St. Franke

Laser absorption spectroscopy with a blue diode laser in an aluminum hollow cathode discharge

A GaN-based blue diode laser is employed for laser absorption spectroscopy in an aluminum hollow cathode glow discharge plasma. A Littrow grating stabilized external resonator is used for tuning the wavelength of laser emission. Scanning the wavelength of the laser probes the absorption profile of aluminum transitions yielding ground state aluminum densities. Hyperfine structure has to be taken into account in order to obtain correct temperatures. The diode laser is used to investigate both the temperature and the density of aluminum atoms sputtered from a cathode surface by ion bombardment from the cathode fall region. The blue diode laser allows quick and easy access to aluminum ground state atoms at low costs.

Study of a neon dc column plasma by a hybrid method

The column plasma of a dc glow discharge in neon is comprehensively studied by a new self-consistent hybrid method. The method is based on the solution of the steady-state fluid equations of charge carriers and the Poisson equation using electron transport coefficients and ionization frequencies which arise from a space-dependent kinetic treatment of the electron component. The column description comprises, in addition, a space-dependent treatment of the excited particles in the plasma, the treatment of the plasma-wall interaction processes of the charge carriers and the determination of the electric field. The hybrid method provides a very efficient self-consistent column description although it avoids rough approximations often applied in fluid methods. Results of the method for a neon column plasma are compared with those of probe measurements and spectroscopic studies. The results confirm the importance of the ionization of excited neon atoms for the charge carrier production and emphasize the necessity of the detailed description of the excited states included in the column model.

Basic concepts of temperature determination from self-reversed spectral lines

Complex high-pressure plasmas have become increasingly important in technical applications such as high-intensity discharge lamps. The knowledge of temperature distributions is of basic interest for the understanding of the physical mechanisms in these plasmas and for a selective manipulation of their properties. It is shown that self-reversed spectral lines provide a powerful diagnostic tool for temperature determination. The two most important approaches for the corresponding data analysis are reviewed and their limitations are discussed. On the basis of these approaches a new method is proposed which avoids the main limitations especially in the application to resonance lines. The temperature has been determined in a Hg/Ar and a Hg/Ar/TlI high-pressure discharge. Measured spectral radiances of the Hg 546.1 and 253.7 nm as well as Tl 377.6 nm lines are analysed and the potentials of the different methods are demonstrated.

Mercury-free high-intensity discharge with high luminous efficacy and good colour rendering index

A mercury-free high-pressure discharge in a quartz vessel is investigated which achieves a high luminous efficacy of more than 90?lm?W?1 and a good colour rendering index of more than 70. It is shown that the favourable properties are achieved by a combination of Xe and AlI3 as mercury is substituted with an admixture of TlI and TmI3. The molecular radiation of the mono-iodide TmI, which is present in large areas of the constricted temperature distribution of the plasma, dominates the spectral radiant flux.

Mercury-Free High Pressure Discharge Lamps Dominated by Molecular Radiation

High intensity discharge (HID) lamps dominated by molecular radiation offer a very promising alternative for use in future light sources. They are able to deliver competitive efficacies of about 110?lm?W?1 and higher, excellent colour rendering index above 90 and a correlated colour temperature in the 3000?4000?K region at the operating point near the Planckian locus. Moreover, these lamps are opening up the possibility of dimming. Due to the fact that they are able to omit mercury they are environmentally friendly.The emission spectra generated by these HID lamps differ significantly from those of conventional lamps. The reason for this is the dominance of molecular radiation processes. In comparison with conventional HID lamps atomic contributions are usually rather small. In the present case they amount to less than about 10% of the total intensity in the visible range.

Temperature profiles of an ablation controlled arc in PTFE: II. Simulation of side-on radiances

The temperature determination by spectroscopic measurements in high-current high-pressure arcs in a polytetrafluoroethylene (PTFE) nozzle under the assumption of an optically thin plasma has been investigated. Assuming local thermodynamic equilibrium the radial temperature distributions as well as the plasma pressures have been determined by fitting a model to measured spectral radiances considering line and continuum absorption. It is shown that absorption has to be included in the error estimate of the experimental results. The different effects, which cause deviations from the optically thin case, have been analysed numerically and by using a simplified analytical model. The theoretically estimated pressures sensitively depend on the Stark broadening. In the studied plasmas the calculated large electron densities indicate a marked reduction of the Stark widths by nonideality effects. The applicability of the experimental method has been proved for suitably chosen lines.

Temperature dependence of VUV transmission of synthetic fused silica

The temperature dependence of the VUV transmission of synthetic fused silica is of interest for commercial applications as well as for fundamental research. In this work the transmission properties of Suprasil 2 from Heraeus with an absorption edge at very low wavelengths is investigated. The absorption edge of this quartz glass shifts from 170 to 180 nm between 789 and 1129 K. The Urbach rule is discussed for the characterization of the temperature dependent transmission curves. The results are applied to the diagnostics of the Hg 185 nm line from a high pressure mercury discharge lamp.

A two-dimensional modeling of the warm-up phase of a high-pressure mercury discharge lamp

The main objective of this work is to provide a better understanding of the warm-up phase of high-intensity discharge lamps. As an example of application, we chose the high-pressure mercury lamp. Based on two-dimensional fluid model parameters, such as the electric current, the length and the diameter of the burner are modified and the effect of the convective transport is studied. This allows us to obtain a thorough understanding of the physics of these lamps in their transitory phase. The simulation of the warm-up phase is a must for the proper predictions of the lamp behavior and can be conducted by solving the energy balance, momentum, and Laplaces equations for the plasma, using the frame of the local thermodynamic equilibrium coupled with the energy balance of the wall.

Modification of light sources for appropriate biological action

The impact of the non-visual action of light on the design of novel light sources is discussed. Therefore possible modifications of lamps dealing with spectral tailoring and their action on melatonin suppression in usual life situations are investigated. The results of melatonin suppression by plasma lamps are presented. It is shown that even short-time exposure to usual light levels in working areas has an influence on the melatonin onset.

Experimental and theoretical investigations on the warm-up of a high-pressure mercury discharge lamp

Modern high-pressure discharge lamps are forced to provide instant light and hot relight capabilities—if possible at lower power units. A detailed understanding of the warm-up of high-pressure discharge lamps is therefore required. Complex fluid model codes were developed for the past years including more and more processes like two-dimensional treatment of convection trying to provide a more comprehensive and consistent description of high-pressure discharge lamps. However, there is a lack of experimental data to examine the performance of these models. This work provides a very complete set of geometrical, electrical, spectroscopic, and thermographic data according to the warm-up of a high-pressure mercury discharge lamp that is compared to the results of a state of the art fluid code. Quantitative agreement is achieved for single parameters like wall temperatures. But the paper also reveals the need for further investigations and improvements of the code.