R12290U_15 Datasheet, PDF (2/4 Pages) Hamamatsu Corporation – ULTRA-FAST PHOTODETECTOR BIPLANAR PHOTOTUBES

ULTRA-FAST PHOTODETECTOR
BIPLANAR PHOTOTUBES R12290U SERIES, R1328 SERIES
CONSTRUCTION
Biplanar phototubes consists of a circular, plane, lightsensitive surface
called a photocathode and a mesh-type anode aligned in parallel to
each other. Figure 1 shows the schematic construction of biplanar
phototubes. The biplane configuration of the photocathode and anode
make it possible to generate high linear output current with subnano-
second response time.
As shown in Figure 1, a power supply capacitor Cb and a noninductive
load resistor RL are built into the housing.
Figure 1: Schematic Diagram
ANODE CATHODE
OUTPUT
CONNECTOR
LIGHT
Cb
RL
Cb: 300 pF
RL : 50 Ω (NONINDUCTIVE TYPE)
+HV
RESPONSE SPEED
If the interelectrode distance of a biplanar phototube is d [m], the ap-
plied voltage is E [V] and the electron transit time is τ [s], then the
pulse response rise time (10 % to 90 %) tr [s] is given by the following
expression and is inversely proportional to the square root of the ap-
plied voltage E.
τ=d
2
q
m
E
=3.37
×
10^-6
×
d _[s]
E
tr.=.0.8τ [s]
Where m and q are the electron mass and charge respectively.
Figure 2: Typical Rise time
1000
800
600
400
R12290U
200
R1328U
100
80
60
40
20
10
500
1000
2000
SUPPLY VOLTAGE (V)
3000
DARK CURRENT
Because biplanar phototubes are used at high voltages, the dark cur-
rent for such devices is normally large compared to conventional pho-
totubes, so dark current values similar to those of conventional photo-
tubes used with lower voltages cannot be expected.
In addition to thermal electrons from the photocathode and ion current,
dark currents are generated by leakage currents flowing through the
insulation material used, which dominates a large portion of the total.
This type of leakage currents flows even in moisture and other impuri-
ties on the surface of the insulation material. For this reason, it is rec-
ommended that not only care should be taken to the handling of such
devices during measurements but also consideration should be taken
to the storage of such devices in a desiccator.
SPECTRAL RESPONSE CHARACTERISTICS
Figure 3(a) shows typical spectral response characteristics of the
R12290U and R1328U series.
Figure 3(a): Typical Spectral Response Characteristics
of R12290U and R1328U
100
80 R12290U-52
60 _R1328U-52
40
R12290U-54
20 ^R1328U-54
R12290U-53
R1328U-53
10
8
6
4
2
1
0.8
0.6
0.4
R12290U-51
R1328U-51
0.2
0.1
100
200
300 400 500
700 1000 1200
WAVELENGTH (nm)
Figure 3(b): Typical Spectral Response Characteristics
of R12290U-55
10^-2
10^-3
10^-4
10^-5
ArF
(193)
10^-6
200
KrF
(248)
250
XeCl
(308)
300
350
WAVELENGTH (nm)
MAXIMUM OUTPUT CURRENT
Biplanar phototubes are used for an application in the observation of
laser pulses using an oscilloscope and the triggering of various cir-
cuits. This requires a high input signal level of more than 50 mV. How-
ever, because it is difficult to conduct electrical amplification of a signal
pulse width in the order 0.1 ns, an extremely high current linearity with
respect to high-power light is required. For instance, when the peak
photocathode current is 100 mA, a voltage of 2.5 V appears at the
both ends of the resistance (25 Ω that the photocathode sees), the
value of which is sufficient enough to drive the oscilloscope and its
trigger circuit directly.
Since biplanar phototubes are constructed with two electrodes of large
facing areas closely paralleled to each other and since they can with-
stand high voltages, they can fetch large currents. Factors which de-
termine the maximum rating of the peak photocathode current are: 1)
space charge, 2) photocathode surface saturation, 3) residual gas
pressure and 4) photocathode surface fatigue, among others. in con-
sideration of these factors, the Hamamatsu R12290U-51 to -54,
R12290U-55 and R1328U series are designed to operate up to 1 A, 2
A and 0.3 A respectively when light pulses of 50 ns width are used.