base on yesterday experiment, we know that, @ chopper frequency 3.5kHz, the laser width is 55μs or the laser duty is 20%. at this duty, the microwave should be delayed by 27μs to give maximum polarization.

today, we will change the duty and the chopper frequency, and find out the relation.

the experiment condition is :

Magnetic field ( no actual value )

  • control voltage = 3.069V
  • supply current = 15.28A
NMR system
  • frequency = 12.8MHz ( indicated that the B field is 0.3T )
  • pulse width = 5 μs
  • level = 150
  • gain = 35dB
  • LPF = 100kHz
  • phase = 90º
Laser
  • power = 4 W
  • current =31.3A
  • chopper frequency = change
  • duty = change
  • pulse width =  duty / frequency
Microwave
  • frequency = 9.05MHz
  • Amplify ratio =  4.23
  • power = 3.5W
  • delay time = change
  • pulse frequency (width ) = 31.5kHz (16 μs)
Field Sweep
  • Peak to Peak voltage = 5V
  • phase = 180º
  • voltage supply = ± 40V
  • current supply = 0.6A
  • delay time = microwave delay time + 6μs
  • pulse frequency = 30kHz
Total polarization time = 300s

the microwave was set that, the end of it is delay 3 μs from the end of laser pulse width. it was calculated by:

delay(M) = duty/ f_{chopper} - 1/ f_{micro} +3

we only finish the 20% laser duty for chopper frequency from 0.75,  1.5, 3, 4, 5, 6, 7.1 kHz. but the laser duty is not constant, but in average, it is 19.5%.  we found that the polarization is higher for higher chopper frequency.

at the end of day, we change the duty to 15.58%, by changing the relative position of 2 slits.

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