JPH05235457A - Ld excited shg laser apparatus - Google Patents

Abstract

PURPOSE:To optimize an optical length even with the rough accuracy of a movement of a laser device or a nonlinear optical device by providing a particular slanting surface on a light incident surface or a light exit surface of at least either of time laser device or the nonlinear optical device. CONSTITUTION:There are in a resonator a laser device 2 for generating fundamental laser light with excitation thereof, and a nonlinear optical device 3 for emitting second harmonic laser light as the fundamental laser light is incident thereon. There is provided a slanting surface 30 satisfying a formula (lambda: wavelength of fundamental laser light, DELTAn: double refraction of a slanting surface formation device with respect to the fundamental laser light, DELTAW: amount of the movement of the device in the width direction on which the slanting surface is formed, tau: slanting angle) on the light exit surface of the nonlinear optical device 3, which slanting surface is moved widthwise thereof for effective adjustment of the optical length. Hereby, even though the movement accuracy in the width direction is set somewhat roughly, the optical length is optimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a laser element for generating a fundamental wave laser beam and a non-linear optical element for receiving the fundamental wave laser beam and outputting a second harmonic laser beam in a resonator. The present invention relates to an LD-pumped SHG laser device used as a recording light source, a printer light source, and the like, and more particularly, to an improvement of an LD-pumped SHG laser device in which an output fluctuation of a second harmonic laser light hardly occurs.

[0002]

2. Description of the Related Art Conventionally, in the fields of optical recording, laser printers and the like, shorter wavelength laser light is required as a light source for the purpose of improving recording density and pixel density, and miniaturization of the entire apparatus is required. ing. For this reason, in recent years, a visible light laser device (hereinafter, referred to as an LD pumped SHG laser device) by second harmonic generation (hereinafter referred to as SHG) of a semiconductor pumped solid-state laser element that can be miniaturized has been actively developed and put to practical use. It is being realized. That is, the semiconductor-pumped solid-state laser device has a good beam quality because it produces little heat during pumping, and therefore has the advantage that a second harmonic can be easily obtained by inserting a nonlinear optical crystal into the resonator. is doing.

In this type of LD-pumped SHG laser device, as shown in FIG. 7, a laser element b which is excited by a semiconductor laser a to generate a fundamental wave laser beam and the fundamental wave laser beam is incident on the second laser element b. A nonlinear optical element c that outputs a harmonic laser beam is arranged in a resonator formed of a high reflection film d and a mirror e.
Nd: YAG or the like is applied as the above, and KTiOPO ₄ (KTP) or the like is applied as the nonlinear optical element c. still,
Such a method in which a nonlinear optical crystal is put in a resonator is called an internal resonator type SHG.

By the way, in order to efficiently output the second harmonic laser light using a nonlinear optical element such as KTiOPO ₄ (KTP), it is necessary to satisfy the phase matching.

That is, this phase matching is to match the refractive index of the fundamental laser light generated from the laser element with the refractive index of the second harmonic laser light output from the nonlinear optical element. Due to the wavelength dispersion, it is not possible to simply match the refractive indices of the fundamental laser light and the second harmonic laser light.

On the other hand, when light propagates in a nonlinear optical crystal, the light is divided into two polarizations, an ordinary light and an extraordinary light, which are orthogonal to each other. This is because the crystal has anisotropy in refractive index. Therefore, by utilizing this anisotropy and changing the polarizations of the fundamental laser light and the second harmonic laser light, the refractive indexes can be matched. The incident angle of the laser light at the time of phase matching is called a phase matching angle, and an angle φ from the x axis to the y axis direction in the xy plane of the crystal optical axis and an xy drawn by the angle φ. It is described by the angle θ from the z axis to the line segment in the plane.

The phase matching angle in the above KTiOPO ₄ (KTP) is a phase matching condition called type II (a fundamental wave laser beam is made to enter two polarizations to a non-linear optical element and one second harmonic laser beam is made to enter). (On the other hand, the condition of outputting polarized light. On the other hand, the condition of making the fundamental laser light incident on the above-mentioned nonlinear optical element in one polarized light and outputting the second harmonic laser light in one polarized light is called a type I phase matching condition) In, the values are φ = 24 ° and θ = 90 °.

At this time, the relationship between the refractive indices of the fundamental laser light and the second harmonic laser light is

[Equation 2] Becomes

Here, the direction in which ordinary light is generated in the crystal is
When the axis and the direction in which the extraordinary light is generated are defined as the e-axis, n _e (ω) and n _o (ω) in the equation (2) are K for the fundamental laser light
Extraordinary light and the ordinary refractive index of the TP, also, n _e (2ω) is the refractive index of extraordinary light to the second harmonic laser beam (2 [omega). In KTP (KTiOPO ₄ ), the o axis coincides with the z axis.

As can be seen from the above equation (2), in the case of the type II phase matching, it is necessary to make two polarized lights incident as the fundamental laser light at the same time. As a method of making these two polarized lights incident, For the sake of simplicity, a method is adopted in which one polarized light inclined from the o axis is made incident and split into two polarized lights in the crystal.

On the other hand, since the LD pumped SHG laser device uses the second-order nonlinear effect, the second harmonic laser beam obtained from the nonlinear optical element KTP is given by the following equation. That is,

[Equation 3] In the equation (3), C is a constant, d is an effective nonlinear optical constant, l is an optical path length, P _o (2ω) is the output of the second harmonic laser light, and P _o (ω) is An ordinary light component of the fundamental wave laser light, P _e (ω) indicates an extraordinary light component of the fundamental wave laser light.

If the incident linearly polarized light P (ω) is incident at an angle α with respect to the o-axis of the crystal, the components of ordinary light and extraordinary light are given by the following equations.

[0013]

[Equation 4] Therefore, in order to efficiently generate the second harmonic (SHG) with KTP, the angle α at which P _o (ω) · P _e (ω) becomes maximum is
It may be incident at an angle of incidence. That is, it is desirable that the fundamental laser light is linearly polarized and is incident on the KTP at an angle of α = 45 ° from the o-axis.

By the way, as a laser element applied to this LD pumped SHG laser device, Nd:
YAG was the mainstream. And Nd: YAG
Is an isotropic crystal, and the polarization of the laser light obtained from this Nd: YAG crystal is random polarization. Therefore, in order to make linearly polarized light incident on KTP by α = 45 ° from the o-axis according to the above conditions, It was necessary to put a Brewster plate in the resonator and selectively extract only a predetermined linear polarization component from the random polarization. However, if a Brewster plate is interposed in the resonator, a loss occurs and the efficiency deteriorates accordingly. Therefore, in the LD pumped SHG laser device to which Nd: YAG is applied, the laser element is pumped by a high-power semiconductor laser. Had to let.

On the other hand, recently, unlike the above-mentioned Nd: YAG crystal, Nd: YVO that laser light can be obtained by linearly polarized light.
_Four crystals are now available as laser materials. That is, in this Nd: YVO ₄ crystal, a linearly polarized light output polarized in the c-axis direction of the crystal is usually obtained.
This Nd: YVO ₄ crystal is used and the c-axis of this crystal is K
Only by disposing the TP at an angle of 45 ° with the e-axis, it becomes possible to meet the above-mentioned conditions. Therefore, the above Nd:
Compared to the case of applying YAG crystal, it is not necessary to insert a Brewster plate that causes loss in the resonator, and a small LD pumped SHG laser device is realized because a semiconductor laser for pumping of low output can fully function by that much. It is becoming possible.

As described above, as a laser element, a small L-shaped crystal in which the main stream is changed from Nd: YAG crystal to Nd: YVO ₄ crystal.
D-pumped SHG laser devices have been actively developed, but recently, LD-pumped SH using type II phase matching has been applied.
In the G laser device, a new problem that the output of the second harmonic laser light easily fluctuates has been discussed [Opt. Lett. 16 (1991)
1665].

That is, according to this discussion, each time the fundamental wave laser light passes through the nonlinear optical element KTP, K
The phase of the polarization component of the fundamental laser light changes due to the birefringence of TP (refractive index difference between ordinary light and extraordinary light), and as a result, the generation of the second harmonic laser light cannot be stably maintained. Pointed out that this is the cause.

Therefore, the present inventor further promotes this discussion and considers that the cause of the above output fluctuation is not limited to KTP but the entire resonator, and aims at the completion of the LD pumped SHG laser device in which the output fluctuation hardly occurs. Analysis was carried out. That is, since the Nd: YVO ₄ crystal, which is a laser element, has a birefringence by itself, the phase of the fundamental laser light resonating also changes due to this laser element, and the output of the second harmonic laser light becomes unclear. This is because there is a possibility that it will become stable. Further, even when an Nd: YAG crystal is applied as a laser element, when excited at a high output, it is considered that the birefringence due to heat is generated in the crystal due to the change in the refractive index due to the heat absorption and the phase is changed.

In the following, LD-excited SHG using a type II phase-matching device represented by KTP as a non-linear optical element and an anisotropic laser crystal such as Nd: YVO ₄ as a laser material is used. Taking a laser device as an example,
Stokes parameters (reference: "Crystal Optics" edited by the Japan Society of Applied Physics, Optics Council) are used to determine the change in the phase of the fundamental laser light in the resonator, and the resulting change in the ordinary and extraordinary components of the fundamental laser light in the KTP. p137, 1975).

First, in the structure shown in FIG. 7, the fundamental wave laser light excited by the semiconductor laser a resonates between the high reflection film d and the mirror e. Here, in order to efficiently obtain the output of the second harmonic laser light, the Nd: YVO ₄ crystal c-axis which is the laser element b has a nonlinear optical element c which is K.
It is arranged so as to form an angle of 45 ° with the o-axis of TP.

Then, the 45 ° -polarized fundamental wave laser light generated from the laser element b made of Nd: YVO ₄ crystal is
A non-linear optical element c made of KTP, a mirror e, a non-linear optical element c, a laser element b, a highly reflective film d, and a laser element b are passed in this order for one round trip. During this time, the phase changes due to the retardation given by the product of the birefringence of each component and the optical path length, and the polarization state changes.

Here, the 45 ° polarized light generated from the laser element b of Nd: YVO ₄ crystal is expressed by Stokes parameters as follows:

[Equation 5] Becomes

Each polarization component at the time of KTP incidence, which is a problem in the LD pumped SHG laser device in the Stokes parameter, is

[Equation 6] And, in case of 45 ° polarization,

[Equation 7] Becomes Then, the output of the second harmonic laser light when the maximum conversion efficiency is obtained from the equation (3) is

[Equation 8] Given in.

On the other hand, regarding the Stokes matrix of each component, when the principal axis serving as a reference is made to coincide with the o axis of KTP, KTP which is the nonlinear optical element c is

[Equation 9] In the equation (9), δ _k is the phase difference due to KTP and is given by the following equation.

[0025]

[Equation 10] In this equation (10), λ is the wavelength of the fundamental laser light, Γ _k is the KTP retardation, Δn _k is the KTP birefringence, and L _k is the KTP optical path length.

Further, the mirror e and the high reflection film d are

[Equation 11] Next, the Nd: YVO ₄ crystal that is the laser element b is c
Since the axis forms 45 ° with respect to the main spindle that serves as the reference,
For the fundamental laser light, the light is Nd: YV in FIG.
The notation is different when passing leftward in the O ₄ crystal and when passing rightward.

When passing through the Nd: YVO ₄ crystal to the left,

[Equation 12] When passing rightward through the Nd: YVO ₄ crystal,

[Equation 13] Becomes

In the above equations (12) and (13), δ _y is the phase difference due to the Nd: YVO ₄ crystal and is given by the following equation.

[0029]

[Equation 14] The (14) wherein, lambda is the wavelength of the fundamental laser beam, gamma _y is Nd: retardation by YVO ₄ crystal, [Delta] n _y is Nd: birefringence of YVO ₄ crystal, and, L _y is the Nd:
The optical path length of the laser device made of YVO ₄ is shown.

Now, the polarization state (S ') of the fundamental laser light after one round trip using these matrices is
It can be calculated by the following formula. That is,

[Equation 15] Substituting each matrix into this equation (15) to obtain S ′,

[Equation 16] Becomes

Therefore, each polarization component after one round trip is expressed by the above equation (6) as

[Equation 17] And the output of the second harmonic laser light due to this is

[Equation 18] Becomes Here, if the ratio with the maximum value of the harmonic laser light output originally obtained from the above equation (8) is R,

[Formula 19] Therefore, it can be confirmed that δ _k and δ _y cause a periodic change.

The condition for obtaining the second harmonic laser light most efficiently from the equation (19) is as follows.

[Equation 20] This condition can be satisfied by using the above equations (10) and (14) as the condition that either the nonlinear optical element made of KTP or the laser element made of Nd: YVO ₄ crystal or both of them are used. It can be realized by adjusting to the optimum optical path length.

That is, the optimum optical path length (L _k ^opt ) and optical path length (L _y ^opt ) of the above-mentioned nonlinear optical element and laser element are expressed by equations (10), (14), and (2).
From equation (0),

[Equation 21] Becomes

Here, when the unit length (m = 1) of this optimum optical path length is calculated using KTP as an example, Δn _k = 0.085
From 7, λ = 1.064 μm,

[Equation 22] Therefore, it is necessary to control the optical path length with accuracy of about 3 μm.

By the way, when processing a device material such as KTP crystal or Nd: YVO ₄ crystal, the current processing accuracy regarding the length is (± 100 μm), and the above condition (that is, about 3 μm) is the limit. It is practically difficult to carry out the processing that satisfies the (accuracy).

However, in such a case, an inclined surface as shown in FIG. 8 is formed on the light incident surface or the light emitting surface of the element material,
Moreover, it is possible to control the optical path length with an accuracy of about 3 μm by moving the element material on which the inclined surface is formed in an appropriate amount in the width direction.

That is, in FIG. 8, the width dimension of the element material is W (mm) and the inclination angle of the formed inclined surface is τ (ra
d) and the shortest optical path length of the device material is L _s (mm), L _s is generally

[Equation 23] (However, m is an arbitrary positive integer).

On the other hand, when the element material is moved by ΔW in the width direction, its effective optical path length (L _eff ) is as shown in FIG.
From (A) and (B), it is given by the following equation.

[0039]

[Equation 24] Therefore, it can be confirmed that the phase change of the polarization component of the fundamental laser light can be prevented by setting the value of ΔW tan (τ) in the following range.

[0040]

[Equation 25] (However, q is an arbitrary positive integer)

[0041]

As described above, at least one of the laser element and the nonlinear optical element is provided with an inclined surface satisfying the above formula (25) on the light incident surface or the emission surface thereof, and the element provided with this inclined surface is provided. Of the LD pumped SHG laser device, in which the phase change of the polarization component of the fundamental laser light can be prevented by moving the laser beam by an appropriate amount in the width direction, and therefore the output fluctuation of the second harmonic laser light is unlikely to occur. It was

However, according to the equation (25), the above ΔW tan
When setting (τ) to an appropriate value, it has been found that the following problems occur when the value of q is set to 2 or more.

That is, when the variable amount of the optical path length in the equation (25) becomes equal to or larger than 2 × L _ko ^opt , the optical path length can be optimized as a matter of course, but as shown in FIG. In the whole (ΔW), a plurality of movement values satisfying the optimization condition periodically appear (three times in FIG. 10), and that much
Since the movable range of one cycle (the amount of movement ΔW1 that satisfies the condition when the output ratio of the second harmonic laser light is set to, for example, 0.9 in FIG. 10) becomes narrow, the width must be reduced to achieve this. There has been a problem that the amount of movement in the direction has to be performed with high accuracy, and the meaning of adopting the above means becomes meaningless.

Further, when the above-mentioned moving operation is performed, the moving stage becomes large, and there is a problem that it goes against the miniaturization which is the maximum advantage of the LD pumped SHG laser device.

The present invention has been made by paying attention to such a problem. The problem is that the optical path length can be optimized even if the movement accuracy in the width direction is set slightly rough.
It is to provide a D-pumped SHG laser device.

[0046]

According to the present invention, when the value of ΔW tan (τ) is appropriately set according to the above equation (25), the problem is solved by setting the value of q to 2 or less. is there.

That is, when the value of ΔW tan (τ) is set within the numerical range given by the following equation (26),
As shown in FIG. 1, since there is only one cycle of the movement value satisfying the optimization condition in the entire movement amount (ΔW) in the width direction, the movable range of one cycle (in FIG. 11, the second harmonic laser beam When the output ratio is set to 0.9 as in the above, the movement amount ΔW2) that satisfies the condition becomes wider.

Therefore, even if the accuracy of movement in the width direction is set to be slightly rough, the output ratio does not change so much, so that the optical path length can be optimized easily.

[0049]

[Equation 26] Here, the condition of the expression (26) is as follows by substituting the expression (21) into the expression (26) (where m = 1),

[Equation 27] It can also be expressed as.

That is, according to the present invention, an LD is provided with a laser element which is excited to generate a fundamental wave laser beam and a non-linear optical element which receives the fundamental wave laser beam and outputs a second harmonic laser beam in a resonator. On the premise of the pumping SHG laser device, an inclined surface satisfying the following relational expression (1) is provided on at least one light incident surface or emission surface of the laser element or the nonlinear optical element, and this inclined surface is provided. It is characterized in that the effective optical path length of the element is adjusted by moving the element in its width direction.

[0051]

[Equation 28] (Where λ is the wavelength of the fundamental laser light, Δn is the birefringence of the element having the inclined surface with respect to the fundamental laser light,
ΔW is the amount of movement of the element having the inclined surface in the width direction, τ
Indicates the inclination angle of this inclined surface. ) By the way, the inclination angle (τ) of the KTP, which is a nonlinear optical element in the above example, is calculated from the above equation (26) as follows:

[Equation 29] Is required.

In a normal LD-pumped SHG laser device, the width dimension of the above-mentioned nonlinear optical element, laser element, etc. is about 3 mm, and the amount of movement (Δ) of the KTP in the width direction.
Considering that W) can be about 1 mm, this (2
Substituting equation (22) into equation 8),

[Equation 30] By setting the inclination angle (τ) in such a range, it becomes possible to easily optimize the optical path length.

Materials which can be applied to the above-mentioned non-linear optical element by such technical means include type II phase-matching KTiOPO ₄ (KTP), KNbO ₃ and KH ₂ P.
O ₄ (KDP), β-BaB ₂ O ₄ (BBO), and
Crystals such as LiB ₃ O ₅ (LBO) can be cited, and materials applicable to the laser device include Nd: YVO ₄ and N
In addition to crystals having anisotropy such as d: YLF, isotropic crystals such as Nd: YAG and Nd: GGG that are excited by a high-power semiconductor laser and exhibit anisotropy due to heat absorption are included.

The inclined surface may be provided on the light incident surface or the emission surface of at least one of the laser element and the nonlinear optical element, and may be provided on both the light incident surface and the emission surface.

When inclined surfaces are provided on both the light incident surface and the light exit surface, one of the inclined angles is τ as shown in FIG.
₁ and the other tilt angle is τ ₂ , the following relational expression,

[Equation 31] Should be satisfied.

[0056]

According to such technical means, an inclined surface satisfying the following relational expression (1) is provided on at least one light incident surface or emission surface of the laser element or the nonlinear optical element, and the inclined surface is The element provided with is moved in the width direction to adjust the effective optical path length of the element.

[0057]

[Equation 32] (Where λ is the wavelength of the fundamental laser light, Δn is the birefringence of the element having the inclined surface with respect to the fundamental laser light,
ΔW is the amount of movement of the element having the inclined surface in the width direction, τ
Indicates the inclination angle of this inclined surface. ) Then, when an element provided with an inclined surface that satisfies the above relational expression is moved in the width direction to adjust the effective optical path length, the optimization condition is satisfied by the entire movement amount (ΔW) in the width direction. Since the movement value to be moved only exists for one cycle,
Even if the movable range of the cycle is widened and the movement accuracy in the width direction is set to be slightly rough, the optical path length can be optimized.

[0058]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[Example 1] LD excitation S according to this example
The HG laser device includes a laser element 2 that is excited by a semiconductor laser 1 to generate a fundamental wave laser light as shown in FIG.
Basically, a non-linear optical element 3 which receives a laser beam and outputs a second harmonic laser beam, a high reflection film 4 provided on the entire surface of the laser element 2 on the semiconductor laser 1 side, and the non-linear optical element 3 and a mirror 5 disposed on the second harmonic laser light emitting side of 3 and a main part thereof, and
On the emission surface of the second harmonic laser light in the nonlinear optical element 3, an inclined surface 30 having an inclination angle (τ) downward in the emission direction is formed, and the light incident surface of the nonlinear optical element 3 and the inclination described above. An antireflection film (not shown) for the fundamental laser light is provided on the surface and the entire surface of the laser element 2 on the side of the nonlinear optical element 3.

In this embodiment, the laser element 2 has a size of 3 × 3 × 1 in which no inclined surface is formed.
mm Nd: YVO ₄ crystal is applied, and four types of KTP crystals whose inclination angles are set as follows are applied as the above-mentioned nonlinear optical element 3, and no inclined surface is formed as a comparative example. (Parallelism of both sides is 0.048
mrad or less) KTP crystal is applied.

That is, the dimensions of the KTP having an inclined surface have a width (W) of 3 mm and a shortest optical path length (L _s ) of 3 mm.
And the tilt angles (τ) are 1.7 mrad and 3.5, respectively.
mrad, 5.2 mrad, and 7.0 mrad.

In addition, the above Nd: YVO ₄ and KTP
Both have a parallelism of 0.04 on both sides of the laser light incident surface.
Optically polished once to less than 8 mrad, then
Optical polishing is performed again by inclining to a predetermined inclination angle. In addition, as described above, KT is applied to both the optical polishing surfaces.
An antireflection film for the fundamental wave laser light is formed on both surfaces of P by a vacuum evaporation method, a high reflection film for the fundamental wave laser light is formed on one side of the Nd: YVO ₄ , and a basic reflection film is formed on the other side. An antireflection film for the wave laser light is formed by a vacuum vapor deposition method.

In the LD-pumped SHG laser device configured as described above, the nonlinear optical element 3 is moved by 1 mm in the width direction by the x-stage 6 by using the measurement system shown in FIG. Was measured. In FIG. 2, 7 is a band pass filter and 8 is a power meter.

The inclination angle (τ) is 7.0 mr.
Figure 3 shows an example of the application of ad KTP.
Shown in. 1 mm in the width direction as is clear from this graph
The second harmonic laser light output while moving shows three peaks.

The peak moving position is when the nonlinear optical element 3 having the tilt angle (τ = 7.0 mrad) has the optimum optical path length, and the second harmonic laser light is efficiently output. Can be confirmed.

Here, the above Δ as the KTP parameter.
Using n _k = 0.0857, L _k = 3 mm, and (1
Substituting into equation (0) and calculating with equation (19), three peaks are shown within 1 mm (1000 μm) as shown in FIG. 4, so the above measurement results can be sufficiently explained by this analysis.

The inclination angles (τ) are 1.7 m, respectively.
rad, 3.5 mrad, and 5.2 mrad KT
The measurement system shown in FIG.
-While moving the stage 6 in the width direction by 1 mm, the output of the second harmonic laser light during that time was similarly measured.

That is, the inclination angle (τ) is 1.7 mra.
In the nonlinear optical element 3 of d, the output increasing tendency of the second harmonic laser light could be confirmed as shown in FIG. 5, but the peak could not be confirmed. It is considered that this can be optimized by making the optical path length a little longer. Further, in the non-linear optical element 3 having the inclination angle (τ) of 3.5 mrad, the output increase tendency of the second harmonic laser light is seen as shown in FIG.
Showed one. Similarly, the inclination angle (τ) is 5.2 mrad
Also in the non-linear optical element 3 of (1), although not shown, the output increasing tendency of the second harmonic laser light is observed and the peak thereof is one.

Thus, the tilt angle (τ) is 3.5 mra.
Since all of those using the non-linear optical element 3 of d to 7.0 mrad show the peak of the second harmonic laser light, it is possible to adjust the optimum optical path length by forming the inclined surface 30 on the non-linear optical element 3. Can understand. However, in order to surely adjust to the optimum optical path length, it is preferable that the output change of the second harmonic laser light is gentle with respect to the movement amount (ΔW) in the width direction of the nonlinear optical element 3. That is, in this example, only one peak is shown during the movement of 1 mm in the width direction, which is excellent because the optical path length can be adjusted accurately even if the movement is performed with a slightly rough accuracy by a simple moving device. Therefore, in this example, it is desirable to set the inclination angle (τ) to 3.5 mrad to 5.2 mrad, and this range is in good agreement with the above equation (29).

On the other hand, in the KTP element according to the comparative example in which the inclined surface is not formed, the second harmonic laser light output does not show a peak and is much lower than the peak value of the KTP element in the example. It was a value. This is because the phase change in the fundamental laser light is not compensated, and it is shown that the second harmonic laser light is not efficiently obtained.

From this, it can be confirmed that the second harmonic laser light can be efficiently obtained by applying the non-linear optical element having the inclined surface.

[Embodiment 2] LD excitation S according to this embodiment
Contrary to the first embodiment, the HG laser device is related to the first embodiment except that a KTP nonlinear optical element in which an inclined surface is not formed and an Nd: YVO ₄ laser element in which an inclined surface is formed are applied. It is almost the same as the LD pumped SHG laser device.

The birefringence of the Nd: YVO ₄ crystal (Δ
n _y ) is Δn _y = 0.209, so this value is (2
When the optimum unit length of the optical path length (L _yo ^{opt at} m = 1) is calculated by substituting it into the equation 1),

[Expression 33] Becomes

Here, when the movement amount (ΔW) in the width direction is considered to be 1 mm and the tilt angle (τ) of the laser element with respect to this amount is calculated,

[Equation 34] Becomes

On the other hand, Nd applied in this embodiment:
YVO ₄ has a width (W) of 3 mm, a shortest optical path length (L _s ) of 3 mm, and an inclination angle (τ) of 0.87.
The Nd: YVO ₄ crystal having mrad and 1.7 mrad and having no inclined surface is used as a comparative example.

For each element made of KTP and Nd: YVO ₄ , the laser light incident surface was optically polished in the same manner as in Example 1, and a vapor deposition film was formed.

Also in this embodiment, similarly to the first embodiment, the measurement system shown in FIG. 2 is used, and the element made of Nd: YVO _{4 is} moved by 1 mm in the width direction by the x-stage, and the second portion in between is moved. The output of the harmonic laser light was measured.

As a result, the output of the second harmonic laser light showed one peak in the device to which the device having the inclination angle τ of 1.7 mrad was applied.

On the other hand, the inclination angle τ is 0.87 mra
In the device of d, the output increasing tendency of the second harmonic laser light could be confirmed, but the peak could not be confirmed.

Further, in the Nd: YVO ₄ device according to the comparative example in which the inclined surface is not formed, the second harmonic laser light output does not show a peak, and in comparison with the peak value of the device according to the embodiment. It was a much lower value.

From this result, the optimum optical path length can be realized by forming an inclined surface on the laser element instead of the nonlinear optical element, and the second harmonic laser light can be efficiently compensated for the phase change in the fundamental laser light. It was confirmed that

[0082]

According to the present invention, when an element provided with an inclined surface is moved in the width direction to adjust the effective optical path length, the inclined surface satisfies the following relational expression (1). Since there is only one cycle of the movement value that satisfies the optimization condition in the entire movement amount (ΔW) in the width direction,
Accordingly, the movable range for one cycle is widened, and the optical path length can be optimized even if the movement accuracy in the width direction is set to be slightly rough.

[0083]

[Equation 35] Therefore, the output fluctuation of the second harmonic laser light is unlikely to occur L
It has the effect of easily providing a D-excitation SHG laser device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an LD pumped SHG laser device according to an embodiment.

FIG. 2 is a schematic configuration diagram of a measurement system for measuring the output of a second harmonic laser beam.

FIG. 3 is a relationship diagram between the amount of movement (ΔW) in the width direction obtained by plotting data from the measurement system and the output of the second harmonic laser light.

FIG. 4 is a movement amount (ΔW) in the width direction obtained by calculation
FIG. 5 is a relationship diagram between the output ratio of the second harmonic laser light and.

FIG. 5 is a relationship diagram between the amount of movement (ΔW) in the width direction obtained by plotting the data from the measurement system and the output of the second harmonic laser light.

FIG. 6 is a relationship diagram between the amount of movement (ΔW) in the width direction obtained by plotting the data from the measurement system and the output of the second harmonic laser light.

FIG. 7 is a schematic configuration diagram of an LD pumped SHG laser device according to a conventional example.

FIG. 8 is an explanatory diagram of a material material having an inclined surface.

9 (A) and 9 (B) are explanatory views of adjusting a light path length by moving a material material in a width direction thereof.

FIG. 10 is a relationship diagram between the amount of movement (ΔW) in the width direction and the output ratio of the second harmonic laser light when there are a plurality of peaks.

FIG. 11 is a movement amount (Δ in the width direction when there is one peak.
FIG. 5 is a relational diagram between W) and the output ratio of the second harmonic laser light.

FIG. 12 is an explanatory diagram of a raw material in which inclined surfaces are formed on both the light incident surface and the light emitting surface.

[Explanation of symbols]

 1 Semiconductor Laser 2 Laser Element 3 Nonlinear Optical Element 4 High Reflection Film 5 Mirror 30 Slope

Claims (1)

[Claims] 1. An LD-pumped SHG laser comprising a laser element which is excited to generate a fundamental wave laser beam and a nonlinear optical element which is irradiated with the fundamental wave laser beam and outputs a second harmonic laser beam in a resonator. In the device, an inclined surface that satisfies the following relational expression (1) is provided on the light incident surface or the emission surface of at least one of the laser element and the nonlinear optical element, and the element provided with this inclined surface is formed in the width direction thereof. The LD-pumped SHG laser device, wherein the effective optical path length of the above element is adjusted by moving the element. [Equation 1] (Where λ is the wavelength of the fundamental laser light, Δn is the birefringence of the element having the inclined surface with respect to the fundamental laser light,
ΔW is the amount of movement of the element having the inclined surface in the width direction, τ
Indicates the inclination angle of this inclined surface. )