FSS Review

28th August 2009

Overview of what I’ve worked on…

• Stabilising voltage supply 0-200V with a Peltier Cooler

• Shield rubidium vapour cell from ambient magnetic fields

• Testing system that will stabilise 110 MHz

Voltage Control

• Source providing a stabilised DC signal: 0-200V

• Varies due to the lock-in amplifier’s signals• Stabilisation at 3 kHz level≡ no ambient

variations above 70 µV• Temperature stabilisation of internal circuit

Peltier Cooler•‘Heat pump’•Connected to Evaluation board to control set voltage and power•NTC thermistor •Progressive power adjustment to see if it operated efficiently•Examined heat sinks

•~-60ºC/V in linear region•Promising about room temperature

• Recent tests examine shielding voltage tuning control from environment

• PT100 thermistor sensitive 20-30°C

to Peltier cooler

4.7 Ω +5% resistor

blocks PT100 temperature sensor

probe tip encased in aluminium grip

to Peltier cooler

4.7 Ω + 5% resistor

aluminium boxPT100 temperature sensor

to voltage supply

Temperature Control

• Current on, temperature rises

• Switched off, short delay before starting to decay

• Blocks led to less extensive and slower cooling

• Exponential decayTemperature profile for aluminium unit to encase the temperature sensor

Module with lid

Two blocks

• Temperature span reduced by factor of 3•Time constant increased by factor of 9

Magnetic Field Shielding

• Lock into 5²S1/2 → 5²P3/2• Spin angular momentum and external field

interaction produce energy level shifts• 780 nm transition wavelength known less

accurately • Test cylindrical shield lined with mu-metal

Results of test with Hall Probe

Fine tuning frequency•~110 MHz•Opto-isolator: 31 FBs and 8 ABs•Set DIP switches on opto-isolator•Apply small voltages to ADC •Spectrum Analyser to locate peak frequency

• On adjustment of voltage, we get ~-1.65 MHz/V (maximum +1V)

• Limitations on voltage gives ~2.5 MHz tuning range

•Need to understand how opto-isolator input mapped to DDS output•Use of schematic diagram