Spontaneous emission can create coherences in a multilevel atom having close lying levels, subjec... more Spontaneous emission can create coherences in a multilevel atom having close lying levels, subject to the condition that the atomic dipole matrix elements are non-orthogonal. This condition is rarely met in atomic systems. We report the possibility of bypassing this condition and thereby creating coherences by letting the atom with orthogonal dipoles to interact with the vacuum of a pre-selected polarized cavity mode rather than the free space vacuum. We derive a master equation for the reduced density operator of a model four level atomic system, and obtain its analytical solution to describe the interference effects. We report the quantum beat structure in the populations.
An initially isotropic medium, when subjected to either a magnetic field or a coherent field, can... more An initially isotropic medium, when subjected to either a magnetic field or a coherent field, can induce anisotropy in the medium and can cause the polarization of a probe field to rotate. Therefore the rotation of probe polarization, due to magnetic field alone, can be controlled efficiently with the use of a coherent control field. We demonstrate this enhancement of the magneto-optical rotation (MOR) of a linearly polarized light, by doing detailed calculations on a system with relevant transitions j = 0 ↔ j = 1 ↔ j = 0. * An article in honor of Prof. M. O. Scully-who led us into many areas of quantum optics and laser physics.
We have studied the nonlinear Faraday effect with intense linear polarized light in an optically ... more We have studied the nonlinear Faraday effect with intense linear polarized light in an optically thick atomic rubidium vapor. We demonstrate that the polarization rotation rate ͑rotation angle per unit magnetic field, in the limit of low field͒ has a maximum value as the intensity and density are increased. We also show that the optimal sensitivity of an optical magnetometer based on this system reaches a saturation value as the intensity and density are increased.
Optical and Quantum Sensing and Precision Metrology, Mar 5, 2021
The propagation of quantum field interacting with a single two-level atom has been studied. Using... more The propagation of quantum field interacting with a single two-level atom has been studied. Using the Gaussian quantum mode functions, we calculate evolution of the quantum state that includes atomic and field variable. We demonstrated the phase and group velocities of the single photon propagation that can be of great importance for long quantum communications. The results can be used for controlling quantum field propagation, and for design of optical elements such as a quantum prism and a quantum lens.
Application of time-resolved ultrashort-pulse-laser–based laser-induced breakdown spectroscopy (L... more Application of time-resolved ultrashort-pulse-laser–based laser-induced breakdown spectroscopy (LIBS) is proposed for diagnostics in hydrocarbon flames at elevated pressures. Earlier study in nanosecond-laser–based LIBS for measuring fuel-to-air (F/A) ratios in stable hydrocarbon flame at high pressures is reported to have high measurement instabilities. A correlated measurement of time-resolved LIBS and electron number density measurement is carried out to develop an understanding of the source of the aforesaid measurement instability. The planned correlated measurements of LIBS and electron number density with short picosecond to femtosecond excitations have potentials to significantly reduce the instability in F/A ratio measurements at high pressure.
We have considered the Raman scattering in molecular media. Applying two laser fields in a two-ph... more We have considered the Raman scattering in molecular media. Applying two laser fields in a two-photon resonance with vibrational transition, we have studied the role of rotational levels for excitation of vibrational coherence. It is shown that the molecular vibrational coherence strongly depends on the effect of coherent population trapping for rotational levels. The obtained results are important for applications of Raman spectroscopy to molecular detection in engineering, chemical, and biological applications.
The interference fringes of an atomic Ramsey interferometer may be narrowed if the two separated ... more The interference fringes of an atomic Ramsey interferometer may be narrowed if the two separated fields have different frequencies and their phase difference is controlled. For spatially separated fields, their width depends inversely on the free flight time of ground state atoms before entering the first field region in addition to the time between the fields. The narrowing effect is stable with respect to velocity fluctuations and for realistic mode functions. We also show that systematic phase shifts and phase fluctuations do not aggravate the ...
We present the recent advances made in fiber-coupled laser-diagnostic methods that are being deve... more We present the recent advances made in fiber-coupled laser-diagnostic methods that are being developed for practical combustion applications. In particular, we describe fiber-coupled, picosecond, coherent anti-Stokes Raman scattering (ps-CARS) spectroscopy, fiber-coupled, nanosecond, ultraviolet planar-laser-induced-fluorescence (ns-UV-PLIF) spectroscopy, and fiber-coupled, particle-image velocimetry (PIV) in details that employ long-length, multimode step-index fibers for temperature, species-concentration, and flow velocity measurements in harsh combustion environments. Gas-phase single-laser-shot thermometry using fiber-based ps-CARS spectroscopy of H 2 is demonstrated in atmospheric-pressure, near-adiabatic laboratory flames. Also demonstrated is a fiber-coupled, 10-kHz UV-PLIF/PIV system for simultaneous detection of OH concentration and velocity in a realistic 4-MW combustion rig. The effects of delivering intense laser beams at visible and UV wavelengths through long optical fibers are investigated. The fundamental physical limits on the transmission of intense laser pulses through silica-based stepindex fibers for CARS, UV-PLIF, and PIV are studied. The potential system improvements are discussed. Development of such fiber-coupled diagnostic systems constitutes a major step forward in transitioning laser-diagnostic tools from research laboratories to practical combustion facilities such as gas-turbine test rigs.
We present the first reported quantification of trace elements in plutonium via a portable laser-... more We present the first reported quantification of trace elements in plutonium via a portable laser-induced breakdown spectroscopy (LIBS) device and demonstrate the use of chemometric analysis to enhance the handheld device's sensitivity and precision.
Laser-induced breakdown spectroscopy (LIBS) evaluates the emission spectra of ions, radicals, and... more Laser-induced breakdown spectroscopy (LIBS) evaluates the emission spectra of ions, radicals, and atoms generated from the breakdown of molecules by the incident laser; however, the LIBS signal is unstable at elevated pressures. To understand the cause of the signal instability, we perform simultaneous time-resolved measurements of the electron density and LIBS emission signal for nitrogen (568 nm) and hydrogen (656 nm) at high pressure (up to 11 bars). From correlations between the LIBS signal and electron number density, we find that the uncontrollable generation of excess electrons at high pressure causes high instability in the high-pressure LIBS signal. A possible method using ultrafast lasers is proposed to circumvent the uncontrolled electron generation and improve signal stability at high pressure.
We report the use of femtosecond laser electronic excitation tagging (FLEET) for velocimetry at a... more We report the use of femtosecond laser electronic excitation tagging (FLEET) for velocimetry at a 100-kHz imaging rate. Sequential, single-shot, quantitative velocity profiles of an underexpanded supersonic nitrogen jet were captured at a 100-kHz rate. The signal and lifetime characteristics of the FLEET emission were investigated in a methane flame above a Hencken burner at varying equivalence ratios, and room temperature gas mixtures involving air, methane, and nitrogen. In the post-flame region of the Hencken burner, the emission lifetime was measured as two orders of magnitude lower than lab air conditions. Increasing the equivalence ratio above 1.1 leads to a change in behavior, with a doubled lifetime. By measuring the emission in a cold methane flow, a short-lived signal was measured that decayed after the first microsecond. As a proof of concept for velocimetry in a reacting environment, the exhaust of a pulsed detonator was measured by FLEET. Quantitative velocity informati...
Nanosecond laser-induced breakdown spectroscopy (ns-LIBS) is employed for quantitative local fuel... more Nanosecond laser-induced breakdown spectroscopy (ns-LIBS) is employed for quantitative local fuel-air (F/A) ratio (i.e., ratio of actual fuel-to-oxidizer mass over ratio of fuel-to-oxidizer mass at stoichiometry, measurements in well-characterized methane-air flames at pressures of 1-11 bar). We selected nitrogen and hydrogen atomic-emission lines at 568 nm and 656 nm, respectively, to establish a correlation between the line intensities and the F/A ratio. We have investigated the effects of laser-pulse energy, camera gate delay, and pressure on the sensitivity, stability, and precision of the quantitative ns-LIBS F/A ratio measurements. We determined the optimal laser energy and camera gate delay for each pressure condition and found that measurement stability and precision are degraded with an increase in pressure. We have identified primary limitations of the F/A ratio measurement employing ns-LIBS at elevated pressures as instabilities caused by the higher density laser-induced plasma and the presence of the higher level of soot. Potential improvements are suggested.
Spontaneous emission can create coherences in a multilevel atom having close lying levels, subjec... more Spontaneous emission can create coherences in a multilevel atom having close lying levels, subject to the condition that the atomic dipole matrix elements are non-orthogonal. This condition is rarely met in atomic systems. We report the possibility of bypassing this condition and thereby creating coherences by letting the atom with orthogonal dipoles to interact with the vacuum of a pre-selected polarized cavity mode rather than the free space vacuum. We derive a master equation for the reduced density operator of a model four level atomic system, and obtain its analytical solution to describe the interference effects. We report the quantum beat structure in the populations.
An initially isotropic medium, when subjected to either a magnetic field or a coherent field, can... more An initially isotropic medium, when subjected to either a magnetic field or a coherent field, can induce anisotropy in the medium and can cause the polarization of a probe field to rotate. Therefore the rotation of probe polarization, due to magnetic field alone, can be controlled efficiently with the use of a coherent control field. We demonstrate this enhancement of the magneto-optical rotation (MOR) of a linearly polarized light, by doing detailed calculations on a system with relevant transitions j = 0 ↔ j = 1 ↔ j = 0. * An article in honor of Prof. M. O. Scully-who led us into many areas of quantum optics and laser physics.
We have studied the nonlinear Faraday effect with intense linear polarized light in an optically ... more We have studied the nonlinear Faraday effect with intense linear polarized light in an optically thick atomic rubidium vapor. We demonstrate that the polarization rotation rate ͑rotation angle per unit magnetic field, in the limit of low field͒ has a maximum value as the intensity and density are increased. We also show that the optimal sensitivity of an optical magnetometer based on this system reaches a saturation value as the intensity and density are increased.
Optical and Quantum Sensing and Precision Metrology, Mar 5, 2021
The propagation of quantum field interacting with a single two-level atom has been studied. Using... more The propagation of quantum field interacting with a single two-level atom has been studied. Using the Gaussian quantum mode functions, we calculate evolution of the quantum state that includes atomic and field variable. We demonstrated the phase and group velocities of the single photon propagation that can be of great importance for long quantum communications. The results can be used for controlling quantum field propagation, and for design of optical elements such as a quantum prism and a quantum lens.
Application of time-resolved ultrashort-pulse-laser–based laser-induced breakdown spectroscopy (L... more Application of time-resolved ultrashort-pulse-laser–based laser-induced breakdown spectroscopy (LIBS) is proposed for diagnostics in hydrocarbon flames at elevated pressures. Earlier study in nanosecond-laser–based LIBS for measuring fuel-to-air (F/A) ratios in stable hydrocarbon flame at high pressures is reported to have high measurement instabilities. A correlated measurement of time-resolved LIBS and electron number density measurement is carried out to develop an understanding of the source of the aforesaid measurement instability. The planned correlated measurements of LIBS and electron number density with short picosecond to femtosecond excitations have potentials to significantly reduce the instability in F/A ratio measurements at high pressure.
We have considered the Raman scattering in molecular media. Applying two laser fields in a two-ph... more We have considered the Raman scattering in molecular media. Applying two laser fields in a two-photon resonance with vibrational transition, we have studied the role of rotational levels for excitation of vibrational coherence. It is shown that the molecular vibrational coherence strongly depends on the effect of coherent population trapping for rotational levels. The obtained results are important for applications of Raman spectroscopy to molecular detection in engineering, chemical, and biological applications.
The interference fringes of an atomic Ramsey interferometer may be narrowed if the two separated ... more The interference fringes of an atomic Ramsey interferometer may be narrowed if the two separated fields have different frequencies and their phase difference is controlled. For spatially separated fields, their width depends inversely on the free flight time of ground state atoms before entering the first field region in addition to the time between the fields. The narrowing effect is stable with respect to velocity fluctuations and for realistic mode functions. We also show that systematic phase shifts and phase fluctuations do not aggravate the ...
We present the recent advances made in fiber-coupled laser-diagnostic methods that are being deve... more We present the recent advances made in fiber-coupled laser-diagnostic methods that are being developed for practical combustion applications. In particular, we describe fiber-coupled, picosecond, coherent anti-Stokes Raman scattering (ps-CARS) spectroscopy, fiber-coupled, nanosecond, ultraviolet planar-laser-induced-fluorescence (ns-UV-PLIF) spectroscopy, and fiber-coupled, particle-image velocimetry (PIV) in details that employ long-length, multimode step-index fibers for temperature, species-concentration, and flow velocity measurements in harsh combustion environments. Gas-phase single-laser-shot thermometry using fiber-based ps-CARS spectroscopy of H 2 is demonstrated in atmospheric-pressure, near-adiabatic laboratory flames. Also demonstrated is a fiber-coupled, 10-kHz UV-PLIF/PIV system for simultaneous detection of OH concentration and velocity in a realistic 4-MW combustion rig. The effects of delivering intense laser beams at visible and UV wavelengths through long optical fibers are investigated. The fundamental physical limits on the transmission of intense laser pulses through silica-based stepindex fibers for CARS, UV-PLIF, and PIV are studied. The potential system improvements are discussed. Development of such fiber-coupled diagnostic systems constitutes a major step forward in transitioning laser-diagnostic tools from research laboratories to practical combustion facilities such as gas-turbine test rigs.
We present the first reported quantification of trace elements in plutonium via a portable laser-... more We present the first reported quantification of trace elements in plutonium via a portable laser-induced breakdown spectroscopy (LIBS) device and demonstrate the use of chemometric analysis to enhance the handheld device's sensitivity and precision.
Laser-induced breakdown spectroscopy (LIBS) evaluates the emission spectra of ions, radicals, and... more Laser-induced breakdown spectroscopy (LIBS) evaluates the emission spectra of ions, radicals, and atoms generated from the breakdown of molecules by the incident laser; however, the LIBS signal is unstable at elevated pressures. To understand the cause of the signal instability, we perform simultaneous time-resolved measurements of the electron density and LIBS emission signal for nitrogen (568 nm) and hydrogen (656 nm) at high pressure (up to 11 bars). From correlations between the LIBS signal and electron number density, we find that the uncontrollable generation of excess electrons at high pressure causes high instability in the high-pressure LIBS signal. A possible method using ultrafast lasers is proposed to circumvent the uncontrolled electron generation and improve signal stability at high pressure.
We report the use of femtosecond laser electronic excitation tagging (FLEET) for velocimetry at a... more We report the use of femtosecond laser electronic excitation tagging (FLEET) for velocimetry at a 100-kHz imaging rate. Sequential, single-shot, quantitative velocity profiles of an underexpanded supersonic nitrogen jet were captured at a 100-kHz rate. The signal and lifetime characteristics of the FLEET emission were investigated in a methane flame above a Hencken burner at varying equivalence ratios, and room temperature gas mixtures involving air, methane, and nitrogen. In the post-flame region of the Hencken burner, the emission lifetime was measured as two orders of magnitude lower than lab air conditions. Increasing the equivalence ratio above 1.1 leads to a change in behavior, with a doubled lifetime. By measuring the emission in a cold methane flow, a short-lived signal was measured that decayed after the first microsecond. As a proof of concept for velocimetry in a reacting environment, the exhaust of a pulsed detonator was measured by FLEET. Quantitative velocity informati...
Nanosecond laser-induced breakdown spectroscopy (ns-LIBS) is employed for quantitative local fuel... more Nanosecond laser-induced breakdown spectroscopy (ns-LIBS) is employed for quantitative local fuel-air (F/A) ratio (i.e., ratio of actual fuel-to-oxidizer mass over ratio of fuel-to-oxidizer mass at stoichiometry, measurements in well-characterized methane-air flames at pressures of 1-11 bar). We selected nitrogen and hydrogen atomic-emission lines at 568 nm and 656 nm, respectively, to establish a correlation between the line intensities and the F/A ratio. We have investigated the effects of laser-pulse energy, camera gate delay, and pressure on the sensitivity, stability, and precision of the quantitative ns-LIBS F/A ratio measurements. We determined the optimal laser energy and camera gate delay for each pressure condition and found that measurement stability and precision are degraded with an increase in pressure. We have identified primary limitations of the F/A ratio measurement employing ns-LIBS at elevated pressures as instabilities caused by the higher density laser-induced plasma and the presence of the higher level of soot. Potential improvements are suggested.
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Papers by Anil Patnaik