FSS Review 28 th 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 blocksPT100 temperature sensor probe tip encased in aluminium grip to Peltier cooler 4.7 Ω + 5% resistor aluminium box PT100 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 decay Temperature 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