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Physics Bulletin
Technology Roundup Lasers
To cite this article: 1974 Phys. Bull. 25 536
View the article online for updates and enhancements.
This content was downloaded from IP address 130.236.82.7 on 27/10/2017 at 02:49
TECHNOLOGY ROONDOP
Losers
Two previous 'Technology Roundup' features have touched briefly on developments in lasers (in March and May of this
year). Since then there have been several
important developments.
As the diversity of applications for laser
technology increases so the range of equipment available from the various manufacturers widens. This diversity is evident
from the rapidly growing list of industrial
applications (apart from more fundamental research areas) - machine tool
technology, vibration and acceleration
measurement, cutting and drilling of difficult materials, flow rate monitoring,
ranging and alignment, typesetting, micromachining, communications and so on.
Quartz & Silice
have fifty years
experience in the art
and science
of crystal growing
MATERIALS
Lithium drifted Germanium Ge (Li). Lithium drifted
Silicon Si (Li). Ammonium dihydrogen phosphate.
A DP. Anthracene. Caesium iodide (thallium
activated). Csl (Tl). Ethylene diamine tartrate E.d.D.T.
Gudnidine aluminium sulphate G.A.S.H. Lithium
sulphate L.H. Pentaerythritol P.E.T. Potassium acid
phthalate K.A.P. Potassium dihydrogen phosphate
K.D.P. Potassium diarseniate K.D.A. Deuterated
K.D.P. Potassium ditartrate K.D.T. Rochelle salt.
Rubidium acid phthalate R.A.P. Rubidium iodide.
S.Kium iodide (thallium activated). Nal (Tl). Sodium
nifdte. Stilbene. Triglycine sulphate T.G.S.
APPLICATIONS
i. Optics, Uv Visible IR. 2. Electro optics. 3. X ray
analysis. 4. X ray spectrometry. 5. Gamma spectro•"i try. 6. Piezoelectric applications. 7. Pyroelectric
For information lick Ufjprupridte box and post to:1
2
3
4
5
6
7
NUCLEAR & SILICA PRODUCTS LIMITED
44-46 The Green, Wooburn Green, High Wycombe, Bucks.
Tel: Bourne End (06285) 25233 Telex 847331
Name
Address
British Subsidiary of Quartz & Silice, Paris.
•••••••••••••••••••I
Or, for further details circle 26 on reply sheet
536
NEW TUBES
Helium-neon lasers have been introduced
by Coherent Radiation Limited of Royston and Rofin Limited of Bishop's Stortford. Specifications of Coherent Radiation's Model 80 series tubes were reported
in March, the main feature being their
stability over a wide range of temperature
and humidity conditions. The units are
available with power outputs of 2, 4
and 6mW. Rofin's Model 7480 He-Ne
laser is based on a NPL design for high
wavelength/frequency stability, quoted as
± 1:108 and ±5 MHz. The output is
2 mW at one of two frequencies.
Techmation Limited of Edgware is now
marketing the Hughes Aircraft argon ion
laser (Model 3067H) in this country which
produces 1 W (single mode) output. The
laser head has a beryllia-oxide bore and is
tap water cooled. By using a method of
electrical regulation the air cooled power
supply is kept to relatively small dimensions. Noise is kept to a minimum by incorporating a light feedback stabilization
system offering better than 1% long term
stability. Options available include single
wavelength or high power multimode
operation.
the TWO-10 is normally infrared at 1 064
um but can be shifted to green (0-532 urn)
by means of a frequency doubler; other
accessories are available for polarization,
harmonic generation and beam shaping.
A smaller version, the Model TWO-22,
has a continuous TEM00 output power of
25 mW at the same frequencies, with a
beam diameter of 1 -2 mm and a divergence of 2mrad.
Another American company whose
lasers are available in this country is GTE
Sylvania and these are obtainable through
Rofin. Its new range includes pulsed, Q
switched, mode locked and continuous
wave YAG lasers with outputs varying from
250 mW to 200 W cw. Sylvania's Model
612 provides 200 W in the multi transverse
mode of operation with a beam diameter
of 6 mm and less than 15 mrad divergence,
at the 1 06 um wavelength. Space is provided inside the 38 cm cavity for elements
such as modulators, and as with the
General Photonics models a frequency
doubler is available. The krypton pump
lamps can be interchanged easily without
disturbing the laser alignment, and the
elliptical cavity is also replaceable. Model
611 is a lower powered version giving
125 W cw. In the same range the Model
618 pulsed Nd:YAG laser offers 125 mJ/
pulse at 30-100 pulse/s (or 10 mJ/pulse at
300 pulse/s). Amplitude reproducibility
from pulse to pulse is quoted as ± 5% and
the pulse rate is variable from single shot
to over 400 pulse/s (higher if the output
mirror is changed).
Rofin can also supply Galax Nd:YAG
laser rods from Allied Chemicals, in
lengths from 2-5 to 10-2 cm and diameters
from 3 to 6 mm. These are grown by the
Czochralski method of pulling from the
melt in a precisely controlled process, and
are tested after fabrication andfinishingto
ensure the performance of the rod when
inserted in the cavity. Figures quoted for
the extinction ratio are 30 dB minimum
between crossed polarizers for a 50 mm
length, and 1 -3 ±015 Nd content (by percent atomic weight) for the rod to rod
uniformity.
HOLOCAMERA
A high energy laser for holographic use,
the K1200 QDH laser from the Korad
division of Hadron Incorporated, CaliYAGS
fornia is now used in a mobile holographic camera. An additional ruby ampliYAG (yttrium aluminium garnet) lasers
are being marketed by severalfirms.Sur- fier is incorporated to boost the output to
4 J/pulse (TEM00) for double pulse operavey and General Instrument Company of
tion and 10 J/pulse for single pulse holoEdenbridge, Kent, has available General
Photonics Corporation's (USA) TWO-10 graphy. All the optics required for either
transmission or reflection mode holoYAG laser which has a 100 mW power outgraphy are contained within a single
put in the TEM00 mode, rising as high as
package weighing under 90 kg. Applica300 mW during multimode operation.
tions envisaged for the holocamera are
Individual pulses of the order of meganondestructive testing, particle studies,
watts can be achieved, by flash pumping
flow visualization, stress analysis, thermal
and Q switching, with durations of around
5 ns. Other operational modes are avail- conductivity and gas diffusion studies and
3 D holography in general.
able, including TEM 01, which give higher
powers than the TEM00 mode but with
Other new laser tubes from America are
greater beam divergence and a different
the Control Laser Corporation's Model
beam profile. Cavity dumping (releasing
570 argon laser pumped dye laser which
all the energy stored inside the laser cavity
has a minimum power of 1 W in the
in a single pulse) is also possible. Output of
mode and linewidths lower than
001 nm at 565-620nm, and the GTE
Sylvania Model 948 single frequency CO2
laser operated at 10-6 um for communications and atmospheric studies. This latter
goes some way to overcoming the difficulties encountered with previous CO2 lasers
which stem from amplitude variations and
mode and wavelength hopping: the long
term frequency stability is better than 1 in
109andthecorrespondingfiguresforamplitude variation are less than 5% and less
than 3%. A rotating mirror Q switch is
available as an accessory, giving up to
1 -7 kW peak power at 300 pulse/s and
operating over the range 100-400 pulse/s.
SPECIALIST DEVELOPMENTS
A neodymium YAG laser capable of
generating 5 x 108 pulse/s is being developed for satellite communication by
GTE Sylvania. The US Air Force has
commissioned the system to reduce interference and interception in the transmission of information between satellites and
to increase the speed and capacity. The
250 mW output is coded to provide a data
transmission rate of 109 bits/s. The additional requirements of working in a space
environment have meant strict limitations
on size and weight, and the substitution of
conductive cooling for the conventional
water and gas methods.
For the study of expansion in such
materials as glass, ceramics and some
plastics where small displacements must
be measured, Linseis GmbH of Harlow,
Essex has produced a laser dilatometer.
Its operation is based on interference between two beams of coherent light split by
a quartz prism from a 633 nm heliumneon source. On recombination of the
reflected and reference beams to form
interference fringes, displacements are detected by photocell and analysed for recording. The sensitivity is better than \ X
(0-15 nm) and the accuracy is increased
further by the elimination of all errors due
to friction, expansion of the measuring
system and compression of the sample by
contact.
MODULATION
From Electro Optic Developments Ltd of
Brentwood comes a laser modulation system employing an electro-optic cell (PC
100) and a video linear amplifier (VLA 30).
The halfwave voltage of the modulator is
typically 200 V and the amplifier will drive
this at frequencies from DC to over 6 MHz.
The risetimes are less than 70 ns and the
system can be used for either analogue or
pulse modulation.
Acousto-optic modulation of the output of the Model 80 He-Ne laser from
Coherent Radiation mentioned earlier is
provided by the Model 304 system based
on a Bragg cell. At 3 -5 MHz the modulation is 70% and at 4-75 MHz it is 50%;
these frequencies can be increased by the
use of beam forming optics or when a
smaller beam diameter is used. The transmission is 4% (static) and 80% (dynamic).
A special feature of this system is a Bragg
angle adjustment which eliminates the
need for special mounts and complex
angle adjustments. The modulator is particularly suitable for communications systems, image recorders and fluorescent
lifetime studies.
An adaptor for flow direction measurement for fitting to the DISA (Bristol) laser
Doppler anemometer system provides
acousto-optic modulation of the light,
allowing translation of the measuring frequency range to another band/ This is
designed to modify the 55 L01 optical unit
for measurements in regimes where flow
reversal may occur, such as oscillating
flows and flows with zero mean velocity.
Another development in the acoustooptic field from Zenith Radio Corporation in Chicago is a laser scanner which
can operate at 10-20 times the speed of
galvanometer type scanning devices. Using
a modulator the beam intensity can be controlled for constant light output across the
scan, or turned 'on' and 'off' as required.
The output scan can be varied from 6 mm
to infinity at rates varying from DC to
20 kHz, using laser light in the region
441-6 to 10600nm.
Again the application areas are quite
diverse: flow detection, laser television,
single line printing, optical character
recognition, laser recording and random
access laser beam positioning.
MEASURING VELOCITY
Measurement of speed, length and vibration in liquids, solids and gases in industrial processes is possible using a laser
velocity meter available from Survey and
General Instruments (designed and manufactured by Cambridge Consultants Limited). The chief advantage over other laser
Doppler devices is the elimination of setting up adjustments and simplicity of
operation which are both desirable in
industrial environments. Also available
from Survey and General is the Visiplane
laser for alignment in building and construction work. This is a small diameter
He-Ne laser beam focused through a
Gallilean telescope and reflected by a
prism enabling a horizontal reference
plane to be swept out by rotation about a
vertical axis (or vice versa). The beam can
be seen at distances up to 1 km and the
laser provides an ideal tool for surveying
and levelling.
Improvements in the technology of silicon and ceramic wafer scribing using lasers
have been announced by Roditi International Corporation (London) for Korad
of America. By scribing on the back side
of the wafers using a special chuck deeper
kerfs can be obtained, up to 80 or 90% of
the wafer thickness. This has significant
advantages over conventional front side
scribing in the protection of delicate circuitry and elimination of costly cleaning
procedures to remove particle debris build
up on the front surface.
Finally a compact Michelson interferometer accessory for coherence measurements and the determination of small displacements and instabilities should prove
useful for workers involved in holography
and interference research. Available from
Eldon AG of Zurich, Switzerland the
device fits directly to all normal lasers.
DISA has overcome the difficulties which conventional laser doppler anemometry systems have in tracking reverseflowsby incorporating an
adaptor which translates the measuring frequency to a higher frequency band
537
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