Abstract
A polarization-resolved beam deflection technique is used to separate the bound-electronic and molecular rotational components of nonlinear refractive transients of molecular gases. Coherent rotational revivals from N(2), O(2), and two isotopologues of carbon disulfide (CS(2)), are identified in gaseous mixtures. Dephasing rates, rotational and centrifugal distortion constants of each species are measured. Polarization at the magic angle allows unambiguous measurement of the bound-electronic nonlinear refractive index of air and second hyperpolarizability of CS(2). Agreement between gas and liquid phase second hyperpolarizability measurements is found using the Lorentz-Lorenz local field correction.
Highlights
The nonlinear optical (NLO) response of gases under intense laser fields has been extensively investigated and plays a critical role in applications of pulse compression [1], high harmonic generation [2], attosecond pulse shaping [3, 4], control of filamentation [5,6,7,8], and separation of molecular isotopologues [9]
Without the implementation of more complicated optical-heterodyne-detection (OHD) [17], neither Optical Kerr Effect (OKE) nor Degenerate four wave mixing (DFWM) are able to measure the sign of the refractive index change
Unlike the OKE and DFWM, the measured signal in a beam deflection (BD) measurement is directly proportional to the induced refractive index change, yielding both the magnitude and sign of the nonlinear refraction (NLR) without the requirement of OHD
Summary
The nonlinear optical (NLO) response of gases under intense laser fields has been extensively investigated and plays a critical role in applications of pulse compression [1], high harmonic generation [2], attosecond pulse shaping [3, 4], control of filamentation [5,6,7,8], and separation of molecular isotopologues [9]. Unlike the OKE and DFWM, the measured signal in a BD measurement is directly proportional to the induced refractive index change, yielding both the magnitude and sign of the NLR without the requirement of OHD It is a simpler technique and may be more implemented than interferometric methods [19]. With a probe polarized at the “magic angle” (54.7°) with respect to that of the excitation polarization, the rotational contribution is completely eliminated from the measurement [24] This isolates the bound-electronic NLR and allows unambiguous determination of the nonlinear refractive index n2,el and the second hyperpolarizability γ [23]. The BD technique provides a thorough characterization of the nonlinear optical response of molecular gases and precise determination of n2,el, γ, rotational and centrifugal distortion constants, dephasing rates, and rotational Raman spectrum in a self-consistent quantitative measurement
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