Laser shield and method of making same

A laser shield which absorbs narrow band radiation of a laser beam while transmitting broad band radiation encompassing the narrow band is provided by diffusing a layer of a chromophore selected from one or more porphyrin complexes which have been modified by metals forming a metallo-porphyrin complex. The chromophore or chromophores are combined with a solvent which are mixed for dissolving the chromophores in the solvent to provide a dissolved chromophore solution. A transparent matrix material is dipped or otherwise brought into contact with the solution for a predetermined time period at a predetermined temperature for diffusing the chromophore into the surface of the matrix material which has been softened by the solvent at the elevated temperature to thereby provide a layer of diffused chromophore which absorbs radiation in a narrow band corresponding to the characteristics of the chromophore while passing a substantial portion of all radiation applied thereto. The strain introduced into the softened surface is then removed by a heat annealing process which also increases the effective concentration of the chromophore by increasing its solubility in the matrix.

BACKGROUND OF THE INVENTION 
This invention relates to a transparent protective laser shield and a 
method for making the same which is adapted to be interposed between a 
laser and a viewer for protecting the viewer from damage by laser beam 
radiation, and more particularly to such a protective shield in which 
chromophore dyes in the form of metallo-porphyrin complexes are diffused 
into the surface of a transparent host material, such as a plastic 
material, forming a diffused layer thereon thereby providing the host 
material with the absorption characteristics desired. 
In a host of medical, industrial and other applications a laser beam may be 
employed for cutting, fusing or performing other functions which may cause 
contact with the eye either by direct viewing or reflection from the 
object being worked on. Since the eye collects and focuses the energy, and 
since the laser beam is generally concentrated, considerable damage can 
result from the application of this energy to the optic nerve. The same is 
true when the viewer happens to be a light sensitive detector which may be 
monitoring the particular operation being performed by the laser. 
Accordingly, laser shields have been provided to enable viewing the laser 
beam in its environment without being subjected to the danger of 
concentrated beam energy. For example, U.S. Pat. No. 3,853,783 describes 
the use of vanadyl phthalocyanine sulfonamides in plastic compositions to 
protect the eyes from exposure to laser radiation with wave lengths in the 
region of about 620 to 720 nanometers. The problem is to get the dyes, 
namely the vanadyl phthalocyanines to be readily soluble in the various 
transparent plastics which are used for the shields. In this patent the 
dyes are directly mixed with the plastic material and molded or cast into 
plates or goggles or shields, etc. which requires difficult and time 
consuming procedures and extreme difficulty in being able to thoroughly 
mix or dissolve the dyes in the plastic material. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide a transparent 
optical protective laser shield which absorbs optical radiation in a 
selected narrow band or band widths and transmits a broad band of optical 
radiation which includes and/or surrounds the absorbed narrow band wave 
lengths matching the laser beam desired to be protected against by 
diffusing the dyes into the host plastic material forming the laser 
shield. 
A further object of this invention is to provide a new and improved laser 
shield and method of making the same which is simpler, increases the 
solubility of the dyes in the matrix and avoids trying to make the dye 
readily soluble in various transparent plastics. 
In carrying out this invention in an illustrative embodiment thereof, a 
protective laser shield which absorbs narrow band radiation corresponding 
to a laser beam while transmitting broad band radiation is provided by 
combining at least one chromophore selected from one or more porphyrin 
complexes which have been modified by metals forming metalloporphyrin 
complexes with a solvent capable of thoroughly dissolving the added 
porphyrin complexes or dyes. The dyes and solvent are mixed for dissolving 
the chromophore in the solvent to provide a dissolved chromophore 
solution. The surface of a transparent matrix material is subjected to the 
dissolved chromophore solution by bringing the surface of the transparent 
matrix material into contact with the dissolved chromophore solution at 
predetermined temperatures for a predetermined period thereby diffusing a 
layer of the chromophores into the surface of the transparent matrix. A 
water vapor free environment is provided for the diffusion process to 
prevent the formation of water vapor on the transparent matrix material 
while the solvent evaporates and the surface cools when the matrix 
material is withdrawn from contact with the dissolved chromophore 
solution. The withdrawn matrix is then heat annealled which in effect 
increases the concentration of chromophore in the cured diffused surface. 
Advantageously, the diffusion of the chromophores into a surface thereby 
forming a layer of the chromophores in the surface of the host or 
transparent plastic matrix material eliminates the previous requirement 
cited in the aforesaid patent for totally mixing or trying to dissolve the 
chromophore throughout the host material as well as any rearrangement or 
concentration of the chromophores in such material when it is cast since 
in accordance with the present laser shield, the chromophores or dyes are 
not cast or molded into the matrix material, but are simply diffused in an 
already formed shield.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The transparent protective laser shield and method of making the same may 
be in the form of a shield, plate, visor, window, goggles etc. which are 
adapted to prevent injury to the viewer from exposure to a laser beam 
having concentrated narrow band radiation which is adapted to be absorbed 
by the protective laser shield when the laser beam is viewed with the 
shield interposed between it and the viewer. In accordance with the 
present invention, the formation of the laser shield involves the 
diffusion of one material more particularly, a chromophore into the 
surface of another namely, the host or matrix material in the form of a 
transparent plastic. The diffusion is achieved by using a solvent to 
"open" or loosen the surface of the host material thereby allowing 
chromophore or dye to diffuse into it forming a layer thereon which 
permits the host material to absorb the radiation applied thereto 
corresponding to the absorption characteristics with the dye which has 
been diffused therein. The chromophores or dyes referred to are generally 
a functional group of chemical compounds that give rise to a color in a 
molecule and with the assistance of an auxochrome such as a hyperoxl or 
amino group produces a dye. In the past such dyes have been used for 
coloring in textiles and/for the same purpose when introduced into 
crystals, glasses, plastics or polycrystalline materials. The aforesaid 
patent illustrates the use of one specific compound in a transparent 
material in which the dye is dissolved into the material, and then cast or 
formed into a shield to absorb rather broad wave lengths. The present 
invention differs by diffusing a layer of dye into the surface of a host 
material as contrasted with mixing the chromophore with the host material 
and casting it into the shield as is done in the aforesaid patent, or in 
applying a coating by painting or otherwise placing a layer of the dye on 
the outer surface of the host material. 
The first step in forming the laser shield in accordance with the present 
invention involves combining a dye into a suitable solvent. Dye is 
characterized as comprising a chromophore or chromophores selected from 
one or more porphyrin complexes which have been modified by metals for 
forming a metallo-porphyrin complex which is designed to absorb radiation 
in a specific narrow band or bands of wavelengths which match the 
wavelengths of the laser beam or beams which are desired to be protected 
against. Examples of such suitable chromophores are t-butylated vanadyl 
phthalocyanine/ and stanous chloride t-butylated phthalocyanine which 
absorb at 694 nanometers and are suitable for protection against a ruby 
laser; the platinum porphyrin of octaethylene porphyrin which is suitable 
for absorbing the double yag laser at 532 nanometers, etc. One or more 
metallo-porphyrin chromophores or dyes may be combined for diffusing one 
or more dyes into the surface of the host material for selective 
absorption of one or more narrow wave lengths in a broader wave length 
band. 
The solvent is characterized by being able to perform the dual function of 
thoroughly dissolving the dye which has been combined therewith as well as 
being capable of entering the surface of the host material to which it is 
applied. Any solvent capable of dissolving the dye or chromophore and 
penetrating or softening the surface of the plastic host material may be 
utilizied for example, dichloromethane, dichlorobenzene, chloroform, etc. 
The combined solvent and chromophore are mixed for dissolving the 
chromophore in the solvent to provide a dissolved chromophore solution. A 
transparent host or matrix material which provide the laser shield may be 
in the form of a window, visor, shield or plate, lens, goggles, etc. The 
host material is preferably a transparent plastic material with broad band 
transmission characteristics such as clear acrylic formed from 
methylmethacrylate, polycarbonate, polyvinyl chloride, polyethylenes, 
polyesters, etc. 
The entire transparent matrix material or a surface thereof is brought into 
contact with the dissolved chromophore solution at a predetermined 
temperature and held in such contact for a predetermined period of time 
for diffusing the chromophore into the surface of the matrix material 
providing a layer therein for absorbing the desired narrow band wave 
length in accordance with the characteristics of the dye which has been 
diffused into the surface of the matrix material. The shield, plate, 
goggle, etc. of the matrix material may be brought into contact with the 
dissolved chromophore solution which may be filtered prior to the contact 
step for eliminating undissolved particulants in the chromophore solution. 
The contact may be done manually or preferably mechanically in order to 
more accurately control the temperature and time cycle. 
One method of providing bringing the matrix material into contact with the 
dissolved chromophore solution is illustrated in the drawing which 
includes a seamless container 10 for holding dissolved chromophore 
solution 12 which container is provided with a cover 14. A motor speed 
control 16 is coupled to a motor drive 18 for rotating a drive pulley 20. 
The drive pulley 20 operates a drive belt 22 for driving a power transport 
pulley 24 for rotating rotary drum 26 with pegs for accommodating flexible 
plastic parts having a plastic plate holder 28 adapted to carry and bring 
the laser shield matrix 25 in contact with the soluble chromophore 
solution 12 carried by the container 10. A nitrogen gas heater 30 is 
provided for the dipping apparatus shown in the drawing which is level 
with the plastic plate attachment 28 in order to apply dry heated nitrogen 
gas to the surface of the plate attachment 28 when a matrix material 25 
mounted thereon is withdrawn from dipping in the solution 12 in order to 
provide a water vapor free atmosphere for the withdrawn plate 25 in order 
to eliminate water vapor when the solvent evaporates and the surface of 
the diffused plate cools. Alternatively, a dehumidifier might also be 
employed. 
Prior to the dipping or contact step, the optical density of the dissolved 
chromophore solution can be checked and the concentration adjusted to the 
desired optical density(OD) by the addition of more dye or solvent. The 
immersing, dipping or contact step is preferably made at a temperature 
between 25.degree. to 50.degree. C. which limits are determined by the 
boiling point of the solvent and/or the melting point of the plastic 
whichever is lower. It is also desirable to control the dipping or 
immersing time to between 1 to 10 seconds with 5 seconds being the best 
dipping or immersing time in order to provide an even diffused layer of 
chromophore in the surface of the laser shield being treated. The time 
period, of course, will also depend on the type of dye, the solvents, the 
type of matrix material and the temperature involved in the diffusion 
process. 
After using the solvent to "open" or loosen the surface of the host 
material thereby permitting the chromophores to diffuse into it, the 
strain introduced into the surface of the host material is removed by a 
heat annealing process whose effects may be tested as the annealing 
process takes place. The heat annealing process increases the effective 
concentration of one or more of the chromophore dyes by in effect 
increasing their solubility in the host matrix material. The heat 
annealing process is a slow deliberate process and will depend on the type 
of host material and the chromophores which are diffused therein. One 
schedule for the annealing process which has been found suitable for 
diffusing dyes into polycarbonate for specific examples which follow is as 
follows: 
______________________________________ 
SCHEDULE A 
CONTROL OF TEMPERATURE FOR ANNEALING 
OF DIFFUSED POLYCARBONATE 
T.sub.min. 
T.sub.max. Time Spent at T 
.degree. C. 
.degree. C. Min. Max. 
______________________________________ 
55 65 2 hrs. 12 hrs. 
100 110 4 hrs. 12 hrs. 
120 125 2 hrs. 12 hrs. 
140 145 0.15 hrs. 
2 hrs. 
Slow (3-18 hr.) temperature drop to room T 
______________________________________ 
Note: 
Time is allowed (3 to 10 min.) for oven to reach listed temperature. 
Although various materials may be utilized in accordance with the present 
invention, two specific examples which have been found suitable in 
accordance with the present invention are as follows: 
EXAMPLE 1 
A porphyrin dye compound t-butylated vanadyl phthalocyanine (t-bu VO Pc) is 
fully dissolved into chloroform at the rate of 0.690 mg/ml, with 5.2 mg/ml 
of antioxidant. This mixture is then warmed in an oven to 37.degree. C. A 
warm (37.degree. C.) plate of polycarbonate is then dipped into this 
mixture for 5 seconds. This plate is then immediately placed into an oven 
at the same temperature. After 24 hours the optical density (OD) at the 
wavelength of interest is read (1.9 OD). The plate is then placed in an 
oven at 60.degree. C. The temperature of this oven is then controlled 
according to Schedule A. The plate is then tested for OD (OD=2.0) and 
strain relief [polarized light or surface explosion with solvent 
(acetone)]. 
A protective coating may be applied. 
EXAMPLE 2 
2.70 mg/ml platinum octaethylporphyrin (Pt OEP) and 0.245 mg/ml t-bu VO Pc 
are dissolved into warm chloroform and a polycarbonate plate is diffused 
as in Example 1 above. After diffusion, the OD's are 3.7 (Pt OEP) and 1.4 
(t-bu VO Pc). After annealing by Schedule A, the OD's rise to 3.8 (Pt OEP) 
and 2.0 (t-bu VO Pc). These pieces may then be processed as in Example 1. 
This process involves the use of chromophores individually or in 
combination, with or without an ultraviolet absorber, and with or without 
antioxidants or other modifiers such as plasticizer hardeners, etc. 
Accordingly, a new and improved laser shield is provided by diffusing a 
layer of dye into the surface of a transparent protective laser shield as 
contrasted to merely applying an outer coating or painting a dye on the 
outer surface of the shield or incorporating the dye throughout the shield 
before it is formed or cast. This provides a more reliable controllable 
laser shield which simplifies the process of forming such a shield 
allowing for more accurate and uniform laser shields to be repetitively so 
formed. 
Since other changes and modifications varied to fit particular operating 
requirements and environments will be apparent to those skilled in the 
art, the invention is not considered limited to the examples chosen for 
purposes of illustration, and includes all changes and modifications which 
do not constitute a departure from the true spirit and scope of this 
invention as claimed in the following equivalents and claims thereto.