We survey the possible time-resolved three pulse nonlinear spectroscopic techniques and their application to gas-phase samples. The role of each of the interacting electric fields is specified, and the nature of the signal is interpreted using the density matrix representation. Simulations of these nonlinear optical signals are based on the perturbative solution of the Liouville equation for the density matrix to third order in the applied fields. We present closed expressions for the integrated and frequency dispersed signals that identify the type of molecular response for each technique and give the signal dependence on the various time delays between laser pulses. We choose a simple experimental system, two-electronic states coupled to a single vibrational mode of diatomic iodine, with weak dephasing, to illustrate various molecular polarization responses in fourwave mixing experiments including pump-probe, reverse transient grating, and photon echo. These signals and their simulations illustrate how the time delays between pulses can be effectively used to control the optical response of the molecular system.

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The roles of pulse sequence and pulse chirp were explored using femtosecond three‐pulse four‐wave mixing (FWM). The experiments were carried out on gas‐phase I2 and the degenerate laser pulses are resonant with the transition between the X (1Σ italicg +) ground and B (3Π 0italicu +) excited electronic states. Impulsive excitation leads to the observation of vibrational coherence in the ground and the excited states. Control over the observed population and vibrational coherence is achieved by using specific pulse sequences. Using chirped pulses results in changes in vibrational coherence. When the FWM signal is spectrally dispersed, the two‐dimensional data (wavelength and time delay) provide important spectroscopic information about the intramolecular dynamics of both electronic states. This information is not typically available in time or spectrally integrated measurements. A theoretical foundation for these observations based on the density matrix formalism is briefly discussed. Copyright © 2000 John Wiley & Sons, Ltd.

This study focuses on a professional development program for science teachers near or on American Indian reservations in Montana. This program was framed by culturally relevant pedagogy premises and was characterized by instructional strategies and content foci resulting from the intersection between three cultures: tribal, science teaching, and science. The study employs a quasi‐experimental design and quantitative methods to examine the impact of the program on teachers' practice and beliefs, and to determine the relationship between student‐centered equity‐focused instruction and students' science test score gains. Results of the analyses indicate that after 2 years in the program teachers changed their teaching practices and beliefs about their ability to teach science and to implement equitable instruction in a way that positively impacted students' performance. Using a multiple regression analysis it was found that gains in teacher beliefs about their ability to implement equitable strategies and the increase of teaching strategies that prompt students to make connections between science and their real‐life issues significantly explained the 36.7% of the variance of student science test scores gains in treatment classrooms. No significant changes in beliefs or teaching strategies were found for comparison teachers. The results obtained from this study contribute to the identification of characteristics of a professional development program that positively impacted the science teaching of American Indian students. © 2012 Wiley Periodicals, Inc. J Res Sci Teach 50:12–32, 2013

Control of coherence and population transfer between the ground and excited states is reported using three-pulse four-wave mixing. The inherent vibrational dynamics of the system are utilized in timing the pulse sequence that controls the excitation process. A slight alteration in the pulse sequence timing causes a change in the observed signal from coherent vibration in the ground state to coherent vibration in the excited state. This control is demonstrated experimentally for molecular iodine. The theoretical basis for these experiments is discussed in terms of the density matrix for a multilevel system.