Laser safety shutoff system

A safety light responsive shutoff switch is provided for a hand-held infrared laser light source to prevent irreparable eye damage to persons who may inadvertently look into the light exit opening of the laser light source while it is operating. This is accomplished by concentrically mounting normally-closed infrared light responsive photoelectric Darlington safety switches around the light exit end of the light source. Light reflected from the laser light source off an object intruding into the laser beam within a danger zone (typically zero inches to ten inches from the light exit opening) produces reflected light at the frequency of the laser light source of sufficient intensity to operate the photoelectric Darlington safety switch devices to turn off the power supply to the laser light source. Light reflected from objects which are outside of the danger zone is of insufficient intensity to operate the light responsive safety switches.

RELATED APPLICATION 
This application is related to the commonly assigned, copending 
application, Ser. No. 07/208,457, filed June 20, 1988. 
BACKGROUND 
The above-identified co-pending application is directed to a portable solid 
state light emitting device employing light emitting diodes (LEDs) and 
laser diodes (LDs). The device disclosed in that application is an 
infrared zoom illuminator capable of providing either a narrowly focused 
beam of infrared light energy from the light source or for illuminating a 
relatively large area, depending upon the manner of operation of the 
focusing element in the device. Since the light emitted from the infrared 
light source is not visible to the naked eye, a person who is not wearing 
infrared night vision equipment cannot determine whether the device is 
operating. Provisions may be made to provide an on/off indicator light on 
the device which emits light in the visible wavelength range. This still, 
however, does not satisfactorily tell an operator if the infrared laser 
light source is burned out or otherwise inoperative. 
Even though the infrared light is invisible, there is a strong temptation 
on the part of some users of such devices to turn them around and look 
into them to see if the device is on or off. The intensity of laser light 
in the infrared region produced by devices of the type disclosed in the 
above-identified co-pending application, or by other laser light sources, 
is such that even a momentary exposure of the eye to such light may cause 
irreparable damage to the retain resulting in partial or total, permanent 
blindness. Consequently, such laser light sources typically are provided 
with warning labels on them to warn users never to look into the light 
source or to point the device at someone who is in near proximity to it. 
Even so, a substantial danger of accidental blinding still exists. 
The above-noted dangers are described in safety manuals given to operators 
of such devices. A great danger for permanent eye damage from devices of 
the type disclosed in the above-identified co-pending application occurs 
in what is known as Class III laser beam intrusion. Class IV devices are 
also a source of danger. Typically, this is for intrusion in the zero to 
ten inch range (or slightly beyond). By intrusion, it is meant that an 
object (such as the eye of the operator of the device) is placed within 
the emitted beam of laser light at a distance which is equal to or less 
than the intrusion distance. For Class III beam intrusion, this "danger 
zone" range is a maximum of ten inches, obviously extending down to zero 
inches. 
Consequently, it is desirable to provide a safety shutoff system to turn 
off the laser light source automatically if any one or anything intrudes 
into the laser beam within the danger zone distance. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved laser safety 
shutoff system. 
It is another object of this invention to provide an improved laser safety 
shutoff switch system for use with any laser device. 
It is an additional object of this invention to provide an improved laser 
safety shutoff switch system for use with laser light sources operating in 
any region of the spectrum, including the infrared region. 
It is a further object of this invention to provide an improved light 
responsive laser safety shutoff switch system capable of responding to 
light reflected from a laser light source from objects which intrude into 
the laser beam within a pre-established danger zone distance. 
In accordance with a preferred embodiment of this invention, an infrared 
illuminator includes a housing with a light exit opening in it and an 
infrared laser light source mounted in the housing. The power supply is 
provided with a control switch for selectively interconnecting and 
disconnecting the light source and the power supply. In addition, a 
normally closed, light responsive, safety switch is located in the housing 
and is connected in series circuit with the light source and the power 
supply for opening such circuit in response to light of a predetermined 
wavelength impinging on the light responsive safety switch means. In a 
more specific embodiment, the laser light source emits light having 
wavelengths in the infrared region; and the light responsive safety switch 
is responsive to light of wavelengths in the same infrared region 
reflected from objects intruding into the beam of light from the light 
source within a pre-established distance from the light source.

DETAILED DESCRIPTION 
Reference now should be made to the drawing in which the same reference 
numbers are used throughout the different figures to designate the same 
components. In addition, the specification of the above-identified 
co-pending application, Serial No. 07/208,457 also is incorporated herein 
by reference, and the same reference numbers are used in FIGS. 1 and 2 
which correspond to the reference numbers for the same components as 
disclosed in that co-pending application. 
FIGS. 1 and 2 are similar to FIGS. 4B and 4C, respectively, of the 
above-identified co-pending United States Application. These figures 
depict the forward end of a portable laser infrared illuminator which has 
been modified in accordance with a preferred embodiment of this invention. 
The main body portion of the device is made of metal. Batteries, one of 
which (26) is shown in FIGS. 1 and 2, are placed in the main body portion 
11 to act as a power supply for the device. This is done in a manner not 
shown in FIGS. 1 and 2 (but described in detail in applicant's co-pending 
application). The battery 26 is urged upwardly, as viewed in FIGS. 1 and 
2, against an electrical connector block 30 made of insulating material. 
This connector block has a projection or extension 31 on it which extends 
upwardly into a circular opening formed by the internal diameter of an 
inwardly turned shoulder 33 on the end of the housing 11. This shoulder 33 
limits the movement of the battery 26 and the block 30 when they are 
pressed upwardly, as viewed in FIGS. 1 and 2, to the position shown in 
FIG. 2. 
Without placement of a cylindrical outer portion or head 14 made of 
insulating material, a spring (not shown) urges the battery 26 into 
physical and electrical contact with a conductive contact member 32 which 
engages the end contact on the battery 26. When the head 14 is not in 
place, the connector block 30/31 is moved to the position shown in FIG. 2. 
This causes the upper surface of the block 30 to physically engage the 
lower surface of the shoulder 33. This in turn causes contact between a 
conductive metal connector tab 35 and the shoulder 33 of the metal housing 
11. The connector tab 35 also is electrically interconnected with a socket 
41 to complete an electrical connection from the socket 41 through the tab 
35 to the shoulder 33 of the metal housing 11. Another electrical socket 
40 is interconnected by a wire or conductor 34 to the contact 32, which 
engages the end of the battery 26. 
The assembly is completed in the same manner described in applicant's 
co-pending application by threading the head 14 onto the end of the 
housing 11. Mating threads of a relatively coarse pitch are provided on 
the outside of the body 11 and the inside of the head 14, respectively. A 
rubber or neoprene O-ring 42 fits over the body 11 and engages the open 
end of the head 14 to provide a water-tight seal between the two parts, as 
shown in both FIGS. 1 and 2. An encapsulated electronics package housing 
50 is placed within the head 14, and the package 50 has a base plate 51 on 
it through which a pair of male electrical contact pins 44 and 45 extend. 
These pins are located to fit within, and make electrical contact with, 
the sockets 40 and 41, respectively. 
The encapsulated electronics package 50 is loosely held within the head 14. 
When the pins 44 and 45 are inserted into the sockets 40 and 41, the head 
14 is permitted to rotate about the housing 50, which is prevented from 
rotation by the connector pins 44 and 45. This causes it to remain in the 
orientation shown in FIGS. 1 and 2 with respect to the housing 11. 
A pair of current limiting resistors 54 and 55 also are mounted in or 
encapsulated within the housing 50. The lower end of these resistors are 
connected to the contact pins 44 and 45, respectively. The upper end of 
the resistor 54 (as viewed in FIGS. 1 and 2) is connected in a series 
circuit through a connector 81 with four photoelectric Darlington switch 
devices 75, 76, 77 and 78 connected together in series. The last of these, 
switch 78, is connected through a connector 80 to the terminal on one side 
of an infrared laser diode 60. 
The diode 60 may be of any suitable type (such as GaAlAs or GaAs, with a 
wavelength of 780 nm). This laser diode produces power on the order of 
five (5) milliwatts or more, and produces a laser beam (in the infrared 
red wavelength spectrum) having a diameter of approximately 1.5 microns or 
less in size. The orientation of the light emitted from the laser diode 60 
is such that the output beam is centered on the axis of the housing 11 and 
the head 14. The other side of the laser diode 60 is connected through a 
connector 69 to the upper terminal of the resistor 55. 
The on/off switching operation to connect power from the battery 26 through 
the above described circuit and back again is effected through the 
connector tab 35 and the underside of the shoulder 33. These elements are 
diagrammatically depicted in the circuit diagram of FIG. 4. FIG. 1 
illustrates the operation of this switch 33/35 when it is open, and FIG. 2 
illustrates the closed position of this switch. The opening and closing of 
the switch is effected by the relative rotation of the head 14 with 
respect to the housing 11 in the manner described in greater detail in the 
above-identified co-pending application. 
To ensure that no visible light is emitted from the device, a filter 61 
also may be cemented into a circular opening in the upper end of the 
housing 50 in contact with the light emitting end of the laser diode 60. 
The characteristics of the filter 61 are such that it passes wavelengths 
of light in the infrared region. If visible light leakage is not 
considered detrimental for some applications, the filter 61 could be 
eliminated, although in most cases it is desirable to provide the filter 
61. 
The head 14 has a relatively large circular hole through it at the upper 
end, as is clearly shown in FIGS. 1 and 2. Three different elements are 
mounted in and cemented in place in this hole. At the center is a suitable 
infrared transparent lens 65. This lens then is secured to an opaque (both 
to visible and infrared light) shield ring 70 which has a downward 
depending flange 71 on it extending around the laser diode 60. This 
ensures that no light emitted from the diode 60 passes through either the 
filter 61 or lens 65 laterally outwardly into other parts of the device 
shown. A third concentric circular element in the form of an optically 
clear ring 74 for reflected infrared energy is located to directly overlie 
the photo responsive parts of the photoelectric Darlington switches 75, 
76, 77 and 78. Thus, the ring 74 transmits reflected infrared energy 
through the ring to the photoelectric Darlington switches 75 through 78. 
The lens 65, opaque guard ring 70, and infrared transparent ring 74, all 
are cemented in place in the end of the housing 14 and rotate with it. The 
other elements shown within the housing 50 rotate with or remain with the 
portion 11 of the device. 
The photoelectric Darlington switches 75 through 78 are selected from 
suitable commerically available silicon detectors and are configured to be 
responsive to the wavelengths to be detected. Typically, these wavelengths 
are the same wavelengths which are transmitted by the laser 60. In the 
example under consideration, the laser 60 transmits light of infrared 
wavelengths. Consequently, the selection of the particular type of photo 
responsive Darlington switch depends upon the wavelength of the infrared 
light transmitted by the laser 60. For the near infrared region (up to 1.5 
microns), the photo responsive portion of the Darlington switches 75 
through 78 preferably is Indium Antimonide (InSb) or some other suitable 
silicon or Gallium compound. For infrared light from the laser 60 in the 
mid infrared range (up to 5 microns), Indium Antimonide detectors or 
detectors made of a lead salt or doped silicon may be used. For the far 
infrared wavelengths (up to 12 microns and beyond), extrinsic silicon or 
Mercury Cadmium Telluride compounds are preferred. All of these photo 
responsive compounds presently exist, and the selection of the particular 
one for use as the photo responsive portion of the Darlington switches 75 
through 78 depends upon the wavelength of the light transmitted from the 
laser 60. 
The device operates, as diagrammatically illustrated in FIG. 4, to prevent 
unintentional injury from occuring by turning off the laser 60 
instantaneously any time there is a beam intrusion within a 
pre-established distance from the upper end of the device shown in FIGS. 1 
and 2. Typically, this distance is less than twenty (20) inches, and 
preferably it is between zero inches and ten inches. If anyone or anything 
intrudes into the laser beam emitted from the laser diode 60 within this 
zone, called the danger zone, the photo electric sensors 75 through 78 
operate to open the power circuit to the laser diode 60, turning it off. 
This is a nearly instantaneous operation, taking place in approximately a 
few microseconds. The time the switches 75 through 78 remain operated to 
open the circuit may be established by a built-in time delay or by means 
of a separate reset switch (not shown). 
The operation is such that whenever an intrusion within the danger zone 
occurs, a portion of the light emitted from the laser diode 60 through the 
lens 65 reflects off the intruding object (shown as the dotted line on the 
right hand side of FIG. 4) and is reflected through the ring 74 onto one 
or more of the photo electric Darlington switches 75 through 78. When 
light of sufficient intensity impinges upon any one of these diodes, the 
Darlington switch controlled by it opens, thereby breaking the power 
circuit between the battery 26 and the laser diode 60. The amount of light 
to required to do this is selected by the trigger level of the Darlington 
switch, the infrared light transmission properties of the ring 74 and the 
intensity of the light emitted from the diode 60. These varying parameters 
may be emperically determined or calculated to cause the operation of the 
photo Darlington switch devices 75 through 78 to occur whenever such an 
intrusion into the danger zone occurs. It is readily apparent that for any 
target (whether it is a person or some other physical object) which is 
encountered by the beam from the diode 60 outside the danger zone, 
insufficient light is reflected back to the photo responsive Darlington 
switches 75 through 78 to operate them. Consequently, these normally 
closed switches remain closed; and the device operates in the manner 
described in detail in the above-identified co-pending application. 
The device which is shown and which has been described above effectively 
operates to shut off the laser diode light source before any permanent 
damage can occur to the eye of a person in the event that an intrusion, in 
fact, is the eye of a person located within the danger zone and looking at 
the lens 65 of the device. The foregoing description of the preferred 
embodiment of the invention should be taken as illustrative only and not 
as limiting of the invention. Various changes and modifications will occur 
to those skilled in the art without departing from the true scope of the 
invention as defined in the appended claims.