System Operations

Eastbourne,

October 2005

Towards the 1-mm:- A realistic goal ?- A vision ?- A myth ?- ???

System Operations: Accuracy

Eastbourne,

October 2005

How to reach the 1 mm ACCURACY ? Is it possible ?

How to reach the 1 mm STABILITY ? Is it possible ?

Which developments are necessary ? Recommended ?

Is the 1 mm a realistic / achievable goal ?

Simple answer:

Yes, but we do not know WHEN

Eastbourne, October 2005

1 mm: What we need …

Good LASER: SSDPL (Solid State Diode Pumped)

Short Pulse Duration: 10 ps

Good Event Timer:

A032-ET (Riga): < 10 ps RMS, < 2 ps nonlinearity, kHz ...

Dassault Modules (Graz E.T.): < 3 ps RMS, < 2 ps nonlinearity

Good detector: C-SPAD, Time Walk Compensated;

Good satellites: ZERO Signature; PLUS strong return signal !

Grace A, Grace B, Champ: No sat signature, good signal

LARET-C: Zero signature, but weak signal

Eastbourne, October 2005

1 mm: Needs a good laser …

UPGRADE THE LASER:

Switch to Solid State Lasers (e.g. kHz);

Excellent Pulse uniformity;

Excellent Stability (shot-to-shot, day-by-day);

Short Pulses (10 ps in Graz) => better accuracy;

We do not see any disadvantage ...

Change from „TUBES“ to „SOLID STATE“ !!!

October 2005

1 mm: Needs strong signals …

With a 10-ps laser, good ET, strong-signal / zero signature sat.:

2 – 3 mm Single Shot RMS precision;

With VERY strong returns (> 300 pe / return): 1 mm SS RMS

Measure Return Signal Strength of EACH return:

C-SPAD: Use Time Difference Comp. / Uncomp. Output

Select returns with > 300 pe only 1 mm RMS

In CALs to 4 km Retro Target: Routinely achieved;

Current project ongoing in Graz; results in Canberra expected

Eastbourne,

October 2005

CAL RMS: From 10 Hz to kHz

SLR Graz: Routine - Calibrations 2003-2005;10 Hz: 500 Returns; kHz: 10 000 Returns

0.00.5

1.01.5

2.02.53.0

3.54.0

4.55.0

2003 2003.5 2004 2004.5 2005 2005.5

CA

L R

MS

[m

m]

CAL RMS [mm]

Eastbourne,

October 2005

CAL P-M: From 10 Hz to kHz

SLR Graz: Routine - Calibrations 2003-2005;10 Hz: 500 Returns; kHz: 10 000 Returns / CAL

-4

-3

-2

-1

0

1

2

3

4

2003 2003.5 2004 2004.5 2005 2005.5

Pe

ak

min

us

Me

an

[m

m] CAL Peak minus Mean [mm]

Eastbourne,

October 2005

1 mm with flash lamp laser ?

Old 10-Hz-Laser system in Graz (but with E.T. etc.):

Peak-minus-Mean: about ± 2 mm variations;

Too big; => difficult to reach the 1 mm goal !!!

With new Solid State Laser (kHz):

Peak-minus-Mean: MUCH better, very stable !!!

about ± 0.3 mm variations only ...

Eastbourne,

October 2005

1 mm: Needs a good satellite …

Use Retros / panels WITHOUT satellite signatures !!!

GRACE-A

GRACE-B

CHAMP

???

2-3 mm SS RMS

Eastbourne,

October 2005

1 mm Accuracy / Stability

All previous comparisons:

From 10 Hz Flash Lamp to 2 kHz Solid State Laser

All other Equipment: Same ...

Event Timer (Graz E.T. / Dassault Modules)

Same C-SPAD; same other equipment ....

Conclusion again:

Change from „TUBES“ to „SOLID STATE“ !!!

Eastbourne, October 2005

Laser Pulse Width and Accuracy

Wide range of pulse widths used in SLR:

10 ps: Graz / kHz / Solid State Laser;

35 –50 ps: Standard Lasers; Flash Lamp Pumped;

110 ps: e.g. Herstmonceux Flash Lamp Pumped;

300 ps: SLR 2000

Any other ?

What is the „best“/„optimum“/„desired“ pulse width ?

Eastbourne, October 2005

Laser Pulse Width Selection

10 ps: Present optimum; no reason for shorter pulses …

No significant contribution to overall systematics anymore;

Excellent for Single-Photon-Detectors;

Allowa to see – and to handle - Single Retros ….

300 ps: Can be eye-safe at e.g. 50 cm dia, if < 150 µJ / pulse

Relatively big contribution to overall systematics;

1mm goal for Lageos => difficult with SPE signals<

Satellite signature problem slightly increasing;

Less problems with LEOs / MultiPhoton Detection

Eastbourne,

October 2005

Measuring Laser Pulse Width

I have no idea how to measure it ...

But Jerry Wiant is doing it