MRC XYPSD Real Time Laser Beam Position Detector User Manual
- June 9, 2024
- MRC
Table of Contents
MRC XYPSD Real Time Laser Beam Position Detector
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:
System 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
Specification
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
- Dimensions: 11.9 x 11.9 mm2 (can be adapted on laser power and wavelength)
- 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)
Housing
Displays
The XYPSD is equipped with a LED line for the intensity level and a LED cross
for position display.
Intensity 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 readout electronics in the
XYPSD is equipped with an intensity scaling for a compensation by dividing the
and y-signal by the I-signal. In that way the measurement is independent of
the actual laser power.
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 6 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.
LED cross for position display
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.
Figure 3: Examples 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.
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.
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.
Intensity 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.
With the upper push button the intensity level can be increased stepwise, while the lower push button decreases the level accordingly. There are 64 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.
Safety
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.
Contact
MRC Systems GmbH Hans-Bunte-Strasse 10
D-69123 Heidelberg Germany Phone: +49-6221/13803-00 Fax: +49-6221/13803-01
Web: www.mrc-systems.de E-mail: info@mrc-
systems.de