JPH0878762A - Q-switched laser - Google Patents

Abstract

PURPOSE: To obtain a Q-switched laser excellent in laser extraction efficiency by reducing the energy density of laser light in a laser resonator to a value equal to or below the damaging threshold of the optical components. CONSTITUTION: Where D is taken as the ratio of maximum energy density that will not cause damage to saturation fluence, η as laser extraction efficiency, L as loss in the resonator in the Q-switch and T as the amount of output coupling of the resonator, the Q-switched laser is constituted so that D<=2, 0.05<=L<=0.2, 0.5<=T, 0.3D<=ηwill be all satisfied.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to Q-switched lasers. In particular, the present invention relates to a device for obtaining the maximum extraction efficiency from the laser medium in a Q-switched laser within a range that does not damage the optical components constituting the laser.

[0002]

2. Description of the Related Art FIG. 8 shows, for example, JOHN J. DEG
NAN, "Theory of the Optima
ly Coupled Q-Switched La
ser, "IEEE JOURNAL OF QUAN
TUM ELECTRONICS, VOL. 25, P
214-220, (1989) is a block diagram for explaining the configuration of the conventional Q-switched laser. Here, 1 is a laser medium, 2 is an excitation source for forming a population inversion in the laser medium 1, 3 is a resonator for giving optical feedback to the laser medium 1 and causing laser oscillation, and 4 is a resonance Q switch for controlling the laser oscillation by changing the Q value of the resonator 3 inside the resonator 3 and 5 are placed inside the resonator 3 and a part of the laser light generated inside the resonator. Is discharged to the outside, and the output coupling amount T is represented by the formula (1). In the formula (1), the resonator internal loss is L,
And the round-trip small signal gain of the laser medium during Q-switch oscillation is represented by ln (G) (where G is the round-trip amplification factor). T = 1-Exp [-L * {z-1-ln (z)} / ln (z)] (1) Here, z = ln (G) / L.

Next, the operation will be described. The laser medium 1 is excited by the excitation source 2 while the Q value of the resonator 3 is kept low by the Q switch. In this case, because Q is low,
Laser oscillation is suppressed, and the excitation energy does not become laser light but is accumulated in the laser medium 1. After that, when the Q value of the resonator 3 is switched to a high value by the Q switch, laser oscillation is suddenly generated in the resonator 3 and the laser medium 1
The energy stored inside is extracted as light, and part of it is emitted from the output coupler 5 to the outside. This emission stops when the energy stored in the laser medium 1 is exhausted, so that a pulsed laser output light is obtained, which is called a Q switch pulse.

Of the energy stored in the laser medium 1, the ratio of the energy converted to the energy of the optical pulse taken out of the resonator 3 is called the extraction efficiency, and the value of the output coupler 5 is maximized to maximize this value. The amount of output coupling is determined. A method of determining the output coupling amount T of the output coupler 5 will be described next. FIG. 9 schematically shows two levels that cause laser oscillation in the laser medium 1. Assuming that the laser medium 1 is spatially uniformly excited and that the laser light in the resonator also has a uniform intensity in the laser medium, the rate equation describing the laser oscillation is as follows: (Atom, molecule, etc.) density N _U , active medium density N _L of the laser lower level, and photon density φ are expressed by equation (2).

[0005]

[Equation 1]

In this equation (2), l is the laser medium 1
, L ′ is the length of the resonator 3, τ _p is the photon lifetime of the resonator 3, v _g is the speed of light in the laser medium 1, τ is the fluorescence lifetime (relaxation time by spontaneous emission), and σ _emi is The stimulated emission cross section of the upper laser level, σ _abs is the stimulated absorption cross section of the lower laser level. In a four-level laser, N _L becomes almost zero. In addition, in the three-level laser, N _u + N _L
In consideration of the fact that is equal to the total active medium density in the laser medium, and the ratio of N _u to the total active medium density is β, equation (2) is rewritten as equation (3). Furthermore, at the time of Q-switch oscillation, the rate of stimulated emission is much higher than the rate of excitation or spontaneous emission.
If these terms are ignored, the laser operation can be described by the rate equation of equation (4) for both the three-level and four-level system lasers.

[0007]

[Equation 2]

By dividing both sides of the two differential equations of the equation (4), the equation (5) is obtained. At the moment when the Q of the Q switch 4 is switched to a high value, the initial value of x is x ₀ , and at this time, no laser light is generated, so if the initial value of y is set to 0, the solution shown in equation (6) is obtained. To be Also, at t-> ∞,
Since pulse oscillation is completed, y = 0, and the value of x in the laser medium 1 at this time is set to x _f and substituted into equation (6), the characteristic equation of equation (7) representing the Q switch operation is obtained. To be

[0009]

(Equation 3)

On the other hand, when the photon density y is converted into the output power P and shown, it is expressed by the equation (8). In the equation (8), S is the cross-sectional area of the laser beam formed by the resonator 3, T is the output coupling amount of the output coupler 5, hν is the photon energy of the laser light, and C ₀ is the speed of light in vacuum. From the equations (7) and (8), the output energy E of the Q switch is given by the equation (9).

[0011]

[Equation 4]

Here, using the relationship of the equation (9), the equation (10) is obtained.
Find the maximum value of. Therefore, h = -ln (1-T),
Rewriting equations (8) and (9) with k = X _f / X ₀ , equations (10) and (11) are obtained. Expression (10), Expression (1
When the output coupling amount T, the maximum output E, and the maximum extraction efficiency η _EX are obtained by using the undetermined coefficient method shown in the equation (12) using the equation 1), the equation (13), the equation (14), and the equation (15) are obtained. Get a relationship.

[0013]

(Equation 5)

That is, in the conventional Q-switch laser configuration method, when the small signal gain is determined by the shape of the pump source 2 and the laser medium, the output coupler 5 having the output coupling amount T shown in the equation (13). The Q-switched laser is composed of the maximum output energy E and the maximum extraction efficiency η _EX.
Was getting This is qualitatively explained as follows. In the pulse generation process after the Q value of the resonator 3 is changed by the Q switch 4, the interaction between the population inversion and the laser light generated in the laser medium 1 increases as the laser light intensity in the resonator increases. Becomes stronger, and the energy stored in the laser medium 1 is easily converted into light energy. In order to obtain this effect, it is effective to make the output coupling amount of the output coupler 5 as small as possible and increase the laser light intensity in the resonator. On the other hand, the optical energy stored in the resonator 3 is attenuated by the intracavity loss while the laser light circulates in the resonator 3. For this reason, when the laser light is confined in the resonator for a shorter time (photon lifetime), the attenuation due to the loss in the resonator is smaller and the laser light can be efficiently extracted to the outside. The larger the amount of output coupling, the shorter the photon lifetime. Due to these two conflicting factors, the optimum amount of output coupling is determined. That is, as shown in FIG. 10, the output coupling amount T has an optimum value T _opt between 0 and 1, and this value is determined by the equation (13). However, this formula is based on the premise that the components of the laser can withstand high energy.As the internal energy density increases, the components will be damaged and destroyed as will be described later. It must be suppressed. In that case, z is reduced and the _Eu- T relationship curve is suppressed to a small value as shown in FIG.

In the conventional method of constructing a Q-switched laser, the energy density in the resonator is generally the most general case. In the case where a mirror constituting the resonator 3 is used as the output coupler 5, a schematic is shown in FIG. As shown schematically, the resonator internal energy density E _cav is given by equation (16).

[0016]

(Equation 6)

[0017]

As can be seen from the expression (15), in the configuration of the conventional Q-switched laser, the extraction efficiency ηEX can be increased by increasing the value of z proportional to the small signal gain. . However, since the optical components that make up the Q-switched laser have a finite damage threshold, it is necessary to set the energy density in the cavity shown in equation (16) to a value below the damage threshold. , Therefore, the value of z is limited. In particular, as can be seen from the formula (16), the smaller the effective stimulated emission cross-section σ _eff is, the higher the energy density in the cavity at the same z value is. Therefore, a smaller z value must be selected. Therefore, there is a problem in that the efficiency shown in the equation (15) becomes low.

The present invention has been made in order to solve the above-mentioned problems. The z value is set higher than that of the conventional structure, and the laser light energy density in the resonator is set to the damage threshold value of optical parts. It is an object of the present invention to obtain a Q-switched laser capable of obtaining the maximum extraction efficiency by increasing the output coupling amount while making the following.

[0019]

In the Q-switched laser according to the present invention, the ratio of the maximum energy density in the damaged cavity to the saturated fluence is D, and the extraction efficiency of the laser is η, which is a subject to be changed. , L is the loss in the resonator of the Q switch and T is the output coupling amount of the resonator, D ≦ 2, 0.05 ≦ L ≦ 0.2, 0.5 ≦ T,
It is configured so that the value of 0.3D ≦ η is satisfied at the same time.

Further, as a laser medium, thulium-doped yttrium-aluminum-garnet (T
m: YAG) and using 0.
5 ≦ T ≦ 0.7 is set.

Alternatively, erbium-doped glass (Er: Glass) is used as the laser medium, and the value of the output coupling amount is set to 0.5 ≦ T ≦ 0.9.

Alternatively, as a laser medium, holmium-doped yttrium-aluminum-garnet (H
o: YAG), and as the value of the output coupling amount, 0.
5 ≦ T ≦ 0.9 is set.

In the Q-switched laser according to the present invention, the laser beam is divided into an expansion area and a reduction area, and an expansion optical system is used at the division points to extract an output from the reduction area. When the expansion ratio of the expansion region to the contraction region of M is M, the ratio of the maximum energy density in the damaged resonator to the saturated fluence on the expansion region side is D, and the extraction efficiency of the laser is set to η Assuming that the loss in the resonator of the switch is L and the output coupling amount of the resonator is T, Dm = D / M ² and Dm ≦
2, 0.05 ≦ L ≦ 0.2, 0.5 ≦ T, 0.3D ≦ η
The values of are simultaneously satisfied.

Further, in the above structure, the value of the magnification M is set to 2.5 ≦ M.

The Q-switched laser according to the present invention uses the ratio of the maximum energy density in the damaged cavity to the saturated fluence as D, and adds a condition within the limit of the energy density in the cavity in the laser. According to the characteristic equation, the extraction efficiency of the laser was defined as η so as to maximize it, and D ≦ 2 was set to satisfy the value of 0.3D ≦ η.

[0026]

In the Q-switched laser according to the present invention, the maximum energy density in the damaged cavity is first determined so that the laser component is not damaged by the optical energy density, or this is normalized by the saturation fluence, and this value is incorporated. The coupling amount and the small signal gain of the laser medium are required to maximize the extraction efficiency. A laser having a high loss L and a high output coupling amount T within a certain range set in this way has a high extraction efficiency, especially when the effective stimulated emission cross section is small.

The Tm: YAG solid-state laser crystal containing Tm ions has a high saturation fluence and an optimum binding amount of 0.5.
When ≦ T ≦ 0.7, high extraction efficiency is achieved.

The Er: Glass solid-state laser crystal containing Er ions has a relatively high saturation fluence and an optimum coupling amount of 0.5 ≦ T ≦ 0.9, which results in high extraction efficiency.

The Ho: YAG solid-state laser crystal containing Ho ions has a relatively high saturation fluence, and the optimum coupling amount is 0.5 ≦ T ≦ 0.9, and the extraction efficiency is high.

The Q-switched laser according to the present invention operates in the same manner even when the laser beam is divided into a plurality of parts and is in a relation of expansion / reduction, and the reduced parts are damaged so that they are not damaged by the light energy density. The maximum energy density in the resonator is determined, and by incorporating this value, the coupling amount that maximizes the extraction efficiency and the small signal gain of the laser medium are obtained. The laser with these values has high extraction efficiency when the effective stimulated emission cross section is small.

Further, for a plurality of laser beams, particularly in the case of a medium having a low saturation fluence in the expansion region, a high extraction efficiency can be obtained by setting the expansion ratio to 2.5 or more.

In the Q-switched laser according to the present invention, the maximum energy density in the damaged cavity is first determined so that the laser component is not damaged by the optical energy density, or the maximum energy density in the damaged resonator is standardized by the saturation fluence, and this value is incorporated. The coupling amount and the small signal gain of the laser medium are required to maximize the extraction efficiency. The extraction efficiency becomes high in the small range where the maximum energy density in the damaged resonator, which is standardized by the saturation fluence thus set, is 2 or less.

[0033]

【Example】

Example 1. A conventional laser device determines the amount of coupling, then
While the amount of binding is reduced by the value determined by the internal energy density, in the present invention, the value determined by the internal energy density is brought into the formula for determining the amount of binding in advance to obtain a value that maximizes efficiency. The results obtained in this way are very different from the conventional ones. First, the relational expression applied to the laser will be described below, and a simple expression approximated to the expression that maximizes the efficiency within the above limits will be described. The effect of the device according to this formula will be described in comparison with the value of the conventional device.

The equation (4) is used as the basic equation for the Q-switch operation to optimize the laser extraction efficiency ηEX. At this time, as a condition, the efficiency equation shown in equation (17),
The characteristic equation ψ ₁ , of the Q-switched laser shown in equation (18),
And the limiting expression ψ ₂ of the energy density in the resonator shown in Expression (19) is used. Here, E _sat is the saturation fluence determined by determining the medium, and E _lim is the intracavity energy density defined by the damage threshold within the cavity.

[0035]

(Equation 7)

Under the conditions of the equations (17), (18) and (19), the maximum efficiency and the conditions for obtaining it are obtained by the undetermined coefficient method shown in the equation (20). Here, as compared with the formula (12) shown in the conventional example, since a formula for limiting the energy density in the resonator is added, z is also added as a parameter to be optimized. From equation (20), equation (21) is obtained as a relational expression of T that gives the maximum efficiency.

[0037]

[Equation 8]

The left side of the equation (21) is monotonically decreasing at 0 <T <1, and only one solution T _opt does not depend on the values of D and L.
have. Furthermore, using T that also stops here, k and z are obtained as in Expressions (22) and (23).

[0039]

[Equation 9]

Equations (22) and (23) are used to determine the output coupling amount T giving the maximum extraction efficiency, the round-trip small signal gain z · L, and these parameters with respect to the value of D. (17) The values of the maximum extraction efficiencies that can be obtained are shown by the solid lines in FIGS. Here, in order to make a comparison with the conventional method of configuring a Q-switched laser, the equation (1
5) is used to show the results of the conventional method. As a result of optimization by adding the condition of the energy density in the resonator, it can be seen that the efficiency is significantly improved when D <3 as compared with the conventional configuration method. Also, the formula (2
The results of 1) and equation (23) are optimum conditions, but the values of output mirror reflectivity and small signal gain are ± 10 with respect to this condition value.
%, The change in efficiency is within 5%, and a sufficiently high efficiency is obtained in this range.

The output coupling amount shown in FIG. 2 is D <3.
In the range of (3), the simple expression (24) can be approximated well, and the round-trip small signal gain ln (G) of the laser medium 1 can be similarly approximated by the expression (25). T = 0.063 · D + 1−EXP (−1.78 · L ^0.33 ) (24) ln (G) = 2.46 · L ^0.44 ·· (1 + 0.61D ^1.3 · L ^−0.12 ) (25) That is, these Equation (26) as an equation for obtaining the numerical value of
In (27), each coefficient is the above value. T = C ₁ · D + 1−EXP (−C ₂ · L ^c3 ) (26) ln (G) = C ₄ · L ^C5 (1 + C ₆ · D ^C7 · L ^C8 ) (27) The amount T of binding thus obtained, Regarding the values of the efficiency η and the loss L in the resonator, the efficiency is remarkably improved in the range of D ≦ 2 as shown in FIGS. That is, when L is 5 to 20%, T is 50% or more, and the efficiency is 0.5 to 0.6 when D = 1 and 0.7 to 0.8 when D = 2. This is an efficiency improvement of 2 times or more to 1.3 times as compared with the conventional apparatus having 0.25 at D = 1 and 0.3 at D = 2. In the region where D is smaller than 1, there is an effect of further improving efficiency.

A comparison between the simple approximation formulas (24) and (25) and the exact formulas (21) and (23) multiplied by the loss L will be described. FIG. 4 shows the calculation result of the equation (21) and the approximation formula (24), and FIG. 5 shows the calculation result of the equation (23) multiplied by the intracavity loss L and the calculation result of the approximation formula (25). Are shown respectively. From these results, it is possible to configure the Q-switched laser so as to have the output coupling amount represented by the equation (24) and the round-trip small signal gain represented by the value obtained by multiplying the equation (25) by the intracavity loss L. As compared with the conventional configuration, it is possible to obtain a Q-switched laser having a high extraction efficiency.

Especially, let us consider a medium of D <3 in which the effect is more remarkable than that of the conventional method. Generally, the damage threshold of the optical components in the resonator varies depending on the pulse width of the laser beam, the polishing accuracy of the surface of the material, the type of coating, etc. It takes a value of 20 J / cm 2. Therefore, a material having a saturated fluence of about 5 J / cm 2 can be given as a material giving D <3. For saturated fluence of 10 J / cm2 or more, Cr3 + or Cr
Solid state laser materials containing metal ions such as 4+, T
Examples include solid-state laser materials containing rare earth ions such as m, Ho and Er. Of these, Tm: YAG and Tm: Y are particularly preferable as solid-state laser crystals containing Tm ions.
Examples of VO4 include Tm: YAG, which has a high saturated fluence. Tm: YAG with oscillation wavelength of 2.01 μm
The saturated fluence at is about 43 at 300k.
J / cm2, from which D is about 0.1 to 0.
Takes a value of 5. The resonator loss is generally about 5% to 30%, although it depends on the resonator configuration. Using these values, T can be calculated from equations (24) and (25).
The output coupling amount in m: YAG becomes a value of 49% to 73%, and accordingly, the small signal gain of the round trip is 0.77.
It takes a value of ˜1.95. In the conventional configuration, this value is 91% to 99% in the amount of output coupling, and the small signal gain in the round trip is 0.01.
It is completely different from ~ 0.05.

Examples of solid-state laser crystals containing Er ions include Er: YAG and Er: Glass. The saturation fluence of Er: YAG having an oscillation wavelength of 1.64 μm is about 24 J / cm 2 at 300 k, and D has a value of about 0.2 to 0.8. Further, the saturation fluence at Er: Glass having an oscillation wavelength of 1.54 μm is about 8 J / at 300 k.
cm2, and thus D takes a value of about 0.6 to 2.5. Considering 5% to 30% as the resonator loss, in Er: YAG, the output coupling amount becomes a value of 50% to 75%, and accordingly, the small signal gain in the round trip is 0.
It takes a value of 82 to 2.32. On the other hand, in the conventional configuration, the output coupling amount is 87% to 99%, and the small signal gain in the round trip is 0.01 to 0.07. On the other hand, in Er: Glass, the output coupling amount has a value of 52% to 86%, and accordingly, the small signal gain in the round trip takes a value of 1.07 to 5.04. On the other hand, in the conventional configuration, the output coupling amount is 55% to
99%, round-trip small signal gain is 0.02 to 2.4, which is a remarkable improvement.

An example of the solid-state laser crystal containing Ho ions is Ho: YAG. (T as a sensitizing material
The saturation fluence in Ho: YAG having an oscillation wavelength of 2.09 μm is about 8 J / cm 2 at 300 k, and the same Q-switch laser configuration as Er: Glass described above is adopted. .

Example 2. Although the cross-sectional area of the laser beam in the resonator is uniform in the above-mentioned embodiments, the above-described method can be applied to the case where a beam expanding / reducing system is included. FIG. 7 shows the configuration of a Q-switch laser when a beam expanding / reducing system is included, and 6 is an expanding optical system for expanding the beam on the laser rod side. Assuming that the beam magnification in the resonator by this optical system is M, the beam diameter is 1 / M and the beam area is 1 / M ² on the reduction optical system side compared to the rod portion. ,
The energy density in the resonator becomes M ² times. Therefore, generally, the damage threshold value in the reduced region becomes the damage threshold value in the resonator. In the case where damage occurs in the enlarged region, the above embodiment can be applied as it is. In this case, as a configuration example, by replacing the value of D with Expression (28), Expressions (24) and (25) can be applied as they are.

D = E _lim / (M ² E _sat ) (28) As a magnifying optical system, a telescope is generally used, but the beam can be magnified by the curvature of the reflecting mirrors facing each other. In this case as well, the same configuration method can be applied. In the formula (28), it seems that the saturation fluence of the laser medium is apparently increased. Therefore, for example, even when Nd: YAG having a low saturation fluence of 0.5 J / cm 2, M is about 2.5 times, D is 0.8 to 3.2
Therefore, the configuration method of the present invention is effective. In the configuration including such a magnifying optical system, the configuration of the present invention is effective for almost all the mediums, but Nd: YAG, Nd: YLF, N are particularly suitable for obtaining a small signal gain.
A remarkable effect is obtained when d: Glass, Ti: sapphire, ruby laser, or the like is used.

[0048]

As described above, according to the present invention, L and T are set to predetermined values so as to maximize the extraction efficiency by using the energy density limit maximum value.
Within the range of 2, there is an effect that a highly efficient Q-switched laser can be constructed with 0.3D ≦ η.

As a medium of the Q-switched laser, Tm: YA
Since G is used and set to a predetermined T, there is an effect that a small value of the round trip small signal gain of 0.8 to 2 can be obtained.

Er: Gl as the medium of the Q-switched laser
Since ass is used and a predetermined T is set, there is an effect that a small value of the round trip small signal gain as high as 1 to 5 can be obtained.

Ho: YA as the medium of the Q-switched laser
Since G is used and set to a predetermined T, there is an effect that a small value of the round trip small signal gain of 0.8 to 2 can be obtained.

Further, the laser beam is divided into an expansion region and a reduction region, the expansion ratio is set to M, and L and T are set to predetermined values so as to maximize the extraction efficiency by using the energy density limit maximum value. Therefore, in particular, Dm ≦ 2,
In the range of 0.3D ≦ η, there is an effect that a highly efficient Q-switched laser can be constructed.

Further, there is an effect that particularly high efficiency can be obtained in the range of 2.5 ≦ M.

As described above, according to the present invention, L and T are set to predetermined values so that the extraction efficiency is maximized by using the energy density limit maximum value, so that 0 is particularly satisfied in the range of D ≦ 2. There is an effect that a high-efficiency Q-switched laser can be constructed with 3D ≦ η.

[Brief description of drawings]

FIG. 1 is a laser configuration diagram showing a configuration of a Q-switch laser according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an output coupling amount that gives a maximum extraction efficiency to a power density in a resonator with a resonator loss as a parameter.

FIG. 3 is a diagram showing the relationship between the round-trip small signal gain of a laser medium that gives the maximum extraction efficiency with respect to the power density in the resonator with the resonator loss as a parameter.

FIG. 4 is a diagram showing the maximum extraction efficiency with respect to the power density in the resonator with the resonator loss as a parameter.

FIG. 5 is a diagram showing a relationship between an output coupling amount that gives a maximum extraction efficiency to a power density in a resonator with a resonator loss as a parameter, and a diagram showing a comparison of approximate expressions.

FIG. 6 is a diagram showing a relationship between a round-trip small signal gain of a laser medium that gives a maximum extraction efficiency to a power density in a resonator with a resonator loss as a parameter, and shows a comparison between an approximate expression and an exact expression.

FIG. 7 is a laser configuration diagram showing a configuration of a Q-switched laser according to another embodiment of the present invention.

FIG. 8 is a laser configuration diagram showing a configuration of a conventional Q-switch laser.

FIG. 9 is a diagram showing an energy level relationship involved in laser oscillation.

FIG. 10 is a diagram showing a relationship between a conventional coupling amount and an output per unit area.

FIG. 11 is a diagram illustrating a relationship between energy densities inside and outside a resonator of a Q-switched laser.

[Description of Reference Signs] 1 laser medium, 2 excitation source, 3 resonator, 4 Q switch, 5 output coupler, 6 magnifying optical system.

Claims (7)

[Claims] 1. In a Q-switched laser, when the ratio of the maximum energy density in the damaged cavity to the saturated fluence is used as D, and the extraction efficiency of the laser is defined as η, it is determined that the Q-switched laser has a maximum efficiency. If the loss in the resonator is L and the output coupling amount of the resonator is T, then D
≦ 2, 0.05 ≦ L ≦ 0.2, 0.5 ≦ T, 0.3D ≦
A Q-switched laser configured to simultaneously satisfy the value of η. 2. A laser medium containing thulium-doped
Yttrium-Aluminum-Garnet (Tm: YA
G) is used and the value of the output coupling amount is 0.5 ≦ T ≦
The Q-switched laser according to claim 1, wherein the Q-switched laser has a value of 0.7. 3. An erbium-doped glass (Er: Glass) is used as the laser medium, and the value of the amount of output coupling is 0.5 ≦ T ≦ 0.9. Q-switch laser. 4. Holmium-doped yttrium-aluminum-garnet (Ho: Y) as a laser medium.
AG) and as the value of the output coupling amount, 0.5 ≦ T
The Q-switched laser according to claim 1, wherein ≤0.9 is satisfied. 5. In a Q-switched laser, a laser beam is divided into an expansion region and a reduction region, and an expansion optical system is used at the division point to extract an output from the reduction region,
Let M be the enlargement magnification of the enlargement region with respect to the reduction region of the enlargement optical system, D be the ratio of the maximum energy density in the damage resonator to the saturated fluence on the enlargement region side, and let the extraction efficiency of the laser be η and maximize it. If the loss in the resonator of the Q switch is L and the output coupling amount of the resonator is T, then Dm = D / M ² and Dm ≦ ² , 0.0
A Q-switched laser configured to simultaneously satisfy the values of 5 ≦ L ≦ 0.2, 0.5 ≦ T, and 0.3D ≦ η. 6. The Q-switched laser according to claim 5, wherein the value of the magnification M is 2.5 ≦ M. 7. A characteristic of a Q-switched laser using a resonator, wherein the ratio of the maximum energy density in the damaged resonator to the saturation fluence is used as D, and a condition within the limit of the energy density in the resonator is added. A Q-switched laser configured to satisfy the value of 0.3 D ≤ η with D ≤ 2 by defining the extraction efficiency of the laser as η by the equation so as to maximize this.