Dye laser frequency tripling at 106 nm

The laser emission from a new substituted-terphenyl dye has been frequency tripled in pure xenon gas to generate tunable vacuum-ultraviolet radiation around 106 nm, close to the LiF transmission limit.     

Mass-correlated pulsed extraction: Theoretical analysis and implementation with a linear matrix-assisted laser desorption/ionization time of flight mass spectrometer

The pulsed extraction (PE) of ions produced by matrix-assisted laser desorption/ionization in time-of-flight mass spectrometers greatly improves mass resolution but, unfortunately, this method is mass dependent. Here we report an approach to expand the capabilities of the PE method so as to provide uniform focusing conditions over a wide mass range. Along with an extraction pulse, an additional pulse is applied to correct the mass dependency of the standard PE method. We describe the algorithm for derivation of this correction pulse waveform, where the first-order focusing conditions are valid all along the mass region of interest. Experimental verification of this method for correction of ion velocities demonstrated better mass resolution than standard PE over a wide mass range.     

Restoration of images degraded by extreme mechanical vibrations

A method of numerically calculating the optical transfer function appropriate to any type of image motion and vibration, including random, has been recently developed. This method has been verified experimentally with real vibrations, and the close agreement justifies implementation in image restoration from blur deriving from any type of image motion, including random displacement. Here, image restorations of actual physically degraded images are presented, based on a constrained least squares improvement of the original Wiener filter. Even for extreme vibrations where the blur extent is much larger than the blurred detail, restoration is quite complete. The key to restoration is the determination of the optical transfer function unique to the particular image motion and vibration causing the blur. Results are also presented for low vibration frequency motion of random blur extent, as well as for high vibration frequencies.     

A tunable picosecond IR laser generating multi-megawatt pulses in the range 3–8 m

We describe a versatile infrared laser system capable of generating picosecond pulses continuously tunable over the wavelength range 3.3–8.4 μm, with peak powers of 1–20 MW. The IR pulse duration is ～1.3 ps with a time-bandwidth product of ～0.3. The system uses stimulated electronic Raman scattering (SERS) in caesium vapour to shift the frequency of a picosecond dye laser into the infrared. The quantum efficiency of the Raman conversion process exceeds 40% over almost the entire tuning range. This technique can be extended to other tuning ranges in the IR by using different atomic vapours and SERS transitions.     

PHYSIOLOGICAL EFFECTS OF ULTRAVIOLET LIGHTON DICTYOSTELIUM DISCOIDEUM SPORE GERMINATION

Abstract— The spore germination in Dictyostelium discoideum consists of four stages: activation, postactivation lag, swelling and emergence. Ultraviolet irradiation (total fluence of 250 J/m²) of spores at any time prior to late spore swelling allows full swelling, but inhibits the emergence of myxamoebae. In the case of freshly activated spores, a UV exposure time of 30 s (total fluence of 50 J/m²) is sufficient to reduce emergence to about 6% when measured after 24 h of incubation. This same fluence results in about 10% viability as measured by plaque forming ability. Experiments utilizing 'fractionated exposures' result in the same percentage inhibition of emergence as that found for 'single exposures' provided the total fluence is equivalent. The higher fluences (250 J/m²) which completely prevent emergence, do not affect the endogenous oxygen uptake of spores during swelling. Ultraviolet light irradiated spores respond to the same activation and deactivation treatments as control unirradiated spores. Ultraviolet irradiation after late spore swelling allows emergence to occur in only a small fraction of the population. This fraction of cells which can emerge after UV treatment is said to have passed a 'competence point', which is believed to be the time when all the events necessary for emergence have been completed. Though the sites of UV inactivation in spores can only be postulated at present, it is apparent that the initial stages of germination (activation, postactivation lag and spore swelling) occur independently of the UV sensitive sites. The final stage of germination (emergence), however, is dependent on UV sensitive functions.     

High-performance liquid chromatography-time-of-flight mass spectrometry and its application to peptide analyses

High-performance liquid chromatography (HPLC) has been successfully interfaced on-line with liquid secondary-ion time-of-flight mass spectrometry, utilizing a continuous-flow interface. Time-of-flight mass spectrometry (TOF-MS) is a low-resolution, high-mass-range technique, compatible with extremely rapid data acquisition rates. Thus a TOF-MS system is extremely well suited for coupling with HPLC. This paper describes the interface used to couple the HPLC and TOF-MS as well as the basic operating principles of such a system. Using both standard and packed-capillary reversed-phase HPLC columns, the HPLC-TOF-MS system has been successfully used to separate and detect peptides, providing molecular weight information for the peptide analytes. Experimental data, including chromatograms (UV, reconstructed ion and selected ion) and mass spectra, are presented to demonstrate the ability of the HPLC-liquid secondary-ion TOF-MS system to resolve chromatographically analytes as well as to resolve mass spectrometrically analytes which are unresolved on the chromatographic column.     

Measurement of initial translational energies of peptide ions in laser desorption/ionization mass spectrometry

The initial kinetic energy distribution of [Arg]-vasopressin molecular ions generated by matrix-assisted UV laser desorption/ionization was measured using a delayed ion extraction, linear time-of-flight mass spectrometer. Energy distributions of the nicotinic acid matrix ions, with or without the presence of peptide, were also measured. These were compared with the kinetic energy distribution of gramicidin-S ions using IR laser desorption. The measured molecular ion kinetic energy distribution from vasopressin is much broader than that from gramicidin-S, and is characterized by a high-energy tail that most likely results from entrainment of anlayte ions in the higher velocity matrix ions and fragments as they leave the surface.     

Mass correlated acceleration in a reflectron MALDI TOF mass spectrometer: an approach for enhanced resolution over a broad mass range

Compared to continuous extraction, pulsed extraction (PE) of ions formed by matrix-assisted laser desorption/ionization (MALDI) in time-of-flight (TOF) mass spectrometers significantly improves mass resolution. Parameters such as extraction voltage, delay time, and correction pulse must be varied, however, to achieve optimum mass resolution over a broad mass range because the PE method is mass dependent. We previously reported a novel method, mass correlated acceleration (MCA), which we have now combined with a reflectron MALDI TOF mass spectrometer to further enhance mass resolution over a broader mass range. Unlike the PE method, MCA is not mass dependent and high resolution mass spectra can be achieved with a single tuning of instrument parameters. The ions may be brought into focus simultaneously, i.e., the multi-channel recording advantage can be more fully realized. The MCA dual-stage ion source design includes an extraction pulse region and an acceleration region that contains a time-dependent waveform correlated with mass. We demonstrate the validity of this novel technique with applications in peptide mixture analysis and protein digests of lysozyme and bovine serum albumin.