I. Pak

Diode laser study of IR multiphoton-induced depletion of rotational sublevels of the ground vibrational state of SF6 molecules cooled in a pulsed free jet

Abstract A pulsed frequency tunable diode laser was used to investigate the IR multiphoton-induced depletion of rotational sublevels of the ground vibrational state of SF6 molecules cooled in a pulsed free jet at exciting energy densities between ≈10-2 and 2.3 J cm-2. The depletion of all rotational sublevels was effective at considerable (≈5–11 cm-1) pumping frequency detunings from the linear absorption spectrum (LAS) of the molecule the width of which under the conditions of experiment (Trot ≈ 18 K) was ≈2–3 cm-1. The fraction of molecules excited by a pumping pulse from individual rotational sublevels was measured and its dependence on the exciting pulse frequency and energy density investigated. The effect of collisions on the depletion of the rotational sublevels was studied.

Tunable diode laser studies of collisionless infrared excitation of SF6 and NH3 molecules

Abstract Factors affecting the efficiency of excitation by CO 2 laser pulses of SF 6 and NH 3 molecules from individual rotational levels of the ground vibrational state have been investigated in a pulsed free jet under essentially collisionless conditions. The dependences of the fraction f J of excited molecules on the laser energy fluence Φ in the range from 10 −6 to 10 −1 J/cm 2 were studied a frequency detunings Δν (up to 0.1 cm − ) of the exciting radiation from molecular transitions. Similar behaviour of these dependences for SF 6 and NH 3 molecules has been observed. The efficiency of molecular excitation is shown to rapidly fall off with pump laser spectrum narrowing.

Diode laser measurements of a pulsed TEA CO2 laser linewidth

Abstract A new technique to measure spectral linewidths of pulsed IR lasers is described. The results for the linewidth Γ of a TEA CO 2 laser are presented. The value of Γ =0.013±0.002 cm -1 obtained experimentally is in a good agreement with the results of model calculations.

Diode Laser Spectroscopy of the Dynamics of Multiphoton Excitation of SF6 Molecules by CO2 Laser Pulses

The dynamics of excitation by CO2 laser pulses of SF6 molecules from individual rotational sublevels J″ of the ground vibrational state have been investigated in a pulsed molecular jet under essentially collisionless conditions. At different energy fluences of exciting laser pulse Φ = 10−5 + 10−1 J/cm2, the dependences of the fraction f J of excited molecules on the rotational quantum number J″ have been obtained, when SF6 molecules were excited on the 10P(16) CO2 laser line, as well as on the 10P(18) and 10P(14) lines at Φ = 0.1 J/cm2. Comparison of experimental results with theoretical predictions18–20 shows rather strong disagreement between theory and experiments both in the population of the υ3 = 1 state and in the role of multiphoton transitions. It is shown that the narrowing of the exciting laser pulse spectrum (the 10P(16) line, Φ ≲ 10−2 J/cm2) results in drastic decrease of the fraction of excited molecules from the (υ3 = 0, J″ = 4) state which is most resonant with laser radiation.

Zeeman effect in the IR spectrum of a molecule without EN electronic moment. Observation with a tunable diode laser

Abstract The Zeeman effect in the infrared absorption spectrum of a molecule without an electronic magnetic moment was observed using a linear spectroscopic technique with a tunable diode laser. In the magnetic field B = 500 kG weak splittings of the asR(4, 1) and asR(4, 0) lines in the v 2 -band of NH 3 were recorded. The values of the Zeeman splittings in these cases were −1×10 -2 cm -1 . The picture of the Zeeman splittings observed is shown to be connected with the difference between the g -factors for the excited (υ 2 = 1) and the ground (υ 2 = 0) vibrational states of the NH 3 molecule. This difference is about (-10)-(15)% of the g -factor for the lower vibrational level of the transition.

Parameters of pulsed supersonic jets of SF6 and NH3 molecules studied using a spectrometer with tunable diode lasers

A qualitative pattern of cooling molecules in a pulsed supersonic jet is given on the basis of literature data. A procedure of measurements is described and known relations are presented which allow the determination of rotational temperatures and concentrations of molecules in a jet using the measured intensities of infrared absorption lines. The parameters of SF6 and NH3 jets have been determined for various pulsed valves by means of tunable diode lasers. We used pulsed supersonic jets to study collisionless infrared excitation of SF6 and NH3 molecules by an intensive laser field. An important point in the treatment of these experiments was to know with sufficient accuracy the concentration of molecules in a jet and their distribution over rotational levels of the ground vibrational state (characterized by the rotational temperature Trot in the case of Boltzman distribution). We determined these parameters from the measurements made by means of tunable diode lasers. Various pulsed valves were tried which allowed us to obtain jets with different gas temperatures and different concentrations of molecules.

Diode laser measurements of a pulse TEA CO2 laser linewidth

A new technique to measure spectral linewidths of pulsed IR lasers is described. The results for the linewidth Gamma of a TEA CO2 laser are presented. The value of Gamma = 0.013/cm +/- 0.002/cm obtained experimentally is in a good agreement with the results of model calculations.

Parameters of pulsed supersonic jets of SF6 and NH3 molecules studied with the use of a spectrometer based on tunable diode lasers

A qualitative description of cooling molecules in a pulsed supersonic jet is given on the basis of literature data. Procedure of measurements is described and known relations are presented which allow one to determine the rotational temperature and concentrations of molecules in a jet using the measured intensities of IR absorption lines. The parameters of SF6 and NH3 jets have been determined for various pulsed valves by means of tunable diode lasers.