Line scanner

A device for scanning a linear section of a UV beam to determine the local intensity thereof along the linear section. The UV beam impinges upon flourescent material and the fluorescent emission distribution is meausred to indicate the UV beam intensity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a system for analyzing the intensity 
distribution across an ultraviolet (UV) laser beam. The various commercial 
and medical applications of laser beams makes it necessary to monitor and 
control the intensity distribution across the face of the beam and various 
techniques have been devised for measuring the intensity profile of laser 
radiation. 
One such technique is disclosed in the above cited patent application in 
which a beam intensity profilometer produces fluorescent emission 
distribution having a spacial distribution linearly proportional to the 
local intensity of the incident UV beam impinging upon the profilometer. 
The spacial distribution of the UV beam is analyzed as a function of the 
fluorescent emission. 
The present invention makes use of the fluorescent materials disclosed in 
the above cited application which provide a visible fluorescent emission 
as a function of the impinging UV beam to be analyzed. However, the 
present invention analyzes a line or linear section across the face of the 
impinging UV laser beam. 
2. Description of the Prior Art 
A number of prior patents exist directed to the measuring of the wave front 
of a laser beam and these include: U.S. Pat. Nos. 3,462,601; 3,549,886; 
3,598,998; 3,680,965; 4,260,251; 4,376,892; 4,490,039; 4,602,272; and 
4,670,646. However, none of these patents disclose the use of a strip of 
UV activated fluorescent material as with the present invention. 
A description of various prior art systems was disclosed in a paper 
entitled "Characterization of UV Laser Beams Using Fluorescence", by 
Telfair et al., delivered at the Society of Photo-Optical Instrumentation 
Engineers (SPIE) on Jan. 15, 1988 in Los Angeles, Calif. and in articles 
entitled "Choosing And Using Laser-Beam-Profile Monitors", by Edwards, in 
Laser Focus/Electron-Optics, May 1987, pgs. 76-84 and "Laser Beam 
Profiling The Automated Way", by Rypma, Photonics Spectra, August 1987, 
pgs. 67-74. 
A material which has been found to be particularly useful in converting 
invisible UV radiation to visible fluorescent radiation is a rare earth 
doped garnet, Ce 3+: Y3 A15 O12 (YAG). The ability of this material to 
fluoresce is described in an article entitled "CATHODOLUMINESCENT GARNET 
LAYERS" by J. M. Robertson, Thin Solid Films, 114 (1984) 221-240. The 
article, however, does not disclose the concept of measuring a high 
powered UV laser beam with an instrument incorporating the doped YAG 
material. 
The above patents and additional publications are described and discussed 
in the above-cited parent application. None of this prior art discloses 
the present system of utilizing UV activated fluorescent material to 
analyze a section of a UV beam. 
SUMMARY OF THE INVENTION 
Against the foregoing background it is a primary object of the present 
invention to provide a line scanner for displaying the intensity 
distribution along any line across an incident UV beam such as that 
produced by an excimer laser. 
It is another object of the present invention to provide a conveniently 
held portable line scanner for analyzing and diagnosing the intensity 
distribution of a UV laser beam. 
It is a further object of the present invention to provide a hand held UV 
beam line scanner that is adapted to be conveniently moved across the face 
of a laser beam to provide a intensity distribution analysis of the beam. 
The scanner of the present invention is a direct reading instrument for 
displaying the intensity distribution along any line in a UV beam such as 
that produced by an excimer laser. The line is formed by a narrow slit at 
the entrance of the aperture and the beam slice formed by this slit 
impinges on fluoresent material located behind the slit. The fluorescence 
distribution along the slit is proportional to the local UV beam intensity 
and, hence, represents the intensity distribution of the UV beam along the 
line.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The line scanner of the present invention analyzes the beam intensity of a 
UV beam by converting the UV radiation to visible light by the use of a 
fluorescent material of the type described in the above-cited parent 
application. The selection of the proper fluorescent material is an 
important part of the present invention. It must have certain 
characteristics such as a high damage threshold for withstanding power 
intensity of high energy UV lasers, and it must emit a fluoresence whose 
intensity is substantially linearly proportional to the local intensity of 
the incident UV beam. The material chosen is from a class of materials 
which are optically transparent to fluorescent wave lengths. 
In the preferred embodiment, the fluorescent material is a Ce 3+; Y3 A15 
O12 (YAG). Besides cerium (Ce), other rare earth elements suitable for 
doping include neodymium (Nd), lanthanum (La) and Europium (Eu). However, 
it is within the terms of the present invention to dope the crystal with 
any suitable rare earth. 
The fluorescent material can also comprise rare earth doped glasses. The 
glass could consist of any class of glasses, such as borosilicate glass, 
doped with any of the rare earth materials including Ce, Nd, Eu and La. 
The fluorescent material can also be suspended in plastic. For example, a 
rare earth doped crystal, a rare earth doped glass or an undoped crystal 
could be pulverized and suspended in a plastic. Also, a plastic can be 
modified by either doping or chemically adding a dye or a rare earth 
element. 
Referring now to FIG. 1, there is shown an incident UV beam 10 having for 
example an intensity distribution shown by line 12 and vector arrows 14. A 
fluorescent distribution element 16 is interposed in the path of UV beam 
10 to receive the incident radiation and provides fluorescent radiation in 
the visible spectrum as indicated at 18. The resulting fluorescent 
radiation is substantially linearly proportional to the local intensity of 
the incident ultraviolet beam 10. Thus by analyzing the fluorescent 
radiation and noting the intensity thereof, the UV laser beam 10 is 
diagnosed and analyzed. 
Whereas the invention of the above-cited parent application provides a 
plate of substantial area to produce the fluorescent emission representing 
the entire area of interest of the incident UV beam, the present invention 
scans a line or linear section of the UV radiation and hence only a line 
or linear section of the incident beam is analyzed at any point in time. 
Referring now to FIG. 2, there is shown the incident UV radiation 10 as 
from an eximer laser. The line scanner of the present invention includes a 
head 20, a handle 21, light transmission element 24, and readout unit 25. 
The line scanner head 20 has a linear aperture 22 which permits a linear 
section of the incident beam to enter the line scanner head for analysis. 
As will be hereinafter described in detail, the entering line section of 
the beam will impinge upon a strip of fluorescent material of the type 
above described and also described in the parent application which will 
fluoresce linearly in accordance with the incident UV beam. The 
fluorescent radiation is transmitted by a plurality of optical fibers 
generally indicated at 24 to the readout unit. 
Referring now to FIG. 3, there is shown an exploded view of the head unit 
20. The unit includes a base member 28 having a cutout portion 30 which 
receives a strip of fluorescent material 32 and the end of a ribbon 24 of 
optical fibers. With the ribbon and fluorescent strip in place within the 
base 28, a cover plate 34 having a rectangular opening 36 is secured to 
the base member 28. Plates 38, 40 provide an aperture slit 22 through 
which the incident radiation passes to impinge upon the fluorescent strip 
32. The entire head assembly is held together by screws as 43. 
Referring now to FIG. 4, there is shown the assembled head unit with the 
fluorescent strip 32 located directly behind the aperture 22. The ribbon 
of optical fibers 24 enters the head assembly and terminates just behind 
the fluorescent strip positioned to receive the fluorescent emission. The 
fibers collect the fluorescence and coherently transmit it to the readout 
unit 25. A coherent fiber bundle must be used to insure a one-to-one 
transfer of the fluorescence to the display. The fiber ribbon typically 
consists of about 250 fibers molded into a flat ribbon approximately 0.2 
mm. thick, 45 mm. wide and 2 m. long. No optics are necessary at the input 
end of the fiber because the acceptance angle of each fiber limits 
fluorescence collection to a small area on the plate directly in front of 
the fiber. The size of the collection area is determined by the acceptance 
angle of the fiber and the distance between the fiber and the plate 32. 
It is understood that the width of the entrance slit determines the width 
of the line section of the beam 10 that is analyzed. It has been found 
that an aperture width of 0.5 mm. provides adequate resolution for 
analysis. The resolution can be increased by decreasing the width of the 
aperture to analyze a narrower linear section of the incident UV beam. 
Referring not to FIG. 5 there is shown a modification in which the lower 
portion of the cutout 30A in the base member is of a greater depth to 
permit the fiber ribbon 24A to be curved at its input end as at 25A. The 
forward bend in the ribbon is directed to the rear surface of the 
fluorescent strip 32A to enhance the light gathering of the fluorescent 
emission by the optical fibers. 
Referring back to FIG. 2 it is seen that the optical fiber ribbon 24 
connects to a detector unit 42 which may include a plurality of detectors 
equal in number to the optical fibers such that the output fluorescence of 
each fiber is converted to an electrical signal. These detectors may be of 
any conventional photo detector type and the fluorescence may be coupled 
to the detectors by appropriate lenses. Scanning the individual detectors 
in the array will produce a signal that can be displayed, for example, on 
a oscilloscope 44. It is understood that the electronics will also produce 
a trigger signal each time the detector array is scanned that triggers the 
start of the oscilloscope sweep. The particular design of the detectors 
and electronic control for the oscilloscope can take any conventional form 
and does not form part of the present invention. 
In operation, the operator holding the head 20 will interpose it in the UV 
beam to be analyzed or diagnosed. The entrance slit 22 will determine a 
slice or linear section of the beam that is passed to the fluorescent 
strip 32. The resulting fluorescence, the intensity of which is linearly 
proportional to the intensity of the slice of the UV beam being scanned, 
will be passed to the readout unit 25 and appear on the oscilloscope 44. 
The operator may move the head 20 so that the aperture 22 sweeps a large 
area of the UV beam or the entire beam and in this manner can obtain a 
readout of the intensity profile of the full area of interest of the beam. 
Referring now to FIG. 6, there is shown an embodiment in which the ribbon 
of optical fibers 24B are of fluorescent material such as sapphire or the 
other materials described above. Plates 38B and 40B provide an aperture 
slit 22C through which incident radiation from beam 10B passes to impinge 
upon a line of fluorescent fibres 24B. It is seen that this embodiment 
eliminates the separate strip of fluorescent material as 32 and 32A in 
FIGS. 4 and 5. 
In FIG. 6, a proportional amount of the fluorescent radiation 14C will be 
transmitted through the optical fibres 24B to the readout 25. 
Having thus described the invention with particular reference to the 
preferred forms thereof, it will be obvious that various changes and 
modifications may be made therein without departing from the spirit and 
scope of the invention as defined in the appended claims.