Ultraviolet Laser Excitation Research Articles

Fluorescence enhancement of DNA-bound TO-PRO-3 by incorporation of bromodeoxyuridine to monitor cell cycle kinetics.

The detection of DNA-incorporated bromodeoxyuridine (BrdUrd) in mammalian cells is a well-known and important technique to study cell cycle. The use of TO-PRO-3 for detection of BrdUrd substitution of DNA by dual-laser flow cytometry has been investigated. Fluorescence enhancement of TO-PRO-3 in BrdUrd-labeled cells is registered in combination with the fluorescence emission of the intercalating dye propidium iodide (PI) as a total DNA stain to give bivariate DNA/BrdUrd histograms. By the low concentration of only 0.3 mircoM TO-PRO-3, BrdUrd detection is optimized, and undisturbed total DNA content by PI can be detected as well. TO-PRO-3 is excited by a red HeNe laser and PI by an argon ion laser. In order to understand the binding of TO-PRO-3, energy transfer from PI to TO-PRO-3 has been measured as well as the influence of an external DNA binding dye such as Hoechst 33258 with Adenine-Thymine (AT) binding specificity. Cell cycle studies of human SCL-2 keratinocytes and mouse 3T3 cells prove the method to be as generally applicable as the classical BrdUrd/Hoechst quenching technique, but without need for expensive ultraviolet laser excitation. No BrdUrd sensitivity could be found for the similar dyes TO-PRO-1 and YO-PRO-3, whereas TO-PRO-5 and YOYO-3 showed only very little sensitivity to BrdUrd labeling as compared with TO-PRO-3. Cell cycle studies of mammalian cells can be done by dual-laser flow cytometry without the need for ultraviolet lasers by using the BrdUrd-dependent fluorescence enhancement of TO-PRO-3. Total DNA content can be measured simultaneously using PI.

Pump laser wavelength-dependent control of the efficiency of kilovolt x-ray emission from atomic clusters

An explanation is presented for the recently reported striking differences in the kilovolt Xe L-shell x-ray emission from Xe cluster targets excited by comparable terawatt ultraviolet (248 nm) and infrared (800 nm) femtosecond laser pulses under nearly identical experimental conditions (Kondo K et al 1997 J. Phys. B.: At. Mol. Opt. Phys. 30 2707-16). A classical analysis of these results, within the framework of the first Born approximation for electron-atom collisions producing inner-shell ionization, strongly suggests that both the times stronger Xe(L) emission under ultraviolet laser excitation and the observed differences in the x-ray spectra are caused primarily by the different ultraviolet and infrared pump laser wavelengths. The kinematics of photoionized electrons in the intense laser fields (-) and the Coulomb-driven expansion of the electron distribution photoionized from the atomic cluster both indicate that the strong pump-laser wavelength scaling in the production of kilovolt x-rays from Xe clusters results from the more localized and controlled electron-cluster interactions afforded by a shorter optical period.

Analysis of Xanthate Derivatives by Vacuum Ultraviolet Laser-Time-of-Flight Mass Spectrometry

A series of liquid O,S-dialkyl dithiocarbonates (xanthate esters) have been synthesized, and time-of-flight (TOF) mass spectra were recorded for their vapors using both ultraviolet (UV) and vacuum ultraviolet (VUV) laser excitation. These compounds are chemical derivatives of low vapor pressure xanthate salts which have found important commercial application as collectors in mineral sulfide flotation circuits. Our experiments demonstrate that esters ionized by short-wavelength VUV light can be detected by parent mass with high efficiency and minimal fragmentation. In contrast, the mass spectra of the same compounds obtained by UV light excitation exhibit a large number of low molecular mass peaks. A preliminary quantitative analysis of the composition of a gas-phase mixture of xanthate esters has also been achieved, which indicates possible subfemtomole detection limits.

Spherical cavity-mode laser with self-organized CuCl microspheres

We report lasing of exciton-polaritons in semiconductor microspheres with spherical cavity modes under subpicosecond ultraviolet laser excitation at low temperature. Small bulk crystals of CuCl are melted and formed into fused microspheres with diameters ranging from a few to several tens of micrometers. The threshold for lasing is 1nJ/pulse, which corresponds to 10(9) photons/pulse. We found that the biexciton-to-longitudinal-exciton transition is responsible for the lasing.

Discovery of the low temperature phase barium metaborate (BBO) and its significance in the search for new type nonlinear optical materials

1 History of discovery of the low temperature phase barium metaborate (BBO)——an excel-lent new-type ultraviolet radiation frequency-doubling crystalline materialTHE first laser excitation in 1960 with ruby (α-Al 2 O 3 : Cr) as a laser crystal and the first doubling of frequency (347. 15 nm) in 1961 by irradiating quartz crystal (α-SiO 2 ) with a 694. 3 nm laser beam have laid the basis for the study of laser and nonlinear optical (NLO) crystals,...

Vibron-mediated electronic relaxation in crystalline chlorine

Luminescence decay of thin solid films of molecular chlorine exhibit distinctly non-exponential temporal behavior following pulsed ultraviolet laser excitation. The temporal characteristics are dependent on sample temperature and laser fluence in the range 11–80 K. This behavior is attributed to internal conversion from the first excited A′( 3Π 2u) electronic state to the ground state, which is accelerated by phonons and localized vibrational excitons (vibrons). This unusual mechanism of electronic relaxation is consistent with a recent theoretical model for the mechanism of explosive desorption of cryogenic films.

Laser-based detection of PAHs and BTXE-aromatics in oil polluted soil samples.

Time-resolved laser-induced fluorescence spectroscopy and fiber optics are applied for the detection of aromatic hydrocarbons in oil contaminated water and soil samples. Time-integrated data accumulation of fluorescence intensities in an "early" and in a "late" time window with respect to the exciting laser pulse simplifies the method in such a way that it becomes very attractive for practical applications. For ultraviolet laser excitation at 337 nm and recording fluorescence signals at 400 nm, typical detection limits of the present set-up are 0.5 mg engine oil/L in water and 5 mg engine oil/kg in soil. A discrimination between BTXE-aromatics and PAHs in oil polluted soil or water samples is possible, when more than one laser wavelength in the ultraviolet is used for the excitation. The possibilities for a thermal discrimination between different aromatics are also discussed.

Formate Ester Norrish Type II Elimination: Diode Laser Probing of Gas-Phase Yields

Time-resolved infrared absorption spectroscopy was utilized to monitor the production of HCOOH, CO2, and CO following ultraviolet laser excitation of gas-phase formate esters. Excitation of ethyl formate at 227.5 nm resulted in formation of HCOOH and CO2. The CO2 quantum yield was estimated to be 0.5 ± 0.1. No evidence for CO formation was obtained at this wavelength. Relative quantum yields for the Norrish Type II elimination of HCOOH from ethyl, n-propyl, n-butyl, isopropyl, isobutyl, and tert-butyl formate were obtained at 227.5 and 222 nm. Normalization of the observed HCOOH yields with respect to the number of γ-hydrogen atoms resulted in reactivity trends at 227.5 nm of 1:3:9 for the abstraction of primary, secondary, and tertiary hydrogen atoms, respectively. At 222 nm, a similar reactivity trend was observed with yields per available γ-hydrogen of 1:3:7 for abstraction of primary, secondary, and tertiary hydrogen atoms. Yields were found to be independent of ester pressure over the range 100−550 m...

Laboratory studies of 3.3 micron emission from naphthalene induced by 193 and 248 nanometer excitation

view Abstract Citations (41) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Laboratory Studies of 3.3 Micron Emission from Naphthalene Induced by 193 and 248 Nanometer Excitation Williams, Richard M. ; Leone, Stephen R. Abstract Laboratory studies of infrared emission from gas-phase naphthalene in the 3.3 micrometer region following ultraviolet laser excitation are used to interpret the unidentified infrared bands observed in many astronomical objects. A time-resolved Fourier transform infrared emission technique acquires the time and spectrally resolved data. Two excitation wavelengths are employed: 193 nm and 248 nm. The infrared emission features are strongly dependent on the initial excitation energy. Wavelength-resolved spectra recorded 6.8 microseconds after the laser pulse show a 45/cm redshift from the gas-phase absorption spectra for 193 nm excitation and 25/cm for 248 nm excitation. We hypothesize that a series of sequence bands originating from the highly vibrationally excited ensemble of molecules is responsible for the observed shift. As collisional and radiative deactivation removes energy from the highly vibrationally excited molecules, the maximum in the emission profile gradually approaches the customary absorption maximum. This indicates that the amount of redshift is strongly dependent on the amount of internal vibrational energy in the molecule at the time of the vibrational transition. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175559 Bibcode: 1995ApJ...443..675W Keywords: Infrared Spectra; Interstellar Matter; Laser Induced Fluorescence; Molecular Excitation; Naphthalene; Red Shift; Ultraviolet Lasers; Vibrational States; Fourier Transformation; Molecular Collisions; Radiative Transfer; Astrophysics; INFRARED: ISM: LINES AND BANDS; LINE: IDENTIFICATION; MOLECULAR PROCESSES full text sources ADS |

Collisional energy transfer in gaseous xenon with vacuum ultraviolet laser excitation of the 5d[1/2]1 atomic level

Time-resolved analysis of the luminescence decay of gaseous xenon has been carried out with one-photon excitation of the 5d[1/2]1 atomic level for the first time. The one-photon selective excitation is realized with a coherent vacuum ultraviolet (VUV) light source generated via nonlinear processes in mercury vapor. Dominant three-body recombination of Xe(5d[1/2]1) atoms with a rate constant of 3.2(0.3)×10−31 cm6 s−1 has been found. Resonance radiation from this atomic level undergoes a self-trapping, which results in its dominant fluorescence decay in the IR with t=4.9(0.7) μs. Branching into two relaxation channels is found at low xenon pressure (5–100 mbar)—both avoiding the 6s[3/2]1 first resonance atomic level and terminating by VUV emission. At higher pressure, the relaxation kinetics changes displaying after 500 mbar the well known effect of ‘‘atomic reservoir’’ and radiation from the A1u/0−u molecular state with lifetime of 101(4) ns. The scheme of energy relaxation involving the 5d[1/2]1 atomic level is discussed.

Laser cross-linking of proteins to nucleic acids. II. Interactions of the bacteriophage T4 DNA replication polymerase accessory proteins complex with DNA

In this paper we examine the interactions of the polymerase accessory proteins subassembly of the bacteriophage T4 DNA replication complex, using single-pulse ultraviolet laser excitation to induce protein-nucleic acid cross-links. The laser-induced cross-linking permits effective "freezing" of the instantaneous equilibrium state of the complex and thus provides a mechanism to dissect the individual protein-nucleic acid interactions involved in complex assembly. We find that the binding of the gene 44, 62, and 45 proteins is dependent not only on the presence of each of the other proteins, but also on the presence of adenine nucleotide cofactors. We find that the nonhydrolyzable analogs of ATP often behave more like ADP than ATP in these experiments. Gene 45 protein is able to induce an increase in cross-linking of the gp44/62 complex to nucleic acids, and this increased cross-linking correlates with changes in the apparent Km of the gp44/62 complex for polynucleotides and with changes in Vmax during ATP hydrolysis. Our results suggest that the enhanced DNA binding is predominately through the gene 62 protein and not the ATPase catalytic subunit (gene 44 protein). Thus the gene 62 protein seems to play an integral role in gp45-mediated enhancement of the ATP hydrolytic activity of gp44. These results are summarized and integrated in the form of a model for the multiple interactions of the accessory proteins with DNA and one another in the presence of mononucleotide cofactors and substrates.

A study of broad band photoluminescence from Si 1-xGe x⧸Si superlattices

Using photoluminescence (PL) obtained with ultraviolet (UV) laser excitation, we have examined Si 1- x Ge x ⧸Si long-period superlattices (SLs) grown by molecular beam epitaxy at 500°C and annealed post-growth at 550 to 750°C. Our as-grown samples show broad PL bands, 120 meV below the band gap when the effects of quantum confinement of holes are added in. The broad PL band peak positions shift to higher energies as the anneal temperature increases. This coincides with a reduction in the activation energies of the broad PL bands. The broad bands from both the as-grown and annealed samples shift to lower energies as the sample temperature increases.

Biexciton lasing in CuCl quantum dots

Lasing of CuCl microcrystals embedded in a NaCl single crystal was observed for the first time. The lasing takes place at 77 K in a sample sandwiched between dielectric mirrors under pulsed ultraviolet laser excitation. The lasing transition is that from biexciton to exciton. The lasing is observed up to 108 K. The optical gain of the sample is almost the same as that of a CuCl bulk crystal in spite of the low concentration of CuCl in the NaCl matrix.

Highly excited triplet state dynamics of benzophenone studied by pump and probe time-resolved thermal lensing spectroscopy

The photodynamics of benzophenone in the highly excited triplet state (T n ) was investigated by use of a pump and probe time-resolved thermal lensing (TRTL) technique. The first excited triplet state (T 1) was populated through the ultraviolet pump laser excitation of benzophenone (S 1←S 0 absorption) followed by the fast intersystem crossing. Subsequently, the T n state was prepared through the T n ←T 1 excitation with the visible probe laser. Benzophenone in the T n state prepared through the 532 nm T-T excitation was found to release 96±6% of the absorbed probe photon energy as heat through the nonradiative transition. The T n →T 1 internal conversion is a predominant deactivation process from the T n state corresponding to the 532 nm T-T excitation. This result indicates that the photodissociation dynamics of triplet benzophenone is strongly dependent of the T n state prepared: we reported the fast photodissociation from the T′ n state corresponding to the 308 nm T-T excitation. Since the TRTL action spectrum in the region of 450–600 nm agreed well with the T n −T 1 absorption spectrum, it was concluded that the photodissociation does not occur from the T n state corresponding to the visible T-T excitation.

Probing the energetics of oligo(dT).poly(dA) by laser cross-linking.

Experimentally determined changes in free energy (delta G(o)) for thymine-thymine interactions occurring in oligo(dT).poly(dA) are dependent on the method used for preparation of the double-stranded template. A rapid laser cross-linking technique was used to examine the equilibrium between oligomers of (dT) bound to either poly(dA) or poly(rA). The single-pulse (4-6 nsec) ultraviolet laser excitation of these polynucleotides causes pyrimidine dimer formation between contiguous oligo(dT) molecules, resulting in a "ligation" of the oligomers. Analysis of the resulting data using standard binding isotherms allowed determination of the degree of cooperativity existing between oligomers. Using the cooperativity, delta G(o), delta H(o), and delta S(o) are calculated, thereby providing thermodynamic parameters for this interaction. The measured cooperativity of oligo(dT) molecule interactions allows direct calculation of the number of 3' ends available as nicked structures or the number of 3' ends associated with gaps for oligo(dT).poly(dA) when used as a substrate for DNA synthesis.

Optical Properties and New Functionality of Nanocrystalline CuCl and Ge

ABSTRACTLasing of nanocrystalline CuCl embedded in a NaCl single crystal wasobserved for the first time. Lasing takes place at 77 K in nanocrystalline CuCl sandwiched between dielectric mirrors under the pulsed ultraviolet laser excitation. The lasing transition is that from bi-exciton to exciton. The lasing is observed up to 108 K. The optical gain of nanocrystalline CuCl is almost the same as that of bulk crystals in spite of the low concentration of CuCl in the NaCl matrix.The origin of visible photoluminescence of nanocrystalline Ge in SiO2 glassy matrix has been studied. Spectroscopic analyses of nanocrystalline Ge indicate that the room-temperature photoluminescence comes from nanocrystalline Ge of diameter of 4 nm or less. High-resolution electron microscopic studies imply that the structure of nanocrystalline Ge of diameter ≤ 4 nm differs from the diamond structure. These data suggest that new nanostructure crystalline Ge having a character of direct optical transition exhibits the visible photoluminescence.

Two-Color Multiphoton Ionization with Ultraviolet and Visible Laser Excitation for the Determination of Polycyclic Aromatic Molecules in Solution

Characteristics of a two-color multiphoton ionization method with ultraviolet and visible pulsed laser excitation have been investigated for polycyclic aromatic molecules in nonpolar solvents. The photocurrent signal generated by the irradiation at 355 nm was enhanced by the additional action of the 532-nm light much more effectively than that at 1064 nm in terms of photon flux, except for a few molecules. The extent of the photocurrent enhancement depended on the solvent as well as on the laser pulse energy. The SN ratio was also affected by the laser pulse energy. Detection limits have been determined for selected molecules. The additional action of the 532-nm light certainly improved the detection sensitivity; the lowest detection limit (S/N=3) for the two-color method was 9.4×10_12M (1.7pgml-1) for anthracene.

Formation of gaseous microparticles by ultraviolet laser excitation of metal carbonyls

The formation of clusters and microparticles was observed as a result of the ultraviolet excitation of Mo(CO)6, Cr(CO)6, and W(CO)6 gases by XeCl laser radiation. It was found that in the case of Mo(CO)6, the product microparticles emitted high-intensity visible luminescence on exposure to the next XeCl laser pulse.

Electronic Raman scattering from 3d8inter-term magnetic excitons in the planar antiferromagnet K2NiF4

Electronic Raman scattering up to 18000 cm-1, arising from excitons related to excited crystal-field levels of the 3d8 configuration of Ni2+, has been observed in the two-dimensional antiferromagnet K2NiF4 using ultraviolet laser excitation. The measurements involve transitions from the 3A2g ground state to the 3T2g (6500-9000 cm-1), 3T1ga (10800-12500 cm-1) and 1Ega (15000-16000 cm-1) excited states. In the magnetic phase only the spin-allowed (3A2g to 3T2g, 3A2g to 3T1ga) spectra show sharp zero-phonon lines split by an applied magnetic field. A molecular field model, acting on the single-ion substrates arising from the combined effect of the spin-orbit coupling and the tetragonal crystal field, is shown to account for the experimental results. Spin-allowed as well as spin-forbidden (3A2g to 1Ega) spectra present broad vibronic bands. The usual phonon Raman scattering is also observed and interpreted.

Resonance Raman Analysis of Fluorescent Compounds Using Micellar Solutions and Ultraviolet Laser Excitation

Micelles composed of specifically functionalized surfactants can be used to great advantage in resonance Raman spectroscopy. In addition to circumventing the problem of luminescence background, micelles allow the use of aqueous solvents which stabilize labile species and improve the signal-to-noise ratio. The first examples of micelle-mediated resonance Raman analysis of fluorescent compounds using ultraviolet excitation are given.