Coherent light generators – Particular temperature control
Reexamination Certificate
2002-07-24
2004-11-02
Porta, David (Department: 2878)
Coherent light generators
Particular temperature control
Reexamination Certificate
active
06813289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to portable laser devices based on a solid-state laser technology, and in particular it relates to hand-held laser devices with direct cooling of a laser rod assembly.
2. Discussion of Background and Prior Art
The laser radiation generated by solid-state lasers is widely used in the industry and medicine. As illustrated in
FIG. 1
a typical laser emitted assembly consists of a laser rod
6
, an exciting lamp
3
, a reflector
8
, a pair of resonant mirrors
5
,
6
and a cooling arrangement
7
,
9
. The wavelength of a laser radiation is determined by the type of a laser rod. The duration of the laser impulse and its energy are primarily set by the power source associated with the laser device. Among lasers most commonly used in the medical field are solid-state lasers utilizing crystals of yttrium aluminum garnet doped by ions of neodymium, erbium, holmium, and also ruby laser on the basis of emery doped by atoms of chromium.
The portability is an important aspect for the effective usage of the medical laser devices. In this respect, miniature laser devices capable of being fitted in a hand of an operator are of great interest to the medical professionals. Among major elements of such handheld laser devices are: a cooling arrangement and a system of aiming and focusing of a laser beam. A power source of such laser device can be positioned either inside or outside of the casing. In the hand-held laser devices a special attention has to be paid to minimizing their dimensions and weight. Exciting lamps, which are mainly used in pulsed solid-state lasers, emit optical radiation which is within the range between 0.2 and 0.7 microns. This range is substantially greater than an absorption band of the laser rod. Therefore, a considerable portion of the exciting lamp optical radiation which passes through the laser rod is wasted by converting into a useless thermal energy. As a result, when the exciting lamp constantly pulses its radiation in the direction of the laser rod to generate a required laser output beam, the temperature of the laser rod rises, diminishing its efficiency. For example, when the temperature of the erbium laser rod rises to 70° C., the laser radiation is almost absent. This makes an efficient cooling arrangement to be a very important component of stable and efficient operation of solid-state laser rod assemblies. In resolving these problems an important factor is that an extensive pulsed thermal energy must be dissipated from a very small surface of the laser rod. Thus, development of effective, miniature cooling arrangements adapted for the removal of thermal energy from the laser rod assemblies is considered to be a key problem in the development of hand-held laser devices.
Currently, there are two basic methods utilized to facilitate heat dissipation from the laser rod assemblies. The first method is based on utilization of a gaseous cooling medium, whereas according to the second method, the liquid cooling medium is used. Minimal absorption of the exciting lamp optical radiation by the coolant, stability of the optical medium and relatively small weight and size of the cooling system are among important advantages of the first method. The liquid cooling of the second method provides considerably higher (compared to the gaseous cooling) heat transfer efficiency from the laser rod to the coolant. On the other hand, use of the liquid coolants does not provide the long-term stability of the optical medium, and often leads to contamination of the optical surfaces of the laser rod, exciting lamp and reflector. Furthermore, the currently available liquid cooling arrangements substantially increase weight and dimensions of the respective laser devices.
It is known that the amount of heat which has to be removed from a laser rod or crystal is dependent upon the following factors: the size of the cooling surface; the difference between the temperature of the laser rod and the temperature of the cooling agent, as well as the speed of the cooling agent in the vicinity of the laser rod surface. When the liquid cooling is utilized, the coefficient of heat transfer is much greater than that of the gas cooling. This is the reason why in the pulsed laser devices, the gas cooling is used very infrequently. However, utilization of the liquid cooling for the cooling of the laser rods and the exciting lamps increases the dimensions of the laser emitter, as well as brings up many other problems associated with the liquid cooling discussed hereinabove.
There are also known cooling arrangements for laser devices which combine the usage of the gaseous and liquid cooling principles. One such arrangement is disclosed by U.S. Pat. No. 5,481,556. According to this disclosure the outer casing of laser cavity containing an exciting lamp, a laser rod and a reflector is cooled by a liquid circulating within a closed circuit surrounding the laser cavity. The liquid coolant and the laser cavity are cooled by an air flow generated by a fan situated within the housing. One of the major drawbacks of this arrangement is that the heat removal from the laser rod is carried out indirectly through cooling of the exterior of the entire laser cavity. This approach substantially diminishes the efficiency of the laser assembly cooling process.
SUMMARY OF THE INVENTION
One aspect of the invention provides a hand-held laser device containing a casing formed with a substantially hollow interior space. A laser emitter is provided within the interior space and includes at least an exciting lamp and a laser rod. A source generating a stream of gaseous coolant is provided within the interior space. A fluid cooling arrangement at least partially surrounding the laser rod is disposed within the stream of gaseous coolant for heat removal therefrom.
The fluid cooling arrangement can be in the form of a liquid cooling arrangement which comprises a housing having an elongated opening passing therethrough. The elongated opening is adapted to at least partially receive the laser rod. An intermediate accumulation chamber is disposed within the casing, so as to communicate with the housing.
As to another embodiment of the invention, at least one connecting element for communication between the housing and the intermediate accumulation chamber is provided. A pumping arrangement is associated with the connecting element, so as to provide circulation of a liquid coolant between the housing and the intermediate accumulation chamber. A buffer space is formed between the exterior and interior walls of the casing. The buffer space communicates with the intermediate accumulation chamber. The exterior of the housing and intermediate accumulation chamber are situated within the stream of gaseous coolant, so as to facilitate heat removal from the liquid coolant contained thereinside. A plurality of cooling fins are formed of a heat conducting material and extend from the inner wall of the casing. The plurality of cooling fins are positioned within the stream of gaseous coolant for heat removal from the liquid coolant situated within the buffer space.
As to a further embodiment of the invention, a hand-held laser device is provided consisting of an elongated casing formed with a substantially hollow interior space. A laser emitter is formed by at least an exciting lamp and a laser rod. A low pressure zone is generated within the interior space to facilitate formation of a stream of gaseous coolant thereinside. An inlet opening is situated at a front end of the housing. A low pressure zone is formed at the rear end of the housing. A stream of gaseous coolant enters the interior space through the opening and axially extends in the front to rear direction for heat removal from the laser emitter. A filter is provided at an inlet opening for filtering a stream of gaseous coolant entering the interior space. Alternately, an inlet opening can be formed at a rear area of the housing, so that upon entering the interior space, the stream of gaseous cool
Efremkin Pavel V.
Gruzdev Valentin A.
Fridman Lawrence G.
Innotech USA Inc.
Monbleau Davienne
Porta David
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