The invention described herein may be manufactured, used, sold, imported, and/or licensed by or for the Government of the United States of America.
The present invention applies to devices for generating laser beams. More particularly, the present invention applies to laser generators that produce pulsed or continuous wave laser beams. The present invention is particularly, but not exclusively, useful as a laser having a pump cavity that manipulates an input pump beam to couple more efficiently into a solid state laser gain material. This will yield an output laser beam from the solid state gain material with greatly increased output power and efficiency relative to similarly sized devices without the input pump cavity device.
The use of laser devices for rangefinding or target designation purposes is well known in the prior art. To be effective, these devices should have certain desirable qualities. Specifically, these devices should be small, lightweight and easy to manufacture. Additionally, the devices should produce a pulsed laser beam that has good output power and a high pulse repetition rate that are suitable for ranging and designation operations.
Previous laser transmitters used in range finding and designation have had some, but not all, of these characteristics. For example, some flashlamp-pumped solid-state laser devices have been used to generate a laser beam of sufficient power for these purposes. However, although flashlamp-pumped lasers effectively generate a single laser pulse, they are not capable of being pulsed at a high pulse repetition rate without adding cumbersome cooling systems, which increases the size and power requirements of the laser transmitter.
Diode-pumped solid-state lasers lead to more efficient pulsed lasing operation and therefore are suitable for range finding and designation purposes, but they require additional optical components to efficiently couple the pump radiation into the solid state gain material. One way to increase the pump coupling in diode-pumped solid-state lasers is to collimate the input pump light before the input pump light enters the laser crystal. To do this, however, an arrangement of collimation lenses is required, and the added weight is an undesirable characteristic for the range finding/designation type of laser. Further, the incorporation of collimation lenses creates significant optical alignment issues that complicate the assembly process for the laser.
It so happens that by implementing the geometry of the laser pump cavity, the coupling efficiency of a solid-state diode-pumped laser device can be increased without using a lens arrangement to collimate input pump light. This obviates the additional weight and assembly disadvantages that are inherent when collimation optics are used with a diode-pumped, solid-state laser device. The geometry of the laser pump cavity can further decrease parasitic lasing within the gain material, which further results in greater lasing efficiency and greater output power for the laser device.
In view of the above, it is an object of the present invention to provide a diode-pumped laser device that can be used for rangefinding and designation purposes. It is another object of the present invention to provide a diode-pumped laser device which provides an output pulsed laser beam without requiring collimation of the input pump light. Another object of the present invention is to provide a diode-pumped laser device with a pump cavity having a predetermined geometry that further reduces parasitic laser modes within the gain material during operation thereof. Another object of the present invention is to provide a diode-pumped laser that is lightweight and battery-operated. Yet another object of the present invention is to design a laser which is easy to use, and which is comparatively cost-effective to manufacture.
A laser device in accordance with the present invention includes a base, a pair of opposing walls that extend uprightly from said base and a cover that is placed on the opposing walls. The base, opposing walls and cover combine to form an enclosure for receiving a laser slab, and they further define a pump cavity for receiving pump light therein. The pump cavity has a decreasing taper, from a maximum width at the input end of the pump cavity to a minimum width at the output end of the cavity.
The lasing device of the present invention further includes the aforementioned laser slab, which is positioned within the pump cavity. To do this, a longitudinal slot is formed at the bottom of the enclosure, in the pallet. The longitudinal slot extends along the length of the enclosure in fluid communication with the pump cavity. The width of the longitudinal slot corresponds to a thickness of the laser slab, and the laser slab is inserted therein during assembly so that it extends upwardly from the longitudinal slot into the pump cavity.
The opposing walls of the cavity are plated with a material which is non-oxidizing and which is highly reflective of input pump light in the infrared range. In the preferred embodiment, the opposing walls are gold-plated. Laser pump light is provided from the input end of the device. A portion of the input laser pump is received in the laser slab input end. The remaining portion of the laser pump is received in the pump cavity. The input pump light is reflected off the gold-plated walls of the enclosure and into the sides of the laser slab, where it is absorbed by the gain material and thus contributes to the solid state laser output. In this manner, the input pump light is used more efficiently by the total reflecting cavity laser of the present invention.
The novel features of this invention will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar characters refer to similar parts, and in which:
Referring initially to
Referring now to
To facilitate assembly of the device, the base 14 is formed with a longitudinal slot 32. The longitudinal slot extends along the length of the enclosure in fluid communication with the pump cavity. Preferably, the slot has a uniform slot width wslot that is equal to wmin, and wslot also corresponds to the thickness t of the laser slab 22 (See
In the preferred embodiment, the opposing walls are coated with a material that is highly reflective in wavelength range at which the pump is emitted by the pump source. For a diode pump, the opposing walls are preferably coated with a material which is highly reflective in the infrared spectrum range, and further which does not oxidize. Preferably, the opposing walls are gold-plated in a manner well known in the art. Only the opposing walls and the internal surfaces of the pump cavity need be coated to practice the present invention, although in practice, it is actually easier to gold-plate all of the surfaces of the enclosure simultaneously.
The monolithic nature of the device is important in that the laser slab blocks 22a, 22b, 22c, supporting laser pallet 23, and cover 18, encompassing the pump cavity 20 and other components mentioned above are mounted directly to the base 14, without requiring the use of optical holders. The manner in which this is accomplished is described more fully in U.S. Pat. No. 6,373,865 by John E. Nettleton et al., entitled “Pseudo-Monolithic Laser With An Intracavity Optical Parametric Oscillator”, which is assigned to the same assignee as this patent application and which is incorporated herein by reference.
The gain material in the laser slab 22a, 22b and 22c, is preferably made of a Neodymium doped Yttrium Aluminum Garnet (Nd:YAG) crystal that is doped to between zero and five percent (0-5%). However, it is understood that other materials could also be used for the doped rectangular prism portion, such as Neodymium Doped Yttrium Orthovanadate (Nd:YVO4), Neodymium Doped Yttrium Lithium Fluoride Nd:YLF and Neodymium Doped YAlO3 Perovskite (Nd:YAP) or doped glass materials. The pallet 23 would then be fabricated from an undoped material that is thermally compatible as described above. The input end 28 and output end 30 are coated with reflective or antireflective coatings for diode laser pumping and lasing operations in a manner well known in the art.
As shown in
The operation of the device can be shown and described in greater detail by referring to
While the total reflective cavity for a solid state laser, as herein shown and disclosed in detail, is fully capable of obtaining the objectives and providing the advantages above stated, it is to be understood that the presently preferred embodiments are merely illustrative of the invention. As such, no limitations are intended other than as defined in the appended claims.