CN107394575A - The frequency doubling device of laser - Google Patents

Abstract

Disclosed is a laser frequency doubling device, which belongs to the field of optical technology. Wherein, the incident light enters the first beam splitter through the first frequency doubling crystal, and is split into first transmitted light and first reflected light by the first beam splitter. The first transmitted light sequentially passes through the beam reducer group, the second frequency doubling crystal, the beam expander group and the first half-wave plate, and then enters the third beam splitter, and is split by the third beam splitter into the second transmitted light and the second beam splitter. For the reflected light, the second reflected light is incident to the polarizing beam splitting prism and is reflected by the polarizing beam splitting prism to form the third reflected light. The first reflected light is incident on the second beam splitter, and is reflected by the second beam splitter to obtain the fourth reflected light. Three transmitted light. The third reflected light and the third transmitted light jointly form a light beam. It can improve the conversion rate in the laser frequency doubling process.

Description

Laser frequency doubling device

technical field

The invention relates to the field of optical technology, in particular to a laser frequency doubling device.

Background technique

Frequency conversion is an effective technique to expand the application range of high-power lasers, which utilizes the nonlinear optical effects of optical media under strong radiation fields to generate new frequencies. Frequency doubling is the most widely used technology in nonlinear optics. Generally speaking, we hope to obtain higher conversion efficiency from fundamental frequency light to frequency doubled light.

Generally, there are two main ways to improve the conversion efficiency of the frequency doubling process: (1) Increase the peak power density of the fundamental frequency light. In the case of a given laser pulse energy and pulse width, the method to increase the peak power density is to reduce the size of the spot. The disadvantage of this method is that when the spot is reduced to a certain extent, the peak power density of the laser exceeds the coating on the end face of the laser crystal. Damage threshold, resulting in device damage; (2) Increase the length of the frequency doubling crystal. As the fundamental frequency light is converted in the frequency doubling crystal, the peak power density of the fundamental frequency light gradually decreases, and the conversion efficiency decreases. Therefore, when the length of the frequency doubling crystal increases to a certain length, increasing the crystal length will not significantly improve the frequency doubling efficiency.

Contents of the invention

In view of this, the present invention provides a laser frequency doubling device, which can increase the conversion rate during the laser frequency doubling process, and thus is more suitable for practical use.

In order to achieve the above-mentioned first object, the technical scheme of the frequency doubling device of the laser provided by the present invention is as follows:

The laser frequency doubling device provided by the present invention includes a first frequency doubling crystal (1), a first beam splitter (2a), a second beam splitter (2b), a third beam splitter (2c), and a beam reducer group (3) , the second frequency doubling crystal (4), the beam expander group (5), the first half-wave plate (6a), the second half-wave plate (6b) and the polarization beam splitter prism (7),

The incident light (X1) enters the first beam splitter (2a) through the first frequency doubling crystal (1), and is split into the first transmitted light (X2) and the second beam by the first beam splitter (2a). a reflected light (x3),

The first transmitted light (X2) sequentially passes through the beam reducer group (3), the second frequency doubling crystal (4), the beam expander group (5) and the first half-wave plate (6a) and then enters the The third beam splitter (2c) is split into second transmitted light (X6) and second reflected light (X4) by the third beam splitter (2c), and the second reflected light (X4) is incident to the the polarizing beam splitting prism (7) and is reflected by the polarizing beam splitting prism (7) to form the third reflected light;

The first reflected light (X3) enters the second beam splitter (2b), and is reflected by the second beam splitter (2b) to obtain a fourth reflected light (X5), and the fourth reflected light (X5 ) enters the polarizing beam splitting prism (7) after passing through the second half-wave plate (6b), and is transmitted by the polarizing beam splitting prism (7) to form third transmitted light;

The third reflected light and the third transmitted light jointly form a light beam (X7).

The laser frequency doubling device provided by the present invention can be further realized by adopting the following technical measures.

Preferably, the beam reducer group (3) includes a first convex lens (3a) and a first concave lens (3b),

The first transmitted light (X2) first passes through the first convex lens (2a) and then passes through the first concave lens (3b);

The main optical axis of the first convex lens (3a) and the main optical axis of the first concave lens (3b) are respectively on the extension line of the optical center of the first transmitted light (X2).

Preferably, the beam expander lens group (5) includes a second concave lens (5a) and a second convex lens (5b),

The first transmitted light (X2) first passes through the second concave lens (5a) and then passes through the second convex lens (5b);

The main optical axis of the second concave lens (5a) and the main optical axis of the second convex lens (5b) are respectively on the extension line of the optical center of the first transmitted light (X2).

Preferably, the first frequency-doubling crystal (1) and/or the second frequency-doubling crystal (4) is composed of a crystal composed of potassium titanyl phosphate or lithium triborate, or a crystal composed of two substances Mixture of crystals made.

Preferably, both the first frequency doubling crystal (1) and the second frequency doubling crystal (4) are coated with enhanced projection films for the fundamental frequency light and the frequency doubling light.

Preferably, the first frequency doubling crystal (1) and the second frequency doubling crystal (4) are made of the same material.

Preferably, the cross-sectional area of the second frequency-doubling crystal (4) is greater than or equal to half of the cross-sectional area of the first frequency-doubling crystal (1).

Preferably, it is assumed that the reduction factor of the beam reducer group (3) is m, and the expansion factor of the beam expander group (5) is n, then m=n.

Preferably, the optical elements constituting the beam reducer group (3) and the optical elements constituting the beam expander group (5) are coated with anti-reflection coatings for fundamental frequency light and frequency doubled light.

Preferably, the wavelengths of the first half-wave plate (6a) and the second half-wave plate (6b) are frequency-doubled light wavelengths.

Preferably, the first half-wave plate (6a) and the second half-wave plate (6b) are coated with anti-reflection coatings for the fundamental frequency light and the double frequency light.

Preferably, the polarization beam splitter prism is coated with a frequency-doubled light anti-reflection film.

As a preference, the reflective surfaces of the first beam splitter (2a), the second beam splitter (2b), and the third beam splitter (2c) are all coated with a high-reflection film for frequency-doubling light with a reflectivity>99.5%, and the first beam splitter Both sides of the first beam splitter (2a), the second beam splitter (2b), and the third beam splitter (2c) are coated with an anti-reflection coating for fundamental frequency light with a transmittance >99.5%.

In the application process of the frequency doubling device of the laser provided by the present invention, the remaining energy after the first frequency doubling conversion of the fundamental frequency light undergoes frequency doubling conversion again after beam shrinkage, and the frequency doubling light obtained by the second conversion undergoes beam expansion After combining with the frequency-doubled light obtained in the first conversion process, it is output to improve the frequency-doubling efficiency. In addition, the frequency doubling efficiency of the traditional extracavity frequency doubling scheme can only reach 50% due to the influence of the damage threshold of the optical device; however, the frequency doubling device of the laser provided by the present invention can be used without damaging the optical device, for example , when the reduction factor of the beam reducer group is 1.4 times, and the expansion factor of the beam expander group is also 1.4 times, wherein, when the first frequency doubling conversion efficiency reaches 50%, the fundamental frequency light in the second frequency doubling process The peak power density reaches the same level as the first frequency doubling process. In this way, the conversion efficiency of the remaining fundamental frequency light can reach 50% during the second frequency doubling conversion process, and therefore, the frequency doubling efficiency at this time can reach 75%. Among them, the frequency doubling efficiency of 75% can be achieved under the parameter of 1.4 times the beam reduction ratio and the beam expansion ratio. The peak power density at the suboctave exceeds the damage threshold. That is to say, in the case of selecting the appropriate reduction factor of the beam reducer group and the expansion factor of the beam expander group, the frequency doubling device of the laser provided by the present invention can significantly improve the electro-optic conversion efficiency, and at the same time, can also reduce the system Complexity.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. The drawings are only for the purpose of illustrating a preferred embodiment and are not to be considered as limiting the invention. Also throughout the drawings, the same reference numerals are used to designate the same parts. In the attached picture:

FIG. 1 is a schematic diagram of optical components and optical paths of a laser frequency doubling device provided by an embodiment of the present invention.

detailed description

In order to solve the problems existing in the prior art, the present invention provides a laser frequency doubling device, which can improve the conversion rate in the laser frequency doubling process, and thus is more suitable for practical use.

In order to further explain the technical means and effects of the present invention to achieve the intended purpose of the invention, the specific implementation, structure, characteristics and details of the laser frequency doubling device proposed according to the present invention will be described below in conjunction with the accompanying drawings and preferred embodiments. Its effect is described in detail below. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, the features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

The term "and/or" in this article is just an association relationship describing associated objects, which means that there can be three relationships, for example, A and/or B. The specific understanding is: A and B can be included at the same time, and A and B can be included separately. A exists, B may exist alone, and any of the above three situations can be met.

Referring to accompanying drawing 1, the laser frequency doubling device provided by the embodiment of the present invention comprises a first frequency doubling crystal 1, a first beam splitter 2a, a second beam splitter 2b, a third beam splitter 2c, a beam reducer group 3, a second beam splitter Frequency doubling crystal 4 , beam expander group 5 , first half-wave plate 6 a , second half-wave plate 6 b and polarization beam splitter prism 7 . The incident light X1 enters the first beam splitter 2a through the first frequency doubling crystal 1, and is split by the first beam splitter 2a into the first transmitted light X2 and the first reflected light X3. The first transmitted light X2 sequentially passes through the beam reducer group 3, the second frequency doubling crystal 4, the beam expander group 5 and the first half-wave plate 6a, and then enters the third beam splitter 2c, and is split by the third beam splitter 2c into The second transmitted light X6 and the second reflected light X4, the second reflected light X4 is incident on the polarizing beam splitting prism 7 and is reflected by the polarizing beam splitting prism 7 to form the third reflected light. The first reflected light X3 is incident on the second beam splitter 2b, and the fourth reflected light X5 is obtained after being reflected by the second beam splitter 2b. The third transmitted light is transmitted by the polarizing beam splitting prism 7 . The third reflected light and the third transmitted light together form a light beam X7.

In the application process of the frequency doubling device of the laser provided by the present invention, the remaining energy after the first frequency doubling conversion of the fundamental frequency light undergoes frequency doubling conversion again after beam shrinkage, and the frequency doubling light obtained by the second conversion undergoes beam expansion After combining with the frequency-doubled light obtained in the first conversion process, it is output to improve the frequency-doubling efficiency. In addition, the frequency doubling efficiency of the traditional extracavity frequency doubling scheme can only reach 50% due to the influence of the damage threshold of the optical device; while the frequency doubling device of the laser provided by the present invention can shrink the beam without damaging the optical device When the reduction factor of the mirror group is 1.4 times and the expansion factor of the beam expander group is also 1.4 times, when the conversion efficiency of the first frequency doubling reaches 50%, the peak power density of the fundamental frequency light in the second frequency doubling process to the same level as the first octave process. In this way, the conversion efficiency of the remaining fundamental frequency light can reach 50% during the second frequency doubling conversion process, and therefore, the frequency doubling efficiency at this time can reach 75%. That is to say, in the case of selecting the appropriate reduction factor of the beam reducer group and the expansion factor of the beam expander group, the frequency doubling device of the laser provided by the present invention can significantly improve the electro-optic conversion efficiency, and at the same time, can also reduce the system Complexity.

Wherein, the beam reducer group 3 includes a first convex lens 3a and a first concave lens 3b. The first transmitted light X2 first passes through the first convex lens 2a and then passes through the first concave lens 3b. The main optical axis of the first convex lens 3a and the main optical axis of the first concave lens 3b are respectively located on the extension line of the optical center of the first transmitted light X2. Because both the convex lens and the concave lens have a refraction effect on light, it can change the characteristics of light propagating along a straight line according to the refractive index according to the position where the light is incident on the convex lens or the concave lens. In this case, only when the main optical axis of the first convex lens 3a 1. When the main optical axis of the first concave lens 3b is on the extension line of the optical center of the first transmitted light X2, it can be ensured that the first transmitted light X2 can still travel along a straight line after passing through the first convex lens 3a and the first concave lens 3b in sequence. spread.

Wherein, the beam expander lens group 5 includes a second concave lens 5a and a second convex lens 5b. The first transmitted light X2 first passes through the second concave lens 5a and then passes through the second convex lens 5b; the main optical axis of the second concave lens 5a and the main optical axis of the second convex lens 5b are respectively on the extension line of the optical center of the first transmitted light X2. Because both the convex lens and the concave lens have a refraction effect on light, it can change the characteristics of light propagating along a straight line according to the refractive index according to the position where the light is incident on the convex lens or the concave lens. In this case, only when the main optical axis of the second concave lens 5a , when the main optical axis of the second convex lens 5b is on the extension line of the optical center of the first transmitted light X2, it can be ensured that the first transmitted light X2 can still travel along a straight line after passing through the second concave lens 5a and the second convex lens 5b in sequence. spread.

Wherein, the first frequency-doubling crystal 1 and/or the second frequency-doubling crystal 4 are made of a crystal composed of potassium titanyl phosphate or lithium triborate or a crystal of a mixture of the two substances. in,

Potassium titanyl phosphate (KTP) crystal is a nonlinear optical crystal with excellent nonlinear optical properties, which has been widely valued and applied. KTP crystal is a positive twin crystal, its light transmission band is 350nm ~ 4.5um, it can realize 1.064um neodymium ion laser and other band laser frequency doubling, sum frequency, phase matching of optical parametric oscillation (generally adopts type II phase matching). Its nonlinear coefficients d31, d32, and d33 are 1.4, 2.65, and 10.7 pm/V respectively, and d33 is more than 20 times that of KDP crystal d36. KTP crystals have a high resistance to light damage threshold and can be used for frequency doubling of medium-power lasers, etc. KTP crystal has good mechanical properties and physical and chemical properties, insoluble in water and organic solvents, non-deliquescence, melting point of about 1150 ℃, partially decomposed when melting, the crystal also has a large temperature and angle tolerance. As a frequency conversion material, KTP crystal has been widely used in various fields such as scientific research and technology, especially as the best crystal for small and medium power frequency doubling. Frequency doublers and optical parametric amplifiers made of the crystal have been applied to all-solid-state tunable laser sources.

Lithium triborate (LiB3O5, abbreviated as LBO) is an excellent high-power ultraviolet frequency doubling crystal with a wide light transmission band, high damage threshold, and large acceptance angle. Its main properties include: ​Transmission band: 0.165~3.2μm, nonlinear coefficient: d31=1.05Pm/V, laser damage threshold: 25GW/cm2, frequency doubling conversion efficiency: 40~60% (1064nm→532nm), application Scope: solid-state laser systems, especially for high-power Nd:YAG frequency doubling, frequency tripling, and optical parametric oscillation and amplification, etc.

Wherein, both the first frequency doubling crystal 1 and the second frequency doubling crystal 4 are coated with anti-reflection coatings for the fundamental frequency light and the frequency doubling light. In this case, when the light passes through the first frequency doubling crystal 1 and the second frequency doubling crystal 4, the light intensity loss will be reduced due to the introduction of the anti-reflection coating, so it can make the light pass through the first frequency doubling crystal 1 and the light of the second frequency-doubling crystal 4 can be transmitted as faithfully as possible.

Wherein, the materials of the first frequency doubling crystal 1 and the second frequency doubling crystal 4 are the same.

Wherein, the cross-sectional area of the second frequency doubling crystal 4 is greater than or equal to half of the cross-sectional area of the first frequency doubling crystal 1 . In this case, the cross-sectional area of the crystal is sufficient to allow all light beams to pass through, and the larger the cross-sectional area of the frequency doubling crystal, the higher the price. Since the spot area at the second frequency doubling crystal 4 is only half that of the first frequency doubling crystal 1, it is only necessary that the cross-sectional area of the second frequency doubling crystal 4 is greater than or equal to half of the cross-sectional area of the first frequency doubling crystal 1. Pass the beam all the way through. The purpose of this is to reduce costs.

Wherein, it is assumed that the reduction factor of the beam reducer group 3 is m, and the expansion factor of the beam expander group 5 is n, then m=n. It can ensure uniform spot distribution of the light beam X7. Wherein, if m≠n, the spot diameters of the beam X4 and the beam X5 are different, and the original spot energy distribution state will be changed after combining the beams, making the spot distribution of the beam X7 uneven.

Wherein, the optical elements constituting the beam reducer group 3 and the optical elements constituting the beam expander group 5 are coated with anti-reflection coatings for the fundamental frequency light and the frequency doubled light.

Wherein, the wavelengths of the first half-wave plate 6 a and the second half-wave plate 6 b are frequency-doubled light wavelengths. In this case, the role of the two half-wave plates here is to change the polarization directions of the two frequency-doubled lights passing through the half-wave plates, so as to realize the combined output of the two frequency-doubled lights at the polarizing beam splitter prism 7 . The light beam X5 becomes horizontally polarized light after passing through the half-wave plate 6b, and the light beam X4 becomes vertically polarized light after passing through the half-wave plate 6a. The half-wave plate has a wavelength range, for example, a laser with a wavelength of 1064nm is not suitable for a 532nm half-wave plate.

Wherein, the first half-wave plate 6a and the second half-wave plate 6b are coated with anti-reflection coatings for the fundamental frequency light and the frequency doubled light. Therefore, the light intensity loss after passing through the first half-wave plate 6 a and the second half-wave plate 6 b is reduced.

Wherein, the polarization beam splitter prism is coated with frequency doubled light anti-reflection film. Therefore, the light intensity loss after the light passes through the polarization beam splitter is reduced.

Wherein, the reflective surfaces of the first beamsplitter 2a, the second beamsplitter 2b, and the third beamsplitter 2c are all coated with a high-reflection film of frequency-doubled light with a reflectivity>99.5%, and the first beamsplitter 2a, the second beamsplitter 2b, Both sides of the third beam splitter 2c are coated with an anti-reflection coating for the fundamental frequency light with a transmittance>99.5%. While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies thereof, the present invention also intends to include these modifications and variations.

Claims (10)

1. A frequency doubling device for a laser, characterized in that it includes a first frequency doubling crystal (1), a first beam splitter (2a), a second beam splitter (2b), a third beam splitter (2c), a beam shrinker Mirror group (3), second frequency doubling crystal (4), beam expander group (5), first half-wave plate (6a), second half-wave plate (6b) and polarization beam splitter prism (7), The incident light (X1) enters the first beam splitter (2a) through the first frequency doubling crystal (1), and is split into the first transmitted light (X2) and the second beam by the first beam splitter (2a). a reflected light (x3), The first transmitted light (X2) sequentially passes through the beam reducer group (3), the second frequency doubling crystal (4), the beam expander group (5) and the first half-wave plate (6a) and then enters the The third beam splitter (2c) is split into second transmitted light (X6) and second reflected light (X4) by the third beam splitter (2c), and the second reflected light (X4) is incident to the the polarizing beam splitting prism (7) and is reflected by the polarizing beam splitting prism (7) to form the third reflected light; The first reflected light (X3) enters the second beam splitter (2b), and is reflected by the second beam splitter (2b) to obtain a fourth reflected light (X5), and the fourth reflected light (X5 ) enters the polarizing beam splitting prism (7) after passing through the second half-wave plate (6b), and is transmitted by the polarizing beam splitting prism (7) to form third transmitted light; The third reflected light and the third transmitted light jointly form a light beam (X7). 2. The laser frequency doubling device according to claim 1, characterized in that the beam reducer group (3) includes a first convex lens (3a) and a first concave lens (3b), The first transmitted light (X2) first passes through the first convex lens (2a) and then passes through the first concave lens (3b); The main optical axis of the first convex lens (3a) and the main optical axis of the first concave lens (3b) are respectively on the extension line of the optical center of the first transmitted light (X2). 3. The laser frequency doubling device according to claim 1, characterized in that, the beam expander lens group (5) includes a second concave lens (5a) and a second convex lens (5b), The first transmitted light (X2) first passes through the second concave lens (5a) and then passes through the second convex lens (5b); The main optical axis of the second concave lens (5a) and the main optical axis of the second convex lens (5b) are respectively on the extension line of the optical center of the first transmitted light (X2). 4. The laser frequency doubling device according to claim 1, characterized in that the first frequency doubling crystal (1) and/or the second frequency doubling crystal (4) is made of potassium titanyl phosphate or three It is made of a crystal of one substance in lithium borate or a crystal of a mixture of two substances. 5. The laser frequency doubling device according to claim 1, characterized in that, both the first frequency doubling crystal (1) and the second frequency doubling crystal (4) are coated with fundamental frequency light and frequency doubling light increase film. 6. The laser frequency doubling device according to claim 1, characterized in that, the first frequency doubling crystal (1) and the second frequency doubling crystal (4) are made of the same material. 7. The laser frequency doubling device according to claim 1, characterized in that, the cross-sectional area of the second frequency doubling crystal (4) is greater than or equal to half of the cross-sectional area of the first frequency doubling crystal (1) . 8. The laser frequency doubling device according to claim 1, characterized in that, assuming that the reduction factor of the beam reducer group (3) is m, and the expansion factor of the beam expander group (5) is n, Then m=n. 9. The laser frequency doubling device according to claim 1, characterized in that the optical elements constituting the beam reducer group (3) and the optical elements constituting the beam expander group (5) are coated with Anti-reflection coating for fundamental frequency light and double frequency light. 10. The laser frequency doubling device according to claim 1, characterized in that, the wavelengths of the first half-wave plate (6a) and the second half-wave plate (6b) are frequency-doubled light wavelengths; As a preference, the first half-wave plate (6a) and the second half-wave plate (6b) are coated with anti-reflection coatings for fundamental frequency light and double frequency light; As a preference, the polarization beam splitter prism is coated with a frequency-doubled light anti-reflection film; As a preference, the reflective surfaces of the first beam splitter (2a), the second beam splitter (2b), and the third beam splitter (2c) are all coated with a high-reflection film for frequency-doubling light with a reflectivity>99.5%, and the first beam splitter Both sides of the first beam splitter (2a), the second beam splitter (2b), and the third beam splitter (2c) are coated with an anti-reflection coating for fundamental frequency light with a transmittance >99.5%.