Spectral Phase Interferometry for Direct Electric-field Reconstruction

0:19 Hello and welcome to a APE in Berlin in Germany. My name is Rita and over the next few minutes I’m going to show you how easy it is to set up your LX spider pulse measuring system. Like our autocorrelator, LX Spider lets you measure pulse durations with incredible accuracy but what makes it more remarkable is that it also measures the group delay distribution of the pulse of spectral components in a single shot manner. Because of this you can do so much more. You can online you the true shape of the pulse, measure the chirp behavior and access a wealth of additional information: all in real time.

1:00 First you have direct access to the pulse spectrum due to the built-in spectrometer. Second, the spectral phase of the pulse is directly measured. Third the spectral phase is instantly analyzed with regard to dispersive contributions. Next the temporal pulse shape is evaluated in real time by fast Fourier transformation, and finally single laser pulses can be measured at low laser repetition rates.

1:33 Nothing this powerful has ever been so compact and affordable and it’s easy to use. There are no buttons or dolls or even a controller unit. You control everything via one software program. Setup is simple too. But before we begin let me show you how a LX Spider works starting with the alignment.

1:59 Step one: Incoming beam passes through a series of optics to reach the splitting mirror. This splits the beam spatially into two separate beings. These beams are then tilted downward to pass through the non-linear crystal. In alignment mode, a steering mirror reflects both beams into the alignment window. After alignment is complete, LX Spider automatically moves the alignment mirror out of the way. This allows the two beams to strike the focusing mirror.  Then merge the entrance of the spectrometer for sensitive phase measurement.

2:36 For robust measurement of the pulse spectrum a diffuser can be turned into the initial beam  path. Its innovative design allows for a more compact size and full automation. Once you’ve aligned the incoming beam our software does all the work for you.

2:56 First open it by clicking the LX Spider icon in the upper right corner of your screen. You should see a green light next to motors initialized. Then click the alignment button to set LX Spider in alignment mode. Finally make sure the input aperture of LX Spider is fully open. You also need to ensure the beam is correctly pre-aligned. It should run at a constant height above the table – equal to the height of the input aperture. An additional alignment aperture can help you do this.

3:31 Now you can put LX Spider in the beam path. Turn it into place until a double spot appears in the alignment window. You’re looking for two half-moons of equal size and brightness one on each side of the crosshair. When that’s complete, clamp LX Spider to the table to ensure it doesn’t move out of place later on. As a final step optimize the two spots in the alignment window by aligning the near mirror. When you’re finished click the alignment button. This will switch LX Spider out of alignment mode. So it will deliver the two upconverted beams to the spectrometer.

4:09 Now we’re ready to obtain the full information on the pulse. To do this we need two data sets, and the first is the pulse spectrum in the right column. Check the measure spectrum box, then use the exposure slider on the left to increase or decrease detector sensitivity. If you prefer, you can also have LX Spider find the ideal level of sensitivity.  Just press the auto exposure button. When you’re ready press the safe spectrum button followed by confirm. Then uncheck the measure spectrum box. And the interferogram of the fundamental signal should be visible.

5:09 First make sure that auto exposure mode is switched off. To start set the spectral range to second harmonic. Then tune the crystal to the correct wavelength by checking the tune to center of gravity box as an alternative. You can manually enter the center wavelength and press the tune button. Be sure to reset the exposure time if needed. If you need to further optimize the signal you can adjust the focus mirror by using the hex key provided with your LX spider. Here’s how:

5:45 On the right side of LX spider are the two alignment screws for the focusing mirror. Use your hex key to adjust the horizontal and vertical tilt. The adjustment is complete when you’ve  reached the highest intensity and best modulation of the green signal curve.

6:03 The last step is to save the calibration. Again, our software makes it easy. Just activate auto exposure mode and set the spectral range to fundamental. Press the safe calibration button and when you’re asked to replace the spectrum choose “no”. Then return the spectral range to second harmonic.  LX Spider will immediately show you the pulse in the spectral domain.

6:28 The previously safe pulse spectrum will appear as a white curve and the current reconstruction of the spectral phase will appear as a blue curve. You can evaluate the chirp of the pulse from the curvature of the phase. If you’d like to see the actual temporal pulse shape click the time domain button. A second graph will open the display. The pulse shape at the Fourier limit in green and the actual pulse shape as a white curve.

6:56 The temporal phase is also shown on the right. Characteristic values of the pulses can be monitored such as the pulse duration and the time bandwidth product. And that’s it. Setup is Complete. You’re now ready to start taking real-time measurements.

This is from the transcript of Spectral Phase Interferometry for Direct Electric-field Reconstruction.