Measurement distance effects on Bayliss difference patterns

The effects of measurement distance in distorting low-sidelobe difference patterns are examined. Previous calculations have used obsolete suboptimum aperture distributions. The Bayliss linear distribution is a versatile, highly efficient and robust optimum distribution; its use allows a single curve of sidelobe measurement error versus measurement distance (normalized to far-field distance 2D²/λ) for a given sidelobe level. Data are given for patterns from a uniform distribution to a 50-dB Bayliss. Difference patterns require slightly larger measurement distances than sum patterns. For example, the first sidelobe of a 40-dB Bayliss pattern is in error by 1 dB at a distance of 7D²/λ. The results should apply approximately for circular apertures as well     

Enhanced performance of the iodine monofluoride (491 nm) laser

The impact of substituting HI for CF₃I as the iodine donor in the discharge-pumped iodine monofluoride (IF) laser at 491 nm has been investigated. More than an order of magnitude improvement in output pulse energy has been observed and is attributed to more efficient production of low-lying (v'<5) vibrational levels of the IF (D') ion pair state. Preliminary evidence indicates that vibrational excitation of HI (X¹Σ⁺ ) assists in the relaxation of the D' state population. The increased net small-signal gain of D'→A' (v'=0→v^") transitions in HI-containing gas mixtures has the effect of intensifying the 491-nm (0.15) bandhead relative to the lower gain transitions     

Design of a low sidelobe double difference beam for a circularaperture

A low-sidelobe double-difference beam is synthesized for a circular aperture in a manner similar to the synthesis of the circular Taylor sum beam and the circular Bayliss difference beam. The method proposed allows the designer to select a peak-to-sidelobe level ratio and an integer N which controls the shape of the close-in sidelobes. Such a beam finds use in main beam ECCM applications     

High-performance highly strainedGa0.23In0.77As/Al0.48In0.52As MODFET's obtained by selective and shallow etch guide recesstechniques

Record high f_TL_g products of 57 and 46 GHz-μm have been achieved in Ga_1-x In_x As/AlInAs MODFETs with a strain compensated channel of x=0.77 and a lattice-matched channel of x=0.53, respectively. Although g_m as high as 950 mS/mm has been obtained by conventional deep recess for the gate, these latter devices show a prominent kink effect which lowers f_T and the voltage gain. By limiting the depth of final nonselective recess etch to 3 nm with the help of selective step etches, f_T as high as 47 GHz and g_m as high as 843 mS/mm have been achieved for MODFETs with x=0.77 and L_g=1.1 μm     

Small-signal gain measurement in a Ti:Al2O3amplifier

A small-signal single-pass power gain of e^5.2=180 has been measured for a signal in the π polarization at 790.7 nm in a longitudinally pumped Ti:Al₂O ₃ amplifier. A double-pass power gain of e^5.2 ≈10⁴ has been attained for the same polarization at 799.8 nm. The ratio of the gain cross sections at 632.8 and 790.7 nm is 1/25. The gain anisotropy at 632.8 nm is g_π/g _σ=2.3. The lifetime of the upper lasing level decreases with increased pumping, probably as the result of amplified spontaneous emission     

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     

Nonlinear optical and electrooptical effects in 2-methyl-4-nitro N-methylaniline (MNMA) crystals

Single crystals of 2-methyl-4-nitro-N-methylaniline (MNMA) have been grown from the melt. The crystal structure was determined (orthorhombic, Pna2_I (2 mm), Z=4, a =17.788(6) Å, b=11.893(4) Å, c=3.907(2) Å). The refractive indexes n_a and n_c were measured between 500 and 700 nm [ n_a(633 nm)=2.148(10), n_c(633 nm)=1.520(3)]. The nonlinear optical susceptibilities coefficients r ₃₁=8 pm/V and r₃₃=7.5 pm/V were determined. Most optical properties can be explained in terms of molecular orientation and polarizability     

Injection control of a multipass amplification of a dischargeexcited XeF (C→A) laser

The laser performance and kinetic properties of the broadband C→A transition of the XeF*-exciplex have been studied under discharge excitation. With a pulsed dye laser as the injection source, amplified output pulses with an energy of up to 4 mJ have been obtained in the wavelength range from 450 to 520 nm. Injection of a well-defined seed pulse in an unstable confocal cavity has been developed into a useful technique for identification of subtle kinetic details of the complicated lasing process in XeF*, such as the role of the competitive narrow-band B→X transition or the influence of the various buffer gases     

Injection control of a long-pulse electron-beam pumped XeF (C→A) laser

An XeF (C→A) laser, pumped at a rate of 290 kW/cm³ with a 600-ns electron-beam pulse, has been operated as an injection-controlled oscillator. A stable cavity has been injected with radiation from a pulsed dye laser source. A significant reduction in laser turn-on time has been achieved, and the laser pulse duration has been extended to 500 ns (FWHM). As a consequence, the laser intrinsic efficiency and specific output energy have been increased by approximately 50%, to 1.8% and 3 J/L, respectively, which represent the best performance obtained thus far for any directly electrically excited XeF (C→A) laser. Also, by injecting a narrowband signal into the cavity, the XeF (C→A) laser linewidth has been reduced by more than two orders of magnitude, to less than 1.3 Å, the resolution of the spectrometer. The laser wavelength has been tuned from 478.6 to 486.8 nm, with less than a factor of two variation in output energy     

A new organic electrooptic crystal:2,6-dibromo-N-methyl-4-nitroaniline (DBNMNA)

A new organic electrooptic crystal, 2,6-dibromo-N-methyl-4-nitroaniline, is reported. The crystal structure was determined by X-ray diffraction (orthorhombic, space group Fdd2, point group mm2, Z=16, a=11.745 Å, b=29.640 Å, c=10.807 Å). The refractive indexes were measured at several wavelengths between 500 and 1100 nm (at 632.8 nm, n_a=1.90, n_b=1.62, and n_c=1.48) and fit the data to a single oscillator Sellmeier equation. A report is presented on measurements of the linear electrooptic effect, yielding the combined coefficients n_a ³r₁₃-n_c³ r₃₃, as well as the first known measurements of the quadratic electrooptic effect in an organic crystal, yielding the coefficients r₄₂ and r₅₁ at 514.5, 632.8, and 810 nm. Good agreement is found between the observed dispersion in the electrooptic coefficients and that predicted by the simple two-level dispersion model     

Gain measurements on the KrF(B→X), XeF(B→X), and XeF(C→A) lasertransitions in an XeF(C→A) laser gas mixture

Optimum energy extraction from an electron-beam-pumped XeF(C →A) laser is achieved with a five-component rare gas halide mixture. The characterization and modeling of laser action in such a gas mixture requires a knowledge of small-signal gain and absorption coefficients not only on the blue-green XeF(C→ A) transition, but also in the ultraviolet (UV) region for the competing XeF(B→X) and KrF(B→X ) transitions. The authors report gain measurements on the XeF(C→A) transition and small-signal gain and absorption coefficients at or near both the XeF(B→X ) (351 and 353 nm) and KrF(B→X) (248 nm) transitions. A study of the gain for the UV and visible transitions as a function of Kr and Xe partial pressure is reported, and its impact on the XeF(C→A) kinetics is discussed     

Ti:LiNbO3 stripe waveguide Bragg reflector gratings

The first demonstration of Bragg reflector grating filters in Ti:LiNbO₃ single-mode channel guides is reported. Filter bandwidths as narrow as 0.14 nm centred at 1.476 μm have been achieved for TE polarisation in Y-cut (X-propagating) material     

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     

Design of bipolar imaging devices (BASIS): analysis of random noise

A design methodology for a bipolar imaging device, the base-stored image sensor (BASIS), has been established by theoretical analysis and experimental verification for random noise. The random noise in BASIS is dominated by the shot noise in readout and transient reset operation. The theoretical analysis has been carried out by introducing the probability density functions for these operations. The readout noise depends on the base-to-collector junction capacitance C_bc , the emitter common current gain h_FE, the storage capacitor C_T, and the emitter voltage V _E. The reset noise has been confirmed to be given by thermal noise. The theoretical results coincide well with the experimental results obtained by TEG devices. An expression for the S/N ratio has been derived theoretically. It is found that h_FE should be made as large as possible and ( C_bc+C_be) as small as possible to improve the S/N ratio for random noise, where C _be is the base-to-emitter junction capacitance     

Bounding the capacity of saturation recording: the Lorentz modeland applications

The authors consider the problem of bounding the information capacity of saturation recording. The superposition channel with additive Gaussian noise is used as a model for recording. This model says that for a saturation input signal, x(t) (i.e., one that can assume only one of two levels), the output can be expressed as y(t)=x˜(t)+z(t ) where x˜(t) is a filtered version of the input x(t) and z(t) is additive Gaussian noise. The channel is described by the impulse response of the channel filter, h(t), and by the autocorrelation function of the noise. A specific example of such a channel is the differentiated Lorentz channel. Certain autocorrelation and spectrum expressions for a general Lorentz channel are derived. Upper and lower bounds on the capacity of saturation recording channels are described. The bounds are explicitly computed for the differentiated Lorentz channel model. Finally, it is indicated how the derived bounds can be applied in practice using physical measurements from a recording channel     

Scaling characteristics of the XeF (C→A)excimer laser

The scaling characteristics and medium properties of an injection-controlled XeF(C→A) laser pumped by a 10-ns-high current density electron beam have been investigated. A five-component laser gas mixture, consisting of F₂, NF₃ , Xe, Kr, and Ar was optimized for the scaled laser conditions, resulting in 0.8-J output pulses at 486.8 nm, corresponding to an energy density of small-signal-gain measurements combined with kinetic modeling permitted the characteristics of the dependence of net gain on the electron-beam energy deposition and gas mixture composition, resulting in an improved understanding of XeF(C→A) laser operation     

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     

Characterization of spontaneous and stimulated emission frompraseodymium (Pr3+) ions doped into a silica-based monomodeoptical fiber

The fluorescence spectrum of praseodymium in a silica host has been investigated through the direct excitation of the ³P ₀, ¹D₂, and 1G ₄ absorption bands, which occur at around 488, 590, and 974 nm, respectively. The observed spontaneous emission consists of four main bands with peaks at 633, 707, 888, and 1080 nm. In each case the level principally responsible for these emissions was found to be 1D ₂. Stimulated emission has been seen for the first time at 888 nm for a threshold of 10 mW absorbed power. In addition, the lasing characteristics at 1080 nm have been investigated     

Studies of diffused phosphorus emitters: saturation current,surface recombination velocity, and quantum efficiency

The surface recombination velocity s for silicon surfaces passivated with thermal oxide was experimentally determined as a function of surface phosphorus concentration for a variety of oxidation, anneal, and surface conditions. This was accomplished by measuring the emitter saturation current density J₀ of transparent diffusions for which the J₀ is strongly dependent on s. At the lowest doping levels, the value of s was confirmed by measurements of s on substrates with uniform phosphorus doping. The impact of these measurements on solar cell design is discussed     

Asymptotic distortion spectrum of clipped, DC-biased, Gaussiannoise [optical communication]

Consider a zero-mean, stationary Gaussian process g(t ), to which a large positive constant A has been added. Define a distortion process h_A(t) as equal to g(t)+A when the latter is negative and equal to zero otherwise. The author calculates the power spectrum of the process h_A(t) asymptotically as A becomes large. The results have application for estimating the nonlinear-distortion power in the recovered signal when many frequency-multiplexed subcarriers collectively modulate a laser's output power, as would be the case for CATV transmission over an optical fiber. The process h_A(t) then models the nonlinear distortion caused by occasional clipping of the DC-biased laser input