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Laser Gyroscope |
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Topics:
Sagnac Effect
HeNe Ring Laser
Ring Laser Modes
Single Mode Etalon
Interference
Fringe Detection
Mode Lock-In
High Precision Angle Measurement |
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Nowadays, Airbus
and Boeing air-planes are equipped with laser gyros for
navigation. Beside their high precision, they have shown
reliability, long term stability as well as a long lifetime.
The basic specifications are:
Range: 10-6 - 103 °/sec
Resolution: app. 2 arc sec
Zero stability: 10-3 °/h
Scale factor stability: app. 3 ppm
The outstanding properties of the laser gyro become clear when
it is compared to other well known measuring devices. For
instance, a micrometer screw with a resolution of 0.01 mm must
have length of at least 3 km before having the same properties.
The field of application of the laser gyro is not limited to
air-planes; it can also be used for the navigation and control
of earth bound vehicles, alignment of telescopes and antennas,
alignment and control for robotics, missiles and satellites,
high precision measurement in the industry, surveying of railway
tracks, oil drilling and so on. Within this experimental system
the basics of the laser gyro are explained and practically
studied at the system, which allows full access to all the
components. The experimental laser gyro (see the figure below)
consists of a rugged turntable on which the ring laser is
mounted. By means of a motorised rotational stage, the angular
motion of the turntable is performed. The ring laser consists of
three laser mirrors arranged at the corners of a 60° symmetric
triangle. The point of rotation lies well within the centre of
this triangle. At the mirror M3 a beam bending device is
positioned in a way such that the clockwise and counter
clockwise travelling modes are superimposed and their
interference intensity is detected by means of two photo
detectors. By counting the beat frequency and multiplying the
result with the scale factor of the set-up, one gets the angle
motion of the turntable.
For the pre alignment of the ring laser, an external solid state
laser emitting at a wavelength of 532 nm is provided.
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Principle of operation
In a ring laser consisting of three mirrors M1, M2, M3 and a
HeNe-laser tube, two travelling modes are propagating inside the
resonator. One travels clockwise and the other counter
clockwise. At mirror M3 a small amount of the intensity of the
individual modes is coupled out by means of a beam bender and
beam splitter superimposed. If the resonator is not turned, both
modes have the same frequency, f1 and f2. As soon as the
resonator is turned around its axis with an angular speed
corresponding to the angular frequency ω these frequencies are
changed due to the Doppler effect. The difference in both
frequencies are detected by the photo detectors PD1 and PD2 with
subsequent signal processing. The so generated fringes will be
summed up by means of a counter. The read out of the counter is
directly proportional to the angle by which the ring laser has
been turned. It is necessary that the ring laser oscillates in
just one mode per direction. This requires a short HeNe-laser
tube which is, however, commercially not available. Therefore, a
single mode etalon is used to force the laser to the desired
operation.
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Required Equipment
| Cat. No. |
Qty. |
Description |
Illustration |
07.0204
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1 |
TC-01 Tube
controller
The controller unit TC-01 serves two purposes. It
provides the high voltage for the main HeNe-Laser tube
and contains a photodiode amplifier for the measurement
of the relative output power of the laser. The discharge
current can be set from 5 to 6.5 mA with the adjusting
knob on the front side. The main switch and the supply
are on the rear side of the device. A key switch
prevents the unauthorized switching on of the laser. The
controller is designed for an operating voltage of 1.8
kV and an ignition voltage of about 8 kV.
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07.0210 |
1 |
PDA-01
Photodiode amplifier 4 channel
The pre-amplifier contains four amplifiers which amplify
the particular signals. On the front side the outputs
are disposed via BNC - sockets. Furthermore the
pre-amplifier contains the off-set compensation and the
generation of the TTL quadrature signals.
A pair of detectors PD1 and PD2 have a common connecting
cable with a jack plug, which is connected to one of the
channels of the pre-amplifier PDA-01. After
pre-amplification, both signals are fed to a comparator
and then a TTL signal is generated from the 180° phase
shifted signals for the frequency counter. The
individual analogue signals can be demonstrated with the
help of an oscilloscope. For this, one connects the
channels of the oscilloscope with the BNC receptacle (+
and -) present on the front side of the device. The exit
for the TTL signals is present as a BNC receptacle on
the rear side of the pre-amplifier.
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09.0162 |
1 |
Gyroscope
base plate, 3 mirror holder incl. mirror, HeNe laser
tube
The ring laser formed by the three laser mirrors is
set-up on a rigid construction consisting of a solid
base with a motor driven turn table. By means of a micro
step controller connected to a PC, the table can be
turned precisely. The HeNe laser tube has a length of
approx. 400 mm and is supplied with sealed Brewster
windows. The tube is mounted with soft rubber rings in
two X-Y adjustment holders allowing the adjustment of
the capillary with respect to the ring laser axes.
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09.0164 |
1 |
Alignment
laser 532 nm , incl. power supply
A pilot laser is used for the first adjustment of the
ring resonator. To enable the pilot laser beam to pass
through the resonator mirrors, which are made highly
reflective for 632 mm. In this case, the green radiation
of a diode pumped, frequency doubled Nd:YAG laser is
used (DSL adjusting laser), which is mounted in an
adjustment holder with 4 axes. For the first adjustment,
the base plate with the adjusting laser is placed on the
base plate of the laser gyro and fixed with a screw.
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10.0160
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1 |
EXP 16 manual
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No
illustration |
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19.0170 |
1 |
Frequency and event counter
120 MHz Digital Frequency Counter
Features:
Frequency and Period measurement
1 Hz ~ 120MHz range
8 Digits Display (0.3-inch LED)
Over-Flow Indicator
5 ppm High Stability Time base
Low Pass Filter Function
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19.0180 |
1 |
Stepper motor controller
The stepper motor controller is connected via a RS232
serial bus to the PC. One step of the controller is
internally divided into 65536 steps resulting in a
smooth DC-like movement of the connected stage.
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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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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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09.0169
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1 |
Set of spare parts for
EXP 16 |
No
illustration |
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