1. Optical BPM Progress A0 Photoinjector July 17th, 2009
Tim Maxwell, Jinhao Ruan,
Philippe Piot & Mike Church

2. Optics Status and Roadmap
1) Laser Autocorrelator (SHG)
For single-shot laser pulse duration measurement
Also for synchronizing laser pulses
Now assembled and functioning
2) Frequency Resolved Optical Gating (FROG)
An autocorrelator with a diffraction grating
Measures λ vs. t shot-to-shot (duration and chirp)
Kit awaiting assembly pending study of autocorrelator

3. Optics Status and Roadmap
3) Fiber Transport
For IR laser transport line from laser room to cave
Fibers and launch optics ready
Need FROG to characterize fiber dispersion effects
4) Laser pulse stretcher (and compressor)
Introduce chirp for EO spectral encoding
Help compensate for fiber dispersion
Above experiments needed to proceed
Fiber measurements to determine compensation needed
FROG to verify performance

4. Single-shot autocorrelator
Autocorrelator based on ~SHG and spatial encoding
When pulses cross simultaneously (brightest and centered blue spot)
blue stripe is autocorrelation of pulse
Split laser pulse, duration
(thickness) exaggerated
BBO Crystal

5. Single-shot autocorrelator
Second-best layout
Half angle between lasers
at crystal of ~19° ~
Revised layout
Half angle between lasers
at crystal of ~9° ~ ~ ~ ~

6. Single-shot autocorrelator

7. Single-shot autocorrelator
For single-shot mode, scan delay to find peak signal and find…
First result last night (7/16/09)

8. Single-shot autocorrelator
Finding time axis calibration factor
Convert micro controller position to time delay: Δt = 2 Δx / c
Scan stepper recording spot centroid as a function of delay
Slope of centroid position vs. delay yields conversion pix to sec
Centroid calculated two ways:
Brightest horizontal trace
X projection
Projection shows roll off in this result (no background correction).
Used linear region of “Trace”
Preliminary calibration: 2.5 fs / pix

9. Preliminary first results
Revisiting peak horizontal trace and x projection from earlier:
RMS laser pulse length 140 fs
…if only I had also measured the bandwidth for comparison.

10. Conclusions
Autocorrelator up and running and seems to work well so far
Clean up the control and analysis scripts (Matlab)
Compare single-shot method (shown here) with scanning method
Vary Ti:Sapph bandwidth and measure pulse length
We had to cut incidence angle in half
Should be able to use bigger angle according to theory
Did I just not see the dot in original set up?
Want bigger angle for in-pipe autocorrelator!
When done with initial exploration, attempt larger angle again?
Extend into Frequncy Resolved Optical Gating with the kit
Assemble and test remaining optics for EO experiment, as mentioned
Somewhat unrelated: Also still looking into wake filed calculations for the proposed EO pipe section…