# Presentation: 797943

## Laser calibration of SVT

-     Jana Bielcikova (Yale University)
- Location and properties of laser spots
- Time variations of laser spot positions
- Drift velocity calibration
- Summary

## Location of laser spots

**three laser spots**
-              **2 spots** are at:
-   hybrid=1, layer=6,
-   ladder=15, wafer=7 (B3L15W7)
-              **1 spot** is at:
-   hybrid=2, layer=6,
-   ladder=7, wafer=1 (B3L7W1)
-   *due to a dead anode this spot appears as*
*  **two spots on two neighboring anodes but*
*  **with an identical timebucket  position*

## Location of laser spots

**B3L15W7**

**B3L7W1**

**anode**

**time**

## Properties of laser spots (I)

**spot 1**

**spot 2**

- N(anodes)=6.2

- N(anodes)=4.1

**spot 1**

**spot 2**

- N(pixels)=18.6

- N(pixels)=47.2

- see Richard Witt’s talk for additional details

## Properties of laser spots (II)

**Laboratory laser tests:**
**anode direction**: σ=6 μm
**time direction**: σ= (5 – 23) μm
- (depending on the position)
*(NIM A439, 2000; SVT proposal)*

**spot 1**
**σ****=4.4****μ****m**

**spot 2**
**σ****=3.0****μ****m**

**anode**

## water cooling    time variations 
          of  laser spot positions 

spot positions change in phase
                         BUT
spots behave differently after SVT is switched on and gets  stabilized 
                    (~ 1 hour !)
            spot 1: 80 microns
                spot 2: stable
                spot 4: 300 microns 

**water cooling  ********  time variations **
**          ****of  laser spot positions**
- spot positions change in phase
-                          **BUT**
- spots behave differently after SVT is switched on and gets  stabilized
-                     (~ 1 hour !)
-             spot 1: 80 microns
-                 spot 2: stable
-                 spot 4: 300 microns

**Time variations of laser spot positions (I)**

**spot 1**

**spot 4**

**spot 2**

- we cannot calibrate out
- the burn in

## Time variations of laser spot positions (II)

**temperature oscillations have a period of about 2.5 min**
**peak-to-peak change is ~70 ****μ****m**

- drift distance of spot 1

## How we can correct for it ?

- due to an unknown offset of the laser tL we do not measure
-      the true laser spot positions d1 and d2
- but  we can use the difference d1-d2   (tL cancels out) to calibrate
-      the drift velocity

-         d1 = v(t1-t0-tL)
-         d2 = v(t2-t0-tL)

- d1 – d2 = d12 = v(t1-t2)

## Drift velocity calibration 

**Calibration procedure:**
- evaluate event-by-event d1-d2
- calculate new drift velocity such that new ‘d1-d2’ is equal to <d1-d2>

**Time difference of spot 1 and 2**

## Corrected laser spot positions 

- black before, red after the drift velocity calibration

- σ=(12.4±0.1) μm

## How does correction work for the other wafer?

**improvement by **
**a factor of 2 !**

## Summary 

- we can use the laser information to calibrate out the temperature variations in the SVT after it is stabilized
-        **improvement of the laser position reproducibility    **
**                        ****(resolution) by a factor of 2**
**                  ****σ****(time)=10****μ****m,  ****σ****(anode)=3-4 ****μ****m **
- calibration of the temperature variations during the burn in
-      after the SVT is switched on (~1 hour) is a challenge
- algorithm will be tested on more data and implemented to the SVT analysis software