M. Jánossy, P. Apai, L. Csillag, Z. Donkó, Z. Horváth, Zs. Lenkefi, P. Mezei, K. Rózsa, Zs. Szentirmay
Gas discharge experiment and modelling. — The obstructed operation mode of glow discharges was studied in helium and hydrogen gas by measuring electrical characteristics of the discharge and the spatial distribution of the electric field (using Stark spectroscopy).
The calculated self-consistent electric field distribution showed a good agreement with
experimental data. Electron multiplication data, energy distribution of electrons absorbed by the anode, energy distribution of ionizing electrons, share of high-energy electrons in ion production and spatial distribution of ion production were obtained from the modelling calculations to provide detailed insight into the discharge operation. The effect of electron reflection of the anode on the discharge characteristics was also investigated and was found to affect significantly the characteristics of the discharge. We have carried out spectroscopic investigations of an argon glow discharge over a cold cathode surface in order to study the different excitation mechanisms (fast neutral, fast ion, electron collisions) of the cathode glow and the negative glow parts of the discharge. In subnormal glow discharges we measured self-generated oscillations. The coupling of two subnormal glow discharge cells resulted in the appearance of nonlinear oscillations of various waveforms.
Lasers in segmented hollow cathode discharges. — In order to improve the hollow cathode laser performances we have worked out a novel discharge geometry which combines the advantages of the conventional and the high voltage hollow cathode dis-charges. The fast electrons accelerated by the cathode fall are focused into the axis of the hollow cathode. These electrons can oscillate between the opposing cathode surfaces ensuring the optimal energy transfer into the highly excited states. The cylindrical cathode cavity matches the TEM00 beam. The sputtered metal has an easy access into the hollow cathode. The discharge is highly stable against arcing and the operating voltage can be increased (independently from the gas pressure) to obtain higher density of fast electrons necessary for laser excitation. High gain and low threshold current were found even in the ultraviolet range. On the Au 282 nm transition we obtained over 55%/m gain which can further be increased by reducing the hollow cathode diameter. The threshold current was below 300 mA. We determined optimal current density for gain and for output power.
These results indicate the continuous VUV laser oscillations (CuII lines around 160nm) might be possible using these type of discharges.
Cathode sputtered He-Zn laser. — Experiments have been carried out on a quasi-cw slotted hollow cathode He-Zn laser, where the Zn vapour was produced by cathode sputtering. Due to the efficient operation of the hollow cathode discharge relatively low threshold currents and high output powers could be obtained. The minimum threshold currents were 0.3 A (758.8 nm), 1.3 A (747.9 nm), 0.7 A (492.4 nm) and 1.1 A (491.2 nm). The maximum peak output power obtained was 70 mW at the blue lines and 78 mW at the infared ones. Addition of a small amount of Ne completely quenched the blue laser oscillation, due to Ne ions strongly populating the lower levels. The cross-section for the Ne ion-Zn atom charge transfer process was estimated to be in the order of 10-14 cm2. This high cross-section points to the possibility to obtain laser oscillation at the 210 nm Zn II transition.
Research on multidimensional lasers. — An efficient laser resonator construction was developed for thin, disc shaped laser-active materials. In our model experiment a laser excited "flying saucer" dye cuvette emitted the expected, rather unusual, but easily focusable conical-wall laser radiation. This off-plane halo resonator can generally be used for all laser materials.
Atmospheric pressure discharge. — A serious problem of environmental protection is continuous determination of the heavy metal content of waters. For this aim a new glow discharge atomic emission source was developed: a stable glow discharge was produced in atmospheric air using water as a cathode. Spectral lines of elements dissolved in water
appeared due to cathode sputtering in the discharge. This phenomenon can be used for the continuous analysis of water.
Surface plasmon decay length measurements. — A novel method was used for the determination of surface plasmon decay length L (x) on thin silver and gold films in the visible and near infrared spectral region. In this method the distribution of light, emitted by surface plasmons which were excited on metal/air interfaces by an ATR (attenuated total reflection) technique, was determined with a CCD detector array and subsequent mathematical analysis.
The obtained optical L(x) data were in good agreement with values measured by using a scanning tunnelling microscope (STM). Theoretical calculations allowed to determine the specific optical constants of the metal films.
Grants:
OTKA F/1 4475 Studies of the cathode region of glow discharges OTKA F/2 7475 Chaotic phenomena in gas discharges
OTKA T-2935 Cathode sputtered hollow cathode lasers OTKA T-4220 Multidimensional lasers
OTKA T-4221 High voltage discharges
OTKA T-4227 Excitation mechanisms in hollow cathode lasers OTKA T-2940 Surface plasmon studies
Publications
N.1. Z. Donkó, K. Rózsa, R.C. Tobin* and K.A. Peard*: Studies on an obstructed glow discharge in helium. Proc. of SASP 94 (Symposium on Atomic, Cluster and Surface Physics) Maria Alm, Austria (Ed. T.D. Märk, R. Schrittwieser and D. Smith), 408-411 (1994)
N.2. K. Rózsa, Z. Donkó, L. Szalai*, R.C. Tobin* and K.A. Peard*: High voltage hollow cathode discharges for UV and VUV laser operation. Ibid. 412-415 (1994)
N.3. Z. Donkó, K. Rózsa, R.C. Tobin* and K.A. Peard*: Modelling and measurements on an obstructed glow discharge in helium. Physical Review E 49, 4, 3283-3289 (1994)
N.4. K.A. Peard*, K. Rózsa and R.C. Tobin*: Parametric study of a high voltage hollow cathode infrared copper-ion laser. J. Phys D: Appl. Phys. 27, 1181-1186 (1994) N.5. K.A. Peard*, R.C. Tobin*, K. Rózsa and Z. Donkó: A high-voltage hollow-cathode
Au-II 282 nm laser. IEEE Journal of Quantum Electronics 30, 1181-1186 (1994) N.6. K.A. Peard*, Z. Donkó, K. Rózsa, L. Szalai* and R.C. Tobin*: Comparison of
Cu-II 780.8 nm lasers using high-voltage hollow-cathode and hollow-anode-cathode discharges. IEEE Journal of Quantum Electronics 30, 2157-2165 (1994)
N.7. Gy. Rubin, M. Jánossy , P. Mezei, P. Apai: On the recombinational enhancement of ionic lines in the afterglow of a pulsed noble gas hollow cathode discharge.
Applied Physics B 58, 105-110 (1994)
N.8. M. Jánossy, P. Mezei: Investigations on a high voltage hollow cathode He-Kr laser.
Pure and Applied Optics 3, 301-305 (1994)
N.9. T. Cserfalvi∗, P. Mezei: Direct solution analysis by glow discharge: Electrolyte-cathode discharge spectrometry. Journal of Anal. Atomic Spectroscopy 9, 345-349 (1994)
N.10. M.B. Danailov∗, P. Apai: 589 nm light generation by intracavity mixing in a Nd:
YAG laser. Journal of Applied Physics 75, 8240-8242 (1994)
N.11. R.C. Tobin∗, K.A. Peard∗, G. Bode∗, K. Rózsa, Z. Donkó and L. Szalai∗: High-gain hollow-cathode metal ion lasers for the UV and VUV. Invited paper, To be published in Proc. of LEOS 7th Annual Meeting, Boston (1994)
N.12. M. Jánossy: Hollow cathode lasers: basic physics and new results. To be published in Proc. of 8-th International School on Quantum Electronics, Varna, Bulgaria 1994 N.13. K. Szõcs∗, Z.Gy. Horváth: Throw away that film, use a leaf! To be published in
American Journal of Physics
N.14. N. Kroó, W. Krieger∗, Zs. Lenkefi, Zs. Szentirmay, J.P. Thost∗ and H. Walther∗ A new optical method for investigation of thin metal films. To be published in Surface Science
Patent
P. Csonka∗, Z. Gy. Horváth, N. Kroó:
Method and apparatus for reduction of scattered light of Fresnel lenses and to change the spatial distribution. OTH P '94 01602 (pending)