CCD testing Enver Alagoz 12 April 2010

CCD testing goals CCD testing is to learn how to – do dark noise characterization – do gain measurements – determine quantum efficiency These experiences will be useful for the LSST wavefront and guider sensor studies at Purdue

CCD testing setup

Apogee CCD camera 12 V power USB control Upgradeable firmware 16 bit digitization TEC cooling (dT = 50 C) Fans for heat-sink RTD under chip and on heat-sink CCD sensor sealed in a inner chamber filled with gas Argon 25 mm opening window Mechanical shutter power USB shutter Kodak KAF-0402ME 768x512 pixels (9x9 μm 2 ) Saturation: 102 K electrons At T CCD = -31 °C Gain [e-/ADU] = 1.6 Readnoise 10.3 e-’s Bias: 2633 counts Dark: 0.03 e-/pixel/sec Microlenses to enhance QE at λ < 600 nm

Kodak CCD QE T CCD = 25 °C QE measurements of Kodak before Apogee camera assembly Micro lenses enhances QE at λ < 600 nm Micro lenses enhances QE at λ < 600 nm poly-Si gate

Camera window reflectance Camera window has 2x fuse silica coated with Broad Band Anti-Reflection (BBAR)

Bias level

Bias and dark measurements - Bias - Dark+Bias

ADU = Analog digital unit Dark measurements

Readout noise Gaussian fit Two bias frames with zero time exposure Subtract from each other and get the readout noise R C = σ/sqrt(2) R C = 6.3 ADU = 10.1 electrons

Light measurements Tungsten lamp 100 W power λ = 580 nm

Gain N C (N E ) = signal noise [ADU] ([e - ]) g = gain [e - /ADU] S C (S E ) = signal [ADU] ([e - ]) σ E = photon noise σ o,C (σ o,E ) = flat field noise [ADU] ([e - ]) R C (R E ) = readout noise [ADU] ([e - ]) Slope of S C as a function of N 2 C is g Using photon statistics

Variance Illumination images A and B Mean signals: S A and S B Ratio: R = S A /S B Multiplication: R x image (B) Subtraction: image (A) – image (B) Take σ 2 /2.0 of residual histogram = variance Plot S versus variance Repeat for all time exposures

Variance

Gain: variance vs mean signal Dark frames are subtracted 100x100 pixels window Gain = 1/slope

Gain T CCD = -20 °C

Optical power measurements

QE Calculation I is mean image for a given wavelength [ADU] D is dark count [ADU] G is gain per wavelength [e-/ADU] W is CCD window transmission per wavelength [%] PD power is the optical power measured by PIN diode [W] Pix area is the single CCD pixel area [m 2 ] PD area is the PIN diode area [m 2 ] T exp is the time exposure [sec] E γ is the single photon energy per wavelength [Joule]

Photons on CCD Measure power from PIN diode Normalize power to CCD pixel area Calculate single photon energy E γ = ħν where ħ = 6.63x [J.s] and ν = c[m/s]/λ[nm] E γ = 1.989x / λ [J] Calculate number of photons on a CCD pixel Etotal [J] = Pin power [W] x time exposure [s] E total /E γ = # of γ’s per CCD pixel area

QE (per pixel/sec) Expected measurements from Kodak (T CCD = 25 °C)

ErrorSourceEffectError in % Wavelength (λ) - Monochromator: 1.wavelength settings 2.wavelength calibration - Bandwidth is out of range of PIN diode responsivity Wrong QE <= 0.1 BiasBias and image data with different clocksWrong QE Pixel windowBadly chosen pixel windowWrong QE I(λ)1.Bad image (e.g. too low signal) 2.Contaminated CCD 3.Non linear CCD behavior 4.CCD is distance from integrating sphere exit port Wrong QE T exp 1.Software latency (15 ms) 2.PC clock latency (?) 3.Shutter latency&integration time (20 ms) Wrong QE PD power 1.Current measurement error 2.Calibration error Wrong QE 5 Window1.Window transmission errorWrong QE<= 0.6 GWrong gainWrong QE Error budget

Next QE measurements at +25 °C to validate results Dark and bias measurements -30 °C Optical light system error budget Write up measurements and methods for a LSST document Plan to use optical setup with WFS testbed …

BACKUP SLIDES

QE Each blue line represents QE results for a time exposure ( sec with 0.5 sec steps)

Integrating sphere Light exit port 4” Detector port 0.5” Light input port 1” Integrated sphere 12” PIN & detector port adaptor 5 PM 1 PM11 AM 8 AM

Photodiodes Two calibrated photodiodes (# 381 and # 384) mm diameter 1 cm2 active area Calibration accuracy ? Wavelength [nm] Responsivity 381 [A/W] Responsivity 384 [A/W] Difference [%]

Photodiode calibration Diodes were calibrated before shipped to Purdue (Ref. Newport) PIN 384 PIN 381

Light power measurements Dark box PIN Sphere exit port PIN displacements

Light power measurements Power measured At 50.8 mm from sphere exit port with: PIN 381 is nW PIN 384 is nW At CCD position 508 mm with: PIN 381 is 11.8 nW PIN 384 is 11.5 nW PIN 381 measured nW at sphere detector port (0 mm) PIN 384 measured nW at sphere detector port (0 mm)

Wavelength scan