Spin Flip/Lazer Polarization Control
There is a laser beam used to pumping up target spin toward the direction of laser polarization. Therefore, if the target spin direction is flipped, it's also necessary to change laser polarization.
During the experiment, the pumping laser is first polarized vertically. Then a quarter wave plate, whose optical axis is 45 degree relative to vertical, will be used to convert the laser to circular polarization. By rotating the quarter wave plate 90 degree, the polarization direction of laser will be changed a sign.
This process is motorized: each quarter wave plate is mounted on a rotatable holder driven by a stepper motor. Meanwhile, each motor is connected to a USB motor controller with 4 digits ID number. The following GUI is interface to these controllers:
Contents
All Devices Subpanel
- Find Devices Button : look for any USB motor controller connected to current computer.
- Device ID List : ID number list for all USB motor controller. Once you choose one of the device, all the other subpanels will be linked to that device.
Notice : for context below, the chosen plate/motor/controller in Device ID List will be called current plate/motor/ controller.
- Auto Calibration Button : Automatic find 0 mark on ever plate holder
Notice : For Auto Calibration, there are error (~1 degree) error. Which means the angle read back on computer might be 1 degree off from the one read on the holder marker. This offset is known. However, there are another method to calibrate the motor using the Manual Calibration subpanel.
- All To Up/Down Pos Button : rotate all plate holder to preset angle marks for spin up/spin down state
- Moving Indicator : Whether any motor is moving = whether laser polarization is under changing.
- Error Indicator : This light will be on if there is any error from the stepper motor, which controls laser polarization.
Preset Position/Limit Switch Status Subpanel
Each quarter wave plate holder is calibrated so that we know which angle mark it should be turn to provide a specific laser polarization. Also, there are two limit switches in the holder (currently only switch#2 is connected). Usually if the plate is rotated to an angle marked between 8~12 degree, the switch will be ON. Therefore, it has been used to double check whether the plate has been rotated to correct absolute angle.
This subpanel is designed for user to preset the quarter wave plate angle and expected limit switch status for the holder chosen in Device ID List. The calibrate data could be found on the quarter wave plate calibration page. Also a copy here:
| Motor ID | Controller ID | Description | Alignment Angle/Degree | Auto calibration Error/Degree | Spin Up Read Back/Degree | Spin Down Read Back/Degree |
|---|---|---|---|---|---|---|
| 1 | N/A | Not In Use | 8.4 | 0.15 | 8.25 | -81.75 |
| 2 | N/A | Not In Use | 8.5 | 0.40 | 8.10 | -81.90 |
| 3 | 0338 | Transverse S Wave | 7.5 | 0.2 | 7.3 | -82.70 |
| 4 | 1474 | Transverse P Wave | 8.8 | 0.00 | 8.80 | -81.20 |
| 5 | 1426 | Vertical S Wave | 10.8 | 0.40 | 10.40 | -79.60 |
| 6 | 1423 | Vertical P Wave | 9.8 | 1.00 | 8.80 | -81.20 |
- Motor ID : The sticker attached to the motor
- Controller ID : ID number of control connected to the motor
- Alignment Angle : When the mark of Q-wave plate is at this angle, all plates will convert a vertical polarized laser to a circular polarized one. Besides, the polarization direction is the same.
- Auto calibration error : is the marker angle on the plate holder, while the holder is shown to be rotated to 0 degree on the computer. The reason why it is not 0, is due to non-perfect precision of automatic calibration.
- Position Up/Down Read Back: The angle setting on the computer for spin state Up/Down.
{| class="wikitable sortable" border="1" frame="hsides" rules="rows" |- ! Motor ID ! Controller ID ! Description ! Alignment Angle/Degree ! Auto calibration Error/Degree ! Spin Up Read Back/Degree ! Spin Down Read Back/Degree |- |1|| N/A || Not In Use || 8.4||0.15||8.25||-81.75 |- |2|| N/A || Not In Use || 8.5||0.40||8.10||-81.90 |- |3|| 0338 || Transverse S Wave || 7.5||-1.50||6.5 (Dec 02, 2008 re-calib)||-83.5 (Dec 02, 2008 re-calib) |- |4|| 1474 || Transverse P Wave || 8.8||0.00||6.5 (Dec 02, 2008 re-calib)||-83.5 (Dec 02, 2008 re-calib) |- |5|| 1426 || Vertical S Wave || 10.8||0.40||10.40||-79.60 |- |6|| 1423 || Vertical P Wave || 9.8||1.00||8.80||-81.20 |}
- Motor ID : The sticker attached to the motor
- Controller ID : ID number of control connected to the motor
- Alignment Angle : When the mark of Q-wave plate is at this angle, all plates will convert a vertical polarized laser to a circular polarized one. Besides, the polarization direction is the same.
- Auto calibration error : is the marker angle on the plate holder, while the holder is shown to be rotated to 0 degree on the computer. The reason why it is not 0, is due to non-perfect precision of automatic calibration.
- Position Up/Down Read Back: The angle setting on the computer for spin state Up/Down.
{| class="wikitable sortable" border="1" frame="hsides" rules="rows" |- ! Motor ID ! Controller ID ! Description ! Alignment Angle/Degree ! Auto calibration Error/Degree ! Spin Up Read Back/Degree ! Spin Down Read Back/Degree |- |1|| N/A || Not In Use || 8.4||0.15||8.25||-81.75 |- |2|| N/A || Not In Use || 8.5||0.40||8.10||-81.90 |- |3|| 0338 || Transverse S Wave || 7.5||-1.50||9.00||-81.00 |- |4|| 1474 || Transverse P Wave || 8.8||0.00||8.80||-81.20 |- |5|| 1426 || Vertical S Wave || 10.8||0.40||10.40||-79.60 |- |6|| 1423 || Vertical P Wave || 9.8||1.00||8.80||-81.20 |}
- Motor ID : The sticker attached to the motor
- Controller ID : ID number of control connected to the motor
- Alignment Angle : When the mark of Q-wave plate is at this angle, all plates will convert a vertical polarized laser to a circular polarized one. Besides, the polarization direction is the same.
- Auto calibration error : is the marker angle on the plate holder, while the holder is shown to be rotated to 0 degree on the computer. The reason why it is not 0, is due to non-perfect precision of automatic calibration.
- Position Up/Down Read Back: The angle setting on the computer for spin state Up/Down.
- Up/Down Pos Box : enter the expected angle, which the quarter wave plate should be rotated to, for spin up/down target state.
- To Up/Down Pos Button : Rotate current plate to that angle specified above
- preset limit switch status check box table : If the switch #1 or #2 is expected to be ON when the plate rotate to spin up or down state, the check the box; else uncheck it. In the case that the limit switch did respond correctly, an error will be raised.
Movement Subpanel
This subpanel control the speed of current plate by specify the step size and speed of the step motor in the holder. Also one can rotate the plate to an arbitrary angle with Destination Position, Start and stop button.
Current Status Subpanel
This panel monitor status of current quarter wave plate (the one chosen in device ID list).
- Voltage bar : power supply voltage
- Temperature bar : temperature of stepper motor driving chip inside the controller box
- Power Indicator : power status of current motor (NONE/HALF/FULL)
- Speed Indicator : speed rating of current motor (STOP/ACCELERATING/FULL SPEED)
- Switch 1/2 Indicator : ON/OFF indicator for limit switch #1/#2
- RT Error Indicator : not used
- Working Indicator : not used
- current position box : angle reading of current plate in degree
- Firmware Ver box : Firmware version of current controller.
Manual Calibration Subpanel
In case that automatic calibration fails or in special requirement, Manual Calibration Subpanel offer another way to calibrate the motors. Basically, calibration here means convert tic count in stepper motor into angle and adjust the offset, so that the angle calculated in computer is the same as the one read from markers on the plate holder.
