Laser tests

• Prague measurements with laser beam at 2006
• Simulation of respons of laser beam at 2006
• Prague 3D+2R position system and laser setup at 2006
• How to measure negative charge with ATLAS SCT hybrid
• Noise bumps with laser beam analysis
• Beta source tests in Prague
• First works with laser beam in Valencia at 2004 are described on Valencia pages
• First works with laser beam ip Prague Charles University 2003

Status of laser tests technique

Main benefits

• cheaper than standard test beams with real particles
• lightweight arrangement allowing easy transport
• generally available in labs
• good repeatability and reproducibility of results

Main features and capabilities

• fine-tuning of readout electronics, timing of signals and DAQ software tuning (algorithms, sequences, delays)
• interstrip or interpixel response with micron resolution
• response measurement - linearity, dependence on other conditions, calibrations
• measurement of pulse shapes for injected charge ranging from fractions to thousands MIPs
• injection of extra large charge for regeneration time measurement or assessment of electronics damage
• measurement of high-rate charge injection (double pulse)
• depletion voltage measurement
• signal / noise ratio
• thermal dependencies of properties
• all previous tests also for irradiated modules (sensor or/and FE)
• thickness homogeneity of sensor with precision in about 100nm sensitivity
• in combination with simulations, good insight in silicon detectors response at theoretical level

Deeper understanding of laser beam interaction with Si detectors

• For 1060nm wavelength – thickness of silicon substrate changes: minima-maxima on interferences give about 30% changes in charge collection in ½ wavelength inside Si (~150nm) – relevant only in large area scans
• For 650nm incomplete charge collection within integration time – charge is created in layer less 4 µm in weak electric field – dependent also from properties of coating layers (electric field gradients, conductivities, lost charge vacancies,…)
• Irradiated detectors: additional diffusions, inhomogeneities

Containt of laser tests

• Testing algorithms of strip detectors
• Set of standard tests and analyses: focusing, strip response, charge sharing
• Different wavelengths: 650nm and 1060nm
• Angle (skew) scans
• Optical head for direct beam power measurements
• Simulations of laser beam in Si
• Deeper understanding of laser beam interaction with Si detectors
• Preparing analysis macros

Testing procedures of strip detectors

• Short pulsed lasers 650 and 1060 nm (CERN)
• DAQ (VME – NI PCI-VME )
• oscilloscope (GPIB)
• pulse generator (GPIB)
• positioning stages 3D-2R (USB)
• 2 power supplies (USB-RS232)

• High voltage (bias) control
• Focusing algorithms – rough, fine
• Position scans
• Timing scans
• Angle scans including deep focusing
• Environmental monitoring (temperature, humidity, power drops, bias drops, remote access and full processing from any place (VNC), automatic emergency system)

Detail list of needed informations and laser tests for strip detectors

Mandatory:(M), recommended:(R)

1. Testing structure (detector) (M)
2. Readout: electronics and DAQ software, negative or positive charge collection (M)
3. Simulation of response (R)
4. Environment under control: temperature (M), cooling (M), humidity (R), special atmosphere (R), emergency system (M)
5. Light source: semiconductor laser
1. wavelength 650nm (R) (surface scans, charge generation up to 4um)
2. wavelength 1050nm (M) (silicon bulk response, charge generation 4mm)
6. Position system 2D (M), 3D+1R (R)
7. Triggering system (R) (for real beta sources)
8. Calibration tests of laser system:
1. Mechanical stability (4.0um, 0.1deg) (M)
2. Optical stabylity of beam to separate this effects (amplitude, timing jitter, noise) (M)
3. Trigger system: scintilators, delay units (R)
4. Focusing of laser (M)
5. Absolute reflectivity measurement (R)
9. Standard tests of detector without laser:
1. IV curve (M)
2. noise scan (M)
3. response curve scan (M)
4. time walk scan(M)
10. Laser beam tests of detector:
1. Perpendicular response scan (M)
2. Different charge injection scan (0 - 10 fC) (M)
3. Bias scan (depletion voltage measurement) (M)
4. Pulse shape scan - measurement of pulse shapes for injected charge ranging from fractions to thousands MIPs (M)
5. Interstrip scans of efficiency and cluster size measurements (M)
6. Surface charge generation scan (R) (check efficiency and timing of collection of charge from surface space - checking of detector design, electrical fields close surface, charge losses)
7. Cluster size scan (M)
8. Efficiency scan (signal / noise ratio) (M)
9. Injection of extra large charge for regeneration time measurement or assessment of electronics damage (R)
10. Measurement of high-rate charge injection (double pulse) (R)
11. Thickness homogeneity of sensor with precision in about 100nm sensitivity (R)
11. Points 9. and 10. repeat for irradiated modules with different dose, different irradiated components (M)
1. Simulation of response of irraditad module, additional diffusions, inhomogeneities (R)