Showing papers on "Laser linewidth published in 1974"

Broadening coefficients for the P(20) CO2 laser transition

Abstract: Accurate line‐shape and linewidth measurements have been made on the P(20) 10.6‐μm CO2 laser transition using optoacoustic spectroscopy and a tunable waveguide CO2 laser. The absorption line shape is shown to be accurately represented by a Voigt line shape and the measured broadening coefficients are γCO2=7.61±0.10, γN2=5.58±0.20, and γHe=4.88±0.18 MHz/Torr, all measured at 298°K.

Improved polycrystalline ceramic lasers

Abstract: Improved polycrystalline ceramic laser rods, composed of cubic solid solutions of 89–96.5 mole% Y2O3, 10–2.5% ThO2, and 1% Nd2O3, were synthesized by a conventional sintering process. This material, called Nd‐doped Yttralox (NDY) ceramic, was produced with laser threshold energies lower than that of the best commercially available Nd:glass laser rod and with a lasing efficiency ∼94% that of laser glass at 40 J of input energy under pulsed mode conditions. In a similar operating mode a NDY rod, containing 5 mole% ThO2 and having dimensions 7.6×0.46 cm, delivered 0.41 J of optical energy when using an input energy of 162 J, a pump pulse of 150 μsec, and output mirror reflectivity of 70%. The lasing efficiencies depended strongly on the method of powder preparation and processing, composition, and the cooling rate from the sintering temperature. The dependence of the fluorescent linewidth on the NDY composition provides a means of appreciably varying the material gain coefficient. Active attenuation coeffici...

An electron resonance investigation of molecular motion in the smectic A mesophase of a liquid crystal

Abstract: This paper reports the angular dependence of the electron resonance spectrum of a spin probe dissolved in a smectic A mesophase. The spectra were analysed to obtain the angular variation of the linewidth coefficients and hence the angular linewidth coefficients. These angular coefficients -may be interpreted by employing a theory of spin relaxation based on the strong collision model for molecular reorientation. Such an analysis yields values for the correlation times for reorientation about the long and short axes of the spin probe as well as the magnitude of the solute order parameter p4. The possibility of interpreting the angular linewidth coefficients in terms of a theory based on the diffusion model for molecular reorientation is also explored. Relatively straightforward expressions for these coefficients can only be obtained from the diffusion model when the orientational order is hrgh, as it is in a smectic phase. The analysis of the angular linewidth coefficients then provides values for the components of the diffusion tensor parallel and perpendicular to the long axis of the spin probe. The large anisotropy in the diffusion tensor may be indicative of the unhindered molecular motion about the long axis. Both models of molecular reorientation in a highly ordered system appear to provide a satisfactory account of the observed angular linewidth coefficients.

An exposure model for electron-sensitive resists

Abstract: We present a mathematical model for the exposure of electron-sensitive resists where an electron beam is incident normal to a substrate coated with a thin layer of resist. We include both the scattering of the incident electrons as they penetrate the resist and the electrons backscattered from within the resist and from the substrate. The calculations yield contours of equal absorbed energy density, and these are interpreted as the contours which bound the resist after development. The absorbed energy density is found as the sum, for all electrons, of the product of the energy absorbed per unit length of trajectory and the flux density of electrons at the point in question. We first calculate the absorbed energy density for an electron beam of vanishingly small cross section (an incident delta function) and then convolve that result with a beam of Gaussian current-density distribution to obtain the reSult for a single beam location. For poly(methyl methacrylate) resist, we study the achievable dot resolution, as a function of the incident charge, for various incident energies-and substrates. Since our main interest is in computer-controlled resist exposures in which patterns are generated as a succession of dots, we calculate the absorbed energy density contours for a line generated in that manner. Detailed comparison is made with the experimental results of Wolf et al., by fitting a single point on one contour at one beam energy to account for the unknown developer sensitivity. The resulting contours predict the undercutting effect experimentally observed for the 5-20-keV beam energies studied. The developed shape and linewidth are found to be nonlinear functions of the incident charge per unit length. Experimental data for the linewidth at 20 keV are presented and compared with theory.

Optical resolution beyond the natural linewidth: A level-crossing experiment on the 32 P 3/2 level of sodium using a tunable dye laser

Abstract: A level crossing experiment on the hyperfine structure of the 32 P 3/2 level of Na23 was performed using a nitrogen laser pumped dye laser for the excitation of the Na atoms. The fluorescent light was observed in time intervals which were initiated up to seven lifetimes after excitation. Therefore the signal was only determined by atoms having survived in the excited state up to the initiating time. The minimum linewidth observed was 6 times smaller than the natural width. Neighbouring crossing signals, which overlap in a level crossing experiment using time integral observation of the fluorescent light, could be resolved. The accuracy of the hyperfine constants of the 32 P 3/2 level could be improved.

A nitrogen ion laser pumped by charge transfer

Abstract: The first nitrogen ion laser pumped by charge transfer from He2+ is reported in this work. Intense laser emission in the violet at 427 nm has been observed and found to have a linewidth less than 0.3 nm. The pumping ion, He2+, was produced by discharge of a fast‐pulsed electron beam gun, APEX‐1, into 7 atm of a mixture of helium and nitrogen. Excitation current densities were 1.4 kA/cm2 at 1 MV over a 1 × 10 cm transverse geometry. Under these conditions, the efficiency of the emission of 427‐nm laser radiation was found to be 1.9% relative to the energy lost by the electron beam in the radiating volume.

cw generation of tunable narrow-band far-infrared radiation

Abstract: Tunable narrow‐band cw generation of far‐infrared radiation has been achieved for the first time in the 70‐μm to 1‐mm wavelength region by noncollinear difference‐frequency mixing of two single‐mode CO2 lasers in GaAs at 80 K. Using a Schottky diode as a heterodyne harmonic mixer with a carcinotron local oscillator, the far‐infrared signal is shown to have a linewidth of less than 100 kHz and a fine tuning capability in excess of 50 MHz.

Frequency Stabilization Of A CW Dye Laser

Abstract: In order to perform ultrahigh resolution spectroscopy, a tunable laser with a narrow spectral width is required. In this paper we describe a single-frequency jet stream cw dye laser that is carefully designed to minimize high frequency laser jitter. The residual low-frequency jitter is reduced to 200 kHz rms by locking the laser frequency to an external reference cavity. The stability of the laser has been verified by observing extremely narrow resonances (700 kHz FWHM) in an iodine molecular beam. The laser frequency can be linearly and smoothly tuned by varying the length of the external cavity. In certain precision spectroscopic applications long-term laser stabilization is needed for the generation of secondary wavelength standards throughout the visible region. By locking the dye laser to a hyperfine transition in a molecular beam of I2, we have demonstrated a long-term stabilization of 6 parts in 1013.

Tunable far infrared methyl fluoride laser using transverse optical pumping

Abstract: Some severe limitations of optically pumped superradiant FIR lasers (700‐MHz linewidth, ragged pulse shape) may be overcome by using transverse optical pumping (TOP). Strong (∼500 W) lines have been produced in CH3F with linewidth <30 MHz, and cavity tuning has been achieved over a range of 460 MHz at 496 μm. Prospects for extending the tuning range and increasing the power are considered.

Single longitudinal mode operation of cw junction lasers by frequency-selective optical feedback

Abstract: cw oscillation in a single longitudinal mode is reported for stripe‐geometry junction lasers operated at room temperature with frequency‐selective optical feedback. The frequency‐selective feedback, obtained by optically coupling a diffraction grating to the diode, is used to select a single mode of the normally multimode spectrum generated by the diode laser itself. Single‐frequency oscillation is observed for currents up to 30% above threshold. The oscillation frequency has a linewidth determined primarily by the internal dynamics of the diode and is tunable over the entire multimode spectrum. Additional experimental results demonstrate the homogeneous broadening of the radiative line in these lasers.

Lifetime of electronically excited NO2: Evidence for a short‐lived state

Abstract: The lifetime of one spin component of the 524 rotational level of some vibrational level of B2 symmetry of the 2B2 electronic state of NO2 has been measured by observing the linewidth of the microwave‐optical double resonance spectrum of that state. The lifetime determined from the zero power, zero pressure linewidth extrapolation is less than 3.39 ± 0.36 μsec and is over an order of magnitude shorter than that usually measured in NO2. This indicates that at least some electronically excited levels of NO2 have lifetimes approaching those calculated from the integrated absorption coefficient.

A narrowband jet stream dye laser

Abstract: The dependence of the optical quality of water and of higher viscosity jet streams on the flow velocity and the geometry of the nozzle is investigated. It was found that disturbing thickness fluctuations can be reduced by the use of thin jet streams with solvents of high viscosity and by working at an experimentally determined optimum flow velocity. The linewidth of a cw jet stream dye laser with a water-Ammonyx and an ethylene glucol solution was measured to be 9 MHz and 3.3 MHz, respectively. The linewidths were independent of the pump power.

Photoluminescence in single-crystal chalcogenides in the system As2Se3-xSx

Abstract: Photoluminescence (PL) and excitation spectra have been measured at temperatures between 5 and 250K single crystals of As2Se3, As2S3 and the mixed system As2Se3-xSx, (0

Attenuated-total-reflection spectral linewidth: Analysis of surface-polariton dispersion relations and damping rates

Abstract: The dispersion relation for surface polaritons is investigated with real wave vector and complex frequency. The numerical solutions obtained for the complex frequencies are used to account for the widths of calculated attenuated-total-reflection lines in the limit of low coupling between the prism and the sample. The case of surface optic-phonon modes in GaP and GaAs is treated, as well as the case of coupled surface-plasmon optic-phonon modes in InSb. Calculated and experimental linewidths are compared for GaAs and InSb. The anomalously large linewidths found for InSb are discussed.

On the theory of a detuned single mode laser near threshold

Abstract: A theory of a detuned single mode laser near threshold is given using the Fokker-Planck equation technique. The Fokker-Planck equation is solved by an eigenfunction expansion. The eigenfunctions and the corresponding eigenvalues are determined by a nonhermitian operator and are calculated numerically in the threshold region. The dependence of the linewidth from the detuning is shown. In the intensity distribution the detuning enters only via a change of the scaling parameter. For the linewidth, however, an additional broadening is found. Finally it is shown that in certain cases the correlation function must not be approximated by a single exponential term.

Optical integrated circuit laser beam scanner

Abstract: A rapid laser scanning system utilizing an optical grating coupler (OGC) reby the angle at which an incident laser beam is outputted therefrom may be varied by the imposition of an electric field on a thin film underlying the coupler at right angles to the path of the laser beam through the thin film.

Laser absorption spectroscopy

Abstract: In laser absorption spectroscopy, an absorption sample cell containing the sample under analysis, is interposed within the optical cavity of a laser. In this manner, the laser beam power available for application to the sample is increased by a substantial factor, for example by 10 or 100 for a given input power to the laser. In addition, the number of usable laser lines of a tunable laser source is substantially increased, for example by 10 or 100 as contrasted with a laser absorption spectrometer wherein the sample is located outside of the laser cavity.

Optical spectra and laser action in Nd3+‐doped CaY2Mg2Ge3O12

Abstract: Crystals of the garnet‐structured germanate CaY2Mg2Ge3O12 have been grown from a melt containing 6 mole% Nd3+. The fluorescence, absorption, excitation spectra, lifetime, and linewidths have been measured and were compared with the results for Nd3+:YAG. The important spectroscopic features of Nd3+:CaY2Mg2Ge3O12 are a lifetime of 305 μsec, a strong absorption in the near infrared, a very intense fluorescence line at 941 nm, and a linewidth at this wavelength of approximately 37 cm−1. Laser action has been achieved at 1058.96 nm at room temperature. An estimate of the laser transition cross section gives a value of σ=6×10−20 cm2.

Spin-flip Raman laser

Abstract: The properties of the spin-flip Raman laser (SFR laser) which depend on stimulated Raman scattering from mobile conduction electrons in InSb under an external magnetic field are presented. The essential parameters are derived from a macroscopic treatment of the stimulated Raman effect and the microscopic theory of the scattering cross-section, and are compared with experimental results. Output pulse powers as large as 1 kW have been measured for 10.6 and 5.3 μm excitation radiation and continuous powers of 1 W for continuous excitation with a 5.3 μm pump source. The SFR laser offers some interesting applications in physics and chemistry, since its frequency is proportional to the applied magnetic field and its linewidth can be made smaller than 1 kHz.