Effective deexcitation time of lithium vapor

The method of numerical simulation was used to study the effective deexcitation time of the resonance transition in lithium vapor at the wavelength λ = 670.776 nm. Taking into account the partial frequency redistribution and the cylindrical geometry of the medium, the rate equations of the population balance of a two-level atom were solved along with the equation of radiation transfer. The light scattering by an atom was simulated by a linear combination of the angle-averaged frequency distribution functions R _II and R _III. The Biberman-Holstein escape factor was calculated as a function of the optical thickness of lithium vapor for different geometries of the luminescing gas and different models of the frequency redistribution functions.     

Decay of the excited state 3<Superscript>2</Superscript><Emphasis Type="Italic">P</Emphasis><Subscript>3/2</Subscript> of sodium atoms taking into account radiation trapping

The effective lifetime of the excited state 3² P _3/2 of sodium atoms corresponding to the transition with λ = 589 nm has been studied numerically. It is shown that the nonmonotonic behavior of the dependence of the Biberman-Holstein escape factor on the optical thickness of sodium vapor measured in the experiment (A. Romberg and H.-J. Kunze, J. Quant. Spectrosc. Radiat. Transfer 39 (2), 99 (1988)) should not be attributed to the manifestation of the effects of partial frequency redistribution.     

A study of partial frequency redistribution of monochromatic source radiation

The consequences of angle-dependent partial frequency redistribution are investigated with a Monte Carlo model for a monochromatic source of radiation incident upon a uniform isothermal slab of resonantly-scattering atoms. The frequency redistribution probability is characterized by Hummer's R_II function. Emergent line profiles are computed for optical depths of up to 10⁵ at line-center.     

Die Bestimmung der Spin-Polarisation aus Transparenz-Änderungen beim Optischen Pumpen mit der Natrium-D1-Linie

A Dehmelt type experiment is performed in which sodium vapor and argon as a buffer are employed. The pumping radiation consists of the circularly polarizedD ₁ line. Since the strongly absorbing magnetic sublevels are depopulated, the vapor becomes more transparent to the pumping radiation with growing polarization. The transparency of the vapor is measured with and without optical pumping as a function of the sodium vapor density. The degree of polarization is determined in simulating the increase in transparency due to polarization by decreasing the sodium vapor density of the unpumped sample. This method requires the knowledge of the exact sodium vapor density in the temperature range of interest (100 to 200° C). The determination of the degree of polarization is based on the assumption, that the atomic absorption cross sectionQ, which depends on the degree of polarizationP and the frequency of lightν, can be written in the formQ(P,ν)=A(P) · B(ν), whereA(P) is a linear function ofP, whileB (ν) must not be changed by optical pumping. As will be shown in a following paper, the degree of polarization determined under this assumptions, describes in good approximation the polarization of the sodium valence electrons.     

Emission characteristics of a discharge iodine vapor plasma in the spectral region of the main absorption maximum of DNA molecules

Radiation of glow and capacitive discharges in inert gas-iodine vapor mixtures is studied in the spectral range 150–210 nm, which coincides with the main absorption maximum of the DNA molecules. Iodine atomic spectral lines at 150.7, 161.8, 170.2, 183.0, and 206.2 nm are observed in the spectra. The emission intensity of the iodine spectral lines is optimized by varying the glow discharge current, capacitive discharge frequency, as well as pressure and composition of the gas mixtures. The glow and capacitive discharges are ignited in cylindrical quartz tubes with interelectrode gaps of 10 and 6 cm. Helium and neon are found to be the most effective buffer gases. The optimum partial pressures of the light inert gases and iodine vapor in the glow discharge are within 0.4–0.6 kPa and 100–150 Pa, respectively. In the capacitive discharge in He(Ne)-I₂ mixtures, the optimum partial helium, neon, and iodine vapor pressures are within 0.8–2.0 kPa, 0.5–1.0 kPa, and ≤ 60 Pa, respectively. It is demonstrated that pulsed bactericidal radiation sources with light pulse lengths of 400–500 ns and continuous radiation sources emitting within the spectral range 150–207 nm can be designed on the basis of low-density iodine vapor plasma.     

Optical properties of mouse biotissues and their optical phantoms

The optical characteristics of a barrier discharge in a mixture of heavy water vapor with argon in the wavelength region 200–315 nm are presented. The dependence of the radiation intensity of the OD (A → X) band at λ = 309 nm on the partial pressure of the D₂O vapor is studied, the mechanism of hydroxyl formation in the plasma is considered, and optimal compositions of pollution-free and inexpensive mixtures based on Ar-D₂O are determined for application in UV lamps, which are promising for use in photomedicine.     

High-contrast atomic dark resonances formed in a ladder system of rubidium atoms in submicron structures

It is shown that high-contrast resonance of electromagnetically induced transparency (EIT) in a ladder Ξ-system of 5S _1/2-5P _3/2-5D _5/2 levels can be formed in optical cells containing a column of rubidium vapor with thickness L in an interval of 100 nm ≤ L ≤ 780 nm. Using bichromatic laser radiation with certain parameters, an 83% contrast of the EIT resonance (or dark resonance, DR) has been achieved for a vapor column thickness of L = 780 nm. An important condition for the formation of high-contrast DR is that the frequency of the coupling laser radiation must be resonant with the frequency of the corresponding 5P _3/2-5D _5/2 transition (for the probe radiation frequency scanned over the 5S _1/2-5P _3/2 transition). It is also shown that a DR can be formed at a record small vapor column thickness of L ≈ 100 nm. Expressions that can be used to estimate the expected DR width at small L values are presented.     

Fifth harmonic generation in sodium vapor

We report experimental investigation of direct fifth harmonic of Nd³⁺: glass laser radiation (1060 nm) in metal vapor. Using various mixtures of sodium vapor and xenon in order to achieve a phase-matching, we observed direct as well as cascade nonlinear processes. The first measurement of effective fifth-order nonlinear susceptibility χ⁽⁵⁾_eff in atoms, is performed.     

Gas-discharge source of the noncarcinogenic UV radiation based on the mixture of helium and heavy-water (D2O) vapor

The spectrum of radiation and the results of optimization are presented for a UV lamp that works on the He-D₂O mixture and is pumped using a repetitively pulsed barrier discharge. The dependences of the radiation intensity of the OD (X-A) band with the wavelength λ ≈ 309 nm on the partial pressure of the heavywater vapor, working voltage across the working capacitor of the high-voltage modulator, and repetition rate of the current pulses are studied.     

Population inversion on transitions to the ground state of atoms upon nonresonance absorption of laser radiation

Lasing at the resonance transitions (D _1? and D _2?lines) of sodium was observed in the superradiance mode upon nonresonance optical excitation in the presence of a buffer gas. The dependences of the lasing intensity on the exciting radiation intensity and on the detuning of its frequency from the frequencies of resonance transitions were studied. It is found that, under specific conditions of the experiment (high pressure of a buffer gas and a rather high radiation intensity), in the case of a large positive detuning of the exciting radiation frequency from the resonance (“working”) transition frequency, the population inversion is produced at the “ working” transition, which results in lasing.     

The Hanle effect with partial frequency redistribution. Construction of a frequency-dependent polarization matrix and numerical solution by a PALI method

The polarized approximate lambda iteration (PALI) technique developed for the weak field Hanle effect relies on the decomposition of the Stokes parameters I, Q and U into six cylindrically symmetrical components. It has been applied to complete and partial frequency redistribution with redistribution matrices in which frequency redistribution is decoupled from scattering polarization. For partial frequency redistribution, the decoupling is obtained by an adequate decomposition of the frequency space into several domains. By angle-averaging frequency-dependent terms in the exact weak field Hanle redistribution matrix for a normal Zeeman triplet, we construct a redistribution matrix with coupling between frequency redistribution and polarization and no domain decomposition. The coupling is contained in generalized frequency redistribution functions that depend on the magnetic field. The redistribution matrix is expanded in the Landi Degl’Innocenti spherical tensors for polarimetry and the Stokes parameters are decomposed into cylindrically symmetrical components. A PALI method is set up for the calculation of these components. The Stokes parameters are calculated for different simple atmospheric models. The positive Q direction corresponds to the linear polarization perpendicular to the solar limb. It is shown that the frequency space decomposition may induce large errors on Stokes U in the transition region between line core and line wings but can safely be used for Stokes I and Q, the errors staying less than 1% at all the frequencies.     

Secondary radiation of synthetic opals loaded by the sodium nitrite ferroelectric

This paper reports on a comparison of transmission, reflection, and secondary radiation spectra of unloaded synthetic opals and samples filled with the sodium nitrite ferroelectric (NaNO₂). The radiation is provided by semiconductor light-emitting diodes operating in the ultraviolet and visible spectral regions. Selective excitation of slow electromagnetic waves in a photonic crystal, an effect observed when the exciting radiation frequency approaches the stop-band edge, is studied.     

Emission characteristics of pulse-periodic barrier-discharge plasma in a mixture of krypton with argon and liquid freon vapor

Radiation of a nanosecond barrier discharge in a mixture of krypton, argon, and carbon-tetrachloride vapor is studied in the spectral range of 150–300 nm. The plasma radiation spectra and the dependences of the intensities of the 258 nm Cl₂(D′ → A′), 222 nm KrCl(B → X), and 175 nm ArCl(B → X) bands on the partial pressure of liquid freon vapor, argon, and krypton, as well as on the discharge excitation conditions, are studied. The optimal compositions of gas mixtures for creating a broadband UV-VUV emitter based on the band system of argon chloride, krypton chloride, and chlorine molecule are determined.     

Implementation of a double-scanning technique for studies of the Hanle effect in rubidium vapor

We have studied the resonance fluorescence of a room-temperature rubidium vapor exited to the atomic ⁵P_3/2 state (D₂ line) by powerful single-frequency cw laser radiation (1.25 W/cm²) in the presence of a magnetic field. In these studies, the slow, linear scanning of the laser frequency across the hyperfine transitions of the D₂ line is combined with a fast linear scanning of the applied magnetic field, which allows us to record frequency-dependent Hanle resonances from all the groups of hyperfine transitions including V- and Λ-type systems. Rate equations were used to simulate fluorescence signals for ⁸⁵Rb due to circularly polarized exciting laser radiation with different mean frequency values and laser intensity values. The simulation show a dependence of the fluorescence on the magnetic field. The Doppler effect was taken into account by averaging the calculated signals over different velocity groups. Theoretical calculations give a width of the signal peak in good agreement with experiment.     

The scattering of line radiation—I. A generalized redistribution function

The theory of the frequency redistribution of radiation during scattering is re-investigated with the aim of producing a generalized frequency redistribution function. The assumption, commonly made, that the atom performing the scattering of the radiation has a constant velocity for the duration of the scattering event is not made in the present investigation. As a result a formal theory is developed which does indeed lead to a generalized redistribution function. Two limiting cases are discussed: in one of the limits, we reconsider the case where the velocity of the atom is constant during the scattering event; the other limiting case describes the situation which occurs when the velocity at absorption, of the atom performing the scattering, is completely uncorrelated with its velocity at emission. This latter case is then more fully discussed with a view to overcoming one of the major difficulties encountered with the existing theories of frequency redistribution, i.e. that complete redistribution in the radiation scattered from an atmosphere being viewed by a distant observer can not be predicted.     

Noninversive partial velocity amplification of radiation by ions due to their rotation in a magnetic field

It is shown that upon the application of an external magnetic field, a gas of ionized particles may experience noninversive partial velocity amplification of radiation by ions due to their Larmor rotation. In this case, virtually all ions may be in the ground state. It may happen that approximately half the number of ions in the medium amplify the incident radiation. The integrated absorption coefficient remains positive due to the enhancement of absorption of radiation by the other half of ions. Noninversive amplification of radiation takes place when the condition ω_c?Γ²/kv _T is satisfied ωw_c is the cyclotron frequency of ions in the magnetic field; Γ is the homogeneous half-width of the absorption line for ions, and kv _T is the Doppler width). In the case of interaction of atomic ions with radiation in the optical range, this corresponds to magnetic fields B?600 G (for the ion mass M～10 amu). Noninversive partial velocity amplification of radiation is a “latent” effect in the sense that it disappears upon averaging over all velocity directions of ions. This effect is associated with the emergence of phase incursion of the induced dipole moment oscillations for ions moving in circular cyclotron orbits, which depends on the ion velocity.     

Amplification of radiation in atomic vapor induced by a linearly polarized laser radiation

We present the results of spectroscopic and polarization studies of dilute rubidium vapor exposed to a single-frequency linearly polarized diode laser radiation in a spectral range of atomic D₂ line. We report the origin of a circularly polarized radiation on V-type transitions of ⁸⁷Rb F _g = 2 → F _e = 3 and ⁸⁵Rb F _g = 3 → F _e = 4, and amplification of this radiation in backward direction caused by a partial population inversion among magnetic sublevels of the ground and excited levels. This is confirmed experimentally by high directivity of backward radiation, absence in its spectrum of ⁸⁵Rb F _g = 2 → F _e = 1 (Λ-type) radiation, as well as by different nature of intensity dependences of backward and fluorescence radiations.     

Continuous-wave frequency mixing and UV generation in sodium vapor

Resonant nonlinear four-wave mixing processes have been studied in sodium vapor. The generation of cw uv radiation and the upconversion of =10.8 m light is reported. The coefficientC=P ₄/P₁P₂P₃ obtained was on the order of 10^–2 W^–2, the pump spectral width being 12GHz. Resonant atomic nonlinearities are shown to be used for effective cw frequency conversion.     

Water vapor differential absorption lidar measurements using a diode-pumped all-solid-state laser at 935 nm

A diode-pumped, single-frequency laser system emitting at 935 nm has recently been developed to serve as the transmitter for water vapor differential absorption lidar (DIAL) measurements. This laser uses Nd:YGG (Y₃Ga₅O₁₂) as the active medium and emits radiation directly at 935 nm without the need of additional frequency conversion processes. The system was diode-pumped at 806 nm and was built up in a master-oscillator-power-amplifier configuration. It generates more than 30 mJ of pulse energy at 100 Hz repetition rate with a beam quality (M ²) of better than 1.4. Since water vapor DIAL demands for stringent requirements of the spectral properties those were carefully investigated in the scope of this paper. Single-frequency operation is achieved by injection seeding and active length control of the oscillator cavity. The range of continuously tunable single-frequency radiation extends to ～0.4 nm centered around 935.31 nm. Values of the spectral purity of >99.996% were determined using long-pass absorption measurements in the atmosphere exceeding the requirements by a large margin. Finally, for the first time water vapor DIAL measurements were performed using a Nd:YGG laser. The reported results show much promise of these directly pumped lasers at 935 nm for future spaceborne but also airborne water vapor lidar systems.     

Photon escape in model planetary nebulae

The effects of optical thickness, velocity gradients and photon redistribution in frequency and direction, as described by the redistribution function R_II, on emission line profiles from simple slab geometry atmospheres are examined. It is found that the optical thickness and differential expansion are the dominant factors affecting photon escape and hence the characteristics and magnitude of the line emission. The importance of frequency and angular photon redistribution as photon escape mechanisms are found to increase with increasing optical thickness and differential expansion.