Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Status of fringe stabilization of Shintake-monitor Taikan SUEHARA The University of Tokyo

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Beam Size Resolution vs. Fringe Phase Fluctuation

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Required Modulation Resolution GOAL : to measure 35 nm beam size by < 2nm resolution Beam sizemodulation 33nm73% 35nm70% 37nm67% 2nm beam size corresponds to 3% modulation (around 35nm). We need 3% modulation resolution. zoom Then, how much stability of laser fringe phase do we need to achieve 3% modulation resolution?  We performed a Monte Carlo simulation to obtain that relation.

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Modulation Error Estimation Assumed measuring condition for simulation is: 45 points (phases) meas., 1 bunch for each point It’s determined by desired measuring time (1 minute) 45 points  1 bunch + same for background reduction = 90 bunches. 90 bunches / 1.5 Hz (ATF2 operation freq.) ~ 60sec. Simulation method is shown below (by example) A sample of error simulation caused by phase jitter

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Required Fringe Stability modulation uncertainty is proportional to phase jitter. About 30nm stability corresponds to 3% (goal) modulation uncertainty. But we should consider another errors. We keep safe factor 3. The result of simulation: As a result, We should develop a 10nm level fringe phase stabilization system.

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Phase Stabilization Status

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 The Method of Phase Detection The laser beams pass through the microscope lens to be magnified, and create fringe pattern. (lens works like a double slit) The phase of the fringe corresponds to relative phase of 2 laser beams. Fringe magnification by a lens with a linear image sensor

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Location of Monitors and a Scanner We cannot place the phase monitor on IP. We place it “off-axis” position. To cancel out difference of the phase between IP and monitor position, we place the same monitor on the other side (ch2). We place a phase scanner (delay line with piezo mover) on one side.

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22Setup Linear image sensor (photo by HPK website) 256 pix, 25um pitch

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Fringe Phase Scanning System Optical delay line used for phase stabilization and scan Resolution of piezo stage is 1nm, corresponds to 2nm phase resolution. The stage can be controlled by PC up to 300Hz (sufficient speed for stabilization).

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Linear Image Sensor Data Raw spectrum. Wave of dense pitchFourier spectrum. Clear peak near 2.5. We use Fourier transform to obtain phase (at central channel) for high resolution and noise reduction. Clear peak can be seen near 2.5 on Fourier spectrum. It corresponds to the wave seen on raw spectrum. We use the Fourier phase (i.e. argument of complex Fourier) of the peak for the phase stabilization. 

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Preliminary Result(1) Simply measured phase for 50 sec. No stabilization. FT peak period: the phase of the Fourier peak freq. Fixed period: the phase of fixed freq. (near the peak). Ch1 and Ch2 are almost opposite because they face opposite directions (it’s expected behavior). This shows correlation of phases at two monitors.

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Preliminary Result(2) Stabilization effect is clearly observed.  = (3.2nm) for ch1 fixed (stabilized channel)  = (7.5nm) for ch2 fixed (unstabilized channel, except long-time drift) Almost achieved 10nm stability for very bad condition (no cover, lenses with rods). We can improve further.

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Phase Monitor Errors (by Position / Angle Jitter)

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Basic Check of Fringe Characteristics Crossing angle & Fringe pitch –Crossing angle is proportional to “ slit distance ” (i.e. inverse- proportional to fringe pitch) Lens mag. & Fringe pitch –Lens magnification is inverse- proportional to fringe pitch Lens NA & Acceptable crossing angle –Clear view until NA –Partial view until a little wider than NA –128 deg. for NA=0.9, 142 deg. for NA=0.95

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Resolution of Fourier Transform With random noise (S/N > 1) Rotate phase, and check maximum error of detected Fourier freq. & phase Freq. error is S/N=1 Phase error (fixed freq.) is 0.1rad.

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Calculation of Jitter Requirement I calculated the jitter requirement for Fourier- limit freq & phase reso. 1um position stability is required for detector and lens (X axis) 10urad angle stability is required for lens and beam. Going to check the jitters by vibration monitor.

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 Other Issues IPBPM & Shintake-monitor –IPBPM with laser port? –How to align laser beam without a slit? Or the slit is available with IPBPM? –Doesn ’ t the laser beam perturbate IPBPM signal? We must prevent the air flow –Temporal cover with acryl board & alumi frame –Black curtain (also for safety of high power laser) Image sensor with smaller pitch –CMOS LIS (7.8um pitch): waiting for arrival

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22Summary To achieve 2nm resolution, we have to obtain 10nm fringe stability. First fringe stabilization result shows < 10nm fringe fluctuation. (because of high reso. by Fourier transform) The requirement for position/angle stability of the monitor and the lens is not so hard. (1um,10urad level) The stabilization of this method is hopeful!

Taikan SUEHARA, ATF2 meeting, KEK, 2006/11/22 以上。