Cameras for scientific experiments A brave attempt to give an overview of the different types and their pros & cons Grouptalk Optical Sciences, may 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 Shift register Output amplifier Advantage: low noise Backdraws: Expensive: not CMOS compatible High powerconsumption

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) Dark counts 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! 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]

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 setup1 kHz 2) Shove setup5 kHz

Time of flight camera (TOF) * measures intensity and time delay of reflections * modulated light source 20 MHz * CMOS sensor * 'dual phase lockin amplifier' per pixel TOF cameraLED 20 MHz Grayscale intensityColorscale TOF

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