We investigate theoretically amplification without inversion (AWI) in a degenerate double Λ syste... more We investigate theoretically amplification without inversion (AWI) in a degenerate double Λ system in coherently driven by two fields. We observe AWI with subnatural linewidth and attribute it to the low frequency coherence.
Springer Series on Atomic, Optical, and Plasma Physics, 2013
ABSTRACT We discuss the process of modulation transfer in a coherently prepared three-level atomi... more ABSTRACT We discuss the process of modulation transfer in a coherently prepared three-level atomic medium and its prospective application to atomic frequency offset locking (AFOL). The issue of modulation transfer through coherence is treated in the framework of temporal evolution of dressed atomic system with externally superimposed deterministic flow. This dynamical description of the atom-field system offers distinctive advantage of using a single modulation source to dither passively the coherent phenomenon as probed by an independent laser system under pump-probe configuration. Modulation transfer is demonstrated experimentally using frequency modulation spectroscopy on a subnatural linewidth electromagnetically induced transparency (EIT) and a sub-Doppler linewidth Autler-Townes (AT) resonance in Doppler broadened alkali vapor medium, and AFOL is realized by stabilizing the probe laser on the first/third derivative signals. The stability of AFOL is discussed in terms of the frequency noise power spectral density and Allan variance. Analysis of AFOL schemes is carried out at the backdrop of closed loop active frequency control in a conventional master-slave scheme to point out the contrasting behavior of AFOL schemes based on EIT and AT resonances. This work adds up to the discussion on the subtle link between dressed state spectroscopy and AFOL, which is relevant for developing a master-slave type laser system in the domain of coherent photon-atom interaction.
We investigate theoretically the pump-probe spectroscopy of coherentlydriven four-level Λ system ... more We investigate theoretically the pump-probe spectroscopy of coherentlydriven four-level Λ system with two closely spaced excited common levels, thereby forming a double Λ system. Using the master equation approach, analytical results are obtained for the absorption spectrum of a weak probe in the presence of a strong pump. The model is applied to the double Λ system 5 2 S 1/2 F = 1, 2 → 5 2 P 3/2 F = 1, 2 of 87 Rb atom. It is shown that the absorption spectrum consists of a triplet, of which one resonance is of sub-natural linewidth depending on the atom-field interaction parameters. The effect of Doppler broadening on the absorption spectrum is also investigated.
We investigate the spectrum of a four-level V-type system. We show that spontaneously generated c... more We investigate the spectrum of a four-level V-type system. We show that spontaneously generated coherence between the two closely spaced excited levels produces interference effects in the absorption. As a result, more transparency windows appear comparing to the normal three-level V system. We can also control the number of the transparency windows to be two or three just by tuning the Rabi frequency of the coupling field. We present an equivalent system without the rigorous requirement of close-lying levels to observe the phenomena. We also experimentally demonstrate the corresponding features in a rubidium atomic beam.
We investigate modulation transfer through pump induced atomic coherence in pump-probe spectrosco... more We investigate modulation transfer through pump induced atomic coherence in pump-probe spectroscopy of Doppler broadened medium of cesium atoms. The mechanism of modulation transfer is discussed for a three level Λ configuration under slow frequency modulation. Modulation transfer is demonstrated by performing frequency modulation spectroscopy (FMS) on a sub-natural linewidth (<2 MHz) electromagnetically induced transparency (EIT) signal. Here the pump laser is modulated by acousto-optic frequency modulation and the modulation is transferred to the probe laser through atomic coherence. Finally the probe laser is locked on the first derivative spectrum of EIT signal. Such atomic frequency offset locking system totally removes the necessity of direct modulation of laser frequency, so that the spectral resolution is limited only by the practical linewidth of the laser systems. Moreover it provides a novel way to eliminate the additional frequency and intensity noise associated with direct frequency dithering, which may limit the experimental resolution.
ABSTRACT We discuss here the effect of laser phase fluctuations on coherent spectroscopy of four-... more ABSTRACT We discuss here the effect of laser phase fluctuations on coherent spectroscopy of four-level N-system interacting with a trichromatic radiation field of frequencies Ω i , (i = 1−3). The laser phase variables are described by the Wiener-Levy diffusion process to specify the bandwidths (Γ i ) and cross-correlations (Γ ij ) that may exist between pairs of laser fields. A general formalism based on the master equation and theory of multiplicative stochastic processes is developed and used to study three-photon and (2+1)-photon absorptive resonances in model N-system of 40Ca+ ion. It is observed that the resonances are suppressed or broadened by all Γ i ,(i = 1−3), while their revival is dependent only on Γ 12 and Γ 23, and yet the revival is only partial even when the relevant fields are critically correlated. In contrast Γ 13 is observed to deteriorate the absorptive resonances. The distinctive features of the steady state and time dependent behavior of the system under three-photon and (2 + 1)-photon resonance conditions and for fluctuating fields are discussed.
The Australian and New Zealand journal of psychiatry, Jan 28, 2015
vesicles. While originally developed to assess postganglionic sympathetic nerve dysfunction in he... more vesicles. While originally developed to assess postganglionic sympathetic nerve dysfunction in heart disease, 123I-MIBG is also used to detect early Lewy body disease, which is known to affect postganglionic sympathetic cardiac neurons before affecting the neurons of the central nervous system. In clinical practice, cardiac 123I-MIBG can help resolve differential diagnoses distinguished by the presence or absence of Lewy bodies. A meta-analysis of 19 studies comprising 1972 patients with parkinsonism showed that 123I-MIBG detects Parkinson disease with sensitivity of 88% and discriminates between Parkinson disease and non-Lewy body parkinsonism with specificity of 85% (Treglia et al., 2012). Another meta-analysis of eight studies comprising 346 patients with dementia showed pooled sensitivity of 98% and specificity of 94% in distinguishing dementia with Lewy bodies from other forms of dementia (Treglia and Cason, 2012). False positives may be generated by complicated diabetes mellitus, treatment with tricyclic antidepressants and incidental Lewy body disease, while false negatives may be caused by very early disease and some rarer forms of Parkinson disease.
We investigate theoretically amplification without inversion (AWI) in a degenerate double Λ syste... more We investigate theoretically amplification without inversion (AWI) in a degenerate double Λ system in coherently driven by two fields. We observe AWI with subnatural linewidth and attribute it to the low frequency coherence.
Springer Series on Atomic, Optical, and Plasma Physics, 2013
ABSTRACT We discuss the process of modulation transfer in a coherently prepared three-level atomi... more ABSTRACT We discuss the process of modulation transfer in a coherently prepared three-level atomic medium and its prospective application to atomic frequency offset locking (AFOL). The issue of modulation transfer through coherence is treated in the framework of temporal evolution of dressed atomic system with externally superimposed deterministic flow. This dynamical description of the atom-field system offers distinctive advantage of using a single modulation source to dither passively the coherent phenomenon as probed by an independent laser system under pump-probe configuration. Modulation transfer is demonstrated experimentally using frequency modulation spectroscopy on a subnatural linewidth electromagnetically induced transparency (EIT) and a sub-Doppler linewidth Autler-Townes (AT) resonance in Doppler broadened alkali vapor medium, and AFOL is realized by stabilizing the probe laser on the first/third derivative signals. The stability of AFOL is discussed in terms of the frequency noise power spectral density and Allan variance. Analysis of AFOL schemes is carried out at the backdrop of closed loop active frequency control in a conventional master-slave scheme to point out the contrasting behavior of AFOL schemes based on EIT and AT resonances. This work adds up to the discussion on the subtle link between dressed state spectroscopy and AFOL, which is relevant for developing a master-slave type laser system in the domain of coherent photon-atom interaction.
We investigate theoretically the pump-probe spectroscopy of coherentlydriven four-level Λ system ... more We investigate theoretically the pump-probe spectroscopy of coherentlydriven four-level Λ system with two closely spaced excited common levels, thereby forming a double Λ system. Using the master equation approach, analytical results are obtained for the absorption spectrum of a weak probe in the presence of a strong pump. The model is applied to the double Λ system 5 2 S 1/2 F = 1, 2 → 5 2 P 3/2 F = 1, 2 of 87 Rb atom. It is shown that the absorption spectrum consists of a triplet, of which one resonance is of sub-natural linewidth depending on the atom-field interaction parameters. The effect of Doppler broadening on the absorption spectrum is also investigated.
We investigate the spectrum of a four-level V-type system. We show that spontaneously generated c... more We investigate the spectrum of a four-level V-type system. We show that spontaneously generated coherence between the two closely spaced excited levels produces interference effects in the absorption. As a result, more transparency windows appear comparing to the normal three-level V system. We can also control the number of the transparency windows to be two or three just by tuning the Rabi frequency of the coupling field. We present an equivalent system without the rigorous requirement of close-lying levels to observe the phenomena. We also experimentally demonstrate the corresponding features in a rubidium atomic beam.
We investigate modulation transfer through pump induced atomic coherence in pump-probe spectrosco... more We investigate modulation transfer through pump induced atomic coherence in pump-probe spectroscopy of Doppler broadened medium of cesium atoms. The mechanism of modulation transfer is discussed for a three level Λ configuration under slow frequency modulation. Modulation transfer is demonstrated by performing frequency modulation spectroscopy (FMS) on a sub-natural linewidth (<2 MHz) electromagnetically induced transparency (EIT) signal. Here the pump laser is modulated by acousto-optic frequency modulation and the modulation is transferred to the probe laser through atomic coherence. Finally the probe laser is locked on the first derivative spectrum of EIT signal. Such atomic frequency offset locking system totally removes the necessity of direct modulation of laser frequency, so that the spectral resolution is limited only by the practical linewidth of the laser systems. Moreover it provides a novel way to eliminate the additional frequency and intensity noise associated with direct frequency dithering, which may limit the experimental resolution.
ABSTRACT We discuss here the effect of laser phase fluctuations on coherent spectroscopy of four-... more ABSTRACT We discuss here the effect of laser phase fluctuations on coherent spectroscopy of four-level N-system interacting with a trichromatic radiation field of frequencies Ω i , (i = 1−3). The laser phase variables are described by the Wiener-Levy diffusion process to specify the bandwidths (Γ i ) and cross-correlations (Γ ij ) that may exist between pairs of laser fields. A general formalism based on the master equation and theory of multiplicative stochastic processes is developed and used to study three-photon and (2+1)-photon absorptive resonances in model N-system of 40Ca+ ion. It is observed that the resonances are suppressed or broadened by all Γ i ,(i = 1−3), while their revival is dependent only on Γ 12 and Γ 23, and yet the revival is only partial even when the relevant fields are critically correlated. In contrast Γ 13 is observed to deteriorate the absorptive resonances. The distinctive features of the steady state and time dependent behavior of the system under three-photon and (2 + 1)-photon resonance conditions and for fluctuating fields are discussed.
The Australian and New Zealand journal of psychiatry, Jan 28, 2015
vesicles. While originally developed to assess postganglionic sympathetic nerve dysfunction in he... more vesicles. While originally developed to assess postganglionic sympathetic nerve dysfunction in heart disease, 123I-MIBG is also used to detect early Lewy body disease, which is known to affect postganglionic sympathetic cardiac neurons before affecting the neurons of the central nervous system. In clinical practice, cardiac 123I-MIBG can help resolve differential diagnoses distinguished by the presence or absence of Lewy bodies. A meta-analysis of 19 studies comprising 1972 patients with parkinsonism showed that 123I-MIBG detects Parkinson disease with sensitivity of 88% and discriminates between Parkinson disease and non-Lewy body parkinsonism with specificity of 85% (Treglia et al., 2012). Another meta-analysis of eight studies comprising 346 patients with dementia showed pooled sensitivity of 98% and specificity of 94% in distinguishing dementia with Lewy bodies from other forms of dementia (Treglia and Cason, 2012). False positives may be generated by complicated diabetes mellitus, treatment with tricyclic antidepressants and incidental Lewy body disease, while false negatives may be caused by very early disease and some rarer forms of Parkinson disease.
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Papers by Niharika Singh