Diode-pumped-laser instrumentation system

A semiconductor-diode-pumped solid-state laser instrumentation system for use in industrial materials processing, spectroscopy, medical surgery, metrology, fiberoptic communication, and related research work in a scientific laboratory is described. The system principally comprises a hand-held instrumentation stylus containing a laser-generating source consisting of a laser rod with an array of semiconductor radiation-emitting diodes disposed in adjacent relation to said laser rod for producing a high-quality and stable beam of laser radiation therefrom. The system is further capable of generating harmonic wavelengths of said radiation at Q-switched and modelocked formats.

The present invention is generally related to a laser-generating system and 
is more particularly concerned with a system adapted to generate a 
high-quality laser beam by the use of a solid-state laser rod optionally 
pumped (excited to produce) by an array of laser diodes to generate a 
laser radiation and harmonic wavelengths thereof. 
BACKGROUND OF THE INVENTION 
This invention relates to an improved embodiment of a laser instrumentation 
device described and claimed by this applicant, in the U.S. Pat. No. 
3,786,907, and an earlier patent related to the same instrumentation 
system, U.S. Pat. No. 3,464,534. Both of these patents describe and claim 
semiconductor diode lasers as sources of laser radiation. However, U.S. 
Pat. No. 3,786,907 specifically discloses and claims a semiconductor 
diode-pumped laser generator for application in various industrial 
processes, more particularly in a laser eraser for correction of 
type-written errors. However the main point in this application resides in 
the use of new techniques and elements for generating laser radiation 
using newly-developed semiconductor diodes, such as light-emitting diodes 
or laser diodes. Both of these diodes are capable of producing spectral 
wavelengths compatible with the solid-state laser rods. However. the laser 
diode possesses the property of higher intensity of radiation and is more 
efficient in irradiating any solid-state laser rod and producing therefrom 
a laser-beam radiation of high performance characteristics. 
The present invention further improves on said device shown in U.S. Pat. 
No. 3,786,907, and demonstrates that by frequency-doubling or Q-switching 
the laser diode's radiation or by using both the frequency-doubling and 
the Q-switching techniques a laser radiation beam is produced which has 
improved spectral and optical characteristics. 
Conventional laser-generating systems employ inert-gas arc lamps, known as 
flashlamps, tungsten-filament lamps, and the like to illuminate (pump) the 
solid-state laser rod to generate laser radiation therefrom. The most 
common source of continuous pumping of laser radiation from a laser rod, 
such as a neodymium-doped yttrium-aluminum-garnet host (Nd-YAG), is the 
tungsten-filament halogen lamp. Another optical-pump source is the krypton 
arc lamp. The pumping lamp emits a blackbody-type radiation, whose 
efficiency in pumping a laser radiation from the solid-state rod, such as 
a ruby rod or a Nd-YAG rod, is between 5 to 6 percent. The light intensity 
from such a lamp heats it to a very high temperature. Therefore, most of 
the energy produced by the lamp is dissipated as thermal energy, which 
contributes to the heating of the laser-generating system, reducing its 
efficiency of emission. Consequently, cooling of the laser-generating 
system is necessary, using a cumbersome equipment of compressed air or 
water circulating through the laser-generating head. The service life of 
the lamp is short, typically 300 to 400 hours. These characteristics of 
the pumping lamp make the laser system bulky and costly to produce. 
The efficiency of laser production of such an optical pumping lamp is also 
very low. For instance, for each 1000 watts of input power to the pumping 
lamp only about 25 watts of laser power is typically produced. This is an 
efficiency of about 2 percent, which is considered satisfactory at present 
because of the lack of other commercial means to produce greater 
efficiency of laser production. Furthermore, since the laser rod is heated 
by the thermal energy dissipated from the pumping light source, the 
efficiency of laser production of the rod also decreases, and its output 
becomes about 0.5 percent that of input. Accordingly, the present 
solid-state laser production techniques are too wasteful in energy 
utilization. For this reason, the laser systems are too costly for 
employment in many technical communities. 
While the applicant's patent, U.S. Pat. No. 3,786,907, represents a new and 
basic principle of laser generation, by the use of a laser diode to pump a 
laser rod, such as Nd-YAG, ruby. erbium-YAG, alexandrite, or the like, the 
present application contains the same basic principle with improved design 
of construction using new elements to enhance additional advantages and 
efficiency to the laser system. As a matter of fact, the present 
disclosure fortifies the original basic system of the applicant's 
invention by the use of state-of-the-art laser-producing elements, fewer 
parts, low-cost materials, compactness in size, and more efficient laser 
pumping semiconductor laser diodes. 
A typical laser diode for pumping laser rods is gallium arsenide (GaAs), 
which emits typically at about 8000 angstroms, with its hybrid from 
gallium-aluminum-arsenide (GaAlAs) emitting at 7500 to 9050 angstroms, and 
indium-gallium-arsenic-phosphide (InGaAsP) emitting at 11,000 to 16,000 
angstroms in the infrared. Any of these laser diodes and their 
derivatives, such as for one gallium-indium-aluminum-arsenide (GaInAlAs) 
can be utilized in the present species of the applicant's invention, since 
each of these diodes has specific advatages, as will be presently 
indicated by reference to the drawings. 
In the present invention, an array of any selected type of the laser diodes 
referenced above can be used. The diode offers a conversion efficiency of 
25 percent and over, in some cases. This means that a 10-watts of input 
power can produce about 2.5 watts of laser radiation from the laser rod. 
An additional advantage of the diode laser over the flashlamp 
(tungsten-arc lamp, for instance) is that the radiation from the diode can 
be collimated and focused on the laser rod axially, matching with the 
TEM.sub.oo mode operation of the rod. TEM.sub.oo operation is the 
fundamental performance format of a laser element and is derived from the 
phrase "transverse electromagnetic mode", which mode simulates a Gaussian 
operational format, a most efficient performance mode of the laser system. 
Since the semiconductor laser diode pumping of the laser rod possesses high 
effiency of radiation, the thermal problems are alleviated and consequent 
cooling operations, as necessary in other types of optical pumping 
methods, are not necessary. Thus, the cost of construction and operation 
of the laser system is reduced. Thermal birefringence effects and possible 
thermal focusing problems are also eliminated in diode pumping. One of the 
most important characteristics of the laser diode is the capability of 
being modulated easily at high speeds with high amplitude stabilization 
that is imparted to the laser rod by the diode performance. 
By focusing the diode array radiation with a converging lens on the optical 
aperture of an optical fiber, the high energy from the diode array can be 
transferred through the fiber cable to a remotely-located laser rod, such 
as that shown in FIG. 2 of the drawing of the invention. This type of 
laser embodiment can enhance the reduction in the size of the laserhead; 
furthermore, a heatsink can be applied to the laserhead to cool it when 
necessary. The system then can be made small and simple in construction. 
Q-switching modelocking, tuning, and frequency-doubling design problems 
also become simplified and less costly, as shown in the present drawings. 
SUMMARY OF THE INVENTION 
Having described the many advantages of the present invention over the 
existing types of solid-state laser systems, the specific and principal 
advantages of the present invention may be further defined as follows: 
To achieve high performance of the present invention, the principal object 
of the invention resides in the incorporation of a state-of-the-art laser 
diodes as the optical pumping source for the solid-state laser rod to 
produce an easily-generated high-quality laser beam at considerably lower 
cost than similar laser rods included in the present laser systems of 
commerce. 
A further object of the invention is to provide a laser system with a 
minimum of operative parts using inexpensive materials and reducing the 
cost of production considerably and furnishing a more stable radiation 
performance than that heretofore has been achieved. 
A still further advantage of the invention resides in its capability of the 
laser radiation to be easily Q-switched to achieve high-power laser output 
at short pulses, such as for nanoseconds, which characteristic becomes 
extremely important for certain types of medical surgery, semiconductor 
circuit development work, and military applications. 
Another advantage of the invention is the provision of a harmonic generator 
(frequency-multiplying device) in the system, such as doubling the 
frequency and shortening the wavelength for applications requiring 
visible-wavelength laser radiations, which can be produced when necessary 
without increasing the number of inherent components of the system. 
A further object of the invention resides in the provision of a remotely 
located gaseous source which is used by transmitting the gas through a 
fibroptic conduit, peripherally to the fiberoptic cable within the 
conduit, to the operative site, when the laser operation requires the 
oxidation of the debris from the focus of the laser beam incident on the 
specimen under operation. 
One other advantage of the present invention is the provision of a 
fiberoptic laser conduit which contains therein a tubular space 
peripherally to the fiberoptic cable therein. The conduit has a tubular 
airtight sheathing externally thereto for purposes of suction of debris 
from the site of a medical surgey, when the device is used in a medical 
treatment by a surgeon. 
A further object of the invention is the provision of a thermoelectric 
cooling device located peripherally to the laser-generating elements for 
maintaining a constant temperature therein in order to achieve the normal 
laser-emitting environment in the diode laser arrays.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawing in FIG. 1, numeral 1 points to the housing or 
stylus of the present invention with an outside container wall shown by 
the hatched structure that embodies the laser system and the optical 
elements that shape the emergent laser beam therefrom. Internally and at 
the uppermost part of the housing or stylus 1 is a chamber 2 containing a 
power-supply means or a rechargeable battery 3 with electric contacts 4 
that can be plugged into a 115-volt electric source for charging the power 
supply source. Centrally to the device 1 is a laser rod 5 with a diode 
array 6 peripherally thereof. The laser rod may be one of several types of 
laser rods, such as Nd-YAG, Nd-glass, ruby, erbium-YAG, alexandrite, or 
the like. The peripherally located diode array 6 is used for producing a 
laser radiation when the switch 7 is closed for activation thereof by the 
power supply or battery 3. The radiation from the diode array 6 becomes 
incident on the laser rod 5, activating it to emission of a laser 
radiation therefrom. 
In producing a high-intensity radiation from the laser diode array a 
quantity of thermal energy may be given off from the diode array 6. This 
heat is dissipated by means of the thermoelectric cooler 8 which is 
located in the periphery of the laser diode array 6 and is connected to 
the power supply 3 through the switch 7 and energized thereby. The 
thermoelectric cooler consists of a circuit having two electric junctions, 
one of which comprises dissimilar metals with their ends joined by welding 
together. When a direct current (such as from the battery) passes through 
this junction it becomes cold (the other junction is not used in this 
case). 
the emitted laser radiation from the laser rod 5 is projected on an optical 
lens 9 located in a housing or receptacle 10 disposed the laser rod 5 and 
is movable up and down in the conical section 11 of the stylus. The 
receptacle 10 is provided on its periphery with screw threads 12 fitted 
into the internal threads 13 of the conical section 11, so that when the 
receptacle 10 is rotated by means of a screwdriver inserted into the slot 
or notch 14 and rotated clockwise or counterclockwise, the lens 9 is 
respectively positioned closer or remotely from the radiation exit port 
14A through which the focused laser beam exits to the exterior to impinge 
on the workpiece. Numeral 15 is the cap member of the stylus 1 which has a 
circular groove 16 inferiorly thereof for accommodating the contacts 4 for 
transfering an external current into the rechargeable battery (or the 
power supply) 3 when inserted into a 115-volt current outlet. 
FIG. 2 represents another embodiment of the invention, in which the housing 
16A contains, similar to that in FIG. 1, a rechargeable battery 17 with 
electrical contacts 18 for charging the battery 17 upon exhaustion 
thereof. Centrally to the housing 16A is a laser rod 19, of a material 
preferably Nd-YAG or Nd-glass or an erbium laser, which is optically 
pumped by a semiconductor laser-diode array 20 when the switch member 21 
is depressed to make contact between the circuits of the diode array 20 
and the battery means 17, which furnishes a direct current of proper 
amount to the diode array 20 to excite it to emission of a coherent 
radiation. 
The emitted radiation from the diode array 20 is projected to the laser rod 
19, as indicated by the arrows, to generate therein a laser radiation 
characteristic of the rod material. The laser rod 19 is partially coated 
with a reflective coating 22 at one end surface and contains no coating at 
its opposite end surface contiguous with the transparent partition means 
22A. Accordingly, the laser beam from the diode array 20 impinges on the 
coating 22 and reflects therefrom to a semitransparent (dichroic) element 
23, from which it reflects unto a mirror 24. The beam from the mirror 24 
again reflects to mirror 25, by passing through the dichroic element 23 
and back to mirror 24 and the coating 22. This process continues (within 
nanoseconds) to radiation saturation, whereupon the laser beam passes from 
the rod 19 through the coating 22 and impinges on the lens 26A, which 
projects the beam convergently to the exterior of the housing 16A through 
the tip or exit aperture 26. The lens 16A and its holder (receptacle) 26B 
have the respective functions as the lens 9 and its holder 10, shown in 
FIG. 1, in positioning the lens 26A up and down the conical section of 
housing 16A. 
In FIG. 3 is another embodiment of the invention shown, in which the 
numeral 27 indicates a laser stylus (tubular housing) with housing 28 
containing a rechargeable power supply or battery 29 which may be inserted 
by means of contacts 30 into the outlet socket of a 115-volt current to be 
recharged thereby. Centrally to the stylus 27 is a laser-generating 
solid-state rod 31 surrounded by a laser-diode array 32, which is 
electrically connected to the power supply 29 through a switch 33. When 
the switch 33 is pressed, it closes the power supply 29 circuit to the 
laser-diode array 32, activating it to emission of a laser radiation, 
which illuminates (pumps) the solid-state laser rod 31 and causes it to 
emit a high-intensity laser radiation characteristic of the rod material. 
The emitted radiation from the laser rod 31 passes through a 
frequency-multiplying (harmonic generator) non-linear crystalline means 
34, which increases the frequency of the radiation, preferably doubles it, 
and decreases the wavelength to one-half its fundamental wavelength. 
Assuming that the solid-state laser rod 31 is a Nd-YAG element, the 
fundamental radiation from it is 10,600 angstroms, and when a 
frequency-doubling occurs the wavelength becomes 5300 angstroms, which is 
in the visible spectral range. A frequency-doubled laser radiation 
possesses higher laser energy (energy=hf, where h is Planck's constant) 
and therefore can function as a higher-power laser radiation than when the 
radiation is in the fundamental 10,600 angstroms. 
The laser beam (frequency doubled) projects through the stylus 27 and 
becomes incident on a focusing lens 35, which directs the focus of the 
laser beam through the radiation exit port 37 to the externally-positioned 
work site. Naturally, the laser rod 31 is coated 100 percent at its end 
adjacent the power supply 29 in the drawing and only partially at its 
opposite end adjacent the harmonic generator 34, so that laser action can 
take place in the rod by the oscillation of the laser radiation therein. 
The lens 35 is mounted in a receptacle 36 having external screw threads 38 
thereon. The receptacle 36 can be moved up and down by rotating it, 
respectively, counterclockwise and clockwise by the use of a screwdriver 
inserted into the slot 39. This action moves the focus of the laser beam 
to and from the exit port 37. The reason for moving the focus axially to 
the stylus 27 is that certain materials of industry, or tissues in medical 
surgery, require focused laser beam and others require defocused radiation 
for processing them. A focused beam gives the highest thermal energy and a 
defocused beam has low energy per square area and can be used for thin 
metallic materials or for surface treatment of organic tissues in medical 
work. 
FIG. 4 illustrates another embodiment of the invention, in which the stylus 
40 receives the laser beam from the laser-generating section 41 through 
the fiberoptic conduit 42. The conduit 42 comprises a flexible external 
tubing 43, the fiberoptic bundle 44, and a peripheral tubular space 45 
therebetween for transmitting a gas to the workpiece through the stylus 
40, or it carries tissue debris by suction from the workpiece through the 
stylus 40, for operations involving medical surgery. The gas may be, for 
instance, pressurized oxygen contained in the tank 45A. The amount of gas 
issuing from the tank 45A is controlled by means of a valve 46. The 
suction apparatus is located in the container 46A. 
Section 41 receives an alternating current from a 115-volt conventional 
electric outlet through the electric cord 47 having an electric plug 48 
for insertion into the electric outlet socket. The alternating current is 
rectified and its intensity is controlled in the power-supply section 49, 
which may be conventional-type rectifier with control instruments. The 
controlled electric current from the power supply section 49 is 
transmitted to a laser-diode array 50 to energize it for producing an 
optical pumping radiation to activate the solid-state rod 51, such as 
Nd-YAG, to emission of radiation therefrom, when the switch 52 is closed. 
Surrounding the laser-generating rod 51 is an electric heat sink (thermal 
means) 50A, which is energized by a current from the power supply section 
49, shown in drawing FIG. 4; this is used for cooling the laser-generating 
means. If both the switch 52 and switch 53 are closed, the Q-switching 
section 54 also become energized to increase the pulse power of the laser 
beam 54A from the rod 51 in the pulsing mode; this action shortens the 
pulse duration while at the same time retaining the laser pulse energy 
constant. When the laser rod 51 is operating in the continuouswave format, 
Q-switching provides shorter and more intense pulses than when the laser 
rod is pulsed by ordinary pulsing methods. The details of the power supply 
49 and the Q-switch 54 are not given because they are commercially 
available as modules and are easily inserted into an electric circuit. 
The Q-switched laser beam 54A passes through a lens 55 and the output 
mirror 56 to the fiberoptic line 42 to be transmitted to the stylus 40 for 
further optical processing therein. Since one surface 51A of the rod 51 is 
fully reflective by a mirror coating and the output mirror 56 is partially 
reflective the laser beam oscillates therebetween for stimulation and 
amplification before it exits through the mirror 56. After passing through 
the output mirror 56, the laser beam becomes continuous with the 
fiberoptic bundle 44, which conduits the laser beam into a harmonic 
generator 57 in the stylus 40. The position of the harmonic generator 57 
may be shifted, if desired, so that the laser beam from the fiberoptic 
bundle 44 can continue its travel without optical transformation and 
impinges on the laser beam collimator 58. The collimator 58 collimates the 
laser beam and transmits it through the lens 60 to another lens 61, which 
focuses the laser beam upon the specimen or workpiece, as desired, 
positioned adjacent to the exit port 62 of the conical section 63. 
The lens 61 is mounted in a circular receptacle 64 and can be moved up and 
down in the groove 65 by means of the button 66 attached to the receptacle 
64. The receptacle 64 is biased by means of a spring 67, so that when the 
operator of the stylus desires to change the focus of the laser beam, he 
pushes on the button 66 to move the lens forward and thereby changes the 
focus position of the laser beam passing through the exit port 62. When it 
is desired to produce a Q-switched laser-beam output, the Q-switch section 
57 is positioned in the beam path, as shown in the diagram of FIG. 4. 
FIG. 5 is a cross-sectional view of the stylus 40 taken in the line 4-4'. 
In the figure, the numeral 68A represents the cross-section of the wall 68 
adjacent the groove 65. Numeral 69 indicates the slots through which the 
gaseous element from the tank 45A is transmitted to the exterior of the 
stylus through the radiation exit port 62. 
In operation of any one of the species described, the respective power 
supply current is turned on by means of the respective switch in each 
embodiment of the invention. This action generates the laser radiation to 
be directed by the respective stylus, externally thereof, for applications 
described earlier in this specification. When the parts of any one of the 
stylus embodiments are to be changed or are to be repaired, the walls of 
the stylus housing are disassembled at the points of assembly, as shown in 
the diagrams, and then assembled after the replacement or repair has been 
undertaken.