title: High-precision laser spectroscopy of the CO A(1)Π - X(1)Σ(+) (2,0), (3,0), and (4,0) bands.
abstract: High-precision two-photon Doppler-free frequency measurements have been performed on the CO A(1)Π - X(1)Σ(+) fourth-positive system (2,0), (3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for rotational quantum numbers up to J = 5, have been determined at an accuracy of 1.6 × 10(-3) cm(-1), using advanced techniques of two-color 2  +  1' resonance-enhanced multi-photon ionization, Sagnac interferometry, frequency-chirp analysis on the laser pulses, and correction for AC-Stark shifts. The accurate transition frequencies of the CO A(1)Π - X(1)Σ(+) system are of relevance for comparison with astronomical data in the search for possible drifts of fundamental constants in the early universe. The present accuracies in laboratory wavelengths of Δλ/λ = 2 × 10(-8) may be considered exact for the purpose of such comparisons.
authors: Department of Physics and Astronomy, and LaserLaB, VU University, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: M L
authors: ML
authors: Niu
authors: Department of Physics and Astronomy, and LaserLaB, VU University, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: F
authors: F
authors: Ramirez
authors: Department of Physics and Astronomy, and LaserLaB, VU University, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: E J
authors: EJ
authors: Salumbides
authors: Department of Physics and Astronomy, and LaserLaB, VU University, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: W
authors: W
authors: Ubachs