# C

### C-band, L-band

Wavelength band classification used for optical communication. The spectral range for C-band and L-band spans from 1530 nm to 1625 nm. Other wavelength band names depending on the spectral range are used as shown below.

• L-band: 1565 nm to 1625 nm
• C-band: 1530 nm to 1565 nm
• S-band: 1460 nm to 1530 nm
• E-band: 1360 nm to 1460 nm
• O-band: 1260 nm to 1360 nm

### Cathode blue sensitivity, Blue sensitivity index

Blue sensitivity index is the photoelectric current generated from the photocathode when a blue filter (CS 5-58) is interposed in the same measurement system as used to measure cathode luminous sensitivity. Blue sensitivity index is an essential parameter in scintillation counting because the NaI(Tl) scintillations frequently used in scintillation counting, produce light emissions in the blue.

### Cathode luminous sensitivity

Cathode luminous sensitivity is the photoelectric current from the photocathode per incident light flux (10-5 to 10-2 lumens) from a tungsten filament lamp operated at a distribution temperature of 2856K. Cathode and anode luminous sensitivity are particularly useful when comparing tubes having the same or similar spectral response.
The cathode luminous sensitivity is expressed in uA/lm (microamperes per lumen). Note that the lumen is a unit used for luminous flux in the visible region and therefore these values may be meaningless for tubes that are sensitive beyond the visible light region.

Radiant sensitivity is the photoelectric current from the photocathode, divided by the incident radiant power at a given wavelength, expressed in A/W (amperes per watt). Quantum efficiency (QE) is the number of photoelectrons emitted from the photocathode divided by the number of incident photons. Quantum efficiency is usually expressed as a percent. Quantum efficiency and radiant sensitivity have the relationship shown in the equation at a given wavelength.$$QE=\biggl( \frac{S \cdot 1240}{\lambda}\biggr)\cdot 100\ [％]$$ S : Photosensitivity (A/W)
λ : Wavelength (nm)

### Cathode type

Cathode luminous sensitivity is the photoelectric current from the photocathode per incident light flux (10-5 to 10-2 lumens) from a tungsten filament lamp operated at a distribution temperature of 2856K. Cathode and anode luminous sensitivity are particularly useful when comparing tubes having the same or similar spectral response.
The cathode luminous sensitivity is expressed in uA/lm (microamperes per lumen). Note that the lumen is a unit used for luminous flux in the visible region and therefore these values may be meaningless for tubes that are sensitive beyond the visible light region.

### CDR (clock and data recovery)

A device for recovering a clock and data. Data output from a CDR is not exactly the same as the input data, and is synchronized with the timing of the recovered clock.

### CDS (correlated double sampling)

A signal processing method most commonly used for reducing readout noise in a CCD. The CCD signal output detected with an FDA contains kTC noise originating from the detection node capacitance. The kTC noise is also referred to as thermal noise and is always generated by reset operation in a charge-to-voltage converter device like a CCD. The kTC noise in the output can be reduced by using CDS which detects the difference in voltage levels before and after the signal charge flows in the detection node. CDS is also used to reduce noise in CMOS image sensors.

### Center limiting resolution

The limiting resolution shows the ability to delineate image detail. This is expressed as the maximum number of line-pairs per millimeter on the photocathode (1 line-pair = a pair of black and white lines) that can be discerned when a black-and-white stripe pattern is focused on the photocathode.

### Channel diameter - MCP

Diameter of the individual channels of an MCP. The MCP pore size and pitch limit the minimum spatial resolution available.

### Channel pitch

The center to center spacing between active elements such as the channels of an MCP or elements of a PMT or photodiode array. The MCP channel or pixel size and pitch limit the spatial resolution available.

### Compton scattering

The phenomenon in which X-rays and gamma rays, etc. are scattered and part of their energy is lost when they collide with particles (electrons, etc.). This phenomenon is known as indicating particle properties of X-rays, etc.

### Crosstalk

A phenomenon in which an electrical signal generated in an element by an incident light signal leaks out into adjacent elements. In an MPPC, a carrier excited in an APD pixel by an incident photon is multiplied in the avalanche process. During this process, photons different from the incident photon might be generated. If these photons are detected by other APD pixels, then the MPPC output will be higher than the number of photons that actually entered the MPPC. This phenomenon is thought to be one cause of crosstalk in the MPPC.

### Cutoff frequency (fc)

The frequency at which the output of a device decreases by 3 dB from the constant output at lower frequencies. The relation between the cutoff frequency (fc) and the rise time (tr) is approximately expressed by the equation.$$tr [s]=\frac{0.35}{fc}[Hz]$$