The application of different types acoustic resonators such as pipes, cylinders, and spheres in photoacoustics is considered. This includes a discussion the fundamental properties these resonant cavities. Modulated pulsed laser excitation modes discussed. theoretical practical aspects high-Q low-Q their integration into complete photoacoustic detection systems for trace gas monitoring metrology are covered detail. characteristics available sources performance resonators, signal...

Nanocrystalline columnar-structured diamond films with column diameters less than 100 nm and thicknesses in the range of 1–5 μm were grown on silicon substrates by chemical vapor deposition (CVD) a microwave plasma reactor purified methane hydrogen used as reactants. Uniform conformal nucleation densities excess 1012 cm−2 accomplished prior to growth seeding explosively formed nanodiamonds, which resulted good optical quality films. The film thickness was measured situ laser reflectometry...

A noncontact all-optical method for surface photoacoustics is described. The acoustic waves (SAWs) were excited employing a KrF laser and detected with Michelson interferometer using 633-nm HeNe laser. Due to an active stabilization scheme developed the displacement of 0.2 Å could be detected. materials investigated included pure such as polycrystalline aluminum, crystalline silicon; films gold, silver, iron, nickel on fused silica; a-Si:H Si(100). In case shape pulse phase velocity...

The method of laser-excited vibrational fluorescence is used to measure the relaxation rates H2 18O in collisions with 18O, Ar, N2, and O2. Pumping various vibration–rotation lines ν1 ν3 stretching levels a tunable infrared laser leads same measured rate constants. In pure are found relax together constant 2.2×10−11 cm3 molecule−1 sec−1, bend overtone relaxes 9.1×10−11 fundamental between 5×10−11 9×10−11 sec−1. Relative intensity measurements show that dominant pathway V→V transfer from...

The structural and electronic properties of the diamond lattice, leading to its outstanding mechanical properties, are discussed. These include highest elastic moduli fracture strength any known material. Its extreme hardness is strongly connected with shear modulus, which even exceeds large bulk revealing that more resistant deformation than volume changes. unique features protect ideal lattice also against failure fracture. Besides fast heat conduction, vibrational movement carbon atoms...

The Young’s modulus and Poisson’s ratio of high-quality silicon nitride films with 800 nm thickness, grown on substrates by low-pressure chemical vapor deposition, were determined measuring the dispersion laser-induced surface acoustic waves. was also measured mechanical tuning commercially available cantilevers, manufactured from same material, using tapping mode a scanning force microscope. For this experiment, an expression for oscillation frequencies two-media beam systems is derived....

Laser-generated surface waves provide new tools for studying material properties, from linear elastic behavior to fracture.

The vibrational relaxation time for the asymmetric stretch ν3 of CH4 is 3.9±0.6 μsec torr in pure and 12, 13, 10, 5.9, 5.5, 5.0, 11, 9.5 (±20%) dilute 3He, 4He, Ne, Ar, Kr, Xe, H2, HD, respectively, at 295°K. fundamental was pumped by a tunable infrared laser. rise bending fluorescence following excitation 30%–50% shorter than decay. In CH4, measurements emission from 2ν4 ν2+ν4 indicate that large fraction energy channeled through these two levels. main path appears to be transfer ν4, with...

The 7.9 eV photons of a ${\mathrm{F}}_{2}$ laser induced photochemical desorption molecular hydrogen from $\mathrm{Si}(111)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1):\mathrm{H}$ surfaces with cross section $(1.2\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\mathrm{cm}{}^{2}$. time-of-flight detection desorbing species and numerical calculations surface heating clearly allowed ${\mathrm{F}}_{2}\ensuremath{-}\mathrm{laser}$ (7.9 eV)...

Sensitive photoacoustic detection of ammonia with near-infrared diode lasers (1.53 microns) and a novel differential acoustic resonator is described; sensitivity 0.2 parts per million volume (signal-to-noise ratio = 1) attained. To eliminate adsorption-desorption processes the polar NH3 molecules, relatively high gas flow 300 SCCM was used for ammonia-nitrogen mixture. The results are compared recent measurements NIR absorption spectroscopy experiments performed an infrared quantum-cascade...

Thin epitaxial BaTiO 3 (BTO) films having a high crystallinity and uniformity of grains were deposited on the SrTiO (STO) substrates. When oxygen pressure is from 0.04 to 70 Pa lattice constant decreases 4.1100 3.9972 Å orientation normal substrate changes (001) (100). The surface topography flat hilly with roughness (rms) changing between 1.2 nm at 0.7 Pa, 3.4 7 6.4 Pa. At temperature 550, 750 850°C varies corrugated structure rectangular grain increases 1.2, nm. BTO also YBCO/LaAlO...

Broadband detection (150-MHz range) of surface acoustic wave transients excited by absorption ps laser pulses in the sample under study is demonstrated. A novel transducer employing a ferroelectric polymer foil as piezoelectric sensor described. In silicon single crystal width observed was limited to 4 ns spatial resolution pulse generation and detection. polycrystalline materials minimum observable determined properties. Accurate values for phase velocity propagation are given silicon,...

A distributed-feedback (DFB) diode laser radiating at 1.53 mum was used for photoacoustic detection of ammonia molecules in the gas phase under flow conditions. The influence adsorption-desorption processes that occur cell and tube walls on measured concentration studied. Dramatic differences adsorption behavior a metal polypropylene are demonstrated. Simulations yield conditions must be fulfilled accurate measurements trace-gas analysis polar molecules.

In a cylindrical cavity the longitudinal mode (002), radial (100), and combination (102) were excited with chopped 3.39 μm He–Ne laser by vibrational excitation of CH4. The recording acoustic resonances was completely controlled microcomputer. This included repeated registration resonator temperature, stabilization measurement modulation frequency, integration signal detected an electret microphone. interaction different standing waves in taken into account. From corrected line profiles,...

Vibrational energy levels of methane in the range 2800 to 6000 cm−1 were excited by a pulsed tunable laser. Infrared fluorescence decays observed at 294 K and analyzed yield V→V transfer pathways rates. Symmetric stretching excitation is converted asymmetric same molecule with rate constant k1=(3.6±0.9) ×10−11 cm3 molecule−1 s−1 (P=0.09). The ν2 ν4 bending vibrations are interconverted somewhat less rapidly. Stretching (0.8±0.2)×10−11 (P=0.022) for fundamentals about twice that overtone or...

The stage of nucleation and growth stressed coherent islands is investigated for the Stranski--Krastanow mode. Both elastic deformations attraction atoms by wetting layer due to a potential are taken into account. It shown that these two effects do not change functional dependence free energy island formation on size result in renormalization surface tension equilibrium concentration adatoms. Analytical expressions rate self-limiting cluster-size distribution obtained. evolution equation...