CN110932073A

CN110932073A - Inner cavity optical parametric oscillator

Info

Publication number: CN110932073A
Application number: CN201911229340.0A
Authority: CN
Inventors: 尹雨松; 王世波; 陈国华; 向杰; 郑财强; 卢旭升; 张威
Original assignee: Tony Laser Technology (dongguan) Co Ltd
Current assignee: Tony Laser Technology (dongguan) Co Ltd
Priority date: 2019-12-04
Filing date: 2019-12-04
Publication date: 2020-03-27

Abstract

The invention relates to an inner cavity optical parametric oscillator, wherein a laser resonant cavity is formed between two reflecting surfaces, a laser medium is positioned in the laser resonant cavity and is used for generating a fundamental wave beam, an optical parametric oscillation cavity is formed between one of the reflecting surfaces of the laser resonant cavity and a third reflecting surface, a nonlinear crystal cut based on the phase matching condition of the wavelength of the fundamental wave beam and the wavelength of an output beam is in optical communication with the first reflecting surface and the third reflecting surface, the optical axis of the fundamental wave resonant cavity is partially overlapped with the optical axis of the parametric oscillation cavity and is partially separated, the fundamental wave beam generated by the laser medium is incident into the nonlinear crystal of the parametric oscillation cavity, and a part of the fundamental wave beam is converted into idler frequency light with longer wavelength and is used as preselected. The separated fundamental beam is directed back to the laser medium for further amplification. A portion of the output wavelength beam is directed out of the oscillator cavity as the output of the laser.

Description

Inner cavity optical parametric oscillator

Technical Field

The invention relates to the technical field of lasers, in particular to a laser with high power and tunable output wavelength broadband.

Background

An Optical Parametric Oscillator (OPO) is a type of Parametric Oscillator that oscillates at an Optical frequency. The laser device converts input laser (pumping light) into two output lights (signal light and idler light) with lower frequencies through a second-order nonlinear optical effect, and the sum of the frequencies of the two output lights is equal to the input light frequency.

Optical parametric oscillators have been developed in the prior art. Such lasers typically have only one cavity and are used both for pump lasers and for optical parametric oscillators. However, such lasers have limited tunability due to the difficulty of the laser crystal in absorbing the beam wavelength generated by the OPO and fabricating devices with low transmission losses. See U.S. patent No. 5,687,186. Eye-safe OPOs have been developed for radar applications located inside or outside the laser cavity. See ISPIE vol.1419, PPS.141-152, "Eye Safe Lasers Components, Systems and Applications" (1991).

Disclosure of Invention

The technical problem underlying the present invention is to overcome the drawbacks of the prior art by providing a method and a device for generating a laser beam of a preselected output frequency having a longer wavelength than the wavelength of the fundamental light. A laser crystal is used in the laser device.

In one embodiment of the invention, a laser cavity is formed between the first reflective surface and the second reflective surface. And the laser medium is positioned in the laser resonant cavity and is used for generating a fundamental wave wavelength. An optical parametric oscillation cavity is formed between the first reflecting surface and the third reflecting surface. A nonlinear crystal satisfying a phase matching condition of a fundamental beam wavelength and an output beam wavelength is in optical communication with the first and third reflecting surfaces. The optical axis of the fundamental wave beam oscillation cavity is partially overlapped with the optical axis of the optical parametric oscillation cavity, and the fundamental wave beam oscillation cavity and the optical axis of the optical parametric oscillation cavity are partially separated. The fundamental beam is directed into an optical parametric oscillator cavity along the oscillator optical axis, incident on the nonlinear crystal, and converts a portion of the fundamental beam into a preselected output wavelength beam having a longer wavelength than the fundamental beam. The first reflective surface reflects the fundamental beam and the output wavelength beam back to the nonlinear crystal to form an additional output wavelength beam. A beam splitter separates an output wavelength beam from the fundamental wavelength beam. The separated fundamental beam is directed back to the laser medium for further amplification. Output beam directing means for directing said separated output wavelength beam back to said nonlinear crystal amplification. A portion of the output wavelength beam is directed out of the oscillator cavity as the output of the laser.

In another embodiment of the present invention, the laser does not include an optical parametric oscillator. In such an embodiment, the laser resonator is disposed between two reflective surfaces, preferably two mirrors. A lasing medium, such as Nd: YAG and Nd: YLF crystals, is provided within the cavity. A Q-switch may also be included within the cavity. A fundamental beam from a laser medium is directed through a nonlinear crystal to produce a preselected output beam having a longer wavelength than the fundamental beam. The fundamental beam and the output frequency beam are reflected by a cavity mirror and pass twice through the nonlinear crystal. The output frequency beam is separated from the remaining fundamental frequency beam and is directed out of the cavity. The fundamental beam is reflected through the laser medium for further amplification.

While the drawings and examples describe preferred embodiments of the invention, it is to be emphasized and understood that the invention is not limited to the embodiments presented.

Drawings

Fig. 1 is a schematic diagram of one embodiment of the laser of the present invention.

Fig. 2 is a schematic diagram of another embodiment of a laser of the present invention.

Fig. 3 is a schematic diagram of another embodiment of a laser of the present invention.

Fig. 4 shows a graph of wavelength coverage for various nonlinear crystals.

Detailed Description

The present invention will be described in further detail with reference to examples.

The present invention provides a method and apparatus for generating a preselected output frequency laser beam having a longer wavelength than the fundamental beam. Preferably, a laser crystal is used in the laser device. In one aspect of the invention, the laser resonator is formed between two reflective surfaces, preferably mirrors. The laser medium is located in the laser resonant cavity and used for generating a fundamental wave beam. The laser medium is preferably a laser crystal, such as Nd: YLF, Nd: YAG, Nd: YVO₄And Ti Saphire or other laser crystal to produce a preselected fundamental wavelength. According to the present invention, the optical parametric oscillator cavity is formed between one reflective surface and a third reflective surface of the laser resonator, preferably a mirror. A nonlinear crystal cut based on phase matching conditions of the fundamental beam wavelength and the preselected output beam wavelength is in optical communication with the first and third reflective surfaces along the resonator optical axis. The nonlinear crystal can be selected from a number of crystals depending on the wavelength of the fundamental wave beam from the laser medium and the wavelength of the desired output beam. These crystals include BBO, LBO, KTP, RTA, RTA, KRTA, LiNbO3 crystals and the like. FIG. 4 shows the partial wavelength coverage of a field-recognized Nd: YAG or Nd: YLF laser pumped nonlinear crystal. The optical axis of the laser resonator and the optical parametric oscillator are at least partially separated. A fundamental beam generated by the laser medium is directed into the optical parametric oscillation cavity and incident on the nonlinear crystal, wherein a portion of the fundamental wavelength beam is converted into a preselected output wavelength beam having a longer wavelength than the fundamental beam. The fundamental wave beam and the output wavelength beam are reflected and then pass through the nonlinear crystal again to form an additional output wavelength beam. The output wavelength beam is separated from the fundamental wavelength beam. The separated fundamental beam is then directed back through a laser medium, preferably a laser crystal, for further amplification. The separated output wavelength beams are directed back to the nonlinear crystal for amplification. Since the output wavelength beam does not pass through the laser crystal or optional Q-switch, problems of absorption and insertion loss of the crystal and other components such as the Q-switch are avoided. Such absorption and insertion losses can limit the tunable wavelength range of the laser and reduce the conversion efficiency of the output wavelength beam.A portion of the output wavelength beam is directed outside the oscillation cavity as the output of the laser. In another embodiment of the present invention, the laser does not include an optical parametric oscillator. In this embodiment the laser resonator is arranged between reflecting surfaces, preferably two mirror mirrors. A lasing medium, such as a Nd: YAG, Nd: YLF, Ti: Saphire crystal or other suitable laser crystal, is provided within the cavity. A Q-switch may also be included within the cavity. A fundamental beam from a laser medium is directed through a nonlinear crystal selected as described above to produce a beam having a preselected output frequency that is longer than the wavelength of the fundamental beam. The fundamental wave beam and the output frequency beam are reflected and pass through the nonlinear crystal. The output frequency beam is separated from the remaining fundamental frequency beam and is directed out of the cavity. The fundamental beam is reflected through the laser medium for further amplification. In summary, the present invention provides an efficient method and apparatus for producing a wide range of wavelengths of light beams of different wavelengths.

Fig. 1 through 3 provide examples of lasers that can produce beams at various output wavelengths that are longer than the wavelengths directly produced by the lasing medium, in accordance with the present invention. One embodiment of the present invention is described with reference to fig. 1. The laser cavity is formed between two reflective surfaces, preferably laser cavity mirrors M1 and M2. Mirror M1 is highly reflective of the fundamental beam and also highly reflective of the preselected output wavelength beam in fig. 1. The lasing material LM is located in the cavity between mirrors M1 and M2 and is in optical communication with mirrors M1 and M2. The laser material is preferably a laser crystal such as Nd: YAG or Nd: YLF laser crystal, although other laser crystals such as Ti: Saphire or Nd: YVO may be used₄Etc. for generating a preselected fundamental wavelength beam and then converted to a longer wavelength beam in accordance with the present invention. For example, a Nd: YAG crystal lased at 1.06 μm can be used to provide an output beam of about 1.5 μm. The optical parametric oscillator cavity is disposed between one resonator reflective surface, such as mirror M1 in fig. 1, and another reflective surface, such as mirror M4, which is partially separated from the laser resonator and has a partially different optical axis. The optical parametric oscillator cavity comprises a reflective surface, such as a mirror, preferablyA fold mirror, most preferably a dichroic fold mirror M3 at an acute angle to the resonator optical axis, preferably a mirror M3 at an angle of incidence α of 30 to 70 to the resonator optical axis, if the M3 substrate is fused silica, this angle should be 50 to 60, such as 56 Brewster angle, the dichroic mirror M3 is highly transmissive to the fundamental beam in both directions, and highly transmissive to the output wavelength beam traveling from left to right in FIG. 2⁴⁺YAG. Ideally, mirror M4 is partially reflective and partially transmissive to the output beam. Thus, a portion of the output beam is reflected back into the optical parametric oscillator and another portion is directed out of the cavity as the output of the laser. Thus, an optical parametric oscillation cavity is defined between the mirror plates M1 and M4. A nonlinear crystal NC is provided within the optical parametric cavity. The nonlinear crystal is cut for phase matching of the fundamental beam wavelength and the output beam wavelength. In the embodiment shown in FIG. 1, the fundamental beam wavelength is 1.06 μm and the output wavelength beam is 1.5 μm. The nonlinear crystal is selected based on the wavelength of the fundamental beam and the desired output beam wavelength. Many such crystals are known in the art. Fig. 4 shows the local wavelength coverage of a nonlinear crystal that can be used for Nd: YAG and Nd: YLF laser crystals. For example, for a laser producing an output wavelength of about 1.5 μm, a KTP or KTA crystal may be used. Alternatively, LiNbO may be used₃And (4) crystals. In operation, the laser material LM can be excited by a flash lamp or a diode pumped laser. An optional Q-switch is used for pulsed operation. At this time, the fundamental wave light beam is directed toward the mirror M2 at a preselected fundamental wave wavelength, for example, 1.06 μ M. The reflected fundamental wave beam is returned by the mirror M2 to the laser material LM, amplified, and then passed through the mirror M3, and the mirror M3 has high transmittance for the 1.06 μ M fundamental wave beam. The fundamental beam will then be directed through a nonlinear crystal NCKTP and LiNbO are preferable₃Or other crystal in which a portion of the beam will be converted to a 1.5 μm wavelength beam. Both the fundamental and output wavelength beams will then be reflected by mirror M1 and pass again through the nonlinear crystal NC where the output wavelength beam is amplified and directed to mirror M3 where the unconverted fundamental beam will pass through the high transmission dichroic mirror M3. An output beam having a wavelength of about 1.5 μ M will be reflected by mirror M3 and directed to mirror M4, mirror M4 being partially reflective and partially transmissive for the output beam wavelength. The reflected output wavelength beam is directed to mirror M3 and reflected back to the nonlinear crystal for further amplification. The fundamental wave and the output beam from the nonlinear crystal are reflected by the mirror M1, and the process is repeated. The mirrors M1 and M4 act as optical parametric oscillator mirrors and, as described above, M4 will also act as an output coupler for the output beam. Alternatively, M1 may be an output coupler.

The device of fig. 2 is similar to that of fig. 1 except that lens M2 is eliminated. The Q-switch is coated with a reflective coating to reflect the fundamental beam, so mirror M2 is not required. Lens M3 is the same as the nonlinear crystal NC in fig. 1. According to the fig. 2 embodiment, mirror M14 acts as one of the optical parametric oscillator mirrors and is highly reflective of the output beam wavelength. The output beam is substantially completely reflected by M14. The mirror M11 reflects the fundamental wave beam and also serves as an output coupler for outputting the wavelength beam. M11 is partially transmissive and partially reflective to the output wavelength beam. Substantially all of the unconverted fundamental beam is reflected by M11 back to the nonlinear crystal NC and a portion of the output beam is also reflected back to the nonlinear crystal NC for further amplification in the optical parametric oscillator cavity. By using separate OPO and laser cavities, the fundamental and output beams can be more easily matched in transverse mode as they pass through the nonlinear crystal by adjusting the parameters of mirror M4 or M14.

Fig. 3 provides another embodiment of the present invention, which does not require the use of an optical parametric oscillator. In this embodiment, mirrors M21 and M22 define a laser cavity. A lasing medium, preferably Nd: YAG, Nd: YLF or Nd: YVO, is provided within the resonator cavity₄The crystal is preferably Nd: YAG laser crystal. Q-switch QS may also be used. For example, for Nd: YAG crystals, the laser light is generated atAt a wavelength of about 1.06 μm. The fundamental light beam is then directed to mirror M23, mirror M23 being highly reflective of the fundamental light beam, in this case 1.06 μ M. The fundamental beam is directed to mirror M24 which is highly reflective to the 1.06 um fundamental beam and highly transmissive to the 1.5 um output beam. The fundamental beam is then directed through the nonlinear crystal NC selected as described above, possibly in conjunction with the description of fig. 1 and 2. The fundamental wave light beam propagated from the nonlinear crystal NC and the output light beam are reflected by the mirror M22 back to the nonlinear crystal, where another part of the fundamental wave light beam is converted into an output wavelength light beam. M22 has high reflectivity for both the output wavelength beam and the fundamental wave beam. The fundamental and output wavelength beams are directed from the nonlinear crystal NC to mirror M24 where the output beam is transmitted out of the laser cavity and the unconverted fundamental beam is reflected to mirror M23 and reflected back to the laser medium LM for further amplification.

Preferably, the laser medium LM is a laser crystal, most preferably a Nd: YAG or Nd: YLF crystal, preferably a Nd: AG crystal. Other laser crystals such as Ti: Saphire and Nd: YVO may also be used₄。

The foregoing is merely a schematic illustration of the present invention, and various changes and modifications may be made in the present invention by those skilled in the art, and the present invention is not limited to the specific embodiments and operational description given above. Accordingly, all modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

1. An intracavity optical parametric oscillator, comprising:

a) a laser resonant cavity: having a laser cavity formed between a first reflective surface and a second reflective surface, the cavity having a cavity optical axis;

b) a lasing medium located within the laser resonator for generating a fundamental wavelength;

c) an optical parametric oscillation cavity is formed between the first reflector and the third reflector, and is provided with an oscillation cavity optical axis, is partially separated from the resonant cavity optical axis, and is partially overlapped with the resonant cavity optical axis;

d) a nonlinear crystal is arranged in the cavity of the parametric oscillator, is positioned on the optical axis of the oscillation cavity and is optically communicated with the first reflector and the third reflector; the nonlinear crystal is for converting a portion of the fundamental wavelength beam to a preselected output wavelength beam having a longer wavelength than the fundamental wavelength;

e) directing the fundamental light beam into an optical parametric oscillation cavity along the optical axis of the oscillation cavity and through a nonlinear crystal to convert a portion of the fundamental wavelength light beam into a preselected output wavelength light beam having a longer wavelength than the fundamental wavelength;

f) the first reflective surface reflects a fundamental beam and reflects at least a portion of an output wavelength beam;

g) for reflecting the fundamental and preselected output wavelength beams back through the nonlinear crystal to form additional output wavelength beams;

h) a beam splitter that separates the output wavelength beam from the fundamental wavelength beam;

i) a fundamental beam guide device that guides the split fundamental beam back to the laser medium for further amplification;

j) output beam directing means for directing said separated output wavelength beam back to said nonlinear crystal amplification;

k) an output coupler directing a portion of the output wavelength beam out of the oscillator cavity as an output of the laser.

2. An intracavity optical parametric oscillator as claimed in claim 1 wherein the first and second reflective surfaces are mirrors.

3. The intracavity optical parametric oscillator of claim 2, wherein the beam splitter is a dichroic mirror.

4. An intracavity optical parametric oscillator as claimed in claim 3 wherein the beam splitter is a dichroic mirror which transmits the fundamental beam and reflects the output frequency beam.

5. The intracavity optical parametric oscillator of claim 4, further comprising a Q-switch located within the laser resonator.

6. The intracavity optical parametric oscillator of claim 3, wherein the lasing medium is Nd: YLF.

7. An intracavity optical parametric oscillator as defined in claim 6 wherein the laser providing the laser output of the preselected frequency comprises a laser resonator formed between a first mirror and a second mirror, the resonator having an optical axis; the laser crystal is positioned in the laser resonant cavity and used for generating a fundamental wave beam; an optical parametric oscillation cavity is formed between the first reflector and the third reflector, the optical parametric oscillation cavity is provided with an optical axis, and part of the optical parametric oscillation cavity is separated from the optical axis of the resonant cavity and is partially overlapped with the optical axis of the resonant cavity; a nonlinear crystal positioned within the parametric oscillation cavity in optical communication with the first and third mirrors along the oscillator optical axis; the nonlinear crystal is in optical communication with the laser crystal such that the fundamental light beam is incident on the nonlinear crystal, and a portion of the fundamental wavelength light beam is converted to a preselected output wavelength light beam having a longer wavelength than the fundamental wavelength; the first mirror reflecting a fundamental beam and an output wavelength beam to direct the fundamental beam and at least a portion of a preselected output wavelength beam back to the nonlinear crystal to form an additional output wavelength beam; a dichroic mirror positioned along a resonator optical axis and an oscillator optical axis between the nonlinear crystal and the laser medium and between the third mirror and the nonlinear crystal; the front end surface of the dichroic mirror faces the laser crystal and is in optical communication with the laser crystal; the front end surface of the dichroic mirror is highly transparent to the wavelength of the fundamental wave; the back of the dichroic mirror is in optical communication with the nonlinear crystal and the third mirror surface, and the back is plated with a film layer which transmits the fundamental wavelength light beam and reflects the output wavelength light beam; an output coupler in the optical parametric oscillator cavity for outputting a portion of the preselected output wavelength beam from the optical parametric oscillator cavity.

8. The intracavity optical parametric oscillator of claim 7, wherein the dichroic mirror incident angle α is about 30 ° to about 70 °.

9. The intracavity optical parametric oscillator of claim 8, wherein the dichroic mirror incident angle α is from about 60 ° to about 60 °.

10. The intracavity optical parametric oscillator of claim 7, wherein the dichroic mirror incident angle α is equal to brewster's angle.

11. The intracavity optical parametric oscillator of claim 7, wherein the laser crystal is selected from any one of Nd: YLF, Nd: YAG, Nd: YVO₄Or Ti, Saphire.

12. The intracavity optical parametric oscillator of claim 7, further comprising a polarizer disposed along an optical axis of the resonator for polarizing the fundamental beam P.

13. An intracavity optical parametric oscillator according to claim 7 wherein the first mirror or the third mirror transmits a portion of the output frequency beam.

14. An intracavity optical parametric oscillator as defined in claim 7 further comprising a Q-switch located within the resonant optical cavity.

15. The intracavity optical parametric oscillator of claim 7 wherein the laser providing the preselected output frequency beam comprises:

a) a first reflecting surface and a second reflecting surface, and forming an optical resonant cavity therebetween;

b) a laser medium located within the cavity for generating a fundamental electromagnetic radiation beam (EMR) of a first preselected wavelength from a front end and a back end of the laser medium;

c) frequency conversion means for converting a portion of said EMR of said first preselected fundamental beam into said preselected output frequency beam having a longer wavelength than said fundamental beam;

d) the frequency conversion device comprises a nonlinear crystal, and phase matching conditions of the fundamental frequency beam and/or the output frequency beam are met by using an angle adjustment method. The nonlinear crystal has a first EMR port for receiving and directing radiation through the nonlinear crystal. Radiation can enter the first EMR port, pass through the crystal and exit the second EMR port, or vice versa;

e) directing the fundamental frequency beam and the output frequency beam from a second EMR port to the second reflective surface to reflect the fundamental frequency beam and the output frequency beam back to the second EMR port to propagate back through the nonlinear crystal;

f) an output beam splitter in optical communication with the fourth EMR port for separating the output frequency beam from the fundamental frequency beam;

g) directing the separated output beam out of the optical resonator;

h) directing the fundamental beam back to the lasing medium;

i) the first mirror is in optical communication with the EMR, and reflects EMR emitted from the back end of the laser medium back through the laser medium.

16. The intracavity optical parametric oscillator of claim 15, wherein the laser medium is a solid state laser medium.

17. The intracavity optical parametric oscillator of claim 15, wherein the lasing medium is selected from the group consisting of Nd: YLF, Nd: YAG, Nd: YVO4, and Ti: Saphire.

18. The intracavity optical parametric oscillator of claim 17 wherein the means for providing a laser output of a preselected frequency comprises forming a laser resonator cavity between the first and second reflective surfaces; exciting a lasing medium within the laser resonator to produce a fundamental beam; forming an optical parametric oscillator cavity between the first reflective surface and the third reflective surface; the optical parametric oscillator cavity has a nonlinear crystal in optical communication with the first and third reflective surfaces; directing the fundamental beam through the parametric oscillator cavity and passing the beam through the nonlinear crystal to convert a portion of the fundamental wavelength beam to a preselected output wavelength beam that is longer in wavelength than the fundamental beam; reflecting the fundamental beam back to the nonlinear crystal to form an additional output wavelength beam; separating the output wavelength beam from the fundamental wavelength beam; directing the split fundamental beam back to the laser medium for further amplification; directing and passing the split output wavelength beam through the nonlinear crystal to amplify the beam; outputting a portion of the output wavelength beam out of the oscillator cavity.

19. The intracavity optical parametric oscillator of claim 18, wherein the nonlinear crystal is selected from the group consisting of BBO, LBO, KIP, KTA, RTA, KRTA, and LiNbO₃。

20. An intracavity optical parametric oscillator as claimed in any one of claims 1 to 17 wherein the nonlinear crystal is selected from BBO, LBO, KIT, KTA, RTA, KRTA and LiNbO₃。