We report a measurement of the 5P3/2 excited-state lifetime using two-pulse photon echoes in Rb vapor. The measurement is precise to ∼1% and agrees with the best measurement of atomic lifetime in Rb. The results suggest that a measurement precise to ∼0.25% is possible through additional data acquisition and study of systematic effects. The experiment relies on short optical pulses generated from a cw laser using acousto-optic modulators. The excitation pulses are on resonance with the F=3-->F′=4 transition in Rb85 or the F=2-->F′=3 transition in Rb87. The resulting photon echo signal is detected using a heterodyne detection technique. The excited-state lifetime is determined by measuring the exponential decay of the echo intensity as a function of the time between the excitation pulses. We also present a study of the echo intensity as a function of excitation pulse area and compare the results to simulations based on optical Bloch equations. The simulations include the effects of spontaneous emission as well as spatial and temporal variations of the intensities of excitation pulses.
We report a measurement of the 5P3/2 excited-state lifetime using two-pulse photon echoes in Rb vapor. The measurement is precise to ∼1% and agrees with the best measurement of atomic lifetime in Rb. The results suggest that a measurement precise to ∼0.25% is possible through additional data acquisition and study of systematic effects. The experiment relies on short optical pulses generated from a cw laser using acousto-optic modulators. The excitation pulses are on resonance with the F=3-->F′=4 transition in Rb85 or the F=2-->F′=3 transition in Rb87. The resulting photon echo signal is detected using a heterodyne detection technique. The excited-state lifetime is determined by measuring the exponential decay of the echo intensity as a function of the time between the excitation pulses. We also present a study of the echo intensity as a function of excitation pulse area and compare the results to simulations based on optical Bloch equations. The simulations include the effects of spontaneous emission as well as spatial and temporal variations of the intensities of excitation pulses.
We explore the sensitivity of the photon echo technique for achieving precise measurements of atomic lifetimes. Using short-pulse excitation of atomic rubidium vapor, we report the most statistically precise measurement of ($26.11\ifmmode\pm\else\textpm\fi{}0.03$) ns for the 52P3/2 lifetime. This statistical uncertainty of 0.11% was achieved in a total data acquisition time of 4 h over several weeks and rivals the most precise measurements in this atomic system. The experiment primarily relies on heterodyne detection and exploits the signal-to-noise ratio of the coherent release of energy along the direction of excitation, which is an exponential decay as a function of pulse separation T, as well as large repetition rates that are feasible in a gently heated vapor cell. We have developed an understanding of the technical limitations responsible for lifetime measurement instabilities on the basis of a simple model, which also enables us to propose a feedback scheme to limit these effects. Studies of the fractional uncertainty of the lifetime suggest that the statistical precision of this technique can be extended to the level of 0.03% in 10 min of data acquisition if the technical limitations are addressed. This level of precision has so far been exceeded by only one other lifetime measurement. Under these conditions, a rigorous investigation of systematic effects could potentially allow the echo technique to achieve the most accurate measurement of atomic lifetimes.
We have measured the radiative lifetimes of ns, np and nd Rydberg states of rubidium in the range 28 < n < 45. To enable long-lived states to be measured, our experiment uses slow-moving Rb atoms in a magneto-optical trap (MOT). Two experimental techniques have been adopted to reduce random and systematic errors. First, a narrow-bandwidth pulsed laser is used to excite the target Rydberg state, resulting in minimal shot-to-shot variation in the initial state population. Second, we monitor the target state population as a function of time delay from the laser pulse using a short-duration, millimetre-wave pulse that is resonant with a one- or two-photon transition. We then selectively field ionize the monitor state, and detect the resulting electrons with a micro-channel plate. This signal is an accurate mirror of the target state population, and is uncontaminated by contributions from other states which are populated by black body radiation. Our results are generally consistent with other recent experimental results obtained using a less sensitive method, and are also in excellent agreement with theory.
Two-pulse photon echoes on the $2^{2}S_{\frac{1}{2}}\ensuremath{-}2^{2}P_{\frac{3}{2}}$ transition in lithium vapor are generated using laser excitation pulses with angular separations of 0.70 and 1.40 mrad. The observed degradation of echo intensity with angling of the excitation pulses is in agreement with theory. The largest echoes radiated by the lithium sample contained 109 photons; the smallest echoes detected contained only an average of 0.04 photons. This intensity range of greater than 1010 represents measurements made over more than 15 natural lifetimes of the 22P23 state despite the degradation due to angling. Modulation of the echo signal due to the hyperfine structure of the 22P23 state is also observed.
We have observed fluorescence and ionization signals resulting from two-photon resonant excitation of thallium in an atomic beam. The output of a pulsed dye laser is used to excite the resonance between the ground state (6('2)P(,1/2)) and an excited n('2)P state of thallium. Both two-photon absorption and three-photon absorption occur simultaneously; the latter results in photoionization of the atom. The excited states populated by two-photon absorption decay via cascade fluorescence back to the ground state; one or more of these spectral components constitute our fluorescence signal. The lifetimes of the excited n('2)P states of thallium have been measured directly by observing the exponential decay of this fluorescence. Calculations are included to ascertain the time required for the fluorescence signal to reach within 2% of a simple exponential decay. This decay is a measure of the lifetime of the initial state, under the condition that none of the fluorescence components arise from states which are populated by cascade through longer-lived states. The lifetimes of the n('2)P(,1/2) and n('2)P(,3/2) states of thallium for n = 7 to 11 are determined in this manner and compared with the values deduced from semi-empirical calculations of oscillator strengths by various authors. For calculations employing the effects of core polarizability in the electron wavefunctions and in the transition matrix elements, the agreement is very good--to within our experimental uncertainty, which is typically(, )<5%. Our measurements are also compared to the four other known experimental values for such excited states of thallium. Some of these previous experiments and calculations were carried out in conjunction with parity non-conservation experiments in thallium. Our measurements may provide useful checks on the accuracy of some of the calculations performed in the evaluation of such experiments. The ionization and fluorescence signals are also studied under conditions of strong saturation of the two-photon resonance with the 7('2)P states. The manifestation of saturation in the ionization signal is a broadening of the excitation spectrum, which is found to greatly exceed that of the fluorescence signal. Furthermore, the ratio of the ionization signal to the fluorescence signal at the peak of the resonance is found to vary linearly at intensities below about 10('9) W/cm('2); this too saturates at higher intensities. Various models are employed to simulate the observed behavior, encompassing both rate equations as well as density matrix formulations. The numerical solutions to these models are compared with the observed behavior; the agreement is found to depend strongly on the assumed experi- mental conditions to which the ensemble of atoms is subjected.
Two closely spaced 778 nm, 4-ps pulses, two-photon resonant with the 5S-5D transition in Rb vapor generate a ground state grating, which later is excited by a similar third pulse, producing conical yoked superfluorescence echo on the 5S-6P, 420-nm transition. The intensity of this emission as a function of the relative delay between the leading excitation pulses is governed by the dynamics of Doppler dephasing and rephasing. This is the first observation of an echo effect induced by a spontaneous relaxation process.
Fluorescence has been detected from Rb atoms following narrow-line excitation by a short coherent optical pulse. The fluorescence oscillates as a function of the pulse area A with maxima for $A=\ensuremath{\pi},3\ensuremath{\pi},5\ensuremath{\pi},\dots{}$ and minima for $A=0,2\ensuremath{\pi},4\ensuremath{\pi},\dots{}$. In addition to demonstrating one of the simplest coherent optical effects, this experiment dramatizes the potential of the technique for determining dipole moments, pulse areas, relaxation times, and lifetimes. The details of the experimental apparatus are described. Results of a computer simulation of the experiment including the actuai excitation pulse shape, absorption frequency width, finite absorption (5-10% of pulse), and loss to a third level are given.