Cameras for scientific experimentsA brave attempt to give an overview of the different types and their pros & cons

Grouptalk Optical Sciences, may 8 2012Jeroen Korterik

Introduction

Lots of different types of camerasEach working principle has it's own strong and weak pointsWhich type to use?How to use it for optimal results?

Introduction: terminology

Analog film

Analog, electronic (CCD/CMOS, PAL/NTSC)

Digital (CCD/CMOS)

Color vs monochrome

CCD versus CMOS

CCD: charge coupled device

Electrons from photodetector (diode)charge a capacitorCharges are shifted out towards the output amplifier row by row, pixel by pixel

Shift registerOutputamplifier

Advantage: low noise

Backdraws:Expensive: not CMOS compatibleHigh powerconsumption

CCD versus CMOS

CMOS: Complementary Metal Oxide Semiconductor

1) Electrons from photodetector (diode)charge a capacitor2) rows of charges are selected by switchingon/off CMOS transistors

•Parallel processing: fast readout•Cheap; standard CMOS technology•Low power•Traditionally noisier than CCD but CMOSis catching up

Performance factors (part1)

Quantum efficiency (QE)

Dark counts

•Wiring and circuitry around/above everypixel's photodiode decreases fill factorand therefore the QE as well•Workaround: etch the backside of thesensor and illuminate from the back('back illuminated CCD/ CMOS')→already seen in 200€ photocameras!

•Spontaneous emission of electronsfrom photodiode•Constant offset in signal due to darkcounts can be corrected but sqrt(dark counts) = shot noise!•Strong dependance on temperature•Liquid nitrogen models (LN): down to-120 degC•Peltier cooled models (TE): down to -70 degC•Backdraw: cooling might also reducethe QE

Performance factors (part2)

Readout noise

•After illumination, charges are read out (charge transport, amplifier, ADC)•This adds noise to the signal•Solution1: longer illumination times•Solution2: slow readout (slow ADC) → some camera's have selectable ADC speed•Solution3: ICCD, EMCCD, sCMOS

Andor Ikon-L 936 TE cooled CCDADC speed [Mhz] Readout noise [e-/pix]

0.05 2.91 7.03 11.75 31.5

Advanced techniques for high speed & low light levels: ICCD, EMCCD, sCMOS

Intensified CCD (ICCD)Intensifier in front of CCD amplifies optical signal* low QE (up to 40% for gen4 intensifier)* ns gating possible* intensifier increases shotnoise by a factor sqrt(2)

Electron multiplier CCD (EMCCD)Electrons out of CCD get multiplied before ADC* high QE (up to 90% for back illuminated CCD)* EM increases shotnoise by a factor sqrt(2)

Scientific CMOS (sCMOS)improved CMOS sensor* high QE ~70%* very high speed ~500Mpix/s* low readout noise 1.2 e-/pix* low dark current 0.2 e-/pix/s

1D cameras

Linescan CCD* High frame (line) rates : tens of kHz* low noise

NMOS Linear Image Sensor* rectangular pixels: 25um wide, 2.5mm high → non critical alignment, catch all the light* high dynamic range due to large quantum well → measure small fluctuation on large background

Homebuilt NMOS LIS cameras:→ with spectrograph: full spectrum per lasershot 1) Push setup 1 kHz 2) Shove setup 5 kHz

Time of flight camera (TOF)

* measures intensity and time delay of reflections* modulated light source LED @ 20 MHz* CMOS sensor* 'dual phase lockin amplifier' per pixel

TOF camera LED 20 MHz

Grayscale intensity Colorscale TOF

Streak Camera

Horizontal direction: intensity vs position (spectrum)Vertical direction: arrival time with resolution down to 100fs