JPH11261137A - Laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized highly efficient end pumping type laser device, the pumping direction of which is decided so as to make the optical axis of the laser beam coincide with the optical axis of the stimulating light and which emits a high-quality laser beam, through the use of a condenser lens having a short focal distance by bringing a laser medium closer to the condenser lens. SOLUTION: A laser device is provided with a cylindrical composite laser rod 1, consisting of a cylindrical laser medium 1 containing laser ions and a cylindrical non-laser medium 3 which is bonded to at least one end face of the laser medium 2, having the same diameter as the medium 2 has, substantially contains no laser ions, and has a thickness (t) which is smaller than the diameter (d) of the medium 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge-pumped laser device in which the pumping direction is determined so that the laser optical axis coincides with the pumping optical axis.

[0002]

2. Description of the Related Art An edge-pumped laser device is included in a laser material by pumping light having a beam shape that matches the spatial mode distribution of a laser for the purpose of performing highly efficient laser oscillation. Excludes only the portion of the laser ion that is effective for laser oscillation to the laser upper level,
It has a structure in which stimulated emission with the laser lower level is stored inside the optical resonator. Here, the process of pumping to the upper laser level and the process of transition from the lower laser level to the ground level involve heating of the non-radiative crystal, and therefore the temperature rise of the laser material is inevitable. Further, when the excitation light includes a spectrum related only to the heating of the laser material without participating in the laser transition, the temperature of the laser material further increases.

[0003] Such a rise in the temperature of the laser material has various adverse effects on the laser operation. That is, when viewed spatially, heat is generated only in a portion related to laser oscillation in the laser material, and the temperature of that portion rises, so that a steep temperature distribution with a localized high temperature portion is formed. . As a result, a local thermal expansion distribution occurs in the laser material, which causes thermal distortion. In extreme cases, when this exceeds the tensile strength of the laser material, the laser material is destroyed. Thermal distortion gives the laser crystal a thermal birefringence effect even if it does not lead to destruction,
This results in impairing the laser oscillation characteristics and impairing the desired output value and the desired deflection characteristics. The above temperature distribution is
The temperature dependence of the refractive index of the laser material results in the formation of a lens that changes with the excitation input condition, thus making the laser oscillation phenomenon unstable.

[0004] Further, in a laser in a category called a quasi-three-level laser, an increase in the operating temperature of the laser material itself has a fatal result. Laser oscillation at 946 nm using a YAG crystal containing Nd ³⁺ as a laser ion is a typical example of a quasi-three-level laser. Also, laser ions occupying the lower level of the laser exist, and the ratio rapidly increases as the temperature rises. Therefore, it becomes difficult to obtain the inversion distribution essential for laser oscillation as the temperature rises, and 946 laser ions occupying the lower laser level are generated.
The laser beam of nm is absorbed and re-excited to the upper laser level, which acts as a loss to the laser oscillation, and as a result, the oscillation threshold increases and the efficiency decreases.

[0005] In order to reduce such various adverse effects, an end face photoexcitation type laser device using a crystal using a composite laser rod in which a laser material and a non-laser material are composited is disclosed in US Pat.
P5,563,899, JP-A-7-17075, United States Statulator
y Invention RegistrationR
eg. Number: H1673 Publisher
d: Aug. 5, 1997 (hereinafter abbreviated as H1673) ". As an example, FIG. 1, FIG. Referring to FIG. 2, the composite laser rod is held in a cooling jacket using an O-ring at a portion of the non-laser material, and the heat generated at the laser material portion generated by irradiation from the excitation light source through the condenser lens is: The non-laser material is also guided and dissipated, and is removed in direct contact with the liquid coolant on a fairly wide side of the composite laser rod. This suppresses an increase in the operating temperature of the laser material. In such a high-power laser device configuration in which the side surface of the composite laser rod needs to be brought into direct contact with the liquid coolant to forcibly cool, the consideration regarding the length required for the non-laser material portion is described in "IEEE Journal of."
selectedtopics in quantum
electronics vol. 3, No1 F
ebruary 1997, pp. 71-81 "," Diode Arrays, Crystal.
s, and Thermal Management
For Solid-State Lasers ”on page 74,“ I study 1-2 times the diameter of the laser rod as the length of the non-laser material. Non-laser material makes sense. Needs at least the diameter of the laser rod. "

The above-mentioned 946 nm oscillation line is a limit wavelength of a titanium sapphire laser which is famous as a wavelength tunable laser in the field of spectroscopic measurement, and is considered to be a valuable wavelength for interpolating between 1064 nm of an Nd: YAG laser. Can be Further, 946 nm is a wavelength of blue 4 which is the second harmonic.
The wavelength of 73 nm is also attracting attention as a light source having high beam quality for optical recording, printers, and the like.
As such a measurement light source, a laser device that is small, has high efficiency, and is excellent in beam quality is required. Here, in order to improve the efficiency, it is desirable to excite the laser ions in the laser material by increasing the intensity of the excitation light. Focal length f
When an excitation beam having a diameter D and a wavelength λ is condensed using the above lens, the condensing size at the focal position is λf / πD, which is proportional to f. For this reason, in order to increase the intensity of the excitation light by reducing the condensing dimension, it is preferable that the focal length f of the condensing lens be as short as possible. However, H1673
Of FIG. 1, FIG. Referring to FIG. 2, the length of the non-laser material needs to be sufficiently longer than the diameter of the laser rod because a cylindrical laser material containing laser ions requires a mechanism for holding the cooling jacket using an O-ring. Since the excitation is performed through this long non-laser material region, it is impossible to reduce the distance between the focusing lens and the laser material of the composite laser rod, and a lens with a short focal length f can be used. It is difficult to achieve high efficiency.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to use a condenser lens having a short focal length by shortening the distance between the condenser lens and the laser material, thereby achieving a small and highly efficient beam quality. It is to realize an excellent laser device.

[0008]

According to the present invention, there is provided a laser apparatus comprising: a cylindrical laser material containing laser ions; and a laser material joined to at least one of both end faces of the laser material. A cylindrical composite laser rod made of a non-laser material having a cylindrical shape having the same diameter as the laser material, substantially not containing laser ions, and having a thickness smaller than the cylindrical diameter; Exciting means for injecting excitation light into a laser material constituting the composite laser rod through a non-laser material constituting the composite laser rod, and causing laser emission by using light emitted from the laser material constituting the composite laser rod as a seed An optical resonator is provided.

Here, it is preferable that the composite laser rod is formed by diffusion bonding a laser material and a non-laser material constituting the composite laser rod. Alternatively, the composite laser rod may be one in which a laser material and a non-laser material constituting the composite laser rod are joined by interposing an adhesive medium or a liquid medium.

The non-laser material constituting the composite laser rod may be made of the same material as the base material of the laser material constituting the composite laser rod. The non-laser material constituting the composite laser rod may be made of a material having a higher thermal conductivity than the laser material constituting the composite laser rod.

Further, in the laser device of the present invention, the excitation means is arranged so that a beam diameter in a laser material constituting the composite laser rod is 1/3 or less of a cylindrical diameter of the composite laser rod. Preferably, the adjusted excitation light is applied to the composite laser rod. Furthermore, it is preferable that the laser device of the present invention includes a holder that holds the cylindrical surface of the composite laser rod and receives heat transfer from the composite laser rod.

Further, in the laser device of the present invention, the optical resonator has a pair of mirrors, and at least one of the pair of mirrors is coated on an end face of the composite laser rod. May be used. In the conventional technique described above, it is necessary to forcibly cool the side surface of the composite laser rod by directly contacting the liquid refrigerant in order to suppress a rise in temperature due to the excitation light, and thus it is necessary to prevent leakage of the liquid refrigerant. In addition, it is necessary to seal the non-laser material portion of the composite laser rod using an O-ring, which is an obstacle to adopting a focusing lens having a short focal length.
In addition, the length of the non-laser material required for reducing the temperature rise and distortion due to heat generated in the laser material portion of the composite laser rod is 1 to less than the diameter of the laser rod. The length is determined based on the knowledge that it is necessary to be twice or more.

On the other hand, the present inventor has proposed that a laser rod is provided at one end of the laser material portion depending on the power level of the excitation light and the size of the excitation beam, or depending on the thermal constant of the laser material portion and the non-laser material portion. By joining a non-laser material portion having a length less than the diameter of the O-ring seal and eliminating the cooling by direct contact with the liquid refrigerant, the structural part necessary for the O-ring seal can be eliminated, thereby overcoming the above-mentioned obstacles. I found it. In addition, the present inventor has performed a theoretical analysis on heat conduction, and if the diameter of the excitation beam is sufficiently smaller than the diameter of the laser rod, the temperature rise due to the heat generated in the laser material will cause the length of the non-laser material portion to be longer than the rod. It has been found that even when the diameter is shorter than the diameter of the laser rod, the length of the non-laser material is almost the same as when the length of the non-laser material is twice or more the diameter of the laser rod.

The present invention has been made based on these findings. According to the present invention, a compact, high-efficiency, and excellent beam quality laser apparatus is realized using a composite laser rod. be able to.

[0015]

FIG. 1 is a perspective view of a composite laser rod 1 for realizing the technical idea of the present invention. In FIG. 1, a non-laser material 3 not containing laser ions and having a thickness t smaller than the diameter d is joined to one side of a cylindrical laser material 2 having a diameter d containing laser ions necessary for laser oscillation.

In this case, the bonding method is such that the bonding surface is optically polished to make optical contact, the temperature is raised to a required temperature below the melting point, and diffusion bonding (diffusion b) is performed.
It is preferable from the viewpoint of the strength of the bonding surface or the optical continuity at the bonding surface to adopt a method of producing a state free from mechanical and optical distortion by performing annealing after annealing. At this time, if it is most important to ensure the reliability of the diffusion bonding or the optical continuity at the bonding surface, the non-laser material 3 is used as the non-laser material 3 because of the consistency of the crystal lattice constant, crystal direction, and the like. It is preferable to use the same material as the base material used in 2. That is, the laser material 2 is made of YAG, YLF, YV doped with laser ions such as Nd, Yb, Tm, Ho, and Cr.
O ₄ , LiSrAlF, LiSrGaF ₆ , LiSrC
aF ₆ or the like, and the non-laser material 3 is YAG, YLF, YVO ₄ , LiS
rAlF, LiSrGaF ₆ , LiSrCaF _{6 and the} like are good. However, if the heat dissipating action in the non-laser material 3 is given top priority, it has a higher thermal conductivity than the laser material 2 under the assurance of reliability by establishing working conditions, and has various optical characteristics. An excellent material such as sapphire may be selected.

As a joining method other than the diffusion joining, if the working materials and working conditions are prepared, the joining is performed by a transparent adhesive medium whose refractive index is adjusted to a value close to the refractive index of the laser material 2 and the non-laser material 3. Or may be joined via a liquid medium. In this case, an adhesive medium or a liquid medium having a high thermal conductivity is selected. Figures 2 and 3
FIG. 3 is a view showing each embodiment of the laser device of the present invention employing the composite laser rod shown in FIG. 1.

In each of the embodiments shown in FIGS. 2 and 3, the composite multiple laser rod 1 is housed and held in a holder 4, optical resonators are arranged on both sides thereof, and excitation light emitted from an excitation light source 10 is provided. This is an example of a configuration in which laser light is condensed using a condensing lens 6 having a focal length f and guided to the laser material 2 through the non-laser material 3 of the composite laser rod 1 to cause laser oscillation. The optical resonator in FIG. 2 includes a coating 7 applied to the end of the composite laser rod 1, which transmits light for the wavelength of the excitation light 5 and exhibits high reflection characteristics for the laser wavelength. And an output mirror 8 provided with a coating for giving partial transmittance to the output mirror 8.
The optical resonator shown in FIG. 3 has a rear mirror 9 provided with a coating 7 showing transmission characteristics with respect to the wavelength of the excitation light and having high reflection characteristics with respect to the laser wavelength, and an output similar to that of FIG. And a mirror 8. In the optical resonator of FIG.
A coating 7 applied to the end face of the composite laser rod 1 corresponds to the rear mirror 9 in the optical resonator of FIG.
By extending this idea, a coating required as an output mirror may be applied to the other end face of the composite laser rod 1 to adopt a configuration in which the optical resonator does not appear as a visible structure. Good. If the optical resonator is coated on both surfaces of the composite laser rod, the degree of freedom of the manufactured optical resonator is lost, but a smaller laser oscillator can be realized. On the other hand, when a pair of mirrors facing each other is arranged as an optical resonator as shown in FIG.
The end face on the side where the excitation light is incident is coated with an anti-reflection coating for both the wavelength of the excitation light and the laser wavelength,
Preferably, the other end face is provided with a non-reflective coating for the laser wavelength.

As can be seen from FIG. 1, since the length t of the non-laser material 3 of the composite laser rod 1 is shorter than its diameter d and that the composite laser rod 1 is not O-ring sealed, Light is condensed on the material 2 by using a condensing lens having a very short focal length as compared with the related art. It is desirable that the focused beam diameter of the excitation light in the laser material 2 of the composite laser rod 1 is smaller than 1/3 of the rod diameter. By making the excitation beam diameter smaller,
Since the oscillation gain of the laser can be increased and the overlap with the laser oscillation mode of the laser resonator is improved, the oscillation efficiency is improved. If the diameter of the excitation beam is made smaller, the temperature rise can be sufficiently reduced even if the thickness t of the non-laser material is further reduced.

The heat on the central axis of the laser material 2 of the composite laser rod 1 generated by the irradiation of the excitation light 5 is conducted in the radial direction of the laser material 2 and reaches the cylindrical surface of the laser material 2. Heat is dissipated or conducted in the direction of the non-laser material 3, that is, in the axial direction, and then conducted radially inside the non-laser material 3 to reach the cylindrical surface of the non-laser material 3 and dissipated.
The holder 4 that holds the composite laser rod 1 also serves to receive and absorb the heat that has reached the cylindrical surface of the composite laser rod 1 and throw it away. For this reason, the contact between the cylindrical side surface of the composite laser rod 1 and the cylindrical inner surface of the holder 4 is achieved by interposing an indium foil so as to reduce the thermal resistance, interposing a thermal compound, or using a grease having good thermal conductivity. It is necessary to consider that there is no gap by interposing 2 and 3 holder 4
In, heat exchange is performed on all side surfaces that come into contact with the surrounding air.

FIG. 4 is a view showing various other examples of the holder for holding the composite laser rod 1. As shown in FIG. FIG.
In (a), radiating fins 11 are provided to increase the heat exchange area in the holder 4. The radiation fins 11 can be forcibly air-cooled. In FIG. 4B, the temperature sensor 12 is placed on a part of the holder 4 and a Peltier element 13 which is an electronic cooling element is attached to control the temperature of the temperature sensor 12 so as not to rise too much. In FIG. 4C, the heat from the holder 4 is carried out to the outside by the cooling liquid flowing through the flow path 14 provided in the holder 4. Here, no temperature sensor is provided, but the temperature of the coolant to be fed is controlled.
In FIG. 4, the heat generated from the composite laser rod 1 is
And the concept of air cooling, electronic cooling, and liquid cooling by the holder 4 has been described, but other modifications within the scope of the technical idea of the present invention are possible.

FIG. 1 shows a composite laser rod in which a non-laser material 3 is bonded to one end face of a laser material 2, but as shown in a perspective view of FIG. When the non-laser material 3 whose thickness t is smaller than the cylindrical diameter d is joined, it is more effective to reduce the operating temperature of the laser material 2. Also in this case, the gist of the present invention, such as transmitting heat to the holder by the cylindrical side surface of the composite laser rod 1 and performing air cooling, electronic cooling, and liquid cooling in the holder, is the same.

The composite laser rod of FIG. 5 can be applied to a bow tie ring laser as shown in FIG. Here, the excitation light from both directions is introduced into the laser material via the non-laser material on both end surfaces, and the single mode oscillation light 15 characteristic of the ring laser can be obtained with a relatively high output. In a ring laser, it is necessary to insert an optical diode 16, an etalon plate 17, sometimes a wavelength selection element, and the like inside the optical resonator. Since these are optical loss elements, it is necessary to secure a gain to overcome them. Excitation from both directions as shown in FIG. 6 is one method, in which non-laser material is placed on both sides of the laser material. Preferably, there is.

[0024]

Conventionally, a composite laser rod having a non-laser material having a length t equal to or greater than the diameter d of the composite laser rod is joined to reduce the operating temperature of the laser material to destroy the crystal. Research and development have been promoted under the idea of trying to push the limits. However, the inventor has found that the desired output is not at such a challenging level, e.g., at the level of a measurement light source, even if the length of the non-laser material is less than the diameter of the rod. I found In particular, it has been found that this saturation phenomenon is remarkable when the condensing dimension of the excitation light is 1/3 or less of the diameter of the rod.

According to the present invention, by joining a non-laser material having a length less than the diameter of the rod, the operating temperature of the laser material can be reduced, and at the same time, the excitation light can be reduced by using a short-focus condenser lens. Of the laser device, the laser oscillation efficiency can be increased, and the size of the laser device can be reduced. 946 nm of Nd: YAG laser
In the quasi-three-level laser represented by the oscillation line of (1), a reduction in the operating temperature is particularly required.
It is possible to realize a small and highly efficient measurement laser oscillator capable of oscillating an important wavelength by such spectroscopic measurement.

LiSrAlF ₆ , LiSrGaF ₆ , LiSrCa expected as a base material of a wavelength tunable laser
Such as F ₆ can not reduce the operating temperature due to low thermal conductivity, limiting the efficiency limits of the beam quality has been a problem. According to the present invention, it is possible to realize a small-sized, highly-efficient, wavelength-tunable laser oscillator for measurement with excellent beam quality even when these base materials are employed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a composite laser rod employed in an embodiment of the laser device of the present invention.

FIG. 2 is a structural diagram of a first embodiment of a laser device of the present invention employing the composite laser rod shown in FIG.

FIG. 3 is a structural diagram of a second embodiment of the laser device of the present invention employing the composite laser rod shown in FIG.

FIG. 4 is a view showing various examples of a holder for holding a composite laser rod.

FIG. 5 is a perspective view showing another example of the composite laser rod used in the embodiment of the laser device of the present invention.

FIG. 6 is a structural diagram of a third embodiment of the laser device of the present invention employing the composite laser rod shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Composite laser rod 2 Laser material 3 Non-laser material 4 Holder 5 Excitation light 6 Condensing lens 7 Coating 8 Output mirror 9 Rear mirror 10 Excitation light source 11 Radiation fin 12 Temperature sensor 13 Peltier element 14 Flow path 15 Single mode oscillation light 16 Optical diode 17 etalon plate

Claims (8)

[Claims] 1. A cylindrical laser material containing laser ions, and a cylindrical shape having substantially the same diameter as the laser material joined to at least one end face of both end faces of the laser material, wherein the cylindrical shape is substantially the same. A cylindrical composite laser rod made of a non-laser material that does not contain laser ions and has a thickness smaller than the cylindrical diameter; a laser material that forms the composite laser rod through the non-laser material that forms the composite laser rod 1. A laser device comprising: an excitation unit for injecting excitation light into a laser beam; and an optical resonator that causes laser oscillation by using light emitted from a laser material forming the composite laser rod as a seed. 2. The laser device according to claim 1, wherein the composite laser rod is formed by diffusion bonding a laser material and a non-laser material constituting the composite laser rod. 3. The composite laser rod according to claim 1, wherein a laser material and a non-laser material constituting the composite laser rod are joined by interposing an adhesive medium or a liquid medium. 2. The laser device according to 1. 4. The non-laser material constituting the composite laser rod is made of the same material as the base material of the laser material constituting the composite laser rod. Laser device. 5. The non-laser material constituting the composite laser rod is made of a material having a higher thermal conductivity than that of the laser material constituting the composite laser rod. The laser device according to claim 1. 6. The pumping means according to claim 1, wherein said pumping means controls the pumping light adjusted such that a beam diameter in a laser material constituting said composite laser rod is 1/3 or less of a cylindrical diameter of said composite laser rod. 2. The laser device according to claim 1, wherein the laser beam is applied to a composite laser rod. 7. The laser device according to claim 1, further comprising a holder that holds a cylindrical surface of the composite laser rod and receives heat transfer from the composite laser rod. 8. The optical resonator has a pair of mirrors,
2. A laser device according to claim 1, wherein at least one of said pair of mirrors is made of a coating applied to an end face of said composite laser rod.