MRC XYPSD User manual

Real-time Laser Beam Position Detector
„XYPSD”
User Manual
XY-PSD – User Manual Version 4 – 28.09.2015 page 1 of

1. Introduction
The XYPSD is a position sensing detector with readout electronics and outputs for x and y position. It is
working on the lateral effect photodiode principle. The position of the laser beam on the diode can be
displayed without relevant time delay on a scope. Thus, even fastest fluctuations can be resolved. This is
the main difference between this detector and beam profilers that can not measure a position in real-time
and integrate over several pulses or fast photodiodes that can not measure any position. In addition to the
x- and y-position there is also an output for the measured intensity level on the detector.
The XYPSD displays the information about the intensity level and the position directly on the housing.
For this purpose an LED line and an LED cross are used, respectively.
The following figure shows the backside with the displays:
2. S stem components
A typical delivery includes the following components:
•Detector with integrated lateral effect diode, readout electronics, and optical filter
•3 measurement cables MCX↔BNC (19 cm)
•Wall power supply 12 V
•User manual
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Figure 1: XYPSD with displays for intensity level
and position
LED cross for
position display
LED line for
intensity level
display
Intensity
output
x and y
position output
Power supply
(12V)

3. Specification
3.1 Technical data
Opto-electronic properties
Bandwidth up to 100 kHz
(The bandwidth can be optimized to a customized value in our
lab. For the resolution of single pulses one should choose:
bandwidth ≥ laser repetition rate)
Sensor area 9.0 x 9.0 mm2
Typical spatial resolution < 1.5 µm (depending on the beam diameter and profile)
Spectral sensitivity VIS version: 320 – 1100 nm
Sensitivity / position vs. voltage approx. 1.2 mV / µm
Mechanical dimensions
Housing 49 x 40 x 23.9 m3
Thread M4
Optical filter (can be adapted on laser power and wavelength)
Dimensions 11.9 x 11.9 mm2
Fastening screws M2
Connectors
x, y, I / Connectors analog x, y: ± 5 V / I: 0 – 7 V / MCX Coax connectors,
standard oscilloscope input (high impedance, ≥ 4.7 kOhm)
Power supply / Connector 12 V, < 200 mA / DC pin-and-socket connector 1.1 mm
Measurement cables MCX↔BNC, standard length1.8 m (other lenghts on request)
3.2 Housing
Figure 2: Housing
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3.3 Displa s
The XYPSD is equipped with a LED line for the intensity level and a LED cross for position display.
3.4 Intensit scaling
The raw signals of the x- and y- position are nearly proportional to the laser intensity and increase with
higher intensities. To eliminate the dependency of the position signals with the laser intensity the read-
out electronics in the XYPSD is equipped with an intensity scaling for a compensation by dividing the x-
and y-signal by the I-signal. In that way the measurement is independent of the actual laser power.
4. Installation and operation
The intensity on the XYPSD should be chosen with values that lead to illumination of at least 3 and not
more than 9 LEDs. This corresponds to voltages of 0.5 to V. You can achieve the correct values by
means of appropriate filters in front of the sensor or by the electronic adjustment as described in section
4.4.. The XYPSD should be aligned to the laser beam in that position where it hits the center of the PSD.
In this case you can detect the widest range of position changes.
4.1 LED cross for position displa
If the laser beam hits the center of the PSD only the green LED of the position display will shine. In
other cases also yellow and red LEDs will shine according to the examples in figure 4.
a) c)
b) d)
Figure 3: E amples for laser beams hitting the PSD (orange spots) and the corresponding position display. The left
pictures are shown from the direction of the position display, i.e. from the rear side of the housing.
If only green and yellow LEDs shine the beam is in a range where a direct correlation between measured
signal and position exists (see section 4.2 “Calibration”). If the red LED shines too, the laser beam is
close to the border of the sensor.
You can get a comparable information regarding the position by using a scope. In order to get this you
can connect the x and y signals to two channels of the scope and choose the scope's x-y-display mode.
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4.2 Calibration
The absolute beam position in x and y depends on intrinsic non-linearities of the PSD. Furthermore there
is a slight influence of the laser beam diameter and the intensity. For high accuracy applications we
recommend to perform a calibration of the detector for a linearization of the position signal by moving
the PSD relative to the laser beam by means of a micro-positioner and measuring the voltages for
different positions.
4.3 Sham fluctuations at low intensities
Depending on the laser beam diameter and the chosen bandwidth sham fluctuations of the beam position
can occur at low intensities although the beam position might be stable. These fluctuations are due to
small intensity deviations of the laser and the noise of the diodes. Please take care for an appropriate
intensity on the PSD.
If the intensity on the PSD is too small, the central green LED will not shine.
4.4 Intensit adjustment
To make sure that the detector operates in an appropriate intensity range, the power level can be adjusted
by tuning the digital potentiometer for intensity variation (see figure 4). For that purpose adjust the laser
beam onto the detector and set the intensity amplification with the digital potentiometer. Please choose
the amplification in that way that at least 3 but not more than 9 elements of the power level display are
shining. The setting can be done by slightly pressing the push-buttons with the metal pin which is
included in the delivery. For each setting direction there is a separate push button.
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Figure 4: PSD-detector. The arrows show
the push buttons of the digital potentiometers
for the intensity settings (under use of the
included metal pin).

With the upper push button the intensity level can be increased stepwise, while the lower push button
decreases the level accordingly. There are 4 steps between the highest and the lowest level. This
corresponds to a factor of 20 of the intensity-scaling.
If you do not find an appropriate adjustment you have to exchange the optical filters in front of the PSD.
If the required filters are not available please contact the manufacturer or distributor.
Notes:
•In a standard delivery we integrate two optical filters in front of the sensor area. These are filte rs
with a high and a low density for coarse and fine adjustment, respectively. Usually the filter
which is the first to be reached is the low density one.
•Please be aware that the sensor area is quite sensitive. If you want to clean it you should do this
carefully with a wet lint-free cotton swab.
If you want to exchange the filters you can detach the plastic screws which fix the filters in the housing.
With a tilt of the detector housing it should be possible to release the filters. Once you put in new filters
please be careful so that you do not damage the detector. Finally you can fix them with the plastic
screws.
5. Safet
The detector has left our factory in a faultless state. Please only store and operate it in dry environments
in order to maintain this state.
The device was designed and manufactured according to the requirements of the European
EMC Directive 2014/30/EU.
Label
6. Contact
MRC Systems GmbH
Hans-Bunte-Strasse 10
D- 9123 Heidelberg
Germany
Phone: [phone]
Fax: [phone]
Web: www.mrc-systems.de
E-mail: [e-mail]
XY-PSD – User Manual Version 4 – 28.09.2015 page of
Supply: 12VDC 200mA
MRC Systems GmbH
SN: 100208DBAxxx
Mo el: PSD-VIS/UV xxHz