iGate - Interference Gating for Android

Expand the capabilities of your transmission electron microscope (TEM) with iGate (interference gating). This App allows dynamic interferometric measurements with time resolutions down to 50 s. Just follow the instructions and enjoy the pure beauty of our dynamic nano cosmos.

The basic idea of interference gating (iGate [1]) is a synchronized destruction of the interference pattern for a defined period of time during an interferometric measurement such as electron holography (EH). The holographic reconstruction process acts as a temporal filter that only retains the information of the undisturbed interferogram outside this period.

The needed disturbance of the interference condition is caused by a slight beam deflection through the deflection system above the microscopes objective lens. This turns out to be an extremely robust switching mechanism, allowing acquisition and evaluation of data over the whole field of view. Furthermore, this new switching mechanism produces only a slight redistribution of the intensity underneath the biprism. In comparison to other realizations of time-resolved measurements in a TEM, no gating of the intensity (by means of a shutter or stroboscopic illumination) is needed. This quasi constant illumination of the specimen and the detector reduces additional parasitic effects like charge variations or thermic transients.

[1] T. Niermann, M. Lehmann and T. Wagner, Ultramicroscopy 182 (2017), 54.

Manufacture of the adapter cable (3.5 mm jack to BNC)

needed: an old BNC cable, cheap headphones, scissors and duct tape.

1. cut the BNC cable

2. mark the cable of the left headphone

3. cutting off the drivers

4. strip all cable ends (connect the 2 ends from left cable to your deflector and the 2 ends from right cable to your electrical biasing system).

5. (advanced) connect shielding and inner lines of headphone cable and BNC cable (soldering and insulating recommended)

Experimental instruction (connecting iGate to TEM, acquisition of time resolved electron holograms)

1. turn your device into flight mode (to avoid alerts during measurements)

2. connect cable ends (or BNC connectors) to your deflector (left cable) and your electrical biasing holder (right side)

3. set the device volume to max

4. plug the jack into your smartphone

5. start the app

6. adjust gating amplitude (form electron hologramm, open live fft to see sidebands, choose noise signal, set gating amplitude to minimum, press L button to unmute gating signal, increase gating amplitude until sidebands in live fft vanish)

7. choose trigger signal

8. adjust signal amplitude

9. unmute trigger signal (press R-button)

10. choose gate fraction

11. choose gate position

12. choose iGate signal

13. start acquisition (measurement)

14. mute both signal

15. start acquire (normalization)

16. change gate position

17. unmute both signals

18. repeat 13. - 17.

For further information contact tolga.wagner@physik.tu-berlin.