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.
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 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.
Ultrafast saturation of signals from an optical process occurs when intense laser pulses, with th... more Ultrafast saturation of signals from an optical process occurs when intense laser pulses, with the duration of the driving laser pulse shorter than the effective decay timescales, interact with the target system. Recently, it has been shown that such saturation is marked by transition from transient-absorption to the transient-gain regime, unlike in continuous-wave or long-duration excitations where saturation occurs once the underdamping regime is achieved. The threshold intensities of the drive pulse that drives the optical signal to saturate can be estimated by calculating the area of the pulse. We demonstrate that depending on the shape of the pulse, the saturation behavior differs. The lineshape dependence of ultrafast saturation of absorption and fluorescence is studied for a variety of pulse shapes. We demonstrate that the saturation threshold is lower for super-Gaussian pulses and almost an order of magnitude lower for sech pulses compared to a Gaussian pulse.
ABSTRACT The insensitivity of ERE-CARS signal to collisional quenching is investigated. It is obs... more ABSTRACT The insensitivity of ERE-CARS signal to collisional quenching is investigated. It is observed that the strong laser pulse helps in keeping both the excited-state population and the ground-state coherence reasonably high, even with significant quenching.
ABSTRACT The effects of collisional-energy-transfer and dephasing rates on ERE-CARS in nitric oxi... more ABSTRACT The effects of collisional-energy-transfer and dephasing rates on ERE-CARS in nitric oxide are investigated. A parametric study of the effects of collisions on the ERE-CARS signal demonstrates a reduced collisional dependence for saturating laser fields.
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.
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 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.
Ultrafast saturation of signals from an optical process occurs when intense laser pulses, with th... more Ultrafast saturation of signals from an optical process occurs when intense laser pulses, with the duration of the driving laser pulse shorter than the effective decay timescales, interact with the target system. Recently, it has been shown that such saturation is marked by transition from transient-absorption to the transient-gain regime, unlike in continuous-wave or long-duration excitations where saturation occurs once the underdamping regime is achieved. The threshold intensities of the drive pulse that drives the optical signal to saturate can be estimated by calculating the area of the pulse. We demonstrate that depending on the shape of the pulse, the saturation behavior differs. The lineshape dependence of ultrafast saturation of absorption and fluorescence is studied for a variety of pulse shapes. We demonstrate that the saturation threshold is lower for super-Gaussian pulses and almost an order of magnitude lower for sech pulses compared to a Gaussian pulse.
ABSTRACT The insensitivity of ERE-CARS signal to collisional quenching is investigated. It is obs... more ABSTRACT The insensitivity of ERE-CARS signal to collisional quenching is investigated. It is observed that the strong laser pulse helps in keeping both the excited-state population and the ground-state coherence reasonably high, even with significant quenching.
ABSTRACT The effects of collisional-energy-transfer and dephasing rates on ERE-CARS in nitric oxi... more ABSTRACT The effects of collisional-energy-transfer and dephasing rates on ERE-CARS in nitric oxide are investigated. A parametric study of the effects of collisions on the ERE-CARS signal demonstrates a reduced collisional dependence for saturating laser fields.
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