THORLABS PDA25K Operating Manual page 2

0dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset:
10dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset:
20dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset:
30dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset:
Note 1: The PDA25K has a 50 series terminator resistor (i.e. in series with amplifier output). This forms a voltage divider with
any load impedance (e.g. 50 load divides signal in half).
2: All measurements performed with a 50 load unless stated otherwise.
3: Detector Package / Power Supply.
4: Although the power supply is rated for 31W the PDA25K actual usage is <5W over the full operating range.
Setup

Unpack the optical head, install a Thorlabs TR-series ½" diameter post into one of the #8-32 (M4 on -EC
version) tapped holes, located on the bottom and side of the head, and mount into a PH-series post holder.

Connect the power supply 3-pin plug into the power receptacle on the PDA25K.

Plug the power supply into a 50 – 60 Hz, 100 – 120 VAC outlet (220 – 240 VAC for -EC version).

Attach a 50 coax cable (i.e. RG-58U) to the output of the PDA. When running cable lengths longer than 12" we
recommend terminating the opposite end of the coax with a 50 resistor (Thorlabs p/n T4119) for maximum
performance. Connect the remaining end to a measurement device such as an oscilloscope or high speed DAQ
card. Caution: Many high speed oscilloscopes have input impedances of 50. In this case, do not install a 50
terminator. The combined loads will equal 25 which could allow ~135 mA of output current. This will damage
the output driver of the PDA25K.

Power the PDA25K on using the power switch located on the top side of the unit.

Install any desired filters, optics, adapters, or fiber adapters to the input aperture. Caution: The PDA25K was
designed to allow maximum accessibility to the photodetector by having the front surface of the diode flush with
the outside of the PDA housing. When using fiber adapters, make sure that the fiber ferrule does not crash into
the detector. Failure to do so may cause damage to the diode and / or the fiber. An easy way to accomplish this
is to install a SM1RR retaining ring (included with the PDA36A) inside the 1" threaded coupler before installing
the fiber adapter.

Apply a light source to the detector. Adjust the gain to the desired setting.
13050-S01 Rev H 2/10/2012
Performance Specifications
3
1.51 x 10 V/A ±2%
3
0.75 x 10 V/A ±2%
7.5 MHz
350 V
-10
3 x 10 W/Hz
5 mV (10 mV max)
3
4.75 x 10 V/A ±2%
3
2.38 x 10 V/A ±2%
3.3 MHz
290 V
-10
1 x 10 W/Hz
6 mV (12 mV max)
4
1.5 x 10 V/A ±2%
4
0.75 x 10 V/A ±2%
1.0 MHz
260 V
-11
4 x 10 W/Hz
6 mV (15 mV max)
4
4.75 x 10 V/A ±2%
4
2.38 x 10 V/A ±2%
300 kHz
245 V
-11
2 x 10 W/Hz
8 mV (15 mV max)
40dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset:
50dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset:
60dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset:
70dB Setting
1
Gain (Hi-Z):
(50Ω):
Bandwidth:
Noise (RMS):
NEP (@ 
):
p
Offset: 40 mV (200 mV max)
5
1.51 x 10 V/A ±2%
5
0.75 x 10 V/A ±2%
100 kHz
325 V
-11
1.6 x 10 W/Hz
10 mV (20 mV max)
5
4.75 x 10 V/A ±2%
5
2.38 x 10 V/A ±2%
32 kHz
500 V
-11
1.7 x 10 W/Hz
15 mV (40 mV max)
6
1.5 x 10 V/A ±5%
6
0.75 x 10 V/A ±5%
11 kHz
675 V
-11
1 x 10 W/Hz
20 mV (75 mV max)
6
4.75 x 10 V/A ±5%
6
2.38 x 10 V/A ±5%
3.3 kHz
900 V
-12
7 x 10 W/Hz
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