Josef Schmiedberger

Radio-frequency plasma jet generator of singlet delta oxygen with high yield

O2(a 1Δg) was generated in a flowing discharge of a radio-frequency (rf) hollow electrode. The radio frequency was 99.9 MHz and the rf power was 200 W. The discharge was done in the gas mixture O2:N2:NO=200:20:10 sccm and then it was chilled reactively by the mixture Ar:NO2=200:10 sccm. The O2(a 1Δg) relative yield of 32% was achieved at the pressure of 0.43 Torr. Usage of the mixtures O2:NO=200:100 sccm and Ar:NO2=100:100 sccm resulted in the O2(a 1Δg) yield of 25% at the pressure of 0.6–0.9 Torr. The effluent was mixed with molecular iodine in a far afterglow region and it was tested in an oxygen–iodine laser. The iodine flow rate was 0.3 mmol/min. A strong enhancement of atomic iodine spontaneous emission at the wavelength of 1315 nm was observed in the optical resonator.

Production of iodine atoms by RF discharge decomposition of CF3I

Generation of atomic iodine by dissociation of CF3I in a RF discharge was studied experimentally in a configuration ready for direct use of the method in an oxygen?iodine laser. The discharge was ignited between coaxial electrodes with a radial distance of 3.5?mm in a flowing mixture of 0.1?0.9?mmol?s?1 of CF3I and 0.5?6?mmol?s?1 of buffer gas (Ar, He) at a pressure of 2?3?kPa. The discharge stability was improved by different approaches so that the discharge could be operated up to a RF source limit of 500?W without sparking. The gas leaving the discharge was injected into the subsonic or supersonic flow of N2 and the concentration of generated atomic iodine and gas temperature were measured downstream of the injection. An inhomogeneous distribution of the produced iodine atoms among the injector exit holes was observed, which was attributed to a different gas residence time corresponding to each hole. The dissociation fraction was better with pure argon as a diluting gas than in the mixture of Ar?He, although the variation in the Ar flow rate had no significant effect on CF3I dissociation. The dissociation fraction calculated from the atomic iodine concentration measured several centimetres downstream of the injection was in the range 7?30% when the absorbed electric energy ranged from 200 to 4000?J per 1?mmol of CF3I. The corresponding values of the fraction of power spent on the dissociation decreased from 8% to 2% and the energy cost for one iodine atom increased from 30 to 130?eV. Due to a possible high rate of the atomic iodine loss by recombination after leaving the discharge, these values were considered as lower limits of those achieved in the discharge.

RF plasma jet generator of singlet delta oxygen and RF discharge pre-dissociation of iodine for oxygen-iodine laser at lowered temperature

A new RF plasma jet generator (DSOG-5) of singlet oxygen has been developed for use in an oxygen-iodine laser. The plasma jet was produced in Al nozzles, which were fed by the radio-frequency (100 MHz) power of up to 200 W. The usual mode of operation was an energy transfer from Ar plasma jet to a neutral O2 gas stream. The yield of singlet delta oxygen was up to 24%. Iodine molecules were dissociated by 200 MHz RF discharge with the power of 60 W prior to injection into the mixing zone of laser. The pre-dissociation enhancement was up to 22% of iodine spontaneous emission intensity. Both the DSOG-5 and the RF iodine pre-dissociation were tested in laser experiments in a transverse flow Discharge Oxygen-Iodine Laser (DOIL). The effluent of DSOG-5 was cooled by liquid nitrogen to temperatures in the range 120-300 K. There was a temperature dependent loss of singlet delta oxygen on the walls. The singlet delta oxygen yield and the atomic iodine luminescence at the wavelength of 1315 nm were measured. The highest luminescence was achieved at pressures of ~1 Torr with the yield of 10-20%. Laser oscillations have not been achieved.

Improved rf plasma jet generation of singlet delta oxygen

Rf oxygen plasma jets were studied experimentally as an alternative source of molecular singlet delta oxygen for an oxygen-iodine laser. The relative yield of singlet delta oxygen was measured under a wide variety of experimental conditions. The rf frequency range was 27.2 - 99.9 MHz and the rf power was up to 200 W. The oxygen output pressure was 0.05 - 0.40 torr and the oxygen flow rate was 195 - 1000 sccm. High purity oxygen or its mixtures with Ar, N2, NO and Hg at the pumping velocity of 250 m3/h were used. The plasma jet was produced in nozzles, having the inner diameter of 1 - 6 mm and the length of 1 - 16 mm. The nozzle materials Al, Ti, Ta and W gave significantly better results than Pt and Ni. The dependence of singlet delta oxygen production on the radiofrequency was increasing monotonously. Other dependencies were not monotonous and exhibited an optimum. The cw mode of operation gave usually better results than a pulsed mode. The most effective admixture was N2, which gave the highest enhancement. This resulted in the relative yield of singlet delta oxygen exceeding 15%.

RF discharge generation of I atoms in CH3I and CF3I for COIL/DOIL

A cw/pulsed radiofrequency discharge coupled by electrodes in coaxial arrangement was used to dissociate iodine atoms from CH3I or CF3I molecules diluted in a carrier gas (a mixture of Ar and He). The discharge chamber was arranged directly inside an iodine injector (made of aluminum) to minimize the recombination of generated atomic iodine and enabling an increased assistance of UV light for a photo-dissociation enhancement of I atoms production. The effluent of the discharge chamber/iodine injector was injected into the flow of N2 downstream the nozzle throat. Measurements of I atoms concentration distribution at different distances from the injection and in two directions across cavity were done by means of absorption measurements at the wavelength of 1315 nm. Dependences of atomic iodine concentration on main RF discharge parameters and flow mixing conditions were measured. This novel method could be an alternative to the chemical generation of atomic iodine and also an efficient alternative to other electric discharge methods of I atoms generation for chemical oxygen-iodine laser (COIL) and discharge oxygen-iodine laser (DOIL).

Advanced Concept of Discharge Oxygen-Iodine Laser

[Abstract] This paper deals with a new advanced concept of discharge oxygen-iodine laser (DOIL). The concept includes a supersonic DOIL with a discharge singlet oxygen generator (DSOG) and a discharge atomic iodine generator (DAIG). A newly designed DSOG, denoted as DSOG-6, comes out from a proposed original physical method of singlet oxygen (SO) generation for a DOIL. The proposed method is based on a fast mixing of hybrid plasma jet of DC electric arc and radio-frequency (RF) discharge with a neutral oxygen stream. This unique method is an alternative to the chemical generation of SO for a chemical oxygen-iodine laser (COIL) and also an alternative to the classic high-frequency discharges used since the first successful experimental demonstration of DOIL in the year 2004. Recently, the main effort in the world is concentrated on search of more efficient DSOG with a higher yield and a higher pressure. Compared to COIL, DOIL does not use dangerous chemicals; it has a longer period of operation and reduced dimensions and weight. The goal of our effort is achievement of laser oscillations in DOIL by the new method, which should allow higher SO yields over 30 % at total pressures exceeding 10 Torr. The method appears to be promising for scaling DOIL up to a high power with a good efficiency at a reasonable price. A newly designed DAIG, denoted as DAIG-2, comes out from a proposed original physical method of atomic iodine (AI) generation for DOIL and COIL. The proposed method is based on cw/pulsed RF discharge dissociation of iodine donors directly inside an iodine injector with an enhanced assistance of UV light and with subsequent immediate supersonic injection of AI into DOIL or COIL. Our method substitutes the classic generation of AI by SO, it saves SO energy for laser generation and it increases efficiency of DOIL and COIL. This unique method also significantly minimizes losses by iodine recombination and losses by premature quenching of SO. It would increase the laser power by ~25 % for COIL and 2-3 times for DOIL with no increase in SO pumping. This method is a promising alternative to the chemical generation of AI and also a more efficient alternative to other discharge methods of AI generation for DOIL and COIL. Compared to the chemical generation of AI, the discharge method does not use dangerous gases such as chlorine or fluorine and it produces a fraction of AI directly in the excited state. Both the subsystems DSOG-6 and DAIG-2 will be used simultaneously in our future supersonic DOIL scheduled for the end of the year 2009.

RF plasma jet generator of singlet delta oxygen in chilled and energy-transfer modes for an oxygen-iodine laser

A new RF plasma jet generator (DSOG-4) of singlet delta oxygen has been developed for use in an oxygen-iodine laser. Two different modes of operation were studied: (1) chilling of the plasma jet by a neutral gas stream and (2) an energy transfer from plasma jet to a neutral gas stream. The plasma jet was produced in an Al cylindrical nozzle, having the cross section of 3 mm2. The chilling mode used mixtures O2:NO to produce the plasma jet, which was subsequently chilled by He, injected at the nozzle exit. The energy transfer mode used mixtures He:NO to produce the plasma jet, which was mixed with a neutral stream of O2, allowing thus energy transfer to oxygen molecules with enhanced selectivity. The RF frequency was 99.9 MHz and the RF power was up to 200 W. Both the modes of operation were tested in a transverse flow Discharge Oxygen-Iodine Laser (DOIL). The singlet delta oxygen yield and the atomic iodine luminescence at the wavelength 1315 nm were measured. The energy transfer mode proved to be an effective alternative of the classic chilling mode. It enables new generating schemes, which may bypass some of the classic limitations in oxygen discharges.

Experimental study of magnetic quenching of laser generation in COIL

A magnetic quenching of generation in a chemical oxygen-iodine laser (COIL) has been studied experimentally. This work gives experimental data on a quenching threshold magnetic field in dependence on a resonator output coupling and an iodine concentration in the laser active zone, respectively.

The research on discharge oxygen iodine laser in Japan

A decade has passed, since Discharge Oxygen Iodine Laser (DOIL) research started in our laboratory. Singlet delta oxygen production tests were carried out using RF discharge singlet oxygen generator of the first version (DSOG-1) in 1993. The maximum yield of 4.2% was achieved by DSOG-1. Efforts for improving RF-DSOG have been continuously carrying on and DSOG-5 is now under operation. The DSOG-5 consists of a jet nozzle having a diameter of 3 mm, an injector quarts nozzle of 2 mm diameter set inside the jet nozzle at coaxial position and a mixing slit nozzle with the height of 0.2 mm set surrounding the jet nozzle exit. High electric field is laid on inside surface of the jet nozzle by 200 W RF power source. The singlet delta oxygen is produced by energy transfer from Argon plasma which is produced in the jet nozzle. It is important for achieving high yield to have a good mixing of oxygen, blown from the slit nozzle and the quarts nozzle, with the Argon plasma. The yield of 24% was recorded when oxygen gas 110 sccm was mixed with 700 sccm Argon gas at the pressure 0.6 torr and the RF power 196 W. With a new laser system reinforced by a discharge iodine dissociation and a laser gas cooling device, oscillation tests were carried out in conjunction with the DSOG-5. Performance of the system was confirmed by an emission from excited iodine atoms which energy was transferred from the singlet delta oxygen. It is obvious that the new system gives a progress for the DOIL oscillation.

Advances in the RF atomic iodine generator for oxygen-iodine laser

Recent advances in the RF atomic iodine generator for oxygen-iodine lasers are presented. The generator is based on the RF discharge dissociation of a suitable iodine donor immediately before its injection to the flow of singlet oxygen. The discharge is ignited directly in the iodine injector, and the configuration is ready for the laser operation. The dissociation fraction was derived from the atomic iodine number density measured at a presupposed position of laser resonator. The dissociation fraction and the fraction of RF power spent on the dissociation (discharge dissociation efficiency) were measured for the following donors: CH3I, CF3I and HI. A significant improvement of the discharge stability was achieved by increasing the cross-sectional area of the exit injection holes and employing a tangential inlet of working gas into the discharge chamber. The flow rates 0.15 mmol/s and 0.19 mmol/s of produced atomic iodine were achieved using the HI and CF3I, respectively. The atomic iodine number density in the supersonic flow attained 4.22 × 1014 cm-3. The dissociation efficiency was substantially better for HI than for studied organic iodides.