Talk ICCDs

Welcome
Time-Resolved Spectroscopy
and Imaging with ICCD Detectors
Olaf Koschützke

Overview
ICCD and image intensifier design
Parameters and specifications
Applications

Why ICCDs?
Image intensifier acts as ultra-fast shutter
Gate widths (= temporal resolution)
as short as 2 ns
Single photon detection

ICCD Design

MCP lmage Intensifier Design
Ultra-fast optical shutter:
ns gating, 50 kHz gate
repetition rates
High vacuum tube
Input window: quartz,
glass, MgF 2, fiber optic
Photocathode
photons → electrons
(photoelectric effect)
-200 V (on), +50 V (off)

MCP lmage Intensifier Design
Micro Channel Plate (MCP):
multiplying of electrons
input 0 V
output +400 V ... +1,000 V
Phosphor screen:
electrons → photons (fluorescence)
+ 6,000 V
Output window:
fiber optic (standard)
glass

MCP (Micro Channel Plate)
Electroding
(on each face)
Lead Silicate
Glass Wafer
Input Events
Channels
(105 - 107 / cm2 )
Output Electrons
Channel diameter: 6 µm (18 mm intensifiers) - 10 µm
(25 mm intensifiers)
VB
-
+

MCP (Micro Channel Plate)
Gain: 1 ... 10,000 el/el (software gain control
0 - 255)
Gain (el/el)
10.000
1.000
100
10
1
400 500 600 700 800 900 1000
MCP Voltage (V)

ICCD Specifications
Image intensifier generations
Quantum efficiency of photocathodes
Effective quantum efficiency of image intensifiers
Gating & irising
Phosphor
EBI (Equivalent Background Illumination)

Intensifier Generations
1. Generation
Image intensifiers without MCP
2. Generation
MCP image intensifiers with multi-alkali photocathodes
3. Generation (Filmed)
GaAs photocathodes on glass input windows
Susceptible to ion damage
⇒ ion barrier film (Al 2O 3) on MCP input
⇒ 1) reduces effective QE by ≈ 1/4
2) 800 V photocathode voltage (slower gating)

Intensifier Generations
3. Generation (Filmless)
Gen III image intensifiers without ion barrier film
⇒ improved quantum efficiency up to 50%
Large reduction of poison gases
Lifetime comparable to any filmed Gen III or Gen II
ANDOR was the first to offer 16 bit ICCDs with filmless
Gen III image intensifiers

Quantum Efficiency
Input Windows
MgF 2 (120 nm)
Quartz (180 nm)
Glass (270 nm)
Fiber optic (380 nm)

Quantum Efficiency Gen II

Quantum Efficiency Gen II

Quantum Efficiency
Filmless Gen III

Quantum Efficiency
Filmless Gen III
Nd:YAG: 1064 nm

Quantum Efficiency
Filmless Gen III
BGT: VIH photocathode + UV coating of
fiber optic input window of image intensifier

Effective Quantum Efficiency
of Image Intensifiers
Noise Factor
N f : = SNR in / SNR out
N f > 1 for all ICCDs
Loss mechanisms and
electron multiplication
statistics
Gen II + III: 25% of
photoelectrons lost in
MCP (75% active area)
Detector Noise Factor
Gen II 1.6
Gen III filmless 1.6
Gen III filmed 2.0
CCD 1
EMCCD 1.3

Effective Quantum Efficiency
of Image Intensifers
Filmed Gen III:
additional ≈ 25% photoelectrons
lost in ion barrier film
Effective QE : = Photocathode QE / Noise Factor 2
Very important for fair comparison with CCD and
EMCCD sensitivity!

Gating
Requirement for ns-Gating
High conductivity of photocathode or
Nickel underlayer or
Metal grid:
Advanced Grid
Technology AGT TM
⇒ fast gating,
higher QE

Gating
18 mm Image Intensifiers
Ultra-fast: 2 ns - 5 ns
Fast: 5 ns - 10 ns
Slow (without Nickel underlay): only 50 ns – 100 ns but
up to 40% higher QE
25 mm Image Intensifiers
Ultra-fast: 3 ns
Fast: 7 ns

Irising
Irising
Delay between center
and edge
Irising < 1/3 of specified
minimum optical gate
Measured for each
ICCD

Phosphors
Phosphors are matched to CCD quantum
efficiency
For fast readout, a fast phosphor is required
Phosphor decays are not a simple exponential
Phosphor Decay Time (10%) Relative Light Output
P43 2 ms 100%
P46 200 ns 20%

Resolution
Resolution of Image Intensifers
Depending on channel diameter, MCP design,
electrical field strength, phosphor grain size
18 mm: Gen II 25 µm, Gen III 30 µm
25 mm: 35 µm
Resolution of ICCD Detectors
Depending on intensifier, coupling, CCD pixel size
1.5 to 2 times effective CCD pixel size ⇒ 20 µm – 50 µm
Reduced in lens coupled ICCD

EBI
EBI (Equivalent Background Illumination):
input illuminance required to produce the same output
brightness as thermal electrons
Output Brightness B
2 B0
Background Brightness B0
EBI
B = G I + B0
Input Illumination I

EBI
Dark current of photocathodes
EBI sets lower detection limit
EBI = 0.02 ... 0.1 photoelectrons/pixel/s
Higher for red sensitive photocathodes (lower work
functions)
EBI can be minimized by:
- storing intensifier in darkness (> 1 h)
- cooling the photocathode
(not necessary in a gated application)

EBI
Negligible in gated applications
1 s
10 ms
100 ms
1 ms

Coupling
2 Methods
1) Fiber Optic Coupling
High efficiency (≈ 30%)
⇒ lower gain ⇒ better dynamic range (> 15 bit)

Coupling
Compact
Low optical distortions
2) Lens Coupling
Flexible (convert ICCD to CCD)
No “chicken wire” effect
Low efficiency ⇒ reduced dynamic range
Larger
Optical distortions

Features
Digital Delay Generator (DDG TM ) built into head
Lowest total propagation delay available (35 ns)
Optical gate width as short as 2 ns
Gate repetition rate up to 50 kHz
Wireless remote control
Ultra-compact design

Digital Delay Generator
Built directly into the camera head
Micro components reduce both total propagation delay
and signal jitter (35 ns ± 2 ns)
Programmable gate pulse delay, width, and TTL trigger
output:
0 ns - 25 s
Resolution:
25 ps (gate pulse delay and width)
16 ns (TTL trigger output)

Fine-tune experiment from any location
around optics table (up to a distance of 12 m)
Change remotely:
- Gate pulse width
- Gate pulse delay
- TTL output delay
- MCP gain
1 4
Operate Windows as with
2 3
an ordinary mouse

Ultra-Compact Design
Only a single PCI controller card,
does not require an external controller box
Design eliminates the need for additional bulky
apparatus:
- Saves space
- Enhances performance
- Easy interface to control complete system
Optional power supply for extra cooling to as low as
–15° at 20°C air temperature and –35°C with 10°C water
Optional input/output box with BNC connectors

Applications
Laser Induced Fluorescence (LIF)
Time Resolved Fluorescence (TRF)
Time Resolved Transient Absorption
Time Resolved Resonance Raman
Spectroscopy (TR3)
UV Resonance Raman Spectroscopy
Single Photon Spectroscopy
Single Molecule Detection
Combustion
Butane flame

Applications
Laser Induced Breakdown Spectroscopy
(LIBS)

Applications
1 µs
typical spectrum from
solution of potassium
pertechnetate dissolved in
0.1 mol/l nitric acid
5 µs
atomic emission lines
start to become visible through
the broadened ionic lines

Applications
10 µs
atomic spectral lines dominate,
clear identification of atomic
species is possible

Applications
Laser Induced Plasma Spectroscopy (LIPS)
Pulsed Laser Deposition (PLD)
Laser Ablation

Applications
1 µs
2 µs
3 µs
O 2 (0,24 mbar) Vacuum
20 ns gate width

Applications
Laser Induced Fluorescence (LIF)