arXiv subjects

Qun Zhang

Publications and source records attributed to Qun Zhang.

41 records · Page 3Linked to original sources

arXiv2008

Observation of Above-Threshold Dissociation of Na$_2^+$ in Intense Laser Fields

We report the observation of above-threshold dissociation of a multielectron molecular system, Na$_2^+$. The process is due to continuum-continuum transitions in a field-dressed molecular continuum. Three well resolved fragmentation channels with different kinetic energy release patterns have been detected, of which, two are associated with ordinary photodissociation via light-induced potentials into Na(3s) + Na$^+$ and Na(3p) + Na$^+$, and one with continuum-continuum transitions and above-threshold dissociation into Na(3p) + Na$^+$. We show that when we dress this molecule with a field whose intensity is ~3 x 10$^{12}$ W/cm$^2$, above-threshold dissociation prevails over other processes, such as field-ionization followed by Coulomb explosion.

physics.chem-ph↗

arXiv2008

Coherent population trapping in a dressed two-level atom via a bichromatic field

We show theoretically that by applying a bichromatic electromagnetic field, the dressed states of a monochromatically driven two-level atom can be pumped into a coherent superposition termed as dressed-state coherent population trapping. Such effect can be viewed as a new doorknob to manipulate a two-level system via its control over dressed-state populations. Application of this effect in the precision measurement of Rabi frequency, the unexpected population inversion and lasing without inversion are discussed to demonstrate such controllability.

physics.optics↗

arXiv2008

In situ accurate determination of the zero time delay between two independent ultrashort laser pulses by observing the oscillation of an atomic excited wave packet

We propose a novel method that uses the oscillation of an atomic excited wave packet observed through a pump-probe technique to accurately determine the zero time delay between a pair of ultrashort laser pulses. This physically-based approach provides an easy fix for the intractable problem of synchronizing two different femtosecond laser pulses in a practical experimental environment, especially where an in situ time zero measurement with high accuracy is required.

physics.optics↗

arXiv2008

Observation of the 5p Rydberg states of sulfur difluoride radical by resonance-enhanced multiphoton ionization spectroscopy

Sulfur difluoride radicals in their ground state have been produced by a "laser-free" pulsed dc discharge of the SF$_{6}$/Ar gas mixtures in a supersonic molecular beam and detected by mass-selective resonance-enhanced multilphoton ionization (REMPI) spectroscopy in the wavelength range of 408 - 420 nm. Analyses of the (3 + 1) REMPI excitation spectrum have enabled identification of three hitherto unknown Rydberg states of this radical. Following the Rydberg state labeling in our previous work [see J. Phys. Chem. A 102, 7233 (1998)], these we label the K(5p$_{1}$) [$nu_{0-0}$ = 71 837 cm$^{-1}$, $omega_{1}^{'}$(a$_{1}$ sym str) = 915 cm$^{-1}$], L(5p$_{2}$) [$nu_{0-0}$ = 72 134 cm$^{-1}$, $omega_{1}^{'}$(a$_{1}$ sym str) = 912 cm$^{-1}$], and M(5p$_{3}$) [$nu_{0-0}$ = 72 336 cm$^{-1}$, $omega_{1}^{'}$(a$_{1}$ sym str) = 926 cm$^{-1}$] Rydberg states, respectively. [Origins, relative to the lowest vibrational level of the X$^{1}$A$_{1}$ ground state, and vibrational frequencies of the symmetric S-F stretching mode are suggested by the numbers in brackets.] Photofragmentation process of SF$_{2}$$^{+}$--SF$^{+}$ + F that relates to the REMPI spectrum was discussed.

physics.chem-ph↗

arXiv2006

The local environmental dependence of galaxy properties in the volume-limited sample of Main Galaxies from the SDSS Data Release 5

Using a volume-limited sample of Main Galaxies from the SDSS Data Release 5, we investigate the dependence of galaxy properties on local environment. For each galaxy, the local three-dimensional density is calculated. We find that galaxy morphologies strongly depend on local environment: galaxies in dense environments have predominantly early type morphologies, but other galaxy properties do not present significant dependence on local environment. Clearly, this puts a important constraint on proposed physical mechanisms.

astro-ph↗