Laser beam combining in potassium vapor

Energy transfer between two laser beams of comparable intensity due to their nonlinear interactions in an atomic vapor was investigated. Strong coupling occurs due to stimulated Rayleigh scattering when the frequencies of the two waves differ by the inverse of the excited-state lifetime. The energy transfer between two nearly equal energy pulses from an alexandrite laser tuned near the 4²S_1/2 →4²P_3/2 transition of potassium vapor was measured. It was found that as much as 85% of the total incident energy was contained in one of the output beams     

A Fraunhofer-wavelength magnetooptic atomic filter at 422.7 nm

A demonstration of the first magnetooptic atomic filter that overlays a strong solar Fraunhofer line is reported. Compared with alkali magnetooptic filters, this filter enjoys a large reduction in solar interference and a significant decrease in the number of noise passbands. The filter utilizes the strong Ca(4p¹P₁-4s¹ S₀) transition at 422.7 nm. Under the weak magnetic field experimental conditions, a maximum transmission efficiency of 55% and a symmetrical double-peaked transmission spectrum with 1.5 GHz wide passbands were observed. The filter's frequency response was measured with a laser intensity modulation technique. No falloff was observed at 176 MHz, the highest frequency available with the apparatus. Calculations indicate that further improvements in filter performance can be achieved by optimizing the magnetic field and the cell temperature     

A chemically driven visible laser transition using fastnear-resonant energy transfer

Evidence is obtained which demonstrates the potential for developing purely chemical visible lasers based on rapid near-resonant energy transfer from metastable excited triplet states of germanium and silicon monoxide (a³Σ⁺,b ³Π) to select metal atoms. In this study, the Group IIIA metal atoms were chosen as the energy receptors for the energy transfer-pump sequence. Excited triplet states were generated from the Ge-O₃, Ge-N₂, Si-N₂O, and Si-NO₂ reactions; the bulk of the experimental results was obtained with a germanium-based system. The energy stored in the long-lived triplet states is transferred to pump X²P_1/2 thallium, indium, and gallium atoms to their lowest lying ² S_1/2 states. The authors observe a system of temporal behavior which suggests the creation of a population inversion producing a gain condition and forming the basis for full cavity oscillation on the Tl 7²S_1/2-6P _3/2 transition at 535 nm     

Continuous anti-Stokes-Raman laser oscillation in an argon-laserplasma

Generation of continuous anti-Stokes-Raman laser (ASRL) oscillation between the 3d²P and 4s²P levels of the argon-ion laser plasma is described. Pump radiation of 648.3 nm (610.3 nm) is up-converted into 437.5-nm radiation with an overall efficiency of more than 20% and an output power of up to 150 mW. Thus far, a detuning of ±9 GHz around the 4p²S intermediate resonance was achieved. The experiments reported have demonstrated that the gain on a normal laser transition may be strongly increased by population transfer and due to coherent processes. Therefore the ASRL technique in general also demonstrates a possibility to overcome the problem of insufficient mirror reflectivities in the vacuum ultraviolet (VUV) region     

Evidence for continuous visible chemical lasing from the fast nearresonant energy transfer pumping of atomic sodium

Energy transfer from selectively formed metastable states of SiO is used to pump sodium-atom laser amplifiers at λ≈569 nm (4d²D-3p²P), λ≈616 nm (5s²S-3p² P), and λ≈819 nm (3d²D -3p²P). The a³Σ⁺ and b³Π states of SiO are generated in high yield from the Si+N₂O→SiO+N₂ reaction. The energy stored in the triplet states is transferred in a highly efficient collisional process to pump sodium atoms to their lowest excited 3d² D, 4d²D, and 5s²S states. Adopting a sequence in which high concentrations of silicon and sodium atoms are mixed and oxidized, a continuous amplification (gain condition) is monitored which suggests the creation of a population inversion among the receptor sodium-atom energy levels and forms the basis for full cavity oscillation on the Na4 d²D-3p²P transition at 569 nm     

Optical absorption and stimulated emission of neodymium in yttriumorthosilicate

A spectroscopic investigation of the biaxial crystal yttrium orthosilicate doped with Nd³⁺(Nd³⁺:Y₂SiO₅) has been performed. Spectrally and orientationally resolved emission cross sections necessary for the evaluation of laser performance on the Nd^{3+ 4}F_3/2-⁴I _9/2 and ⁴F_3/2-⁴I_11/2 transitions have been determined. The Judd-Ofelt theory has been applied to measured values of optical absorption line strengths to obtain the orientation averaged intensity parameters: Ω₂-3.34×10^-20 cm², Ω ₄=4.35×10^-20 cm², and Ω₆=5.60×10^-20 cm². These Judd-Ofelt intensity parameter values are significantly different from those previously reported by A.M. Tkachuk et al. Using these intensity parameters, the Nd^{3+ 4}F₂ metastable state lifetime is predicted to be 225 μs. Measured low Nd concentration ⁴F_3/2 lifetimes of 214 μs indicate a high radiative quantum efficiency. Because of the Stark level splitting of the Nd^{3+ 4}F_3/2 and ⁴I_9/2 manifolds, laser operation at twice one of the Cs atomic resonance filter acceptance wavelengths is possible     

The influence of velocity-changing collisions on resonantdegenerate four-wave mixing

The phase-conjugate signal observed in resonant degenerate four-wave mixing on the 6³P₂ to 7³ S₁ transition of atomic mercury in a Hg-Ar discharge is investigated. At a fixed argon pressure the variation of the signal with pump powers is explained by a model that includes the effects of velocity-changing collisions (VCCs). As the argon pressure was varied from 0 to 1 torr an increase in the phase conjugate signal was observed and is ascribed to a change in the discharge dynamics with argon pressure and to the influence of VCCs. To further clarify the role of collisions and optical pumping, degenerate four-wave mixing spectra are examined as a function of pump power. Line shapes are briefly discussed     

Simultaneous multiple wavelength laser action in various neodymiumhost crystals

The oscillation condition of a simultaneous multiple wavelength laser has been established and used to analyze the possibility of simultaneous oscillation in various neodymium host crystals, such as Nd:YAG, Nd:YLF, Nd:BEL, and Nd:YAP crystals at the transitions from ⁴F_3/2-⁴I_13/2 and ⁴F_3/2-⁴I _11/2. It is shown that this kind of laser can be realized in all the described crystals in a pulsed state. In general, continuous wave (CW) operation, however, can only be achieved for Nd:YAP. On the basis of these results, CW simultaneous double wavelength lasing has been achieved in a Nd:YAP crystal for the first time at both 1.0795 μm and 1.314 μm     

Thermal shifts of the spectral lines in the 4F3/2 to 4I11/2 manifold of anNd:YAG Laser

A report is presented of the thermal shifts of eleven of the twelve lines from the ⁴F_3/2 Stark energy levels to the ⁴I_11/2 energy levels in an Nd:YAG laser for a temperature change from 20-200°C. The thermal shift difference between the Stark sublevels R₁, R₂ in ⁴F_3/2 is found to be about -0.6±0.6 cm^-1/100°C. Within experimental uncertainty, all of the lasing lines either moved to longer wavelength or remained unchanged with increasing temperature     

Measurement of the stimulated emission cross section for the 4F3/2-4I13/2transition of Nd3+ in YAlO3 crystal

A method for the simultaneous measurement of the stimulated emission cross section and fluorescence lifetime by studying the relation between laser parameters and the laser relaxation oscillation frequency is discussed. The stimulated emission cross section for the ⁴F_3/2-⁴I_13/2 transition of Nd³⁺ ion in YAP crystal was measured to be (22±1)×10^-20 cm²     

On the dynamics of population inversion for 3 μm Er3+lasers

A generalized model for 3-μm (⁴I_11/2 →⁴I_13/2)Er lasers is proposed. The essential energy transfer processes present in the single-doped Er ³⁺ systems (up-conversion from ⁴I_13/2, up-conversion from ⁴ I_11/2, cross-relaxation from ⁴S _3/2), as well as those present in Cr³⁺ codoped Er ³⁺ systems, are taken into account. In the frame of this model, the main features of 3 μm Er³⁺ lasers, such as long pulse or CW operation, the change of emission wavelength as a function of pumping conditions, and the effects of codoping with Ho³⁺ or Tm³⁺ ions, are explained     

Optimal probability-of-error thresholds and performance for twoversions of the sign detector

Expressions are obtained for specifying the optimal error probability (minimum P_e) thresholds λ₀₁ and λ₀₂ for the traditional and modified sign detectors, respectively. These thresholds are shown to depend on the parameters p, P₁, and M where: M is the number of observations z_i used in the test statistic; P₁=P(H₁ ) is the prior probability for hypothesis H₁ that signal s₁ is present and 1-P₁ =P(H₀) corresponds to the hypothesis H₀ that signal s₀ is present; and p=Pr{z_i⩾0|H₁} with s₀=0 for the traditional sign detector and p=Pr{z_i⩾λ|H₁ }=Pr{z_i<λ|H₀} with λ =(s₀+s₁)/2 for the modified sign detector. The expressions for λ₀₁ and λ₀₂, are given explicitly, and shown to be independent of P₁ for sufficiently large M. Optimal P_e versus M performance curves, corresponding to both versions of the sign detector, are obtained for a representative range of values for p and P₁     

Room temperature Dy:YLF laser operation at 4.34 μm

A Dy:YLF laser operating on the ⁶H_11/2 to ⁶H_13/2 transition at 4.34 μm and using a laser pumping scheme is reported. This pumping scheme is necessitated by the short upper-laser-level lifetime and the small effective stimulated-emission cross section. A suitable laser for this application is the Er:YLF laser operating at 1.73 μm. A simple model that approximates Dy:YLF laser performance well is presented. Results on laser performance, including a determination of the slope efficiency and threshold as a function of the output mirror reflectivity and a correlation of the pulse length with the laser output energy, are reported. Overall laser efficiency is found to be limited primarily by the ratio of the pump wavelength to laser output wavelength and the terminated four-level laser operation     

Tunable laser pumped 3 μm Ho:YAlO3 laser

The tuning characteristics of the ⁵I₆ -⁵I₇ transition in a Ho:YAlO₃ laser, intracavity pumped by a 1.079 μm Nd:YalO₃ laser, were studied. Operation on seven distinct lines between 2.844 and 3.017 μm was found, and the threshold and relative slope efficiency of each line was measured. Several of these lines were previously unreported     

On universal hypotheses testing via large deviations

A prototype problem in hypotheses testing is discussed. The problem of deciding whether an i.i.d. sequence of random variables has originated from a known source P₁ or an unknown source P₂ is considered. The exponential rate of decrease in type II probability of error under a constraint on the minimal rate of decrease in type I probability of error is chosen for a criterion of optimality. Using large deviations estimates, a decision rule that is based on the relative entropy of the empirical measure with respect to P₁ is proposed. In the case of discrete random variables, this approach yields weaker results than the combinatorial approach used by Hoeffding (1965). However, it enables the analysis to be extended to the general case of Rⁿ-valued random variables. Finally, the results are extended to the case where P₁ is an unknown parameter-dependent distribution that is known to belong to a set of distributions (P⁰₁, &thetas;∈Θ)     

Measurement of the characteristics of the optical-microwavedouble-resonance effect of the 87Rb D1line for application as an atomic frequency standard

The OMDR (optical-microwave double resonance) spectrum of ⁸⁷ Rb with the aim of using a frequency-stabilized GaAs semiconductor laser instead of an Rb lamp as a pumping source in a gas-cell-type Rb frequency standard. Natural isotope ⁸⁷Rb was sealed in a glass cell with buffer gases (Ar/N₂=1.2, total pressure=39 torr). The double resonance signal in the 5P_1/2(F=2)←5S_1/2( F=1) transition appearing at the resonance to the F=2←1 hyperfine transition of the 5S_1/2 state was detected. The optimum operational cell temperature was 56°C. The peak-to-peak frequency width of the atomic hyperfine resonance discriminator used to stabilize the microwave frequency shifts induced by detuning of the laser frequency, changes in the laser and microwave powers, and temperature drift of the cell were investigated     

VUV stimulated anti-Stokes Raman emission in inverted atomicselenium

Stimulated anti-Stokes Raman scattering at 145.7 nm in inverted Se is generated by photolysis of OCSe at 193 nm and the subsequent up-conversion of 205.1-nm pump radiation. The tuning profile is characterized with OCSe pressure, the energies and relative timing of the pump and photodissociation lasers, and CO and Ar buffer-gas pressure. The use of CO as a buffer gas is discovered to be detrimental to the anti-Stokes output. Sixteen competing stimulated emission channels are found to suppress anti-Stokes emission on exact 4p ^{4 1}S₀-4p³ 5s³ P⁰₁ pump resonance     

Connectivity properties of a packet radio network model

A model of a packet radio network in which transmitters with range R are distributed according to a two-dimensional Poisson point process with density D is examined. To ensure network connectivity, it is shown that πR²D, the expected number of nearest neighbors of a transmitter, must grow logarithmically with the area of the network. For an infinite area there exists an infinite connected component with nonzero probability if π R²D>N₀, for some critical value N₀. It is shown that 2.195<N ₀<10.526     

Holmium YLF amplifier performance and the prospects for multi-Jouleenergies using diode-laser pumping

Laser studies that examined the amplifier characteristics of holmium-doped yttrium lithium fluoride (YLF) at 300 K are discussed. An inversion ratio n⁵I₇/n _Ho of 0.37 was reached, resulting in a measured small-signal gain coefficient of 0.50 cm^-1. In a flashlamp pumping experiment, an output energy of 240 mJ was achieved for 38.5 mJ of input energy, resulting in a large gain of 6.2. An amplifier model developed for diode laser pumping was adapted to consider this flashlamp-pumped case. The agreement between the theory and the experiment is good. Multipass amplifier calculations using the model suggest that the Ho:Tm:YLF laser crystal can support a 12% electrical to optical efficiency at 300 K, even in the presence of upconversion     

Observation of a large number of new laser lines from12CD3F gas optically pumped with a continuouslytunable high-pressure pulsed CO2 laser

An observation is reported of a large number of new laser lines from ¹²CD₃F gas optically pumped with a continuously tunable high-pressure pulsed CO₂ laser. Making use of the coincidence of the 10 μm P and R branches of CO₂ with the v₃ and v₆ vibrational-rotational absorption bands of ¹²CD₃F, 180 laser lines were found in the wavenumber range between 8 and 55 cm^-1, all of them yet unknown; these lines are studied for characteristic properties of laser action. All laser lines are assigned as pure rotational transitions in the vibrational excited or ground states