Steps Toward a Prototype Atomic Clock Nathan Belcher

Steps Toward a Prototype Atomic Clock Nathan Belcher Senior Research Midterm Talk 12. 13. 07

Acknowledgements Prof. Irina Novikova n Prof. Eugeniy Mikhailov n Chris Carlin n

Outline Overall goal of project n Background n Hardware n DAVLL n Data and results n Future work n

Overall Goal of Project To create a prototype atomic clock n Need: n n n Laser Transition Laser Frequency Locking System Counter

Overall Goal of Project continued n Have: n n Vertical-cavity surface-emitting laser (VCSEL) Transition in rubidium-87 --> 5 S_1/2 to 5 P_1/2 (794. 7 nm) Dichroic atomic vapor laser locking (DAVLL) Counter

Outline Overall goal of project n Background n Hardware n DAVLL n Data and results n Future work n

Background n Atomic transition in rubidium-87 n 5 S_1/2 to 5 P_1/2

Background continued Use electromagnetically induced transparency to measure transmitted light n The closer to hyperfine splitting resonance, the more transmission n Counter locked to maximum transmission which corresponds to clock frequency n

Background continued Lambda system requires two fields at different frequencies n Problem: inherent in lasers are small random shifts in frequency around a set frequency (“jumps”) n Bigger problem: if two lasers are physically separate, the “jumps” are random n

Background continued Solution: use phase modulation to create two fields out of one physical laser n Why? Both fields “jump” with each other so relative frequency can be set by external generator n Creates carrier with sideband comb n

Background continued n Three phase modulation formulas

Background continued n Carrier to sideband spacing determined by input frequency

Outline Overall goal of project n Background n Hardware n DAVLL n Data and results n Future work n

Hardware n VCSEL

Hardware continued n Temperature stability

Hardware continued n VCSEL constant current source

Hardware continued n Measuring setups n Phase modulation measurement

Hardware continued n n n Fabry-Perot cavity Second mirror moved by piezoelectric Piezoelectric controlled by voltage source, with low frequency modulation

Hardware continued n Another measuring setup n n Finding rubidium resonances Vapor cell can be either isotropically pure Rb-87 or natural abundance Rb-85 and -87

Hardware continued n Modulators n Commercial digital synthesizer (Agilent E 8275 D) n n Up to 14 d. Bm of power at very precise frequencies Stellex Mini-YIG crystal oscillator n Current controlled tunable crystal with frequencies ranging from 5. 95 GHz to 7. 15 GHz at 15 d. Bm

Hardware continued n Inside of Stellex oscillator

Hardware continued n Stellex oscillator calibration measurements

Hardware continued n Solenoid and shields n n External non-homogeneous fields that interact with vapor cell, shifting state frequencies Need to control field vapor cell feels, so surround cell with solenoid to produce constant homogeneous magnetic field and shields to limit outside magnetic fields

Hardware continued

Outline Overall goal of project n Background n Hardware n DAVLL n Data and results n Future work n

DAVLL n Allows locking of frequency of VCSEL to specific rubidium resonance frequency

DAVLL continued n Optical hardware

DAVLL continued n Absorption and differential spectra

DAVLL continued Electronics are used to amplify the raw signal from the optics and adjust the current to the laser accordingly n Example: if laser’s frequency is higher than zero point on raw signal, electronics will supply less current so frequency decreases n

DAVLL continued n Flow chart of electronics

DAVLL continued There have been issues with the raw signal n Raw signal offset with respect to zero point n This offset causes tension between raw signal and feedback to laser n Makes us question whether laser locked on resonance or if signals not representative of locking n

DAVLL continued Auxiliary input useful to find correct range laser needs to be in for resonances n Some work done to make voltage scales of function generator and raw signal approximately equivalent n This will allow us to compare Aux and Raw Signals to make sure locked on resonance n

Outline Overall goal of project n Background n Hardware n DAVLL n Data and results n Future work n

Data and Results n VCSEL Modulation n Used Agilent E 8275 D and Stellex oscillator With Agilent, saw 1 -to-1 sideband-to-carrier ratio at 14 d. Bm at 6. 834 GHz With Stellex, saw sidebands greater than carrier at 15 d. Bm at 6. 834 GHz

Data and Results continued n Agilent modulation

Data and Results continued n Stellex modulation

Data and Results continued n Rubidium resonances n n n Two vapor cells: isotropically pure Rb-87 and natural abundance Rb-85 and -87 Pure Rb-87 cell inside shields, used to achieve EIT Mixed Rb-85 and -87 cell used in DAVLL as reference cell

Data and Results continued n Isotropically pure Rb-87 cell

Data and Results continued n Natural abundance Rb-85 and -87 cell

Data and Results continued n Electromagnetically induced transparency (EIT) n n Occurs when all electrons are driven to ‘dark’ state that does not interact with either electromagnetic field Laser has 100% transmission

Data and Results continued n EIT in Irina’s pure vapor cell

Data and Results continued n EIT in my pure vapor cell

Future Work n True DAVLL locking n Understand offset issues and work through them Add counter to system n Test clock against frequency from Agilent n