Coherent light generators – Particular temperature control – Liquid coolant
Reexamination Certificate
2000-05-08
2001-12-11
Davie, James W. (Department: 2881)
Coherent light generators
Particular temperature control
Liquid coolant
C372S036000, C372S075000
Reexamination Certificate
active
06330259
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to solid-state lasers and more specifically to a high power semiconductor laser diode pumped package that provides efficient coupling to a laser rod and integrates cooling of laser diode arrays and the laser rod.
BACKGROUND OF THE INVENTION
High-power laser diode packages and diode-pumped solid-state lasers are commonplace on the laser market. Diode bars consisting of 1-100 individual light-emitting stripes produce output power up to hundreds of watts under continuous-wave operation and higher peak powers in pulsed operation. A difficulty exists in efficiently coupling the light emitted from these high power laser diode arrays into a laser rod due to the inherent asymmetry of the laser diode output beam. Additionally, effective waste heat removal from both the diode arrays and the laser rod is very difficult in small, compact packages. Therefore, low thermal resistance and high heat transfer to the coolant is very desirable. Low thermal resistance values result in low diode operating temperature and longer diode lifetime as well as avoiding deleterious wave front distortions in the laser rod. Diode-pumped solid-state lasers in the prior art require two separate cooling loops for the diode arrays and the laser rod. This adds size as well as complexity to the overall package, which is a detriment when weight or optical cavity length issues are a consideration. Some prior art laser diode packages use micro channel cooling and some prior art rod laser designs use a small flow channel around the rod, but to our knowledge no prior art combines micro channel cooling of both the laser rod and diodes in one cooling loop. This is accomplished in the instant invention because the diodes are mounted to the laser rod using a transparent polymer adhesive, resulting in a monolithic or integrated structure, which is then easy to cool as a unit. In the prior art as well as the instant invention it is much more important to accurately control the temperature of the diodes by controlling the coolant temperature than it is to control the temperature of the laser rod, as the diode's output wavelength is temperature dependent. The rod's refractive index varies radially with the temperature as the heat flows from the center of the rod to the periphery, and this gradient slope changes very little in the operating temperature region of the diodes. Therefore, they can be cooled together with the same coolant. U.S. Pat. No. 5,521,936 to Irwin, issued May 28, 1996, discloses a laser device with a cooling tube around the laser rod and a separate sleeve surrounding the diode array that defines a coolant channel for cooling the diode array. U.S. Pat. No. 5,627,850 to Irwin, issued May 6, 1997, discloses a laser diode array but makes no mention of integrating the cooling of a laser rod with the laser diode array. Additionally, a key aspect of the invention is the use of a very high temperature (+1,000° C.) ceramic/copper direct bond process, whereas the instant invention uses a room temperature UV bonding process.
SUMMARY OF THE INVENTION
The present invention, a diode—pumped solid state laser called the “Laser Cube™”, is as versatile as it is revolutionary! From a couple of watts to multi-hundreds of watts, the “Laser Cube™” delivers performance and cost benefits that were heretofore deemed impossible. By creating a laser with the pump diode and gain media functioning as one, instead of disparate units, the “Laser Cube™” pushes efficiency, beam quality, end power data points to extreme levels while maintaining an ultra compact and cost effective package. This breakthrough, technology offers the following features and Benefits:
Ultra Compact (1 cm3) and
The miniature and lightweight
Lightweight (<3 g)
“Laser Cube ™” can be of
benefit to laser marking, and
robotic fiberless processes,
as well as many other
industrial, medical, military,
and telcom applications. OEM
users will appreciate the ease
with which the “Laser Cube ™”
can be integrated into current
designs.
High Power and High Beam
High power does not have to
Quality
come at the expense of beam
quality! Homogeneous pump
distribution as well as
advanced cooling technology
resu1ts in superior beam
quality.
Extremely Efficient
Exceedingly low thermal
Micro-Channel Cooling of
resistance results in both
Both Laser Diodes and
long diode life and excellent
Gin Medium
beam quality due to low
thermally induced wavefront
distortions.
Extremely Efficient
The “Laser Cube ™” is a close-
Utilization of Pump
coupled, radially side-pumped
Energy Without Focusing
design with integral
Lenses
diode/rod/reflector
construction. This results in
an extremely efficient laser
with low scattering and
reflection losses.
Very Low Parts Count
Novel room temperature
With Simple
assembly techniques results in
Manufacturing Techniques
a production friendly package
with low manufacturing costs
repeatable performance, and
high yields.
Ultra-Short Cavity
With a cavity length of 13 mm
length
or less, ultra-short pulsed Q-
switched and cavity dumped
lasers are possible due to the
short photon round trip time.
According to the present invention, a laser diode bar or bar's comprising a plurality of individual laser diode stripes are radially displaced, around a laser rod or gain medium where the longitudinal length (or array axis) of the laser diode bar is aligned along a major axis of the laser rod. The present invention integrates the pump diode's, laser rod, and reflector in a close-coupled, radially side-pumped construction for very efficient and homogeneous deposition of the pump energy into the central region of the laser rod, without focusing lenses. This integrated packaging results in a laser with low scattering and reflection losses. A unique cooling method is further integrated into the invention and is based on contiguous micro channel cooling of both the laser diode and laser rod. The invention is assembled as a monolithic unit at room temperature using UV adhesive technology that can be easily automated for robotic assembly. The unique packaging of the laser results in minimal parts count and further adds to a production-friendly package. The miniature size of one cubic centimeter or less and weight of less than three grams make it ideally suited for robotic fiber less material processing applications.
The present invention is a radial laser diode pumped solid state laser that utilizes “inserts” between each radial diode “spoke” that serves to define micro flow channels for cooling both the laser rod as well as the diodes. In the preferred embodiment a vapor deposited conduction layer, that is built up in thickness using an electroplating method is used to carry current radially to the diodes. In another embodiment, fingers or brushes on the inserts contact the diodes and carries through the diode radially around the rod.
The laser has two end pieces; and a laser rod is inserted through a hole in each end piece. In the preferred embodiment the laser rod has a highly doped core and an undoped annylan region. The doped core may be Y6 and the host may be phosphate glass. The end pieces each have five (in the preferred embodiment) extending radially from the laser rod. Slots in the spokes allow laser diode bars as well as artificial (contaminate protecting) diodes to be put in the slots. The number of slots and spokes can be any number, but 3-11 are reasonable with 5 being the preferred embodiment. Inserts are placed between the diode “spokes” and when potted in place serve to define a sleeve for containing coolant, thus confining the coolant to a thin layer close the rod and diodes. The last insert is split into two halves with an insulating layer between each halve. When a dielectric material is inserted and bonded in place each half insert becomes an electrode with foil electrodes slid into pre-manufactured slots on the top (external) portion of each insert half. In another embodiment small fingers extending from the inserts contact the diodes and carry current c
Davie James W.
Martin Rick
Patent Law Offices of Rick Martin P.C.
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