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     

Mixed isotope multiatmosphere CO2laser

A sealed transversely excited multiatmosphere pulsed laser is reported in which the active media is a combination of three isotopes:¹²C¹⁶O2,¹²C¹⁸O2, and¹²C¹⁶O¹⁸O. Lasing action is obtained on all 12 vibrational-rotational bands with continuous tuning observed between line centers at pressuresfrac{1}{2}tofrac{1}{4}of those required with conventional¹²C¹⁶O2lasers.     

Absolute frequencies of lasing transitions in seven CO2isotopic species

The band centers, rotational constants, absolute frequencies, and vacuum wavenumbers for¹²C¹⁶O2,¹³C¹⁶O2,¹²C¹⁸O2,¹³C¹⁸O2,¹²C¹⁶O¹⁸O,¹⁴C¹⁶O2, and¹⁴C¹⁸O2have been simultaneously computed from 590 beat frequency measurements between pairs of adjacent00deg1-[10deg0,02deg0]I and II band CO2laser transitions. The input data included the 56 beat frequencies measured between adjacent¹²C¹⁶O2rotational lines by Petersen et al. The absolute frequencies are directly related to the cesium frequency standard via the 29 442 483.315 (0.025) MHz 10.18 μm I-R (30) and the 32 134 266.891 (0.024) MHz 9.33 μm II-R(10) transitions in¹²C¹⁶O2which were measured by Evenson et al. The results described in this paper will provide the means for setting up easily reproducible secondary frequency standards in the8.9-12.3 mum wavelength band.     

Infrared microwave sideband laser spectroscopy in the CO laserregion

The method of infrared microwave sideband laser spectroscopy developed by G. Magerl, et al. (ibid, vol.18, p.1214-20, 1982) for application in the 9-11-μm region with a CO₂ laser has been extended to application in the 5-6-μm region with a CO laser. The experimental details, performance of the system, and typical spectra are described. Frequency measurements of spectra in the 01¹1←00⁰0 band of ¹⁴N₂ ¹⁶O and the 20⁰←00⁰0 band of ¹⁶O¹²C³²S are compared to the results of previous precise measurements by heterodyne techniques to show that the accuracy is limited mainly by the resettability of the CO laser frequency     

Observation of a strong vibrational population inversion by CO laser excitation of pure solid carbon monoxide

Under irradiation of a pure solid CO sample at low temperature by a CW CO laser beam,¹³C¹⁶O,¹²C¹⁸O and¹³C¹⁸O molecules are excited to high vibrational levels, up toupsilon = 23, and a strong population inversion is observed. The¹²C¹⁶O molecules are pumped to theupsilon = 1level by laser line absorption in the low frequency phonon sideband, and the vibrational energy is subsequently transferred to the other isotopes. Quantum yield, efficiency, and heat release are discussed to clarify the mechanism.     

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     

Sequential decoding based on an error criterion

An analysis of sequential decoding is presented that is based on the requirement that a set probability error P_e be achieved. The error criterion implies a bounded tree or trellis search region: the shape of this is calculated for the case of a binary symmetric channel with crossover probability P and random tree codes of rate R. Since the search region is finite at all combinations of p and R below capacity, there is no cutoff rate phenomenon for any P_e>0. The decoder delay (search depth), the path storage size, and the number of algorithm steps for several tree search methods are calculated. These include searches without backtracking and backtracking searches that are depth- and metric-first. The search depth of the non-backtracking decoders satisfies the Gallager reliability exponent for block codes. In average paths searched, the backtracking decoders are much more efficient, but all types require the same peak storage allocation. Comparisons are made to well-known algorithms     

Optical and noise characteristics of amorphous Si/SiC superlatticereach-through avalanche photodiodes

In order to improve the performance of the a(amorphous)-Si:H/SiC:H superlattice avalanche photodiode (APD), a-Si:H/SiC:H superlattice reach-through APDs (SRAPDs) have been fabricated on ITO(indium tin oxide)/glass substrates by plasma-enhanced chemical vapor deposition (PECVD). For a typical electron-injection SRAPD, the ratio of room-temperature electron and hole impact ionization rates (α/β) is 10.2 at an electric field 3.33×10⁶ V/cm, the optical gain is 506 at an applied reverse-bias V_R=18 V and an incident power P_in=5 μW emitted from a He-Ne laser, the rise time is 1 μs at a load resistance R_L 1 kΩ, and the excess noise factor is 6.53 at a multiplication M=48     

Molecular-beam growth of homoepitaxial InSb photovoltaic detectors

Molecular-beam epitaxy has been used for the first time to fabricate np junctions in InSb grown onto p-type InSb (100) substrates. Diodes formed by the epitaxial growth of a silicon-doped layer on undoped homoepitaxial material exhibited a bulk generation-recombination-limited R₀A value of 10⁵ Ω cm² and D_λpk * of 3×10¹² cm Hz^1/2 W^-1 at liquid nitrogen temperature     

An EMQ-switched CO2 laser as a pump source for afar-infrared laser with a high peak power and a high repetitionrate

A modified current pulsed Q (EMQ)-switched CO₂ laser which is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current is discussed. The laser produces a very stable output with a peak power greater than 1 kW at a repetition rate of 1000 p.p.s. for all transitions in the P and R branches of the CO₂ spectrum. A CH₃F laser pumped by the EMQ-switched laser produces 496 μm radiation in a 6.5 W peak, 100 ns pulses at 500 p.p.s. in the lowest loss EH₁₁ mode     

The calculation of the probability of detection and the generalizedMarcum Q-function

A highly reliable, accurate, and efficient method of calculating the probability of detection, P_N(X,Y ), for N incoherently integrated samples, where X is the constant received signal-to-noise ratio of a single pulse and Y is the normalized threshold level, is presented. The useful range of parameters easily exceeds most needs. On a VAX/11 computer with double precision calculations, better than 13-place absolute accuracy is normally achieved. There is a gradual loss of accuracy with increasing parameter values. For example, for N=10⁹, and with both NX and Y near 10⁷, the accuracy can drop to ten places. The function P_N(X,Y ) can be equated to the generalized Marcum Q-function, Q_m(α,β). The corresponding limits on α and β are roughly 4500 for the 13-place accuracy and 60000 for ultimate (INTEGER×4) limit     

Analysis of CH3OH far infrared laser lines optically pumped by sequence band and isotopic CO2lasers

Assignments are presented for seven far infrared (FIR) laser lines of CH3OH pumped by theS-9P(31),18-10R(24),13-9R(26), and13-9P(16)CO2laser lines, plus an interesting speculation for the FIR line pumped by the18-9P(12)CO2line. Frequencies have been deduced to a substantially improved accuracy of ±0.001 cm^-1from IR and FIR spectroscopic combination differences for most of the assigned lines as well as three other predicted transitions. In addition, accurate frequencies are given for 13 predicted FIR laser transitions which are expected from the IR spectrum to be pumped by three¹⁶O¹²C¹⁸O laser lines.     

Phase-difference distribution for a narrow-band non-Gaussian noiseand related statistics

A probability density function _Pm(R₁,R₂,Δ) is presented for a narrowband noise process in which R₁ and R₂ are two envelope samples and Δ is the phase difference. For m=1 the process is Gaussian, but for m=2,3, etc., it is non-Gaussian. New second-order statistical properties are identified for it as well as the density function for the resulting envelope when a signal is added to the noise. These results are given, though the major concern is with the density of the phase difference Δ and the density of &thetas;, the response of an FM detector fed with the noise     

Amorphous silicon/silicon carbide superlattice avalanchephotodiodes

An a-Si/SiC:H superlattice avalanche photodiode (SAPD) has been successfully fabricated on an ITO/glass substrate by plasma-enhanced chemical vapor deposition. The room-temperature electron and hole impact ionization rates, α and β, have been determined for the a-Si/SiC:H superlattice structure by photocurrent multiplication measurements. The ratio α/β is 6.5 at a maximum electric field of 2.08×10⁵ V/cm. Avalanche multiplications in the superlattice layer yields an optical gain of 184 at a reverse bias V_R=20 V and an incident light power P_in=5 μW. An LED-SAPD photocouple exhibited a switching time of 4.5 μs at a load resistance R-1.8 kΩ     

Statistical inference under multiterminal rate restrictions: adifferential geometric approach

A statistical inference problem for a two-terminal information source emitting mutually correlated signals X and Y is treated. Let sequences Xⁿ and Yⁿ of n independent observations be encoded independently of each other into message sets M_X and M_Y at rates R₁ and R ₂ per letter, respectively. This compression causes a loss of the statistical information available for testing hypotheses concerning X and Y. The loss of statistical information is evaluated as a function of the amounts R₁ and R ₂ of the Shannon information. A complete solution is given in the case of asymptotically complete data compression, R₁, R₂→0 as n→∞. It is shown that the differential geometry of the manifold of all probability distributions plays a fundamental role in this type of multiterminal problem connecting Shannon information and statistical information. A brief introduction to the dually coupled e-affine and m-affine connections together with e -flatness and m-flatness is given     

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     

Extremal properties of rate distortion functions

An attempt is made to determine whether it is true that for a fixed distortion level Δ the rate-distortion function R( P,Δ) has in the distribution P no local maxima with values different from the global maximum. It is shown that, in general, the answer is negative. However, the answer is positive for Hamming distortion measures. Moreover their R is Schur-concave     

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     

Computing the probability of undetected error for shortened cycliccodes

The authors present a general technique for computing P _e for all possible shortened versions of cyclic codes generated by any given polynomial. The technique is recursive, i.e. computes P_e for a given code block length n from that of the code block length n-1. The proposed computation technique for determining P_e does not require knowledge of the code weight distributions. For a generator polynomial of degree r, and |g| nonzero coefficients, the technique yields P_e for all code block lengths up to length n in time complexity O(n|g |2^r+|g|). Channels with variable bit error probabilities can be analyzed with the same complexity. This enables the performance of the code generator polynomials to be analyzed for burst errors