A DIODE LASER FREQUENCY STANDARD USING VELOCITY MODULATION

THIS PROJECT WILL DEVELOP A FREQUENCY STANDARD FOR THE URANIUM-STOMIC VAPOR LASER ISOTOPE SEPARATION (U-AVLIS) PROCESS USING A VISIBLE DIODE LASER LOCKED TO AN ATOMIC RESONANCE. A KEY FEATURE IS THE USE OF THE VELOCITY MODULATION METHOD TO PROVIDE A HIGH SIGNAL/NOISE LOCKING DISCRIMINANT WITHOUT THE NEED TO MODULATE THE LASER, AND WITH THE HIGH POWERS FOR SUB-DOPPLER EFFECTS. PHASE I WILL PRODUCE XENON IONS IN AN ALTERNATING CURRENT GLOW DISCHARGE TUBE OPERATED AT REDUCED PRESSURE TO PRODUCE A POSITIVE COLUMN REGION ABOUT ONE HALF METER LONG. THE ELECTRIC FIELD IS THIS PART OF THE DISCHARGE ACCELEATES THE IONS, CAUSING A SMALL DOPPLER MODULATION OF THEIR ABSORPTION FREQUENCIES. A PORTION OF THE DIODE LASER BEAM IS DIRECTED DOWN THE BORE OF THE DISCHARGE, THEN DETECTED WITH A PHOTODIODE. THE PHOTOCURRENT IS AMPLIFIEDAND DEMODULATED AT THE DISCHARGE FREQUENCY, PRODUCING A DERIVATIVE LINESHAPE THAT WILL BE USED TO LINE LOCK THE LASER BY ELECTRONIC FEEDBACK. THE EFFECTS OF PLASMA TEMPERATURE, PRESSURE, AND COMPOSITION ON THE DEMODULATED SIGNAL/NOISE RATIO AND CENTER FREQUENCY WILL BE EXAMINED.