observing the absorption of Mg resonance radiation ($^{3}P_{0,1,2}\ensuremath{\rightarrow}^{3}S_{1}$) out of each level. The mixing time was short compared to the
3P1 lifetime, so that the populations of the three metastable levels were in thermal equilibrium with each other. This produced an apparent lengthening of the
3P1 lifetime, which would introduce a large systematic error if the degree of mixing were not known. Cenventionally, one observes the fluorescence from the excited levels to obtain their lifetimes. Because the lifetimes of the
3P2 and
3P0 states are too long, fluorescence from these states cannot be observed, and the observation of fluorescence from the
3P1 state alone provides insufficient information to determine its lifetime.
We have studied superfluorescence (SF) in Ca vapor evolving on the 3d4s ^3 D_J -4s4p ^3 P_J-1 transitions at 1.9 µm by exciting the 4s^21 S_0 -4s4p ^1 P_1 with a pulsed dye laser. SF is generated following population transfer by spin-changing collisions with an inert gas Ar from the 4s4p ^1 P_1 and 3d4s ^1 D_2 levels. We show for the first time to our knowledge that the time delay for SF evolution follows the 1/sqrt N dependence expected for the case of uniform excitation of the vapor column by collisional transfer. Here, N is the number of participating atoms that was measured directly from the photon yield. The measured photon yield for the signal as a function of Ar pressure was found to be consistent with rate equations that simulate the buildup of populations in the ^3 D_J levels based on known collisional rates. This suggests that collisional rates can be directly inferred on the basis of SF photon yields and the atomic level populations. The pulse shapes for SF show temporal oscillations that depend on two distinct factors. The first is the presence of a number of independently evolving regions in the gain medium, and the second is the presence of spatial modes. Temporal ringing is a well-known effect related to the exchange of energy between the atoms and the radiation field during pulse propagation. However, the temporal ringing observed in this experiment is far more pronounced than in previous SF experiments due to a particular choice of evolution parameters. This should make it feasible to compare our results with detailed numerical simulations that have been carried out previously.
We have observed stimulated emission on the transitions 43S1−33PJ° near 518 nm following pulsed laser excitation of Mg vapor near the 31S0−33P1° resonance at 285 nm. The emission has a divergence similar to the pump laser and closely follows the incident laser in time. The mechanism apparently involves pumping an accidental coincidence 31S0−33P1° and 33PJ°−53DJ, permitting depletion of the lower level of the triplet transition. Photoionization of the Mg vapor creates a large electron density (≲1013 cm−3); electron-impact collisions are presumed to mediate the process, transferring population from the laser-pumped 31P1° level to the triplet manifold.
The lifetime of the metastable
3P1 state of Mg has been remeasured by a dye-laser excitation technique. The metastable state was populated by an intense pulse of 4571-\AA{} radiation from a flashlamp-pumped dye laser, and the decay of the population was monitored by observing the absorption of 5173-\AA{} resonance radiation from a Mg discharge lamp. The measured value for the
3P1 lifetime is 4.5 \ifmmode\pm\else\textpm\fi{} 0.5 msec.