High power and multiple wavelength Raman laser of visible light

Abstract

A multi-wavelength laser device equipped with a linear cavity along which a first direction and a second direction opposite to the first direction are defined is disclosed. The apparatus includes, along the first direction, a first optical component, a gain and Raman medium, a sum frequency generation crystal, a first second-harmonic generation crystal and a second optical component. The first optical component allows a pumping light to transmit therethrough and be incident in the first direction. The gain and Raman medium receives the pumping light from the first optical component and generates a first infrared base laser light having a first wavelength and a second infrared base laser light having a second wavelength. The first and second optical components form a laser cavity for oscillation of these two infrared base laser lights. The sum frequency generation crystal receives the first and second infrared base laser lights and generates a first visible laser light having a third wavelength. The first second-harmonic generation crystal receives the first infrared base laser light and generates a second visible laser light having a fourth wavelength. The second optical element allows the first and the second visible laser lights to emit out along the first direction.

Claims

1. A method for generating a multi-wavelength laser light including a first visible laser light having a first wavelength and a second visible laser light having a second wavelength, the method comprising steps of: providing a first optical component to allow a pumping light incident in a first direction to transmit therethrough; providing a second optical component; sequentially disposing a gain and Raman medium, a first lithium triborate (LBO) crystal and a second LBO crystal along the first direction between the first and the second optical components; generating a first infrared base laser light having a third wavelength and a second infrared base laser light having a fourth wavelength using the pumping light by the gain and Raman medium; generating the first visible laser light via the first LBO crystal; generating the second visible laser light via the second LBO crystal; allowing the first and the second visible laser lights to transmit along the first direction, and allowing the first and the second infrared base laser lights to be reflected along a second direction opposite to the first direction by the second optical component; substantially reflecting the first and the second visible laser lights while substantially transmitting the first and the second infrared base laser lights through a surface of the gain and Raman medium in the second direction; and adjusting a power of the first and the second visible laser lights under an operation temperature between 14 to 28 degrees Celsius, wherein the power of the first and the second visible laser lights is kept at a watt level while the first and the second wavelengths remain unchanged.

2. The method according to claim 1, wherein the second infrared base laser light is generated via a self-stimulated Raman scattering, and at least one of the first and the second LBO crystals is a second-harmonic generation crystal.

3. The method according to claim 1, wherein the first and the second LBO crystals are used as a sum frequency generation crystal and a second-harmonic generation crystal respectively when the third wavelength is twice the first wavelength.

4. The method according to claim 3, wherein the first and the second wavelengths are 559 and 532 nanometers respectively.

5. The method according to claim 1, wherein the first and the second LBO crystals are used as a second-harmonic generation crystal and a sum frequency generation crystal respectively when the fourth wavelength is twice the first wavelength.

6. The method according to claim 5, wherein the first and the second wavelengths are 588 and 559 nanometers respectively.

7. The method according to claim 1, further comprising: disposing a third LBO crystal between the gain and Raman medium and the first LBO crystal, wherein the third LBO is configured to receive the first and the second infrared base laser lights from the first and the second LBO crystals and generate a third visible laser having a fifth wavelength.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing a laser device for generating laser light of visible wavelengths;

(2) FIG. 2A is a schematic diagram showing a Raman laser for generating high-power and multiple-wavelength laser light with visible wavelengths according to one embodiment of the present invention;

(3) FIGS. 2B-2E are schematic diagrams showing the Raman laser for generating high-power and multiple-wavelength laser light with visible wavelengths according to other embodiments of the present invention;

(4) FIG. 3 is a schematic diagram showing a Raman laser for generating high-power and multiple-wavelength laser light with visible wavelengths according to one other embodiment of the present invention;

(5) FIG. 4 is a schematic diagram showing a Raman laser for generating high-power and multiple-wavelength laser light with visible wavelengths according to one other embodiment of the present invention;

(6) FIG. 5 is a schematic diagram showing a Raman laser for generating high-power and multiple-wavelength laser light with visible wavelengths according to yet another embodiment of the present invention;

(7) FIG. 6 is a schematic diagram showing the output power of the laser device made in accordance with the embodiment of FIG. 2A at different operating temperatures;

(8) FIG. 7 is a schematic diagram showing the input and output powers for a laser device made in accordance with the embodiment of FIG. 2A at room temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(9) The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purposes of illustration and description only; they are not intended to be exhaustive or to be limited to the precise form disclosed.

(10) Please refer to FIG. 2A, which shows a Raman laser for generating high-power and multiple-wavelength laser light with visible wavelengths according to one embodiment of the present invention. The present invention utilizes an infrared base laser light of another wavelength generated due to the Raman effect and travelling to and fro in the linear cavity to trigger visible laser light of different wavelengths. In the embodiments of FIGS. 2A-2D and 3-5, the infrared based laser lights of two different wavelengths is simultaneously generated in the resonant cavity due to the self-excited Raman phenomenon of the gain medium, and the embodiment in FIG. 2E, two different wavelengths of infrared base laser lights are generated by the gain medium and the Raman medium, respectively. Those skilled in the art may choose applicable component configurations according to their needs, without exceeding the scope of the present invention.

(11) According to FIG. 2A, a high-power and multi-wavelength laser of visible light 100 has a linear cavity 110 having a first direction and a second direction opposite to the first direction. Along the first direction, the linear cavity 100 includes a first optical component 130, a gain and Raman medium 120, a sum frequency generation crystal 140, a first second-harmonic generation crystal 160 and a second optical element 150.

(12) In one embodiment, the first optical component 130 can be an assembly made by placing an optical layer 131 on a lens 133. The first optical component 130 has high transmittance (for example, the reflectivity is lower than 0.2%) for a pumping light L.sub.pump (with a wavelength of 808 nm) incident along the first direction from a diode laser light source 1, and is good to be used for allowing the pumping light L.sub.pump to transmit therethrough and be incident in the first direction. The gain and Raman medium 120 receives the pumping light L.sub.pump from the first optical component 130, and generates a first infrared base laser light L.sub.base1 having a first wavelength and a second infrared base laser light L.sub.base2 having a second wavelength. For example, a diode laser light source provides an incident pumping light L.sub.pump with a wavelength of 808 nm. The gain and Raman medium 120 includes neodymium doped vanadate (for example, Nd:YVO.sub.4), which not only can absorb the energy of the pumping light L.sub.pump via the doped material and convert it to a first infrared base laser light L.sub.base1 having a wavelength of about 1064 nm, but also can rely on self-stimulated Raman scattering to generate a second infrared base laser light L.sub.base2 having a wavelength of approximately 1176 when the reflectivity of the first optical element 130 and the second optical element 150 of the linear cavity 110 for the first infrared base laser light L.sub.base1 reaches 99.8% or more, that is, when the first infrared base laser light L.sub.base1 can be effectively locked in the linear cavity 110 to form a standing wave.

(13) These two basic laser lights existing in the linear cavity 110 can be used as a means of forming laser light with different wavelengths of visible lights. From another point of view, the first infrared base laser light L.sub.base1 and the second infrared base laser light L.sub.base2 are reflected back and forth among the linear cavity 110, and the distance between the first optical element 130 and the second optical element 150 is such that the two basic laser lights form a standing wave to maintain a certain power thereof.

(14) The sum frequency crystal 140 can be a lithium triborate (LBO) crystal formed with a particular cutting angle. The sum frequency crystal 140 receives the first and second infrared base laser light L.sub.base1/L.sub.base2 from the gain and Raman medium 120, and generates a first visible laser light L1 having a third wavelength. For example, in the aforementioned embodiment, when the wavelengths of the first and second infrared base laser light L.sub.base1/L.sub.base2 are 1064 and 1176 nm respectively, the first visible laser light L1 generated by the sum frequency crystal 140 has a wavelength of about 559 nm.

(15) The first second-harmonic generation crystal 160 is a lithium borate crystal (LBO) crystal formed with another special cutting angle different from that for the sum frequency crystal 140, receives the first infrared base laser light L.sub.base1 passing through the sum frequency crystal 140, and generates a second visible laser light L2 having a fourth wavelength. According to the above example, when the first infrared base laser light L.sub.base1 has a wavelength of about 1064 nm, the second visible laser light L2 generated by the first second-harmonic generation crystal 160 via frequency doubling has a wavelength of about 532 nm.

(16) According to an embodiment of the present invention, the second optical element 150 is a lens having an optical film on the surface facing the first direction, and have not only high reflectivity up to 99.8% for the lights with the wavelength within a range covering those of the first and second infrared base laser light L.sub.base1/L.sub.base2 (for example, 1060-1180 nm), but also high penetration or low reflectivity as low as less than 0.3% for the lights with the wavelength within a range covering those of the first and second visible laser light L1/L2 (for example, 530-590 nm), so that the first and second visible laser light L1/L2 are emitted in the first direction. Laser lights with wavelengths of 532 and 559 nm are of different color in the visible range and of great value in medical applications such as retinal photocoagulation in the fields of ophthalmology and dermatology. The high-power laser cavity 110 of the present invention can simultaneously provide two or more kinds of visible laser light, which is an important breakthrough.

(17) According to the embodiment shown in FIG. 2A, an optical film 121 is disposed on the surface of the gain and the Raman medium 120 facing the second direction in order to prevent the first and second visible laser lights L1/L2 from entering the gain and the Raman medium 120 from the second direction, such that the gain and the Raman medium 120 in the second direction is highly reflective (for example, 95% or higher reflectivity) for the light with the wavelength within a range covering those of the first and second visible laser lights L1/L2 (for example, 530-590 nm). Meanwhile, the gain and the Raman medium 120 in the second direction has high penetration (for example, reflectivity of 0.3% or less) for the lights whose wavelengths are within a wavelength band covering the wavelengths of the first and second infrared base laser light L.sub.base1/L.sub.base2 (for example, 1060-1180 nm). In this way, the first infrared base laser light L.sub.base1 can continue to pass through the gain and Raman medium 120 to generate the second infrared base laser light Lbase2 having a wavelength of about 1176 nm by means of the self-excited Raman scattering, while the first and second visible laser lights L1/L2 are reflected back and transmitted in the first direction. According to the configuration of the present invention, the gain and Raman medium 120 will not be interfered with by the first and second visible laser lights L1/L2, so the power of the cavity 110 can be maintained under a preferred condition.

(18) FIGS. 2B-2E show some different embodiments of high-power and multi-wavelength visible Raman lasers in accordance with the present invention, similar to that in FIG. 2A. The Raman laser 100 includes a linear cavity 110 having a first direction and a second direction opposite to the first direction. Along the first directions, the first optical element 130, the gain and the Raman medium 120, the sum frequency crystal 140, the first second-harmonic generation crystal 160, and the second optical element 150 are disposed. The differences are that the first optical element 130 and the gain and Raman medium 120 are implemented in a variety of slightly different component configurations.

(19) In the embodiment shown in FIG. 2B, the first optical element 130 is configured in the form of an optical film on the surface of the gain and the Raman medium 120 facing the first direction, and thus the lens 133 in FIG. 2A can be eliminated. As a result of reducing the number of components, the optical path loss in the linear cavity 110 can be further reduced.

(20) In the embodiment shown in FIG. 2C, the first optical element 130 is configured in the same manner as the first optical element 130 shown in FIG. 2A, and the optical film 121 for filtering the light entering the gain and Raman medium 120 from the second direction is disposed on a lens 123 located between the gain and Raman medium 125 without an optical film and the sum frequency crystal 140. The combination of elements 121, 123, and 125 in the figure constitutes a gain and Raman medium 120. With such a component arrangement, the component arrangement of the linear cavity 110 is highly flexible since the respective optical films 131/121/151 are respectively disposed on separate lenses, and the optical films can be replaced at any time as needed.

(21) In the embodiment shown in FIG. 2D, the first optical element 130 is configured in the form of an optical film on the surface of the gain and Raman medium 120 facing the first direction.

(22) In the embodiment shown in FIG. 2E, the functions of the gain and the Raman medium 120 can be realized by a combination of the gain medium 129, the Raman medium 127, and the optical film 121. The gain medium 129 may be a neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal, which can convert a pump light L.sub.pump having a wavelength of 808 nm into a first infrared base laser light L.sub.base1 having a wavelength of about 1064 nm. The Raman medium 127 contains neodymium-doped vanadate (for example, neodymium-doped yttrium vanadate Nd:YVO4) which can generate Raman-scattering due to excitation of the first infrared-based laser light L.sub.base1 having a wavelength of about 1064 nm, and generate a second infrared base laser light L.sub.base2 having a wavelength of approximately 1176 nm.

(23) Please refer to FIG. 3, where another embodiment of a high-power and multi-wavelength visible Raman laser in accordance with the present invention is shown. As illustrated, the high-power and multi-wavelength visible light Raman laser 200 comprises a linear cavity 210 having a first direction and a second direction opposite to the first direction. Along the first direction, an optical component 130, a gain and Raman medium 120, a second second-harmonic generation crystal 180, a sum frequency crystal 140, and a second optical component 150 are arranged.

(24) The second second-harmonic generation crystal 180 is a lithium borate crystal (LBO) crystal formed with yet another special cutting angle different from that for the sum frequency crystal 140 and the first second-harmonic generation crystal 160, receives the second infrared base laser light L.sub.base2 from the gain and Raman medium 120, and generates a third visible laser light L3 having a fifth wavelength. According to the above example, when the second infrared base laser light L.sub.base2 has a wavelength of about 1176 nm, the third visible laser light L3 has a wavelength of about 588 nm which lies within the wavelength band covering the wavelengths of the first and the second visible laser lights L1/L2 (such as 530-590 nm). The property and functions of the sum frequency crystal 140 are the same as those in the aforementioned embodiments, and therefore there is no need to repeat the information.

(25) Since the intensity of the second infrared base laser light L.sub.base2 generated by Raman scattering is much lower than that of the first infrared base laser light L.sub.base1, in order to make the two or more visible laser lights generated have a similar power to meet the need of industrial applications, it is necessary to consider the strength of the two basic laser lights and choose appropriate positions along the first direction of the linear cavity of the present invention for different lithium borates (LBO) crystals. In the embodiments as shown in FIGS. 2A-2E, the sum frequency crystal 140 needs to be disposed ahead of the first frequency doubling crystal 160 along the first direction, so that the second infrared base laser light L.sub.base2 which is relatively weaker can directly enter the sum frequency crystal 140 to generate the first visible laser light L1, and the first infrared base laser light L.sub.base1 passing through the sum frequency crystal 140 and partially absorbed, the intensity of the remaining laser light is still high enough for the first second-harmonic crystal 160 to generate the second visible laser light L2 having sufficient power. In contrast, in the embodiment in FIG. 3, the sum frequency crystal 140 needs to be disposed after the second frequency doubling crystal 180 in the first direction, so that the second infrared base laser light L.sub.base2 which is relatively weaker can directly enter the second second-harmonic crystal 180.

(26) Please refer to FIG. 4, which is a schematic diagram of a high-power and multi-wavelength visible Raman laser 300 according to another embodiment of the present invention. In accordance with the same concept set forth above, those skilled in the art can appreciate that if a second visible laser light L2 having a fourth wavelength and a third visible laser light L3 having a fifth wavelength are desired, one may alternatively dispose the second second-harmonic crystal 180 in front of the first second-harmonic crystal 160 along the first direction in the linear cavity.

(27) Please refer to FIG. 5, which is a schematic diagram showing a Raman laser 400 for generating high-power and multiple-wavelength laser light with visible wavelengths according to yet another embodiment of the present invention. According to FIG. 5, a high-power and multi-wavelength laser of visible light 400 has a linear cavity 410 having a first direction and a second direction opposite to the first direction. Along the first direction, the linear cavity 410 includes the first optical component 130, the gain and Raman medium 120, the second second-harmonic crystal 180, the sum frequency generation crystal 140, the first second-harmonic generation crystal 160 and the second optical element 150. The technical features of the elements are the same as those described in the previous sections, so there is no need to repeat the information.

(28) In order to simultaneously obtain visible laser lights L1/L2/L3 of three different wavelengths, three types of frequency modulation crystals, which are the second second-harmonic crystal 180, the sum frequency crystal 140, and the first second-harmonic crystal 160 can be sequentially arranged in the linear cavity, so that the first/second/third visible laser lights L1/L2/L3 can be generated by means of frequency doubling or sum frequency under the condition that the first and second infrared-based laser lights L.sub.base1/L.sub.base2 generated by the gain and Raman medium 120 are continuously transmitted to and fro between the first optical element 130 and the second optical element 150.

(29) Based on the above, in accordance with another aspect of the present invention, a linear cavity for generating a high power visible laser light is provided. Along a first direction, the linear cavity comprises a first optical component 130 allowing a pumping light L.sub.pump incident in the first direction to transmit therethrough, a gain and Raman medium 120 receiving the pumping light L.sub.pump from the first optical component 130 and generating a first infrared base laser light L.sub.base1 having a first wavelength and a second infrared base laser light L.sub.base2 having a second wavelength, a first LBO crystal receiving the first and the second infrared base laser lights L.sub.base1/L.sub.base2 and generating a first visible laser light L1 having a third wavelength and a second optical component 150 allowing the first visible laser light to emit out thereof along the first direction.

(30) In addition, the gain and Raman medium 120 has high transmittance for the lights with wavelengths in the first wave band covering the first and the second wavelengths in a second direction opposite to the first direction and high reflectivity for the lights with wavelengths in the second wave band covering the third wavelength in the second direction. The first optical component 130 has high reflectivity for the lights with wavelengths in the first wave band in the second direction and high reflectivity for the lights with wavelengths in the second wave band in the second direction. The second optical component 150 has high transmittance for the second wave band in the first direction and high reflectivity for the first wave band in the first direction.

(31) The linear cavity of the present invention can generate high-power laser light. The first visible laser light L1 described above is only an example, and the LBO crystal used as the sum frequency crystal 140 in the aforementioned embodiments is configured to obtain the first visible laser light L1 via the sum frequency effect. The users may configure different LBO crystals as frequency-doubling crystals to obtain visible laser lights having different wavelengths, or simultaneously dispose a plurality of LBO crystals between the gain and Raman medium 120 and the second optical elements 150 along the first direction in the linear cavity so as to simultaneously obtain visible laser lights having different wavelengths.

(32) FIG. 6 shows the output power of the laser device made in accordance with the embodiment of FIG. 2A at different operating temperatures. Based on the data shown in the figure, it is understood that, when the room temperature is in the range of 14-28 degrees Celsius, the power of the visible laser lights with two different wavelengths generated by the laser device is kept at the watt level, which can meet the needs of the industry. When the operating temperature is about 20 degrees Celsius, the visible laser light with wavelength of 532 nm reaches the highest output power while the output power of the visible laser light with wavelength of 559 nm is the lowest. When the operating temperature is around 16 and 23 degrees Celsius, the output power of visible laser lights with two different wavelengths is almost 4 watts. Notably, the test data shown in FIG. 6 is made by using a laser light of 31.6 watts as the pumping light.

(33) The data shows that the laser device according to the present invention can provide multi-wavelength visible laser lights having output power of several watts with the supply of pumping light of about 30 watts. Because the power of the visible lasers generated by different LBO crystals at different temperatures are different, according to an embodiment of the present invention, the output power of the first visible laser light and the second visible laser light can be adjusted by controlling the operating temperature. For example, when the powers of the two laser lights for use needs to be close, the operating temperature can be controlled at around 16 or 23 degrees Celsius; if the power of the laser light with wavelength of 532 nm is required to be higher than that of the laser light with wavelength of 559 nm, the temperature can be controlled at between 16 and 23 degrees Celsius, preferably at around 20 degrees Celsius.

(34) Referring to FIG. 7, where the input and output powers for a laser device made in accordance with the embodiment of FIG. 2A at the room temperature of 23 degrees Celsius are illustrated. When the power of the incident pumping light exceeds 10 watts, the total output power reached the level of the watt level, and when the power of the incident pumping light is close to 32 watts, output powers of the visible laser lights with wavelength of 532 nm and 559 nm both reach 4 watts, and the total output power reaches 8 watts.

(35) Through the abovementioned embodiments, the Raman laser for generating high-power and multiple-wavelength laser lights with visible wavelengths according to the present invention may use the linear resonance cavity under the same configuration, and can obtain high-power visible laser lights with different wavelengths by means of different device arrangement, which is a technology breakthrough.

(36) While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.