Frequency Induction Electrodeless Light Source Emission Spectrum Diagnosis

This thesis focuses on two main topics:1.the discharge modes of the RF induced low pressure electrodeless lamp;2.molecular radiation in microwave induced metal halide discharge.In order to get deeper physical understanding to these two practical electrodeless light sources,emission spectroscopic diagnostics is used in the experiments.By modulating the frequency and power of the RF signal,two discharge modes in the RF induced electrodeless lamp are observed:electrostatic discharge mode(so called E mode) and electromagnetic discharge mode(so called H mode).The ignition conditions of E mode discharge and H mode discharge are functions of the frequency: the higher the frequency,the easier the ignition.The temporary study to the ignition process shows that the E mode discharge is a necessary precondition to ignite the H mode discharge.The duration of the E mode discharge and the stable time of the H mode discharge decrease as the ignition voltage increases.By comparing the spectral intensity ratios:Kr811.3nm/Hg436.8nm and Hg 365.0nm/ Hg546.1nm,we can know:during the transiton from E mode discharge to H mode discharge,the proportion of high energy electron is increased due to the frequent electron-electron collisions,which compensate the loss of high energy electrons in the inelastic collisions.The electron energy distribution function approaches the Maxwellian distribution.By comparing the spectral intensity ratio of Hg546.1nm line and Hg435.8nm line,it is observed that the density of metastable atom is increased as the current in the E mode discharge.The trend is opposite in H mode discharge. During the transition,the induced azimuthal current is enhanced greatly.The discharge returns to stable in the H mode due to skin effect.The temperature profile of microwave induced NaI plasma is determined by emission spectroscopy with Abel inversion and the Boltzmann Plot.The central temperature is determined to be 3609K at 70W microwave input.The temperature profile is a typical wall-stable type.The spectra of microwave induced NaI molecule are dominated by the renowned Na D lines,which locate at 589.0nm and 589.6nm.The continuous radiation between 300nm and 600nm is believed to be the molecular radiation of NaI, though very week.The chemical reaction between Na and the bulb material makes it impossible to fill NaI into a practical microwave lamp alone.Barrels method is employed to determine the temperature profile of microwave induced InI,InBr and SnI₂ plasma.As the increase of microwave power,the temperture profile becomes more even due to the slightly cooling down in the center and warming up in the outer of the plasma.The central temperature of InI plasma is 4450K at 96W microwave input.The error is less than 8.4%.The continuous radiation of microwave induced InI discharge covers the whole visible range,which makes the color rendering index more than 90.The corrected color temperature is 6805K at 107W microwave input.The spectra of InBr and GaI are quite similar to that of InI due to similar molecular structure.The ignitions of AlI₃ and InI₃ are more difficult than InI,because of the dissociation of metal trihalide into metal monohalide and halogen.Halogen is believed to quench the discharge by absorbing free electrons.The spectra of SnI₂ also cover the whole visible range,with the intensity peak at 660nm,resulting in lower color temperature than InI.The central plasma temperature is 4419K at 74W microwave input,while the corrected color temperature is 3274K.By simulating the Morse potential curve and using Franck-Condon principle,it is believed that the continuous radiation of microwave induced InI discharge originates from the transitions of 8 Rydberg states to the lower repulsive state:C state of InI molecule.The ¹âˆ‘₀₊⁺(â…¢)-¹âˆ₁ transition of InI molecule contributes to the continuous radiation between 265nm and 411nm,while the ³âˆ_0-(â…¢)-¹âˆ₁ transition results in the continuous radiation between 410nm and 667nm.