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Laser Beam Analysis |
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Topics:
Diodelaser
HeNe-Laser
Gaussian Beams
Beam Intensity Distribution
Beam Expansion
Beam Shaping
Computerised Recording |
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In almost all cases a laser
application requires a laser beam with low divergence emitted in
the so called fundamental Gaussian mode (TEM00).
This is not always guaranteed for each laser and especially for
high power laser systems because the emission may be multimode.
Considering the laser diodes, which possess even elliptical beam
shapes, it is important to have a tool for analysing the
structure of the beam shape for different types of laser in
order to be sure to fulfil the required demands for a particular
application.
Especially for laser printing, material processing, fibre optics
coupling, optical data storage and laser pumping the spatial
intensity distribution of the laser used must be well defined.
The smallest obtainable spot size diameter of a ;aser beam
depends besides its wave-length on the purity of the spatial
mode spectra of the laser. In case of the laser printer the
desired resolution will not be obtained if the laser emits
additional transverse modes.
If more transverse modes exists, the beam shape is no longer
circular and depends on the number of higher transverse modes
causing a variety of different patterns to occur.
This also means that the intensity distribution is different and
the application will not fulfil the desired performance. Within
this project, a laser beam profiler based on the knife edge
method is used to measure the spatial intensity distribution. As
probe lasers a HeNe-laser and a diode-laser are used.
The HeNe-laser emits a pure Gaussian TEM00 whereas the
diode-laser emits an elliptical beam. By means of different
optical elements (beam expander and cylindrical lenses), the
influence on the intensity distribution will be measured and
discussed. The collection of the data is performed automatically
by a PC with special software. For this reason an extra board is
built into the PC which controls the beam analyser, collects and
stores the data either on floppy or the hard disk of the PC.
Based on the recorded data a 2D graphical presentation of the
intensity profile is displayed on the monitor or printed out on
an ink-jet colour printer.
Principle of operation
A precise knife edge is moved through the beam path of the
Laser. As the blade moves across the beam, light is blocked from
reaching the photo detector and the measured signal decreases to
zero. The signal is then differentiated to obtain the beam
profile. When the path to the detector is fully opened the
entire intensity of the beam is measured and used as calibration
value. To increase the resolution the number of knife edges is
increased whereby the orientation of each blade is different. In
this set-up a number of seven knife edges is used in order to
increase the resolution as well as to measure spatial intensity
distributions which are significantly different from a Gaussian
one.
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Required Equipment
| Cat. No. |
Qty. |
Description |
Illustration |
02.0500
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2 |
Profile
rail OCM 650, 500 mm
The main components of the experimental systems are the
optical rails OCM 650. They are manufactured
distortion-free and are of thermally stabilized
aluminium. The surface is electro-polished and black
anodized. Because of the precise manufacturing, the
smoothness deviation is less than 25 µm/m and the
deviation of the symmetry axis of the rail is less than
10 µm/m, thus maintaining the optical axis during
displacement of the carrier.
The rail has a dovetail like profile. Gear racks can be
inserted and fixed into the slots.
|
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02.2063
02.2126
02.2132 |
1
3
2 |
Mounting
plate OCM 650, RMS threading
Mounting
plate OCM 650 for click 25
Mounting
plate OCM 650 for click 30
Mounting plates are used to hold optical mounts. A
characteristic feature of the mounting plates is the
“click” mechanism of the inserts based on spring loaded
spheres. Snapping in the groove of the inserted click
mount, the optical element is kept in an exact position.
On the other hand, the system allows a quick and easy
change of the mounted inserts.
The mounting plates are made out of special anodized
aluminum. Mounted onto the carrier 20 mm, the mounting
plates can be placed onto an optical rail.
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02.3022
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1 |
XY-adjustment holder OCM 650 with 25 mm mount and
carrier 20 mm
This frequently needed component is ideal for the fine
adjustment of lenses, microscope objectives, diode
laser, etc. with respect to the optical axis of the rail
set-up. The displacement area is 5x5 mm. Different
mounts can be attached to the adjustment holder. This
model provides a holder for 25 mm cylindrical
components.
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04.0010 |
1 |
Microscope
objective x 10 with RMS thread
The figure on the right shows the microscope objective
screwed into an adjustment holder, however, it comes
without the holder. The objective has a magnification of
10 and a numerical aperture of 0.3 and it is commonly
used to collimate the divergent light emitted by laser
diodes.
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04.0032 |
1 |
Beam
expander 8x mounted in click mount 25
The beam is expanded eightfold with this telescope and
serves the purpose of reducing the divergence, thus
resulting in more plain wave fronts. The telescope is
adjustable and the divergence of the expanded beam can
therefore be changed to produce, for example, curved
wave fronts. The beam expander is also mounted into a
click 25 mm mount and can be used in connection with the
mounting plate (02.2126).
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04.0080
04.0082 |
1
1 |
Cylindrical lens f=25.4 mm in click 25
Cylindrical lens f=80 mm in click 25
Different glass lenses are mounted onto a special
anodized aluminum click mount 25 mm by two threaded
mounting rings to be used in connection with a mounting
plate (02.2126).
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05.0214 |
1 |
DIMO diode laser module 820
The diode laser module contain different laser diodes
with various output power and wavelength. The wavelength
is subject to certain deviations within the range as
given in the table below. The integrated Peltier element
allows a temperature control in the range of 15 to 40° C
by means of the control unit LDC-01.
Each laser diode is firmly connected to its own
controller.
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05.0302 |
1 |
HeNe-Pilot
laser OCM 650-30
The laser consists of a well to its housing centrally
aligned HeNe laser. The HeNe laser is a two-mode laser
with a frequency difference of 900 MHz between both
orthogonal modes, which are randomly polarised. This
means that, although both modes are linearly polarised,
the polarisation depends on the tube geometry. The beam
diameter is 0.5 mm at the exit and the divergence is 1.5
mrad. The output power is 2.5 mW and belongs to the
laser safety class 3b.
The diameter of the housing is 30 mm and provides
grooves to make use of the click facilities of the
mounting plates with click mounts. The laser comes with
its power supply HVPS-01, however, the shown mounting
plates ( 2 x 02.0030) must be ordered separately.
|
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07.0200 |
1 |
LDC01
Laserdiode controller
The controller unit LDC01 provides reliable and save
operation of the expensive laserdiode. It contains the
control circuits for power monitoring, temperature
control and current setting. The values for the
temperature and the diode current can be read from two
large-format LED displays on the front panel of the
unit. The desired values for the temperature and current
can be set with precision multi-turn potentiometers. At
BNC sockets on the rear of the device, analogue output
signals of the temperature and current as well as the
synchronising signal of the internal modulator and the
photodiode amplifier of the external photo detector are
provided. Via a BNC socket, an external modulator can be
connected. In addition the controller contains an
internal modulator for modulating the laser diode output
power for investigation of the dynamic behaviour of the
pumped laser as spiking, measuring of lifetimes, etc.
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09.0292 |
1 |
„Rotating knife edge“ detection head incl. holder, PC
board and software
This module includes the detector head, computer plug-in
card, control software and 10 % and 0.5 % transmission
optical filter. The wavelength range is 400 to 1100 nm
and the measurable beam size range (1/e2)
is 30 µm up to 9 mm. The unit is mounted on a carrier in
such a way that the entrance is in line with the optical
axis of the rail system.
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10.0290
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1 |
EXP 29 manual |
No
illustration |
Required Options
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19.1000
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1 |
IBM compatible PC
including VGA monitor and keyboard
For some experiments a PC is a must whereas others
can operate without one. However, some nice features may
be not accessible. Due to the steadily changing models
and operating systems a picture is not given. Please ask
for current models.
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No
illustration |
Options
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09.0299
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1 |
Set of spare parts |
No
illustration |
19.1100
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1 |
Ink jet color printer
600x600 dpi
For the print-out of measurement values and graphs,
a printer with at least the given resolution should be
present. Also here due to the steadily changing models a
picture is not given. Please as
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No
illustration |
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