Biswajit Ray

Transaction Costs, Collective Action and Survival of Heterogeneous Co-management Institutions: Case Study of Forest Management Organisations in West Bengal, India

Abstract Cost-effective natural resource management is important for equity and efficiency. Yet transaction costs of cooperation may pose a challenge to heterogeneous co-management institutions. We conducted a survey in seven Forest Protection Committees of West Bengal, India to examine this hypothesis empirically. We find that: (1) among several factors, caste heterogeneity, distance to forest, political heterogeneity, land inequality and trust systematically influence transaction costs and collective action; and (2) robust institutions bear less costs of cooperation. The implication is that transaction costs related to heterogeneity may exert significant influence on successes or failures of co-management.

Theoretical study of electromagnetically induced transparency in a five-level atom and application to Doppler-broadened and Doppler-free Rb atoms

We report theoretical studies of a Λ-type five-level atomic system. The density matrix equations are set up and solved numerically to obtain the probe absorption line shape of Rb D2 transitions for cold (Doppler-free) and room temperature (Doppler-broadened) atoms. Simulated spectra for Doppler-broadened systems lead to four velocity-selective dips along with an electromagnetic induced transparency (EIT) peak as observed earlier from the co-propagating pump–probe spectroscopy of Rb D2 transitions. Effects of pump power and spontaneous decay rate from the upper levels on the simulated spectra are also studied. For cold atoms a very pronounced EIT peak is observed when the pump frequency is on resonance with one allowed transition. We find that lower pump power leads to a much sharper EIT signal in this case. A simulated dispersion curve shows a rapid variation of the refractive index that may lead to a sharp reduction of the group velocity of photons.

Diode laser spectroscopy of He, N2 and air broadened water vapour transitions belonging to the (2ν1 + ν2 + ν3) overtone band

The line shape parameters of rovibrational transitions of water vapour belonging to the (2ν1 + ν2 + ν3) overtone band due to collisions between absorber molecules and noble gas helium have been measured in the spectral range between 11988.494 cm−1 and 12218.829 cm−1 using NIR diode laser spectrometer. In addition nitrogen and air broadening effects on some water vapour transitions belonging to the same band have also been studied. Wavelength modulation spectroscopy along with phase sensitive detection technique are used to record first derivative (1f) signal of buffer gas broadened water vapour transitions. Observed line shapes are fitted to standard Voigt profiles by non-linear least squares fitting program to extract the line shape parameters, like line strength and pressure broadening coefficients. The broadening effects induced by different types of buffer gases on water vapour line shapes are compared. Rotational quantum number (J) dependence of broadening coefficients of water vapour transitions is also examined.

Velocity selective optical pumping effects and electromagnetically induced transparency for D2 transitions in rubidium

It is shown that the pump-probe spectroscopy of Λ-type system for the D2 transition of 87Rb exhibits additional absorption enhancement peaks due to velocity selective optical pumping along with the electromagnetically induced transparency (EIT). The separation of these peaks is consistent with the hyperfine splitting of the upper levels. For 85Rb the peaks are not clearly discernible since the hyperfine splitting is much smaller.

Nonlinear resonances caused by coherent, optical pumping and saturating effects in the presence of three laser fields for the 85Rb-D2 line

Atomic coherence resonances such as electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) signals are observed in a Doppler broadened multi-level system for the D2 line of 85Rb atoms in a vapour cell considering different types of atom–laser coupling schemes. Besides the coherence resonances, the nonlinear resonances like velocity selective optical pumping (VSOP) dips and velocity selective resonances (VSR) are also observed for the non-zero velocity selective groups of atoms. In the presence of pump, control and probe laser fields, we observe two EIT signals in a double Λ-type system and two EIA signals in a double V-type system. We are able to see the EIA signal for the non-zero velocity group of atoms when the pump laser is locked with an open transition by a small red detuning. We also report the experimental observation of simultaneous EIT and EIA signals in a (Λ+V)-type system. The effect of frequency tuning of the control laser is also studied in the presence of the frequency locked pump laser. A simple theoretical analysis explains the experimental results.

Temperature and magnetic field effects on the coherent and saturating resonances in Λ- and V-type systems for the 85Rb-D2 transition

Variations of the coherent resonance, i.e. an electromagnetically induced transparency (EIT) peak with the cell temperature in Λ- and V-type systems are observed for the 85Rb-D2 transition. In a Λ-type system, the amplitude of the EIT peak gradually decreases and it is finally masked by the broadened optical pumping dips with the increase of the cell temperature. But for the V-type system, the EIT and the saturation peaks are greatly enhanced with the increase of the cell temperature. The effect of the external magnetic field on the EIT resonance is also investigated considering both types of systems. For the Λ-type system in place of a single EIT resonance, five transparency windows with broadened width and reduced contrast are obtained depending on the Zeeman levels formed by the applied magnetic field. In the V-type system, the coherent resonance peak could not be resolved in the presence of the external magnetic field, but a greater number of saturation peaks with broadened width appear in the probe transmission spectrum. A theoretical model is adopted to represent the experimental results. Good agreement is found between the experimental and numerically simulated results.

Dissociation of carbonyl sulfide by 150 keV Ar+ ion impact

We report on the formation and dissociation of the multiply charged carbonyl sulfide (OCS) molecular ions, OCSq + (where q = 1?4), formed in the collision of neutral OCS molecules with 150 keV Ar+ projectiles, detected using coincidence techniques. From the coincidence map of the fragments we have separated complete two- and three-body dissociation channels resulting in various ionic fragments. Comparing the slope of the coincidence islands with theoretical values, determined from the charge and momentum distribution of the correlated particles, we postulate different decay modes behind each of the fragmentation channels. We also discuss momentum imaging and the kinetic energy release of each of the dissociation channels of OCSq +, which give further information about the momentum balance and the geometry of the precursors in OCS fragmentation.

Collisional narrowing and pressure broadening of the oxygen A-band transitions

Abstract Measurement of pressure-dependent half-width of the rovibronic transitions of the oxygen A-band shows that the width remains almost unchanged at low pressure. Simulations based on soft collision model reveal that the collisional narrowing of the Doppler component compensates the pressure broadening up to a pressure of nearly 100 T. At higher pressure the line shape is non-Voigt type and has reduced but constant Doppler broadening.

Observation and theoretical simulation of electromagnetically induced transparency and enhanced velocity selective optical pumping in cesium vapour in a micrometric thickness optical cell

Observation of electromagnetically induced transparency (EIT) and enhanced velocity selective optical pumping (VSOP) signals in a micrometric cell with cesium is reported. The line shape and non-linear features observed in the case of fluorescence in the direction parallel to the cell windows and the transmission spectra observed along the propagation direction of the probe beam show considerable differences in the spectral profile. A theoretical model based on five level optical Bloch equations is used to simulate the spectra. The Doppler convolution includes all possible orientations of atomic velocities with respect to the laser beam direction. Atoms moving nearly parallel to the windows and perpendicular to the collinear pump and probe beams have much lower Doppler shift and hence produce considerable narrowing of the Doppler background in the fluorescence spectra. The coherence decay rate is also low for such atoms as they do not meet with the cell walls. The simulated curves reproduce the observed sharp EIT peaks and enhanced broad VSOP signals for the closed probe transition in the fluorescence and absorption spectra. The observed effect of detuning of the pump frequency on the non-linear features is also reproduced by the simulation.

High contrast electromagnetically induced transparency in a nitrogen filled Rb vapour cell

We observe the electromagnetically induced transparency (EIT) spectra inside a nitrogen filled Rb vapour cell (Rb-N2) in a five-level Λ-type system of D2 transition of Rb atom. The high contrast EIT resonance in buffer gas filled Rb cell is obtained under our experimental conditions. The effect of velocity changing coherence preserving collisions to obtain the contrast resonance in buffer gas cell has been discussed. We measured the dependence of EIT width and height on pump intensity and find that the EIT width (FWHM) and peak height have a linear dependence on pump intensity. Our experimental results show that the presence of N2 buffer gas reduces the power broadening of the observed resonances.