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1.
Absorption cross sections of Cr3+in the metastable2E states of pink ruby (0.05 percent Cr2 O3 ) have been measured forE perp C between 4000 Å and 7000 Å at 297°K and 115°K. Both 0 degree and 90 degree ruby rods were measured in a flash absorption apparatus having a spectral resolution of 50 Å. The broad excited state absorption bands centered at 5600 Å appear to correlate with the positions of2T1 (3T1 ) level, while the narrow band centered at 4540 Å correlates well with the predicted2A2 (1E ) level. The effect of excited state absorption on laser operation is discussed in this paper. 相似文献
2.
An upper limit of5 times 10^{-10} seconds has been determined to the time of nonradiative relaxation between4T2 and2E states of ruby. The value was inferred from slope comparison of the experimental and theoretical rise curves ofR -line fluorescence. 相似文献
3.
The population of the metastable6p^{3} 2D_{3/2}^{0} bismuth level has been determined by time-resolved absorption spectroscopy at times in the range1-10 mu s after the start of the discharge in a bismuth vaporneon mixture, for a neon pressure of 13 mbar and a specific discharge energy of 1 mJ . cm-3. An exponential decay of the population is observed and lifetimes of 3.0, 4.5, and 5.3 μs are obtained at temperatures of 830, 790, and 755°C, respectively. Measurements of the nine strongest fluorescent transitions to the metastable level confirm that a population of the order of 1013cm-3is established in the early stage of the discharge and exceeds by three orders of magnitude the peak population of the bismuth resonance level6p^{2} 7s^{4}P_{1/2} . It is concluded that the absence of laser emission at 472.2 nm in the system studied is due to excessive population of the metastable level6p^{3} 2D_{3/2}^{0} during the early stage of the discharge. It is proposed that this high population arises from the dissociation of Bi2 dimers by electron impact and that the loss of electron energy to dissociation and to excitation of the vibrational and rotational levels of the dimers is responsible for the very low population achieved in the6p^{2} 7s 4p_{1/2} level. 相似文献
4.
The feasibility of submillimeter wavelength (870 GHz) lasing in Al2 O3 is discussed. The proposed scheme is based on the pumping of the2bar{A} level of ruby via a ruby laser operating on its R2 line. Lasing is expected on the2bar{A} rightarrow bar{E} transition of the split2E level. 相似文献
5.
Two types of three-level quantum counters, based on the Bloembergen and the inverted scheme, are discussed with respect to their application for up-conversion of far-infrared (FIR) radiation to visible light. It is reported on a tunable quantum counter of the inverted type: in optically pumped ruby, photons at 29 cm-1are absorbed by the transitionbar{E} (2E ) →2bar{A} (2E ) and lead to an increased R2 - fluorescence radiation. By Zeeman splitting of the2E levels, tuning of the detected frequency from 29 cm-1to higher and lower frequencies is possible (with 1 cm-1/Tesla). Using the 891-GHz radiation of an HCN laser we determine for the quantum counter a power conversion efficiency of the order of 10-6and a frequency bandwidth of 360 MHz. We find the interesting result that phonon bottleneck due to resonant trapping of 29 cm-1phonons can lead to an increase of the quantum efficiency by orders of magnitude. 相似文献
6.
Infrared spontaneous and stimulated emission from Ho3+in BaY2 F8 is reported. In addition to the familiar5I_{7} rightarrow 5I8 transition at 2 μ,5F_{5} rightarrow 5I5 emission at 2.4μ and5I_{6} rightarrow 5I7 emission at 2.9μ are discussed. There are several unusual features of the 2-μ laser emission. At room temperature, phonon-terminated laser emission is observed at 2.171 μ. At 77 K a complex CW laser output is observed in a wavelength interval lying on the shoulder of a fluorescence line. The complex output is attributed to oscillation in transverse modes of the resonator. Oscillation is not observed in the strongest emission line, despite a large terminal state splitting of 310 cm-1. These results are explained on the basis of a theory developed earlier for transition metal ion lasers. The validity of the model is supported by demonstrating the tunability through loss modulation predicted by theory. The observation of these effects is made possible by the very low internal scattering loss in the crystals. The5F_{5} rightarrow 5I5 laser lines near 2.4 μ represent relatively low gain transitions with pulse durations limited by accumulation in a longer lived terminal state. The dynamics of laser emission indicate the possible absence of thermal equilibrium in the excited state. For the 2.9-μ transition the bottleneck posed by a longer lived terminal state may be eliminated by the addition of Eu3+or Pr3+, but laser emission could not be obtained. 相似文献
7.
Additional excitation mechanisms, apparently overlooked in [1], but previously reported to be responsible for the selective excitation of the Hg II7p 2P_{3/2} upper state of the 6150-Å laser line in mercury-helium lasers, are referenced and discussed. It is pointed out that asymmetric charge transfer and Penning-type ionization reactions can also account for the selective excitation of the Hg II7p 2P_{3/2} state as well as direct electron impact excitation from the Hg I ground state. 相似文献
8.
Induced-emission cross sections in neodymium laser glasses 总被引:5,自引:0,他引:5
A method for calculating induced-emission cross sections in neodymium laser glasses, based on simple absorbance measurements, has been demonstrated. Absorption and emission transition probabilities of four silicate-base neodymium laser glasses have been characterized in terms of the Judd-Ofelt (JO) model of crystal-field-induced electric-dipole transitions. Absolute absorption intensities in 3669A, ED-2, LSG-91H, and S33 glasses were measured and used to determine three phenomenological intensity parameters for each glass which accounted for the measured intensities to within 5 percent (rms). Emission intensities between the metastable4F_{3/2} and terminal4I J levels were then calculated for each glass, together with the4F_{3/2} radiative lifetime, fluorescence branching ratios, and radiative quantum efficiency. Calculated values of these quantities for 3669A and S33 glasses are compared with measured values appearing in the literature. Using experimental line shapes for the4F_{3/2} rightarrow 4I_{11/2} transitions at 1.06μ, induced-emission cross sections for these glasses were calculated. 相似文献
9.
10.
Srinivasan T. Egger H. Ting Luk Pummer H. Rhodes C. 《Quantum Electronics, IEEE Journal of》1983,19(12):1874-1876
The first demonstration of the use of the optical Stark effect to secure resonance for a two-quantum process in the ultraviolet is reported. Following excitation of molecular hydrogen by 193 nm radiation, intense stimulated emission on both the Lyman and Werner bands is observed. The Werner (2-5)Q(1) transition at 117.5 nm exhibits a conversion efficiency of ∼0.2 percent. It is found that electron collisions with excited molecules provide the most probable mechanism for excitation of theC^{1}Pi_{u} levels with a rate constant estimated to bek_{e} sim 7 times 10^{-6} cm3/s. 相似文献
11.
《IEEE transactions on information theory / Professional Technical Group on Information Theory》1976,22(3):349-352
It is shown that(n_{o},k_{o}) convolutional codes with unit memory always achieve the largest free distance among all codes of the same ratek_{o}/n_{o} and same number2^{Mk_{o} of encoder states, whereM is the encoder memory. A unit-memory code with maximal free distance is given at each place where this free distance exceeds that of the best code withk_{o} andn_{o} relatively prime, for allMk_{o} leq 6 and forR = l/2, 1/3, 1/4, 2/3 . It is shown that the unit-memory codes are byte oriented in such a way as to be attractive for use in concatenated coding systems. 相似文献
12.
The use of electron spin resonance for measurement of the ground state population (GSP) of Cr3+in a ruby rod during optical pumping is described. For a 7.7 cm long rod at 90°K and a mirror reflectance productR_{1}R_{2} > 0.08 , the GSP at laser threshold was found to be 55 ± 5 percent in good agreement with theory and previous optical measurements. At room temperature, a limiting value of approximately 30 percent for the GSP was approached at high pump energies. Observations of the relativeR_{1}(3/2), R_{1}(1/2) thresholds at 90°K as a function of mirror reflectivity indicated that the2E excited state absorption cross section at the laser wavelength is less than5 times 10^{-21} cm2. Detection of total internal reflection oscillations in cooled ruby lasers from ESR observations is also described. 相似文献
13.
《IEEE transactions on information theory / Professional Technical Group on Information Theory》1964,10(1):72-74
Upper and lower bounds are established for the mean-square variation of a stationary processX(t) whose power spectrum is bounded byomega_{c} , in terms of its average powerP_{0} and the average powerP_{1} of its derivative. It is shown thatleft( frac{2}{pi} right)^{2} P_{1} tau^{2} leq E {|X(t+tau )-X(t)|^{2}} leq P_{1} tau^{2} leq omega_{c}^{2}P_{0}tau^{2} where the upper bounds are valid for anytau and the lower bound fortau < pi / omega_{c} . These estimates are applied to the mean-square variation of the envelope of a quasi-monochromatic process. 相似文献
14.
Induced-emission cross sections for the4F_{3/2}rightarrow 4I_{11/2} and4F_{3/2} rightarrow 4I_{13/2} transitions of Nd3+in glasses can be determined with a satisfactory precision by a simplified method, based on the Judd-Ofelt theory, from the measurement of the integrated absorbance of the 750-nm band and of the effective linewidth of the fluorescence band. 相似文献
15.
TheB^{3} Sigma-_{u} rightarrow X^{3}Sigma-_{g} system of S2 has many of the characteristics required of a tunable laser: a broad fluorescence spectrum and a Franck-Condon shift between theB andX states. In this paper, theupsilon' = 4 level of theB^{3} Sigma-_{u} rightarrow X^{3}Sigma-_{g} system of S2 is pumped by the absorption of the 308 nm XeCl excimer radiation. Rare gas-S2 collisions redistribute the population among theupsilon' levels, and the subsequent emission contains intense bands throughout much of the neat UV and visible region of the spectrum. Broad-band gain is reported on two blue-green bands (2,17) and (3,18) populated by rare gas relaxation. Absorption is reported on the near UV bandsupsilon' = 0 rightarrow upsilon" rightarrow 6,7,8 where the lower levels are filled by the transient population cascading down theX state manifold. A fluorescence study is presented which examines the potential advantages and limitations of this system. 相似文献
16.
Using a dispersive prism, the room temperature YAlG : Nd laser has been made to oscillate CW on a total of seven4F_{3/2} rightarrow 4I_{11/2} transitions ranging in wavelength from 1.0519 μm to 1.1226 μm and a single4F_{3/2} rightarrow 4I_{13/2} transition at 1.319 μm. 相似文献
17.
This paper indicates both experimentally and graphically how the distribution of carriers changes above a critical temperature Tc , which is related to the density of states ρ in the band tails. Thus,kT_{c} = E_{0} , whererho = rho_{0} exp (DeltaE/E_{0} ). The emission spectrum shifts with changing excitation (band filling) at lower temperatures (T < T_{c} ) and stays at a constant value independent of excitation at higher temperatures (T > T_{c} ). Experimental results of photoluminescence studies with GaAs crystals show that the quantity E0 , obtained from the dependence of the peak energy upon the degree of excitation is the same as the quantitykT'_{c} , obtained from the dependence of the peak energy upon temperature. This is in agreements with the analysis. For lasing diodes, the threshold will increase steeply with increasing temperature above Tc , if the excited carriers are located mostly in the exponential states of the band tail.E_{0} = (10 sim 20) meV and Tc = (120 sim 250deg K) are typical for crystals of heavily compensated GaAs. 相似文献
18.
We demonstrate that it is important to know both the observed fluorescence lifetime (τ) and the excitation pulsewidth (Gamma ) in order to determine the effect of changes inGamma on the measurement of one- and two-photon excitation spectra. IfGamma/tau is greater than 3, it is sufficient to measureI_{F}/I_{L}^{n} orI_{F}/N_{L}^{n} forn -photon excitation spectra (n = 1 and 2), where IF is the peak fluorescence intensity, IL is the peak intensity of the excitation pulse, and NL is the total number of photons per pulse. WhenGamma/tau is less than 3, however, the pulsewidth dependence ofI_{F}/I_{L}^{n} orI_{F}/N_{L}^{n} should be treated by using the pulse-width correction functions defined in this paper. A simple method to estimate observed fluorescence lifetimes is also described where one needs only to measureGamma and the time interval between the peak intensity of an excitation pulse with a Gaussian or near Gaussian temporal profile and the peak fluorescence intensity. Tables of correction factors are provided which can be used to generate accurate values of these functions for arbitrary ratios ofGamma/tau using interpolation techniques. The treatment of the effect of non-Gaussian excitation pulses on the measurement of one- and two-photon excitation spectra is discussed. 相似文献
19.
Experimental results for the behavior of the emission of the discharge-excited first- and second-positive bands of N2 and flow-tube measurements for the deactivation of theA^{3}Sigmamin{u}max{+} andB^{3}Pi_{g} levels of N2 by SF6 are presented. The results of both these experiments are used to explain the operating mechanisms of the N2 /SF6 laser. 相似文献
20.
An upper limit of 4 ns has been determined for the nonradiative relaxation times between the4T2 and2T1 states of ruby. This value was deduced from the rate of rise of the red2T1 fluorescences from ruby crystals pumped by the second harmonic of a 1.06-μ laser. 相似文献