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Fabry Perot Resonator |
Topics:
Two Beam
Interface
Multiple Beam Interface
Finesse, Free Spectral Range
Visibility, Coherence Length
Ideal, Real Fabry Perot
Stability Criterion
Spectral Analysis |
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These
experiments show the properties of optical resonators especially
the „Fabry Perot“ resonator which is the most important of all
stable laser resonators.
The properties and behaviour of such a resonator will be
discussed and measured as well as the resonance properties, the
free spectral range and finesse.
The stability criteria of confocal, hemi spherical and plane
parallel resonator types are defined and measured. Finally, the
investigated resonator will be used as a spectrum analyser, a
so-called scanning Fabry Perot, and the mode spectra of the HeNe-laser
is measured.
The resonator mirrors are mounted in precision adjustment
holders. One mirror is mounted on a piezoelectric translator (PZT)
which is controlled in amplitude and frequency by means of a
high voltage controller. The beam of the provided HeNe-Laser can
be expanded and directed into the resonator.
One mirror adjustment holder is mounted on a special carrier for
fine linear movement, so that the distance of the resonator
mirrors can be varied in order to investigate the stability
criteria with different types of mirrors.
Scanning the length of the resonator by means of the PZT over
some resonances, the finesse or the quality factor is measured.
The signal of the photodiode used and a signal which is
proportional to the PZT scanning amplitude are displayed on an
oscilloscope showing the Airy function for some resonances.
By using the known free spectral range of the Fabry Perot
resonator, the mode spectra of the HeNe-laser can be measured
and interpreted. Some parts of this experiment can also be used
in connection with the experimental HeNe-laser to demonstrate
the single mode operation when an etalon is used inside of its
resonator. By tuning it, the gain profile of the HeNe-Laser can
be measured.
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Examples of investigation
and measurement
Looking for the confocal case
By using the integrated gear and pinion drive of the mirror
adjustment holder provided with the Piezo element, the length of
the resonator can be altered in a precise way.
Once the confocal case has nearly been obtained, the amplitude
of the interferogram increases significantly. Subsequently the
measurement of the most essential parameters of the Fabry Perot
resonator can begin.
Measurement of the finesse
By suitable choice of the amplitude of the Piezo voltage and of
the time base of the oscilloscope, one gets the graphical
representation as shown on the left. It permits conclusions of
the finesse of the resonator. But special attention has to be
paid to the fact that the value of the finesse may deviate
appreciably from the theoretical value due to the mirror‘s
reflectivity. Here the discussion of the real finesse has to
follow.
Free spectral range
The probe laser emits two orthogonally polarised modes. When the
amplitude of the Piezo voltage is adjusted in such a way that at
least two orders of the resonator are covered, one gets a
graphical representation on the oscilloscope as shown on the
left side. The spacing of the orders allows for the
determination of the free spectral range provided that the
distance of the laser mirrors is known.
The free spectral range can be measured now for different
distances of the mirror.
Measurement of the mode spacing
When the free spectral range is known, the spectral mode
distance of the HeNe-laser can be determined. It becomes
apparent that the Fabry Perot resonator is a suitable instrument
for monitoring the modes of a laser. Discussions come up if the
represented line width is the line width of the laser or of the
Fabry Perot resonator. The representation of the modes of a
laser is an eminent result of this experiment.
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Required Equipment
| Cat. No. |
Qty. |
Description |
Illustration |
02.0504 |
1 |
Profile
rail OCM 650
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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02.2126 |
3 |
Mounting
plate click 25, incl. carrier
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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02.2132 |
2 |
Mounting
plate click 30, incl. carrier
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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02.5406 |
1 |
Mirror adjustment holder
left
Same as 02.5404, however mounted as
„left“ version, that means the mirror is opposite to the
optical beam which is considered to travel from left to
right. A combination of a right and left versions is
always used to set-up an optical resonator, where the
mirrors are oriented face to face.
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04.0020 |
1 |
Achromat
f=20 mounted in click 25 mount
A high performance achromat with a focal length of 20 mm
is fixed inside the 25 mm click mount. The free opening
is 8 mm.
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04.0050 |
1 |
Biconcave lens f=60 mm in click 25 mount
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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04.0052 |
1 |
Biconcave lens f=-10 mm in click 25 mount
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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04.0306 |
1 |
Optic
cleaning set
Especially for optics used in connection with laser
applications, cleaning the optic surfaces is a must for
satisfying operation of the laser. For this purpose soft
cleaning tissues wetted with pure aceton are used. To
hold the folded tissues clamp pliers are provided. To
store the leaning liquid, a bottle with dispenser top is
provided. However, due to drug administration laws this
bottle comes empty and the required aceton must be
provided locally.
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04.0402
04.0404
04.0406 |
1
1
1 |
Laser
mirror, flat, T4%@ 632 nm
Laser
mirror, R=75, T4%@ 632 nm
Laser
mirror, R=100, T4%@ 632 nm
The laser mirror holder LSF 650 is designed to
accommodate sensitive Laser mirrors with a diameter of
1/2” (12.7 mm).
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04.0480
04.0482
04.0484 |
1
1
1 |
Laser
mirror with piezo element mount, flat, T4% @ 632 nm
Laser
mirror with piezo element mount, R=75, T4% @ 632 nm
Laser
mirror with piezo element mount, R=100, T4% @ 632 nm
To attach the mirror to a piezo electric element, it is
mounted into a holder which fits to the thread of the
piezo element. By means of a threaded ring the mirror is
pressed and centred against a soft rubber ring.
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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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07.0003 |
1 |
Set of 3 BNC Connection leads
BNC cable with a length of 0.8 m with attached BNC
connectors on both sides
|
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07.0102 |
1 |
PIN Si
Photo detector BPX 61 complete with housing
In a housing a PIN Si photo detector is mounted. Via a
BNC connection the signal is fed to the respective
pre-amplifier or oscilloscope. The module is clicked
into the mounting plate, where it is fixed by means of
three separate spring loaded balls which snap into the
groove of the detector housing.
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07.0236 |
1
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FPC 01
Piezo controller
All voltages necessary for the supply of the Piezo-crystal
and all monitor signals are generated by the controller
FPC-01. It also contains a photodiode amplifier. The
output voltage can be adjusted from 10 to 150 V and the
frequency of the integrated modulator for triangular
signals up to 100 Hz. A monitor signal which is
proportional to the selected Piezo-voltage is provided
via a BNC - socket at the rear. The amplification of the
built-in photodiode amplifier can be selected from 1 to
100 in five steps.
|
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09.0034 |
1 |
Piezo
element mounted in mirror adjustment holder and carrier
with pinion drive
A Piezo-crystal is built into the laser mirror
adjustment holder and has a threading on its front side.
The individual mirrors are mounted by means of a screw
cap which has a soft rubber ring at its inside. The
carrier is provided with a pinion driving screw and a
gear rack which is inserted into the slot of the profile
rail. Sensitive linear displacement variations of this
laser mirror holder can be performed.
|
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09.0036 |
1 |
Beam
expander lens in adjustment holder
A biconcave lens with a diameter of 5 mm is used as the
first element of a beam expander. The lens is mounted in
a disk which is inserted into a click holder which
itself is clicked into an adjustment holder. This holder
is adjustable in the X and Y direction and in two
orthogonal angles.
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10.0030
|
1 |
Exp 03 manual |
No
illustration |
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Required Options
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19.0140 |
1 |
Dual trace oscilloscope 100 MHz
Features:
Frequency Range: 150 kHz ~ 100MHz
Fully Digital Phase Locked Loop Technique Design
High Frequency Stability: ±10ppm
High Input Protection Level: +30dBm, ±25VDC
Reference Level Range: -30dBm ~ +20dBm
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Options
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09.00039
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1 |
Set of spare parts |
No
illustration |
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