The detector monitoring project
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The detector monitoring project P. Amico P. Ballester, W. Hummel, G. Lo Curto, L. Lundin, A. Modigliani, L. Vanzi (all @ the European Southern Observatory). Talk Roadmap. General Introduction to detector characterization and testing ESO’s detector roadmap: from vendors to science.

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Talk roadmap

The detector monitoring projectP. AmicoP. Ballester, W. Hummel, G. Lo Curto, L. Lundin, A. Modigliani, L. Vanzi(all @ the European Southern Observatory)

Talk roadmap
Talk Roadmap

  • General Introduction to detector characterization and testing

  • ESO’s detector roadmap: from vendors to science.

  • Detector monitoring in La Silla

  • Detector monitoring in Paranal

  • The monitoring plan

Once upon a time there was the perfect scientific detector
Once upon a time there was the perfect scientific detector:

  • Up to 99% QE

  • over 355 million pixels

  • No - framing detectors

  • No – defined by filter

  • No – defined by filter

  • Detect 100% of photons

  • Large number of pixels

  • Time tag for each photon

  • Measure photon wavelength

  • Measure photon polarization

Detectors are now nearly perfect

But the devil is in the details ………


Just to name a few


QE (wavelength, T, t)


Linearity, well depth (T,bias, flux!)

Gain precision and stability



Charge Transfer Efficiency

Stray light


Bias Level

Dark current

Mux glow

Cosmic rays

Read noise

Microphonic noise

Pickup noise

Odd-even column effect

Just to name a few:

Many behaviours to measure

985 nm

990 nm

995 nm

1000 nm

1005 nm

1010 nm

Many behaviours to measure

Fringing of Silicon sensor

Persistence in hawaii 2rg
“Persistence” in Hawaii-2RG

  • switch from LPE to MBE does not eliminate persistence

  • latent image can be seen for many hours

  • persistence on all arrays tested

Courtesy G. Finger

Persistence in hawaii 2rg1
“Persistence” in Hawaii 2RG

  • depends on fluence not on flux

  • N < Nsaturation = 105eno persistence (?)

  • switch from LPE to MBE does not eliminate persistence

  • latent image can be seen for many hours

  • Causes: traps, temperature effects?

Courtesy G. Finger

Once upon a time there was a detector








La Silla






Once upon a time there was a detector…


1 in house characterization
1. In-house characterization

  • CCD pedigree (type, specs, output, pixel size)

  • RON and Conversion factor (inverse gain, CONAD)

  • Quantum Efficiency (QE)

  • Cosmetic defects

  • Linearity (peak-to-peak, rms, range, sat. level)

  • Dark Current

  • Cosmic X-ray events

  • Charge Transfer efficiency

  • Measurements conditions (T, pre-scan/overscan, bias voltages, date) and sample images.

  • Additional tests: IR - sensitivity profile of pixel.

Talk roadmap

Plasma cleaning devices

Successful plasma cleaning inside the assembled OmegaCam cryostat

Courtesy S. Deiries

After some minutes the large volume (approx. 200 l) of the cryostat was filled

by a violet glowing plasma.

A normal cleaning process takes not longer than 10 minutes!

Comparison of cosmetic quality 40k 80 k
Comparison of cosmetic quality 40K / 80 K

T=40 K

T=80 K

Cut levels -250 e /200 e , DIT 900 sec

Courtesy G. Finger

La silla ccds optical
La Silla CCDs (optical)

  • Weekly linearity tests with beta light (only FEROS and HARPS with LEDs) performed by SciOps.

  • Semi automatic tool with GUI to acquire, analyze, e-mail, publish data on the web (one click per action). Feedback is displayed on the screen

  • Test results e-mailed to instrumentation engineer and instrument scientist.

La silla ccd detectors
La Silla CCD detectors

  • Values measured: bias level, average count rate, gain, ron, linearity, shutter delay. Database spanning several years.

  • We use the traditional Photon Transfer method to derive gain from photon statistics (5%)

  • Method documented (among others) in Downing, 2006SPIE.6276E...8D:

  • Linearity relays on beta light (or LED) stability to compute average count rates at different exposure times -> shutter stability required (with the exception of HARPS for which the LEDs are downstream of the shutter).

Led vs beta light in feros

P. Francois

P. Francois

P. Francois

LED vs. Beta Light in FEROS

The HARPS CCD is not accessible; beta light tests are therefore not feasible.

Similarly, for FEROS, insertion of the beta light is

inconvenient, as it has an impact on the instrument stability.

Instead LEDs, placed just above the CCDs are used.

This technique is proven to be fully satisfactory using the FEROS LEDs (high stability power source, no feedback).

La silla ccd detectors1
La Silla CCD detectors

  • Uniform scheme across instruments for detector testing.

  • The look & feel of the interface is the same.

  • The end product is the same

  • There is a database spanning several years to be used for trending.

Detectors in paranal
Detectors in Paranal

Total of 25 detectors.44 more expected

Optical detector monitoring conad and linearity for giraffe
Optical detector monitoring:CONAD and linearity for GIRAFFE

Nir detector monitoring ron and dark level isaac aladdin
NIR detector monitoring:RON and dark level (ISAAC Aladdin)

What can be improved
What can be improved?

  • Basic parameters (BIAS, RON) are measured and monitored daily.

  • Fundamental parameters (gain) still not implemented for all instrument.

  • Other measurements (e.g. linearity, fringing, contamination, etc) not yet monitored.

  • Measurements of the same quantity are made differently for different instruments (different pipelines).

    • “measured in a raw file (high gain mode) as 100x100 pixels sigma, corrected for fixed-pattern contribution”

    • “measured on single raw frames, with no corrections”

  • La Silla and Paranal independent from each other (which is partly compatible with the different operational scheme).

The detector monitoring plan
The detector monitoring plan

  • A true Chile-Germany interdepartmental collaboration: Sciops & Instrumentation (Paranal, La Silla) + QC + Data Flow System Dept. (DFS), +…

  • Started as an IR detector monitoring project for Paranal.

  • Its scope was widened last year, to include optical detectors.

  • Once the group of “volunteers” was formed, the first step had been to collect all the documentation available and condense it in a document. This document summarizes the goals and objectives of the plan, presents an extensive description of all (well, almost all) the tests and measurements ever conceived for detectors and attempts at describing the algorithms we believe are best to measure a certain quantity.

  • It is not meant as a strict to-do-list to be completed, but as a driver for an ambitious project.

  • It is open to a wide audience (instrument scientists, instrumentation engineers, astronomers, etc) and it welcomes the contributions and expertise of many.

Goals of the project
Goals of the project

  • Standardize the test procedures whenever applicable (e.g. define a unique way to measure linearity).

  • Unify test procedures for IR and Optical detectors whenever applicable and describe the differences in all other cases.

  • Unify the measurements procedures and the use of data reduction recipes and algorithms.

  • Utilize available resources, such as data taking templates, pipeline recipes, existing reporting tools (QC web pages, Autrep), previous experience (e.g. LaSilla test procedures, ODT, IRI, etc).

Cpl detector monitoring functions
CPL Detector Monitoring Functions

  • - Study of operational pipelines

    • RON, BIAS/DARK supported for most instruments

    • First development required is for a common detector linearity recipe.

  • - CPL Implementation

    • Algorithms distributed as CPL data reduction functions

    • Pipeline recipes invoke a single function

  • Pipelines Implementation

    • Instrument templates may have to be retrofitted