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Test Facilities News

ECHO-7 News                                                                                  Back to top

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Echo 7th Harmonic Observed                                                    May 19, 2011

The 7th harmonic of the 1590nm seed laser was observed this evening.  The 7th harmonic at 227 nm was only seen when both lasers are on. However, the signal was still generated when energy modulation is much larger than slice energy spread, so the key advantage of echo is yet to be demonstrated.

We will try to use our first TCAV to increase the beam slice energy spread in our next run (July 2011) so that we can demonstrate echo in the realistic scenario when energy modulation is comparable to energy spread. This should suppress the signals when only one of the lasers is on (i.e. in this case the blue line in the attached picture should be very close to the black line and only the red line has peaks).

Though there are still a lot of things need to be investigated (e.g. the heating from first TCAV is not as large as expected, etc), the results so far are encouraging.

First Beam from Transverse Cavity seen on Spectrometer      April. 27, 2011

After a long down time where we increased the resolution of the spectrometer by a factor of three, installed two transverse cavities, moved the 2nd acceleration structure further upstream and hooked it up to RF station one and many more smaller changes, Echo-7 is finally running again. Here is the one of the first pictures of the beam after the second T-cav on the spectrometer screens. The picture shows the longitudinal phase space distribution. The vertical axis is time and horizontal axis is energy.

Echo-7 featured in Slac Today                                                                                   Apr. 19, 2011 

Clich here for the article.


Echo-7 featured in Nature Photonics                                          Nov. 1, 2010

Echo-7 was featured in an article on EEHG in the journal Nature Photonics:

P. Zeitoun et al., "X-ray lasers: Coherent and compact", Nature Photonics 4, 739-740, 2010.

Click here for a pdf.


PRL paper published                                                                     Sep. 9, 2010

The paper submitted to PRL was published this week:

 D. Xiang et al., "Demonstration of the Echo-Enabled Harmonic Generation Technique for Short-Wavelength Seeded Free Electron Lasers", PRL 105, 114801, 2010.



PRL paper submitted                                                                     July 17, 2010

A paper was submitted to Physical Review Letters (PRL). The pre-print is linked below:

 D. Xiang et al., "First demonstration of the echo-enabled harmonic generation technique for short-wavelength seeded free electron lasers", SLAC-PUB-14199, 2010



Echo signal confirmed                                                                    July 9, 2010

The echo signal that was initially observed was spectrally resolved and clearly shows the presence of Echo-3 and 4, as well as HGHG signals.  The figures below show the wavelength spectra for the radiation measured at the exit of Undulator 3, with no beam energy chirp (left) and with a chirp (right).  The chirp is realized by accelerating the beam off-crest (about 10 degrees) in the 2nd x-band accelerating structure.  Theory predicts that when the beam is given such a chirp, the spectra shift differently for HGHG and EEHG.  For more details, see the publication by Z. Huang, et al




IPAC papers submitted                                                                May 19, 2010

Two papers have been submitted for the 2010 International Particle Accelerator Conference (IPAC10) to be held in Kyoto, Japan from May 23-28.  The papers are linked below:

 "A proof-of-principle echo-enabled harmonic generation experiment at SLAC"

 "Preliminary results of the echo-seeding experiment ECHO-7 at SLAC"



Echo signal observed (possibly)                                                  May 18, 2010

A possible echo signal was observed today when both lasers were simultaneously interacting with the electron beam.  A confirmation is needed with a separate measurement.



Beam/Laser Interaction in Undulator 2 observed                     May 8, 2010

Interaction between the beam and laser in undulator 2 was observed on Saturday, May 8.  Similar to the interaction in undulator 1, the 1590nm laser generates energy modulation in the beam during interaction in the undulator, and this energy modulation is converted to density modulation in chicane 2.   

laser-beam timing scan




Beam/Laser Interaction in Undulator 1 observed                     April 22, 2010

Interaction between the beam and laser in undulator 1 was achieved on Thursday April 22nd.  The 0.4ps RMS electron bunches were synchronized to the 0.4ps RMS laser pulses in the undulator, and a strong enhancement of Coherent Optical Transition Radiation (COTR) and Coherent Undulator Radiation (CUR) was observed during interaction.  The 795nm laser generates energy modulation in the beam during interaction in the undulator, and this energy modulation is converted to density modulation in chicane 1.  The density modulated beam generates coherent radiation at optical wavelengths when it travels through undulator 2 and when it hits a downstream OTR screen.  The coherent radiation was enhanced by almost one order of magnitude. 




Undulator 3 installed                                                                    April 14, 2010

Undulator 3 has been installed.  The echo beamline is now complete.  




Undulator Radiation Observed                                                  March 10, 2010

Today at 3pm we observed clear undulator radiation from the first modulator in the Echo-7 beam line at NLCTA. The Pi-mode together with the sigma-mode of the undulator radiation gave us four-lobes, as in the picture above. The number of photons is estimated to be about 10 million which should be sufficient for the fast photodiode. We'll test laser and electron beam timing later this week. So stay tuned for more good news.
Congratulations to Dao, Janice, Doug, Stephen, Pierre-Louis, Mark and Michael, who were present in the control room, and all others who are working hard to make Echo-7 happen.


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