Cameras for scientific experiments

A brave attempt to give an overview of the different types and their pros & cons Grouptalk Optical Sciences, may 8 2012 Jeroen Korterik

Introduction

 Lots of different types of cameras  Each working principle has it's own strong and weak points  Which 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 capacitor Charges are shifted out towards the output amplifier row by row, pixel by pixel Advantage: low noise Backdraws: Expensive: not CMOS compatible High powerconsumption Shift register Output amplifier

CCD versus CMOS

CMOS: Complementary Metal Oxide Semiconductor 1) Electrons from photodetector (diode) charge a capacitor 2) rows of charges are selected by switching on/off CMOS transistors • Parallel processing: fast readout • Cheap; standard CMOS technology • Low power • Traditionally noisier than CCD but CMOS is catching up

Performance factors

(part1)

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

Dark counts • Spontaneous emission of electrons from photodiode • Constant offset in signal due to dark counts 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 reduce the 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 CCD ADC speed [Mhz] Readout noise [e /pix] 0.05

1 3 5 2.9

7.0

11.7

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