The influence of electrode materials and surface roughness on the discharge homogeneity of F2 based excimer
laser gas mixtures is investigated in a small x-ray preionised discharge chamber. The temporal and spatial
evolution of the discharge is monitored by taking photographs of the discharge luminosity with an ICCD camera.
It is found that for the same surface roughness, discharges with nickel coated aluminum electrodes are more
homogeneous than the discharges using chromium or gold coated aluminum, massive copper, aluminum, brass
and steel electrodes. Moreover, the surface roughness of copper electrodes does not have a large influence on the
homogeneity of discharges in F2 doped excimer laser gas discharges.
The net gain and spontaneous emission at 193 nm have been measured in x-ray pre-ionized discharges excited by a single pulse charge transfer scheme in Ar and F2 containing mixtures with He and Ne as a buffer gas. With a pumping pulse of ~ 100 ns (FWHM) and a specific peak power deposition of ~ 1 MW cm-3 bar-1 in a gas mixture containing F2 : Ar : He (0.1% : 5% : 94.9%) at 2 bar total pressure the spontaneous emission with a peak intensity of ~ 200 W srad-1 and a pulse width (FWHM) of ~ 60 ns was measured. The net gain profile with a peak value ~ 20% cm-1 and a pulse width FWHM ~ 60 ns has been obtained under the same pumping conditions.
The net small-signal gain was measured in a discharge-pumped KrCl laser (222 nm) operated at high gas
pressures of around 3.3 bar. The pump power-density was varied between 200-650 kW cm-3. The experiments
were carried out on a three-electrode laser system. The net small-signal gain was measured in an oscillator-amplifier configuration and reached up to 1.4 % cm-1. Values for the small-signal gain g0 of 1.50 % cm-1, the
nonsaturable absorption &agr; of 0.07 % cm-1 and the saturation intensity Isat of 0.8 MW cm-3 were calculated for
a specific power-density of 320 kW cm-3.
The influence of the buffer gases on the discharge homogeneity of F2doped excimer laser gas mixtures is investigated in a small x-ray preionised high-pressure discharge chamber. The spatial and temporal development of discharges in He/F2 and Ne/F2 gas mixtures is monitored via its fluorescence using an intensified CCD camera with a gating time of 300 ps. The formation and development of discharge filaments in He/F2 gas mixtures is completely different from that in Ne/F2. Under the same start up conditions, discharges in Ne/F2 are dominated by cathode hotspots where as no hot spots are visible in discharges in He/F2 gas mixtures. However, the discharges in Ne/F2 gas mixtures appear to be more uniform even though the discharge width decreases in time and hotspots are persistent on the cathode surface.
High-pressure gas discharge experiments are carried out in a novel three-electrode prepulse-mainpulse configuration with two discharge volumes. The design is capable to break down both x-ray preionized volumes at the same time. First experiments in Xe/HCl/Ne mixtures reveal spatially very homogeneous discharges for up to 350 ns with a power deposition of 260 kW/cm3. For discharges in Kr/HCl/Ne mixtures we observe also very homogeneous discharges for a similar long pulse duration when a low krypton concentration of 10 mbar is used. For discharges in mixtures with a higher krypton concentration of 100 mbar we still observe very homogeneous discharges for 200 ns. Furthermore the total discharge current is established 8-10 times faster than in other systems.
Discharge instabilities in F2 based excimer gas lasers are investigated using a small-scale discharge system. After preionizing the gas volume, a fast rising voltage pulse initiates the discharge. The temporal development of the discharge is monitored via its fluorescence by an intensified CCD camera with a gating time of 10 ns. Homogeneous discharges are produced in gas mixtures of He/1mbar F2 and He/1mbar F2/30mbar Xe at a total pressure of 2 bar for pump pulse duratins up to 70 ns (FWHM). The addition of Xe to He/F2 mixture does not lead to discharge instabilities while the introduction of more F2 results in hotspot and filament formation.
For some specific application areas like (V)UV lithography or special processing of certain materials with high average power (V)UV lasers excimer lasers have to be developed further. In this contribution we will summarise the recent progress of our VUV excimer laser programme on the ArF and F2 laser. Key point in our research programme is the production of long laser pulses in the order of 100 ns (FWHM). An existing laser chamber was modified and optimised for the ArF laser research programme. Different excitation circuits have been tested. For long pulse operation the laser is operated in the ferrite switched resonant overshoot mode using 18 cm2 of ferrite in the switch for a discharge volume of approximately 60 x 0,7 x 1,2 cm3. Long optical pulses of up to 116 ns have been obtained with a lean gas mixture and a very low self-inductance of the electrical circuit of the packing capacitors. For the F2 laser a new discharge chamber and a new X-ray preionisation source was designed. With this set-up it was possible to produce a F2 laser with a large optical cross-section of 1,5 x 2,4 cm2 operating at an intrinsic efficiency of 0,1%. With a different electrical circuit the system produced long optical output pulses of 70 ns (FWHM) in a gas mixture of helium and 3 mbar F2 at a total gas pressure of 2 bar.
An ArF excimer laser has been operated using four different spiker-sustainer excitation circuits. We report on the large differences in the laser output energy caused by nanosecond- scale variations in the preionization timing with each circuit.
The discharge conditions of the multi-atmospheric e-beam sustained Ar-Xe laser are investigated. It is observed that the quasi-stationary period of a laser pulse depends on the e-beam current, the discharge power deposition and the gas density. The laser efficiency can be as high as 8%. The pulse energy with optimum efficiency depends strongly on the gas density. The best results are obtained for 4 bar with an input power of 8 MW/l. The pulse duration with corresponding output energies are 12 microsecond(s) with 10 J/l and 16 microsecond(s) with 16 J/l for e-beam currents of 0.4 and 0.9 A/cm2 respectively. An analysis of the quasi-steady state conditions that include the effects of electron collision mixing and atomic quenching is presented. The effects of output power saturation by the fractional ionization and atomic collisions are in agreement with the observations. The analysis clarifies the optimum performance conditions.
High energy extraction from UV pre-ionized molecular fluorine lasers is hampered by the short period of discharge stability and the spatial inhomogeneity of the discharge. So far stable discharge operation is reported for small discharge cross sections with an area less than 0.8 cm2 and efficiencies in the order of 0.15%. To increase the energy extraction of the molecular fluorine laser the discharge cross section should be enlarged. Here we report on the successful operation of a molecular fluorine laser with a large discharge cross section of 1.5 multiplied by 2.4 cm2 (electrode spacing times discharge width) which operates at a high intrinsic efficiency of 0.45%. Crucial for obtaining this result is the development of a short pulse, high intensity x-ray preionization source.
M. Oskar van Deventer, John Angelopoulos, Hans Binsma, A. Boot, P. Crahay, Emmanuel Jaunart, Peter Peters, Andrew Phillips, Xing-Zhi Qiu, John Senior, Maurizio Valvo, Jan Vandewege, Peter Vetter, Ingrid Van de Voorde
This paper presents different architectures for high split, wide range bidirectional SuperPONs.One of the ways to achieve such SuperPONs is by the introduction of erbium- doped-fiber-amplifiers or semiconductor optical amplifiers (SOA) in order to overcome the strongly increased power budgets in comparison to conventional PONs. This will however present new challenges in overcoming the 'noise- funneling' effect caused by the parallel amplifiers. Four different approaches are studied: 1) using of on/off switchable semiconductor optical amplifiers, 2) using parallel erbium-doped-fiber amplifiers, 3) using electro- optic regeneration, and 4) using conventional SDH, ATM and APON technology. A description is given of each architecture, including advantages and drawbacks. These architectures serve as input to further studies performed by the ACTS-PLANET consortium. The power-budget studies showed that it is technically feasible to develop a SuperPON with a 2048 split and a 70-100 km range.
An enhanced multistage optically amplified passive optical network (PON) known as SuperPON is presently being investigated by the ACTS-PLANET consortium as a possible future solution for broadband access networks. As it is extremely probable that user bandwidth requirements will continue to increase substantially in the short to medium term it is highly pertinent to consider the upgradeability of SuperPON topologies. In this paper capacity upgrades in the wavelength, space and time domains for both the downstream and upstream directions are discussed with reference to a particular basic SuperPON.
The high pressure atomic xenon laser is becoming the most promising light source in the wavelength region of a few microns. The merits are high efficiency (so far up to 8 percent), high output energies (15 J/liter at 9 bar), high continuous output power (more than 200 W/liter), no gas dissociation and thermal heating of the lower laser level. Compared with the well-known low pressure xenon laser the power performance is now roughly a factor thousand higher. The operation of the system, based on three-body-collisions, uses the metastable state of the xenon atom as the ground state so that in the recirculation of energy a high quantum efficiency is obtained. Furthermore the homogeneous line broadening caused by the high collision frequency has also a strong beneficial effect on the efficiency. However, the required intense homogeneous excitation of the gas medium at high density is from a technical point of view a great challenge. From our experimental and theoretical work we found that at optimum performance the input power must be 1 to 2.5 [KW cm-3 atm-2]. We describe our results obtained with e-beam sustained and x-ray preionized systems delivering pulsed energies in the range of joules per liter. Furthermore we describe our recent results on continuous RF excited wave guide systems of about 37 cm length with output powers in the range of watts.
KEYWORDS: Pulsed laser operation, Gas lasers, Molecular lasers, Neon, Vacuum ultraviolet, High power lasers, Electrons, Electron beams, Diodes, Resonators
A long pulse molecular F2 laser ((lambda) equals 157 nm) with an optical pulse width of 160 ns and an output energy of 1.7 J (4.6 MW/cm2) pumped by an electron beam has been realized. The only restriction for the optical pulse width of the laser seems to be the duration of the excitation pulse. No signs of self terminating laser pulses due to bottle-necking in the lower laser level have been observed.
A transverse RF excited gas discharge has been successfully used to produce a CW Ar-He-Xe laser. A maximum output power of 330 mW has been obtained from an experimental device with 37 cm active length and a 2.25 (DOT) 2.25 cm2 cross-section. This corresponds to a specific output power of about 175 mW/cm3. Under these preliminary optimum conditions the gas pressure was 85 Torr (Ar:He:Xeequals59:40:1). The laser output spectrum consisted of 5 atomic xenon lines (2.03, 2.63, 2.65, 3.37 and 3.51 micrometers ). The 2.03 micrometers and 2.65 micrometers lines were the strongest ones. Complementary to this device a quartz capillary was tested as laser tube for the atomic Xe laser. With this configuration it was possible to sustain a longitudinal DC as well as a transversal RF discharge in the laser gas mixture. Combined excitation was also possible for this device. This enabled us to compare the laser performance in both the DC and the RF mode in the same device. Preliminary measurements showed us that the highest output power in the DC mode was less than 1 mW, while the RF excited laser yielded about 130 mW. The gain coefficient was found to be extremely high. Laser generation was obtained for a wide range of reflectivities R of the outcoupling mirror. At the minimum reflectivity of 5% an output power of 20 mW was obtained. Results obtained from both systems are discussed.
An efficient atomic Xe laser pumped by a combination of an e-beam and an electric discharge has been made. In the present study we investigated the laser operation as a function of gas pressure. The best results were obtained at a pressure of 7-8 bar under optimized excitation conditions. The specific output energy reached 10 J/l and the specific laser power 12 MW/1. The efficiency is about 2%. When both e-beam and sustainer current are present simultaneously the efficiency can rise to 7-9% in a 0.25 |?s interval.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.