W. T. Toner

A MEASUREMENT OF THE 1S-2S TRANSITION FREQUENCY IN MUONIUM

Doppler-free two-photon laser spectroscopy has been employed to measure the 12S12−22S12 transition in the muonium atom (μ+e−). A value of 2 455 529 002(33) (46) MHz has been obtained, which agrees with QED calculations within two standard deviations. The Lamb shift contributions are tested to the level 8×10−3. The corresponding measurements in hydrogen and deuterium using the same apparatus and laser system provide a test of the applied systematic corrections and have verified the systematic error of 46 MHz quoted. The mass of the positive muon has been derived from the isotope shift in this transition and yields a value of 105.65880(29)(43) MeVc2.

The anti-Stokes resonance Raman spectrum of photoexcited S1 trans-stilbene

Abstract Anti-Stokes resonance Raman spectra of S1 trans-stilbene have been measured for vibrational wavenumbers up to 1570 cm−1. Trans-stilbene in n-hexane was excited at 290–310 nm and probed at 580–620 nm, respectively, with 8 ps resolution. All the dominant bands seen in the Stokes spectrum of the S1 state are also seen in the anti-Stokes spectrum. Some anti-Stokes bands, notably those at 1570, 1240, 1180, 980, 720 and 285 cm−1, decrease markedly in relative intensity on a 2~ 10 ps timescale, displaying dynamics similar to those observed for the changes in the band position and bandwidth of several features in the Stokes spectrum.

Two independently tunable and synchronised femtosecond pulses generated in the visible at the repetition rate 40 kHz using optical parametric amplifiers

Abstract We report on a 40 kHz repetition rate travelling wave optical parametric amplifier (OPA) system designed for ultrafast spectroscopy. Two independently tunable OPAs seeded from a single white light continuum source each generate 40–75 nJ per pulse over a 480–730 nm spectral range when pumped by 1 μJ, 130 fs, 400 nm pulses derived from a Ti:sapphire regenerative amplifier. After removal of chirp, the cross-correlation between the two OPAs was measured to be 150 fs. Bandwidth was 205 ± 85 cm −1 , consistent with the transform limit of the compressed pulses. A single OPA gave up to 280 nJ per pulse signal energy when pumped with 3 μJ per pulse.

Two-photon laser spectroscopy of the muonium 1S–2S transition

The 12S1/2(F=1)−22S1/2(F=1) energy interval in muonium has been investigated by Doppler-free two-photon laser spectroscopy. The transition was observed by uniquely identifying and counting the muons released after the photoionization of the 2S state by the same laser field. The measured transition frequency of 2455 528016(58)(43) MHz is in good agreement with QED calculations. The experiment can be interpreted as a test of the Lamb shift contributions at the 1% level. The method is also well suited for a precise determination of the mass of the positive muon in a muoniumhydrogen isotope shift measurement.

Time-resolved spectroscopy study of the triplet state of 4-diethylaminobenzonitrile (DEABN)

The nonradiative deactivation processes of intramolecular charge transfer (ICT) and intersystem crossing (ISC) and their dependence on solvent polarity for DEABN have been studied using transient absorption (TA) spectroscopy. The TA spectra have been taken in non-polar hexane and polar acetonitrile solvents within the 400–630 nm spectral region at time delays of 2 ps to 6 ns. The results are complemented by nanosecond time-resolved resonance Raman (TR3) spectra of the triplet state of DEABN over the 700 to 2300 cm−1 frequency range. There is no significant difference between the Raman spectra recorded in hexane, acetonitrile and methanol solvents and this implies the triplet state has only one form. Comparison of DEABN triplet Raman spectrum with ab initio DFT geometry and vibrational analysis of DEABN ground state and triplet state TR3 spectra of the closely related compound dimethylaminobenzonitrile (DMABN) indicates the DEABN triplet state is planar or near planar in structure with noticeable biradical character.

The picosecond transient Raman spectra of S1 excited oligophenyls, oxazols and stilbene derivatives

Abstract Picosecond time-resolved resonance Raman spectra of electronically excited laser-dye molecules, oligophenyls, oxazols, and stilbene derivatives in solution have been obtained. The spectral profiles of several transients are observed to change on the picosecond timescale.

Spectroscopy of the 1S-2S energy splitting in muonium

A new measurement of the 1/sup 2/S/sub 1/2/-2/sup 2/5/sub 1/2/ energy splitting in muonium (/spl mu//sup +/e/sup -/) by Doppler-free two-photon laser spectroscopy yields a value of 2 455 529 002 (33) (46) MHz, where the 33 MHz error arises from statistics and the 46 MHz uncertainty is due to systematic line shifts. The experiment agrees with quantum electrodynamics theory within two standard deviations. The mass of the positive muon can be derived as 105.65880 (29) (43) MeV/c/sup 2/ from the measured muonium-hydrogen and muonium-deuterium 1S-2S isotope shifts. The measurement may alternatively be interpreted as a test of the equality of the electric charges of muon and electron with a precision of 1.4 (1.2) l0{-8}. >

Picosecond Absorption Measurements of Photosystem 1 from the Cyanobacterium, Chlorogloea fritschii

Absorption measurements in the picosecond time scale of Photosystems 1 and 2 (PS1, PS2) have proved more difficult than those of photosynthetic bacterial reaction centres as the associated light harvesting complexes have not proved amenable to removal, rendering it necessary for the measurement of very small absorption transients with considerable background absorbance. Previous measurements on PS1 absorption transients on a picosecond timescale have been performed with excitation flashes of 10–35 ps (1–4), giving risetimes for excitation of the reaction centre of no less than 15 ps. Giorgi et al (5, 6) and our own preliminary data (5) showed that absorption transients at 670–680 rm which could be ascribed to light-harvesting chlorophylls occurred at more rapid times than the absorbance change of P700. Shuvalov et al (2) identified an absorbance change at 693 nm with a lifetime of 32 ps which they attributed to the formation of reduced acceptor A-. Such an absorbance transient has been observed by Wasielewski (6)o.

Measurement of the muonium 1S‐2S transition frequency

Resonant ionization spectroscopy has been employed for measuring the 12S1/2−22S1/2 frequency difference in the hydrogen‐like muonium atom to 2 455 529 002(33)(46) MHz. The 1S‐2S two‐photon transition was induced Doppler‐free using two counter‐propagating laser beams. The 2S state was photo‐ionized by a third photon from the same laser field. The measurement agrees with QED theory within two standard deviations. The mass of the positive muon can be extracted from the isotope shifts in this transition to hydrogen and deuterium to 105.658 80(29)(43) MeV/c2.

Measurement of the muonium 1S-2S transition frequency

A new measurement of the 1S-2S energy splitting of muonium by Doppler-free two-photon spectroscopy has been performed at the Rutherford Appleton Laboratory in Chilton, Didcot, UK. Increased accuracy is expected compared to a previous experiment. Spectroscopy of this transition promises an improvement of the muon mass value.