Laser mass spectrometry study of the properties of fullerene structures

Fullerene films grown by various methods are studied using mass spectrometry. The mass spectra of the films formed onto an aluminum foil using thermal deposition (TD) or supersonic molecular beam (SMB) exhibit a small change in the mass peak distribution in the C₁₂₀ dimer range as compared to the initial fullerene powder during desorption by laser radiation irrespective of the radiation wavelength (λ = 259, 518 nm). Under the action of laser radiation with wavelength λ = 259 nm, fullerene films grown on a silicon substrate with an SMB also exhibit a small change in the mass peak distribution in the C₁₂₀ dimer range. At λ = 518 nm, the mass peak distribution in the dimer range shifts significantly toward small masses, so that the intensity maximum corresponds to M ≅ C₁₀₂. This fact is assumed to be related to the polymerization of an SMB fullerene film caused by heating due to the absorption of laser radiation with a wavelength λ = 518 nm.     

Near IR laser light visualizators using nonlinear GaSe and other layered crystallites

Two methods of preparation of the devices for visualization of pulsed and continuous near-IR (near infrared) are described and the results of conversion of pulsed and continuous IR (800–1360 nm) laser radiation into the visible range of spectra (400–680 nm) by using a transparent substrate covered with the particles (including nanoparticles) of effective nonlinear materials of GaSe _x S_{1 − x} (0.2 ≤ x ≤ 0.8) are presented. Converted light can be detected in transmission or reflection geometry as a visible spot corresponding to the real size of the incident laser beam. Developed device structures can be used for checking if the laser is working or not, for optical adjustment, for visualization of distribution of laser radiation over the cross of the beam and for investigation of the content of the laser radiation. Low energy (power density) limit for visualization of the IR laser pulses with 2–3 ps duration for these device structures are: between 4.6–2.1 μJ (3 × 10⁻⁴−1 × 10⁻⁴ W/cm²) at 1200 nm; between 8.4–2.6 μJ (4.7 × 10⁻⁴−1.5 × 10⁻⁴ W/cm²) at 1300 nm; between 14.4–8.1 μJ (8.2 × 10⁻⁴–4.6 × 10⁻⁴ W/cm²) at 1360 nm. Threshold damage density is more than 10 MW/cm² at λ = 1060 nm, pulse duration τ = 35 ps. The results are compared with commercially existing laser light visualizators.     

Measurement of refractive index of biaxial potassium titanyl phosphate crystal plate using reflection spectroscopic ellipsometry technique

The paper reports the measurement of refractive indices and anisotropic absorption coefficients of biaxial potassium titanyl phosphate (KTP) crystal in the form of thin plate using reflection ellipsometry technique. This experiment is designed in the Graduate Optics Laboratory of the Addis Ababa University and He-Ne laser (λ = 632.8 nm), diode laser (λ = 670.0 nm) and temperature-tuned diode laser (λ = 804.4 and 808.4 nm), respectively have been employed as source. The experimental data for n _x , n _y are fitted to the Marquardt-Levenberg theoretical model of curve fitting. The obtained experimental data of refractive indices are compared with different existing theoretical and experimental values of KTP crystals and found to be in good agreement with them.     

Spectral-luminescent properties of LiRbLa<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript> solid solutions

The luminescent properties of LiRbLa_{2 − x} Eu _x (MoO₄)₄ (x = 0.002, 0.02, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0) solid solutions are investigated under laser excitation {λ_ex = 337.1 nm). It is established that the composition containing 50 at % Eu³⁺ is the brightest of the considered set of phosphors and has the highest quantum yield.     

Continuous frequency up-conversion in a double-Λ scheme of Na2

 In a double-Λ level configuration of Na₂ molecules, involving rotational–vibrational levels of the X, A and B bands, continuous resonant frequency mixing ω₄=ω₁−ω₂+ω₃ is demonstrated. A DCM dye laser at 661 nm (λ₁) pumps a molecular Raman laser at 746 nm (λ₂) in a sodium heatpipe, which is used to generate the molecular vapour. In the same heatpipe, both fields are mixed with the radiation of an argon-ion laser at 514 nm (λ₃) to generate up-converted laser radiation at 473 nm (λ₄). For laser powers of 200 mW (λ₁), 700 mW (λ₂, internal power) and 140 mW (λ₃), an output power of 120 μW (λ₄) has been achieved. Dependences of the generated radiation on the pump fields (powers and detunings) and polarization features are presented; influences of coherent coupling and population transfer mechanisms are discussed. Received: 7 October 1996     

Investigation of Rb <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript> atomic lines in strong magnetic fields by fluorescence from a half-wave-thick cell

It has been experimentally demonstrated that the use of the effect of significant narrowing of the fluorescence spectrum from a nanocell that contains a column of atomic Rb vapor with a thickness of L = 0.5λ (where λ = 794 nm is the wavelength of laser radiation, whose frequency is resonant with the atomic transition of the D ₁ line of Rb) and the application of narrowband diode lasers allow the spectral separation and investigation of changes in probabilities of optical atomic transitions between levels of the hyperfine structure of the D ₁ line of ⁸⁷Rb and ⁸⁵Rb atoms in external magnetic fields of 10–2500 Gs (for example, for one of transitions, the probability increases ∼17 times). Small column thicknesses (∼390 nm) allow the application of permanent magnets, which facilitates significantly the creation of strong magnetic fields. Experimental results are in a good agreement with the theoretical values. The advantages of this method over other existing methods are noted. The results obtained show that a magnetometer with a local spatial resolution of ∼390 nm can be created based on a nanocell with the column thickness L = 0.5λ. This result is important for mapping strongly inhomogeneous magnetic fields.     

Spectral-luminescent properties of AgLa<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> solid solutions

The luminescent properties of AgLa_{1 − x} Eu _x (MoO₄)₂ (x = 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) under laser excitation (λ = 337.1 nm) are studied. It is shown that, upon substitution of Eu³⁺ for La³⁺, the symmetry of luminescence centers does not vary. According to the X-ray diffraction data, all samples have scheelite-like structure; the pattern of variation in volumes of their unit cells counts in favor of the presence of a continuous series of solid solutions. It is found that an increase in the europium concentration in AgLa_{1 − x} Eu _x (MoO₄)₂ leads to an increase in the luminescence intensity with a maximum at x = 0.9.     

Optical magnetometer with submicron spatial resolution based on Rb vapors

It is shown experimentally that use of fluorescence and transmission spectra obtained from nanocells with the thickness of column of rubidium atomic vapor L = λ/2 and L = λ, respectively (λ = 794 nm is the wavelength of laser radiation close to resonance with D ₁-line transition of Rb atoms), by means of a narrowband diode laser allows spectral separation and study of variations of probabilities of atomic transitions between ground and excited states of hfs of D ₁ lines of ⁸⁵Rb and ⁸⁷Rb atoms in the range of magnetic fields from 10 to 5000 G. Small thickness of atomic vapor column (∼390 nm and ∼794 nm) allows applying permanent magnets simplifying essentially creation of strong magnetic fields. Advantages of this technique are discussed as compared with the technique of saturated absorption. The obtained results show that a nanocell with submicrom thickness of vapor column may serve as a basis for designing a magnetometer with submicron local spatial resolution which is important in case of measuring strongly inhomogeneous magnetic fields. Experimental data are in good agreement with the theoretical results.     

Kilohertz high power extracavity KGW yellow raman lasers based on pulse LD side-pumped ceramic Nd: YAG

We report an efficient operation of a kilohertz nanosecond extracavity KGd(WO₄)₂ (KGW) crystal Raman yellow laser, which is pumped by a 532 nm lasers based on pulse laser diode (LD) side-pumped ceramic Nd: YAG, BBO electro-optical Q-switched and LBO crystal extracavity frequency doubling. With the 5 W, 10 ns and 1 kHz output power pumped at 532 nm, we obtained 2.58 W, 7.4 ns, 1 kHz second Stokes Raman laser output at 579.54 nm for 768 cm⁻¹ Raman shift of KGW crystal, corresponding to a conversion efficiency of 51.4%. By changing the KGW crystal orientation, we further obtained 3.18 W, 7.8 ns, 1 kHz Raman pulses at 588.33 nm for 901 cm⁻¹ Raman shift, corresponding to a conversion efficiency of 63.3%. The beam quality factors M² of 579.54 and 588.33 nm were (M _x−579.54² = 5.829, M _y−579.54² = 6.336) and (M _x−588.33² = 6.405, M _y−588.33² = 6.895), respectively.     

The exponent λ (x, Q2) of the proton structure functionF2(x, Q2) at lowx

The exponent λ of the structure function F₂ ∼x ^−λ is calculated using the solution of the DGLAP equation for gluon at lowx reported recently by the present authors. The quantity λ is calculated both as a function ofx at fixedQ ² and as a function ofQ ² at fixedx and compared with the most recent data from H1     

Laser-initiated ignition of hydrogen-air mixtures

The subject of investigation is the kinetic mechanisms intensifying chain reactions that proceed in a hydrogen-air mixture when O₂ molecules dissociate under the action of laser radiation with wavelength λ _I = 193.3 nm and are excited into the b ¹Σ _g ⁺ electron state by radiation with λ _I = 762.346 nm. The efficiencies of both methods to initiate ignition are compared. Numerical simulation shows that the ignition temperature for the laser-induced excitation of O₂ molecules into theb ¹Σ _g ⁺ state is lower than for the dissociation of O₂ molecules by UV laser radiation, with the energy supplied to the mixture being the same. However, both photochemical methods are much more efficient than mere heating of the mixture by laser radiation or another source of heat.     

MuSR study of weakly magnetic Y(Co1−x Al x )2

All previous experiments have suggested that Y(Co_1−x Al _x )₂ is a weak itinerant ferromagnet for 0.12<x<0.20. The muon transverse damping rate (λ) increases rapidly near the Curie point forx≥0.155 and for one sample withx=0.145. The value of λ increases with decreasing temperature for other samples withx<0.155 but shows no feature at the Curie point.     

Picosecond three-color holographic digital interferometry

The possibilities of multicolor digital holographic interferometry are experimentally studied upon measuring displacements of a surface in radiation of a picosecond Nd:YAG laser with the radiation frequency conversion into harmonics (λ₁ = 1.06 μm, λ₂ = 0.53 μm, and λ₃ = 0.35 μm). It is shown that three-color digital holographic interferometry makes it possible to increase the measurement accuracy of displacements. The peculiarities of multicolor digital holographic interferometry by picosecond pulses are discussed.     

A μSR Study of Er Spin Dynamics in (Y1−x Er x )Ni2B2C Superconductors

Zero field μSR has been used to probe rare earth spin dynamics in the magnetic superconductors, Y_1−x Er _x Ni₂B₂C. The muon spin relaxation function is stretched exponential, exp (−(λt)^β), in form, as usually found for spin glass systems above the glass temperature. However, the Y_1−x Er _x Ni₂B₂C compounds show no evidence of coexisting superconducting and static spin glass ground states even at concentrations below the critical value (x=0.6) for long range antiferromagnetic order. The temperature dependence of both the muon spin relaxation rate λ and the exponent β suggests that Er spin dynamics change significantly at the superconducting transition temperature. This revised version was published online in September 2006 with corrections to the Cover Date.     

Photoinduced improvement of the properties of light-emitting diodes

Results from studies of the effect of the action of optical radiation on the characteristics of light-emitting diodes (LEDs) produced using the binary heterostructure Ga_xAl_1−xAs (λ=0.88 μm) are presented. High sensitivity of the LED to the following parameters of the optical radiation is shown: flux density, quantum energy, and exposure dose. The action of optical radiation in the form of a band with a maximum at 255 nm on the LED heterostructures lowers the leakage current into the bulk, decreases the loss identified as surface leakage current by about an order of magnitude, increases the radiated power by 50–100% in the current region up to 10⁻³ A, and increases the overall light output of the diodes. Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 109–114, August, 1997.     

First lasers created at the Institute of High Current Electronics of the Russian Academy of Sciences (Siberian Division)

This paper presents the designs and radiation characteristics for lasers operating by self-limited transitions of nitrogen (λ=337.1 nm) and neon (λ=614.3 nm) and pumped by a pulsed longitudinal discharge, and for atmosphericCO ₂ lasers (λ=10.6 μm) pumped by a transverse electron-beam-initiated discharge or by a transverse discharge with uv preionization. These lasers were put into operation at IHCE in 1969 (the nitrogen and neon lasers), in 1971 (theCO ₂ laser pumped by an electron-beam-initiated discharge), and in 1972 (theCO ₂ laser pumped by a transverse discharge with uv preionization). Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 14–17, August, 1999.     

CsCl effect on the optical properties of the 80GeS2–20Ga2S3 base glass

Optical properties of chalcogenide glasses belonging to the series (80GeS₂–20Ga₂S₃)_100−x (CsCl) _x with x=0;5;10;15;20 were investigated. The linear refractive indices (n ₀) were determined by prism measurements at four wavelengths: 633 nm, 825 nm, 1311 nm, and 1511 nm. Z-scan experiments were performed at 800 nm to measure the non-linear indices (n ₂) and the absorption coefficients (β). CsCl additions in the base glass (80GeS₂–20Ga₂S₃) are characterized by a white shift of the transmission in the visible range and a strong decrease of both n ₀ and n ₂. As the same time, β is also decreasing and this results in a figure of merit FOM=2βλ/n ₂ that remains relatively low at 800 nm, meaning that this series of highly non-linear glasses should be very suitable for optical switching applications at telecommunication wavelengths.     

GaS0.4Se0.6: Relevant properties and potential for 1064 nm pumped mid-IR OPOs and OPGs operating above 5 μm

We present measurements of the transparency, refractive index dispersion, nonlinear coefficient, damage threshold, and two-photon absorption of mixed GaS _x Se_{1 − x} crystals and show that GaS_0.4Se_0.6 is a promising nonlinear material for down conversion of pulsed 1064 nm radiation to the mid-IR above 5 μm without significant two-photon absorption.     

Spectra of the selective heat radiation of Yb2O3 under the laser thermal excitation

The dependence of the spectra of the near-IR and visible selective heat radiation (SHR) of the Yb₂O₃ polycrystals that are synthesized using the laser thermal method on the excitation intensity of the CW electric discharge CO₂ laser at the wavelength λ = 10.6 μm is experimentally studied. The SHR spectra are determined by the multiphonon excitation of the vibronic states of the ² F _5/2 term in the Yb³⁺ ions and the radiative transitions to the vibronic states of the ground term ² F _7/2.The laser heating of the polycrystals to the melting point causes the anomalous growth of the SHR spectral peaks in the wavelength range λ ≥ 1040 nm due to an increase in the intensity related to an increase in the probabilities of the radiative vibronic transitions owing to the thermal increase in the phonon density. The effective conversion of the thermal energy of the Yb₂O₃ polycrystals into the SHR indicate the significant role of the radiative cooling of surface.     

Optical characteristics of a transverse discharge in neon at atmospheric pressure

We present the results of investigation into radiation of a pulsed transverse discharge in neon at a pressure of 10–200 kPa. Survey spectra of plasma radiation, time characteristics of radiation, and the effect of small impurities of water vapors and air on the optical characteristics of a neon plasma were studied. We show that at a pressure of residual gases at a level of 10 Pa intense OH*, NO*, and N _* ² bands are observed in radiation of the plasma of a nanosecond transverse discharge in Ne against the background of continuous plasma radiation, and in the spectral region with λ>400 nm radiation was observed on the H_β 486.1 nm and NeI 585.3 nm lines, and (when P≥100 kPa) on the line at the 3s–3p-transitions of a Ne atom. The radiation intensity of the third continuum of neon increases with pressure and with energy contribution to plasma, with its maximum being located in the VUV spectral region (λ _max <200 nm). To whom correspondence should be adressed. Uzhgorod State University, 46, Pidgirna St., Uzhgorod, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 5–10, January–February, 1999.