Searcharxiv⌕ Search

arXiv subjects

Pankaj K. Jha

Publications and source records attributed to Pankaj K. Jha.

28 records · Page 2Linked to original sources
arXiv2012

Coherence Enhanced Transient Lasing in XUV Regime

We report the effect of a coherent drive on transient lasing in three-level $Λ$ and $Ξ$ configurations ($c\leftrightarrow a\leftrightarrow b$). We show that the presence of a resonant coherent drive on the $a\leftrightarrow c$ optical transition can yield an order of magnitude enhancement of the output laser energy on a $a\rightarrow b$ XUV or X-ray transition than with no coherent drive. We demonstrate the crucial role of coherence $\varrho_{ac}$ for the laser power enhancement. Contrary to the forward direction (with respect to the pump), where forward gain can be enhanced for some choice of the drive Rabi frequency $Ω_{c}$, coherent drive on the $ac$ transition always suppresses the backward gain.

physics.atom-ph↗
arXiv2011

Quantum interference controlled resonance profiles: From lasing without inversion to photo-detection

In this work we report a quantum interference mediated control of the resonance profiles in a generic three-level system and investigate its effect on key quantum interference (QI) phenomena. Namely in a three level configuration with doublets in the ground or excited states, we show control over enhancement and suppression of the emission (absorption) profiles. This is achieved by manipulation of the strength of QI and the energy spacing of the doublets. We analyze the application of such QI induced control of the resonance profile in the framework of two limiting cases of lasing without inversion and photo-detection.

physics.atom-ph↗
arXiv2011

Effective unidirectional pumping for steady-state amplification without inversion

We discuss an opportunity to achieve amplification without inversion in three-level cascade scheme using an effective unidirectional pumping via bidirectional incoherent pump. Analytical solution to the population and the coherence are obtained in the steady-state regime. With a proper choice of the parameters, obtained here, the possibility for amplification without inversion is presented.

physics.atom-ph↗
arXiv2011

Phase dependent interference effects on atomic excitation

We present an experimental and theoretical study of phase-dependent interference effects in multi-photon excitation under bichromatic radio-frequency (rf) field. Using an intense rf pulse, we study the interference between the three-photon and one-photon transition between the Zeeman sub-levels of the ground state of $^{87}$Rb that allows us to determine the carrier-envelope phase of the fields even for long pulses.

quant-ph↗
arXiv2011

Experimental observation of carrier-envelope phase effects by multicycle pulses

We present an experimental and theoretical study of carrier-envelope phase (CEP) effects on the population transfer between two bound atomic states interacting with pulses consisting of many cycles. Using intense radio-frequency pulse with Rabi frequency of the order of the atomic transition frequency, we investigated the influence of CEP on the control of phase dependent multi-photon transitions between the Zeeman sub-levels of the ground state of $^{87}$Rb. Our scheme has no limitation on the duration of the pulses. Extending the CEP control to longer pulses creates interesting possibilities to generate pulses with accuracy that is better then the period of optical oscillations.

physics.atom-ph↗
arXiv2010

Analytical solution to position dependent mass Schrödinger equation

Using a recently developed technique to solve Schrödinger equation for constant mass, we studied the regime in which mass varies with position i.e position dependent mass Schrödinger equation(PDMSE). We obtained an analytical solution for the PDMSE and applied our approach to study a position dependent mass $m(x)$ particle scattered by a potential $\mathcal{V}(x)$. We also studied the structural analogy between PDMSE and two-level atomic system interacting with a classical field.

cond-mat.other↗
arXiv2010

Coherent control of atomic excitation using off-resonant strong few-cycle pulses

We study the dynamics of a two-level system driven by an off-resonant few-cycle pulse which has a phase jump $ϕ$ at $t=t_{0}$, in contrast to many cycle pulses, under non rotating-wave approximation (NRWA). We give a closed form analytical solution for the evolution of the probability amplitude $|C_{a} (t)|$ for the upper level. Using the appropriate pulse parameters like phase-jump $ϕ$, jump time $t_{0}$, pulse width $τ$, frequency $ν$ and Rabi frequency $Ω_{0}$ the population transfer, after the pulse is gone, can be optimized and for the pulse considered here, enhancement of $10^{6}-10^{8}$ factor was obtained.

physics.atom-ph↗
arXiv2010

Coherent Excitation of a Two-Level Atom driven by a far off-resonant Classical Field: Analytical Solutions

We present an analytical treatment of coherent excitation of a Two-Level Atom driven by a far-off resonant classical field. A class of pulse envelope is obtained for which this problem is exactly solvable. The solutions are given in terms of Heun function which is a generalization of the Hypergeometric function. The degeneracy of Heun to Hypergeometric equation can give all the exactly solvable pulse shapes of Gauss Hypergeometric form, from the generalized pulse shape obtained here. We discuss the application of the results obtained to the generation of XUV.

quant-ph↗