JP2000250082A - Laser wavelength converter - Google Patents

Abstract

[PROBLEMS] To provide a laser wavelength converter having a phase matching angle adjusting method which is small in size, has little change with time, and does not cause contamination due to lubricating oil or the like. SOLUTION: A crystal supporting member 22 for arranging and supporting a nonlinear optical crystal 10 on a laser optical axis has an arc-shaped orbital surface 22a on a surface including the laser optical axis and defining an incident angle of the crystal.
The nonlinear optical crystal 10 is disposed movably in the direction of the laser optical axis on the orbital plane to constitute a laser wavelength converter. The adjustment of the phase matching condition is performed by moving the nonlinear optical crystal 10 on the orbital surface 22a to change the incident angle of the incident laser light Li so that the angle coincides with the phase matching angle. In addition, the nonlinear optical crystal is provided with a temperature adjusting means, and the crystal temperature is changed to change the phase matching angle, and adjustment and control are performed so as to match the incident angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser wavelength converter for converting a laser wavelength by adjusting a phase matching angle when performing angle phase matching by making a laser beam incident on a wavelength conversion crystal.

[0002]

2. Description of the Related Art A second harmonic generation (SHG) technique for generating a harmonic having twice the frequency of an incident fundamental wave using a nonlinear optical crystal is known as a frequency in information processing using light as a medium. The amount of information can be increased accordingly,
Optically, since the beam spot size can be miniaturized as the wavelength becomes shorter, there is a great merit in that finer observation and finer processing become possible, and it can be said that these are in the stage of practical use in recent years.

[0003] Inside a nonlinear optical crystal that generates second harmonics, a nonlinear polarization wave propagated at the same speed as the phase velocity of the fundamental wave due to the nonlinear polarization induced by the strong photoelectric field of the laser light, Second harmonics (hereinafter, referred to as “SHG waves”) emitted by sub-radiation propagate together.

Here, if the phase velocity of the polarized wave and the phase velocity of the SHG wave are the same, the propagating SHG wave and the dipole radiation occurring at any point in the crystal have the same phase, so that coherent addition is performed and high efficiency is obtained. Second harmonics can be generated. Matching the phases of the polarized wave and the SHG wave in this way is called phase matching, and a condition for obtaining the maximum conversion efficiency is called a phase matching condition. The phase matching condition can be obtained by making the refractive index of the crystal equal to the refractive index of the SHG wave at the wavelength of the incident wave.

As a method of satisfying the phase matching condition, a method utilizing birefringence of a nonlinear optical crystal is mainly used. Birefringence is a phenomenon in which the refractive index of an anisotropic crystal differs depending on the incident direction. When light of different wavelengths is incident on the optical axis of the crystal, the respective refractive index characteristics change on the refractive index vector plane. , The angle of incidence at which the two light beams have the same refractive index can be obtained. By making the fundamental wave incident at this incident angle, the refractive index at the wavelength of the incident wave can be made equal to the refractive index at the wavelength of the SHG wave. Such phase matching is called angular phase matching, and an incident angle satisfying the phase matching condition is called a phase matching angle.

Conventionally, in order to match the phase matching angle calculated as described above, the nonlinear optical crystal can be swing-adjusted with respect to the incident optical axis while holding the nonlinear optical crystal on the optical axis of the wavelength converter. The phase matching condition is satisfied by arranging a fine movement stage configured as described above and relatively adjusting the angle between the optical axis of the crystal and the incident fundamental wave to match the phase matching angle.

[0007]

However, in the adjustment method for adjusting the phase matching angle using the fine movement stage as described above, the wavelength converter becomes large or complicated.
There is a problem that the entire laser device including the wavelength conversion device becomes large. In addition, a continuous wave laser (C
In a wavelength converter for a W laser, a space for disposing a fine movement stage between mirrors is required, which increases the size of the wavelength converter, and the rigidity of the optical resonator decreases with the increase in size. For this reason, there has been a major obstacle in trying to reduce the size and stabilize the laser by mounting the wavelength converter inside the laser device body.

Further, since the fine movement stage is configured for the purpose of fine movement adjustment in the optical apparatus, the resistance to the ambient air such as vibration, ambient temperature change, mechanical external force, etc. for a long time after installation is generally low. In addition, there is a problem that a change in the incident angle to the nonlinear optical crystal due to a change with time is caused to deteriorate the wavelength conversion light rate.

Further, the lubricant used in the sliding portion of the fine movement stage gradually evaporates during long-term use and adheres to the surface of the nonlinear optical crystal and peripheral optical elements. The contaminants adsorbed in this way absorb the laser beam and become heat, which changes the alignment of the optical system and lowers the wavelength conversion light rate. In addition, as the contamination progresses, the non-linear optical crystal and surrounding optical elements become There was a problem of causing damage.

Therefore, in order to cope with the above-described problem, the adjustment mechanism is fixed with an adhesive or the like after the initial crystal incidence angle is adjusted using a fine movement stage, or the fine movement stage is not used. After adjusting the angle of incidence with an external adjustment jig or the like, a method of fixing the nonlinear optical crystal or the crystal holder with an adhesive or the like is devised.

However, when the adjusting unit is fixed, the light enters the wavelength converter by, for example, adjusting a laser oscillator as a light source, replacing an optical element on a path for guiding light from the laser oscillator, realigning peripheral devices, and the like. When the optical axis of the laser beam changes, there is a problem that it is difficult to adjust the incident angle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and is directed to a wavelength conversion element which is small, has little change with time, and does not cause a problem of contamination without using a fine movement stage as in the prior art. An object of the present invention is to provide a method for adjusting a phase matching angle and a wavelength converter using the method.

[0013]

In order to solve the above problems, in a first embodiment of the present invention, a predetermined phase matching angle is adjusted by adjusting an incident angle of an incident laser beam with respect to an optical axis of a nonlinear optical crystal. In the wavelength conversion for performing the angle phase matching so as to convert the wavelength of the incident laser light,
A crystal support member that arranges and supports the nonlinear optical crystal on the optical axis of the incident laser beam at a predetermined phase matching angle includes a track surface having an arc-shaped curved surface at least in a plane that defines the incident angle, The optical crystal or the holder holding the crystal is movably arranged on the orbital plane, and the adjustment of the incident angle to the nonlinear optical crystal is performed by moving the holder holding the crystal on the nonlinear optical crystal. This is done by adjusting the position along the surface.

According to a second aspect of the present invention, a crystal support member for arranging and supporting the non-linear optical crystal at a predetermined phase matching angle on an optical axis of a laser beam incident thereon is provided in a plane defining an incident angle. The angle of incidence on the nonlinear optical crystal is adjusted by selectively arranging the plurality of crystal support members having the different inclination angles.

According to the above-described method, the nonlinear optical crystal can be arranged on the optical axis of the laser beam at an arbitrary inclination angle without using a fine movement stage, and the nonlinear angle can be adjusted by adjusting the inclination angle. The incident angle of the incident laser light with respect to the optical axis of the optical crystal can be adjusted to match the phase matching angle.

In the wavelength conversion for performing the angle phase matching, the nonlinear optical crystal is provided with a temperature adjusting means for adjusting the temperature of the crystal to constitute a laser wavelength conversion device. This is performed by adjusting the temperature of the nonlinear optical crystal to change the phase matching angle of the nonlinear optical crystal so as to match the angle of incidence.

According to such a method, the nonlinear optical crystal can be arranged and supported on the optical axis of the laser beam at a fixed arrangement angle without using a mechanical adjustment mechanism such as a fine movement stage. By adjusting the crystal temperature and changing the phase matching angle of the nonlinear optical crystal to match the incident angle of the incident laser light, the phase matching condition can be satisfied.

By constructing the laser wavelength converter using the above-described adjustment method, a laser wavelength converter that is small, does not change with time, and does not cause a contamination problem without using a fine movement stage is provided. be able to.

In addition, the nonlinear optical crystal is provided with a temperature adjusting means for adjusting the temperature of the crystal, together with the crystal supporting member in the configuration of the first embodiment, and constitutes a laser wavelength conversion device. The setting of the angle of incidence on the crystal is achieved by adjusting the position of the nonlinear optical crystal disposed on the orbital plane or the holder holding the crystal along the orbital plane, or adjusting the position of the nonlinear optical crystal. At the same time, the crystal temperature is adjusted by the temperature adjusting means, and the temperature is adjusted by the temperature adjusting means after setting the incident angle.

According to such a configuration, the angle of incidence on the wavelength converter changes due to realignment of the peripheral optical device or the like, or as a result of replacing the nonlinear optical crystal, the phase matching condition changes due to the unique condition of each crystal. In such a case, an appropriate adjustment method can be performed according to the amount of change. For example, when the amount of change is small, phase matching can be performed only by adjusting the temperature of the crystal. On the other hand, when it is difficult to adjust the phase matching angle only by adjusting the temperature of the nonlinear optical crystal, a constant Under temperature conditions, the incident angle is roughly adjusted to the phase matching angle by adjusting the position of the crystal (or crystal holder) on the arc-shaped orbital plane, and then fine adjustment is made by adjusting the crystal temperature. Is possible.

Incidentally, the laser wavelength converter provided with the temperature adjusting means as described above further comprises a conversion output detecting means for detecting the intensity of the laser light which is wavelength-converted and output by the wavelength converting crystal, It is preferable that the temperature adjusting means be configured to control the temperature of the nonlinear optical crystal so that the intensity of the laser beam detected by the converted output detecting means is maximized.

According to the above configuration, for example, the crystal supporting member for supporting the nonlinear optical crystal and the supporting member for the peripheral optical system are slightly deformed due to an external temperature change or the like and slightly deviate from the phase matching condition. Also, by controlling the temperature of the nonlinear optical crystal and controlling the light intensity of the output laser light output from the nonlinear optical crystal to a maximum value, the laser wavelength converter can always be operated with the maximum efficiency.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a laser wavelength converter according to the present invention and an adjustment method thereof will be described with reference to the drawings. First, FIG. 11 shows a laser wavelength conversion device 100 of the present invention using a confocal laser scanning microscope 500.
In this embodiment, a laser beam output from a laser light source 510 is introduced into an apparatus of a laser scanning microscope using an introduction optical system 520 such as an optical fiber or a reflection optical system. A laser wavelength conversion device 100 according to the present invention is provided in the device, and the introduced laser light is wavelength-converted to a desired light wavelength, and then passes through the illumination lens 530 and enters the half mirror 540. The illumination light reflected by the half mirror is applied to two-dimensional beam scanning means 55.
0, a minute laser spot is formed on the surface of the sample A on the stage through the objective lens 560.

The observation light reflected by the sample A is
The light is magnified to a predetermined magnification via the optical axis 0, passes through the two-dimensional beam scanning means 550 and the half mirror 540, and passes through the condenser lens 57.
The light is condensed at 0, the peripheral refracted light is removed at the pinhole 575, and the light enters the detector 580 for laser wavelength observation. The observation light incident on the detector 580 is photoelectrically converted and
After being input to the signal processing device 590 together with the control signal from the dimensional beam scanning means 550 and subjected to signal processing,
An enlarged image of the sample A is displayed on a monitor 595 such as an RT or a liquid crystal display panel.

FIG. 10 shows an example of the configuration of a laser wavelength converter 100 used in a laser device as in the above example, in which an external resonance type wavelength converter is configured using a CW oscillation laser as a laser light source. .

In the external resonator type wavelength converter 100 shown in FIG. 10, an optical resonator is composed of resonator mirrors 120 and 125 and a prism 130 provided on a resonator base (not shown). Laser light Li
Is converted to a desired light wavelength. A nonlinear optical crystal 10 is disposed and supported on a crystal supporting member 20 configured to adjust a phase matching condition for performing angular phase matching. The fundamental laser light Li emitted from the laser oscillator 510 and incident on the wavelength converter 100 via the mode match lens 525
Is condensed by the mode match lens 525, irradiated on the nonlinear optical crystal in the external resonator, resonated by the optical resonator, efficiently converted in wavelength, and output from the output side resonator mirror 125 as output light Lo. Is done.

The power density of the incident laser light is high and Q
When applied as a wavelength converter such as a switch pulse laser, the resonator configuration as shown in FIG. 10 is not necessary, and the configuration can be made without disposing the resonator mirrors 120 and 125 and the prism 130.

Here, the nonlinear optical element 10 used for wavelength conversion can be appropriately selected according to the wavelength of the incident fundamental laser light Li and the wavelength of the laser light required by the laser device. For example, a second harmonic generation (SHG) that generates light having twice the frequency of the fundamental laser light and an optical parametric oscillation (OPO) that outputs a sum frequency of two different fundamental waves are used alone or in combination. By combining a plurality of stages, the output laser light Lo of a desired wavelength is obtained.
Can be output.

For example, when an Nd: YAG laser or an Nd: YVO ₄ laser is used as a laser light source and the incident laser light Li having an oscillation wavelength of 1064 nm from this light source is output as a green laser light having a wavelength of 532 nm, which is a second harmonic, Known nonlinear optical crystals such as KTP (KTiOPO ₄ ) and MgO: LN (Mg
O: LiNbO ₃ ), LBO (LiB ₃ O ₅ ), etc., and the incident angles (θ, φ) with respect to these crystal axes are determined by the respective phase matching angles (θ = 90 de).
gφ = 26 deg), (θ = 84.2 deg), and (θ = 90 degφ = 11.3 deg).

In the case where another second harmonic generation stage is provided after the wavelength conversion stage, or when the above-mentioned nonlinear optical crystal is provided in the resonator of the laser light source,
Green laser that outputs 532nm SHG wave, wavelength 420
When the output light of a blue laser that outputs SHG waves of nm is used as an incident fundamental wave, and a second harmonic is output, BBO (β-BaB ₂ O ₄ ) and CLB are used as nonlinear optical crystals.
Using O (CsLiB ₆ O ₁₀ ), the incident angle θ of these crystals with respect to the optical axis was set to 47.6 de for a green laser, for example.
g, 62 deg (phase matching angle).

Hereinafter, the laser light Li incident on the wavelength conversion device 100 is changed to a green laser light having a wavelength of 532 nm, and the BBO crystal is used as the nonlinear optical crystal 10 to output an output wavelength of 266 nm.
The method of adjusting the angle of incidence on the nonlinear optical crystal 10 will be described in more detail by taking as an example the case where the SHG wave is obtained.

First, in FIG. 2, a BBO crystal having a crystal length of 10 mm was used as a nonlinear optical crystal, and Ty was obtained at a crystal temperature of 293 ° K.
Calculation and plotting of the relationship between the incident angle of the incident laser light with respect to the crystal optic axis and the wavelength conversion light rate (or SHG wave intensity) when the incident laser wavelength is converted from 532 nm to the output laser wavelength of 266 nm by peI phase matching. It is.

From this calculation result, the phase matching condition in the above example is the center phase matching angle of 47.64 deg, and the full width at half maximum where the wavelength conversion efficiency is half the value of the center phase matching angle (tolerance of the phase matching angle). Is about 0.01deg. Therefore, it can be seen that the incident angle adjusting means for adjusting the angle phase matching may be configured to have a resolution of about 0.001 deg or more.

FIG. 1 schematically shows a first embodiment of a laser wavelength converter according to the present invention. The laser wavelength conversion device of the present embodiment uses the optical axis of the crystal (Z axis in FIG. 1) as a crystal support member 20 for arranging and supporting the nonlinear optical crystal 10 on the incident laser optical axis Li in the wavelength conversion device. Is provided with a cylindrical track member 22 having an arcuate curved surface 22a in a plane defining an incident angle θ with respect to the non-linear optical crystal 10 in the laser optical axis direction (left-right direction in the drawing) on the track surface. It is arranged so as to be movable. Adjustment of the incident angle to the nonlinear optical crystal 10, that is, adjustment to the phase matching angle, is performed by adjusting the position of the nonlinear optical crystal 10 on the orbital plane.

For example, under the above-mentioned wavelength conversion conditions, the length of the nonlinear optical crystal BBO in the laser optical axis direction is L = 10 mm, the radius of curvature of the cylindrical raceway surface 22a is R = 570 mm, and the length of the cylindrical raceway surface 22a is R = 570 mm. The movement adjustment amount is 10 mm. At this time, BBO crystal 1
When 0 is moved by 1 mm at the bottom of the cylindrical surface of the cylindrical track member 22, the change of the incident angle θ with respect to the crystal optical axis is δθ = 0.1 de.
g, and the angle adjustable amount is θ _MAX = 1 deg.

On the other hand, the angle adjustment width and resolution required when performing angle phase matching under the wavelength conversion conditions are as follows from FIG. 2 that the effective angle adjustment width is 0.15 deg (47.55 deg to 47.7 deg).
Since the angular resolution is about 0.001 deg, the above-mentioned configuration satisfies the condition of the angle adjustment width, and the resolution on the moving amount to satisfy this angular resolution is 10 μm on the orbit plane. Therefore, it can be configured using a known micrometer, PZT driver unit, or the like.

The cylindrical track member 22 is made of, for example, a machining center, a grinding machine, an electric discharge machine, an electric glass such as ceramics or BK7, an inorganic material such as quartz, or a metal material such as an aluminum alloy or an iron-based alloy. It can be obtained by using a known machine tool such as a grinder, and performing a surface treatment such as plating as necessary.

As the material of the cylindrical race member 22, it is preferable to use a material having a small linear expansion coefficient with respect to temperature, or to control the temperature of the manufactured race member 22 within a certain temperature range. Specific examples of these include:
For example, the former uses Zerodur (optical glass) or Super Invar (Fe, Ni, Co alloy), and the latter uses a method of controlling the temperature of the entire wavelength converter or cooling water that has been kept at a constant temperature by a chiller or the like. A method of keeping the temperature of the constituent members of the resonator and the like can be exemplified.

Further, according to the conditions of use of the wavelength conversion performed using the nonlinear optical crystal, the phase matching determined by each condition of the wavelength conversion when the light is incident parallel to the crystal long axis direction from the incident end face side displayed on the crystal. The nonlinear optical crystal is cut out in advance so as to substantially coincide with the corner. In addition, an end face treatment such as an anti-reflection coating (AR coating) for the used wavelength is performed. Therefore, in the case of the present embodiment, after the nonlinear optical element 10 is disposed substantially in the center of the cylindrical track member 22 so as to be substantially parallel to the incident laser optical axis, the fine adjustment of the incident angle is performed. Thus, angular phase matching can be achieved.

Next, as a second example of this embodiment, the laser beam incident on the wavelength
m blue laser light, and B
A case where an SHG wave having an output wavelength of 210 nm is obtained using a BO crystal will be described.

FIG. 3 shows a case where a BBO crystal having a crystal length of 10 mm is used as in the case of FIG. 2 and the incident laser wavelength is 420 nm and the output laser wavelength is 210 nm by Type I phase matching at a crystal temperature of 293 ^° K.
7 is a graph in which the relationship between the incident angle of the incident laser light with respect to the crystal optical axis and the wavelength conversion light rate in the case of wavelength conversion is calculated and plotted.

From this calculation result, the phase matching condition in this example is a center phase matching angle of 75.88 degrees, and the tolerance of the phase matching angle is about 0.015 degrees. Therefore, the incident angle adjusting means for adjusting the angle phase matching is 0.001 deg as in the first embodiment.
It is sufficient that the configuration has a resolution of about the same, and the effective adjustment width on the angle required when performing angle phase matching under this wavelength conversion condition should be about 0.2 deg (75.8 deg to 76.0 deg) from FIG. I understand.

Accordingly, even under the wavelength conversion conditions of the present embodiment, it is possible to easily adjust the incident angle with the same configuration as that of the first embodiment, and to construct a compact wavelength converter. Can be.

In the above embodiment, the track member having an arc-shaped curved surface is the track member 22 having a cylindrical shape having a curvature only in a plane defining the incident angle (in the optical axis direction of the laser beam). The case where the track member 22 is used in one stage has been described. For example, this is used as a track member having a spherical shape having a curvature also in a plane perpendicular to the laser optical axis (a direction perpendicular to the paper surface in FIG. 1). The adjustment mechanism may be provided also in the direction, or the track member 22 having the cylindrical shape may be provided in two stages in the same direction or the orthogonal direction (the bottom of the track member 22 is supported below the cylindrical track member 22). A cylindrical track member is further provided), and these can be individually and freely adjustable.

With such a configuration, in addition to the above-described adjustment of the phase matching angle, the incident angle of the polarization plane of the incident laser light with respect to the nonlinear optical crystal can be adjusted. Further, in the embodiment in which the cylindrical raceway surface has a two-stage configuration in the same direction, the effective angle adjustment width can be increased,
By configuring the radii of curvature of the cylindrical surface to have different values, for example, it is possible to easily adjust the angle phase matching by using one for coarse adjustment and the other for fine adjustment.

Next, FIG. 4 shows a second embodiment of the laser wavelength converter according to the present invention. In this embodiment, the angle of incidence of the laser beam on the nonlinear optical crystal 10 is reduced. A wedge-shaped support member 21 having a fixed inclination angle, which is disposed and supported so as to have a predetermined angle with respect to the incident laser optical axis Li in the inside, is used. The phase matching angle is adjusted by arranging one or a plurality of these wedge-shaped support members 21 so as to adjust the incident angle θ with respect to the crystal optical axis so as to match the phase matching angle under the wavelength conversion condition. It is to let.

Here, as an example, a case where an LBO crystal is used as a nonlinear optical crystal and a fundamental laser beam having a laser wavelength of 1064 nm is converted into an SHG wave having a wavelength of 532 nm will be described as an example.

First, under these wavelength conversion conditions, the angular adjustment width and resolution required for performing angle phase matching can be obtained by the same calculation as in the first embodiment using the BBO crystal. L with crystal length L = 5mm in the laser optical axis direction
For BO crystal, half-width is 0.6deg and resolution on angle is
It is required to be about 0.06deg.

The wedge-shaped support member (hereinafter referred to as a wedge substrate) 21 can be made of the same material as in the first embodiment by the same well-known processing method. In this embodiment, the length of the wedge substrate in the laser optical axis direction is 30 mm,
A plurality of the wedge substrates having different inclination angles by changing the thickness difference between both ends every 30 μm are prepared, and these are arranged to be exchangeable. At this time, the change in the inclination angle is about 0.06 deg between the wedge substrates, and the required angle resolution 0.0
It is almost the same as 6deg.

Accordingly, by appropriately selecting a plurality of wedge substrates prepared as described above and combining a plurality of them, the angle of incidence on the LBO crystal, that is, the angle between the laser optical axis and the optical axis of the LBO crystal is changed. The incident angle can be adjusted by selecting a wedge substrate that meets the phase matching condition.

Next, a third embodiment of the laser wavelength converter according to the present invention will be described. In this embodiment, a nonlinear optical crystal is provided with a temperature adjusting means for adjusting the temperature of the crystal, and a laser wavelength conversion device is configured. Adjusting the incident angle to the nonlinear optical crystal adjusts the temperature of the nonlinear optical crystal. In this way, the phase matching angle of the nonlinear optical crystal is changed to match the angle of incidence.

FIG. 5 schematically shows a laser wavelength converter according to this embodiment. In this embodiment, the temperature of this crystal is applied to a nonlinear optical crystal 10 disposed on the incident laser optical axis Li. The heating-side contact surface of the Peltier element 31 is arranged in close contact with the temperature-adjusting means 30 for controlling the adjustment, and a radiator plate 32 is arranged on the cooling-side contact surface facing the heating-side contact surface. Then, the crystal temperature is adjusted by controlling the value of the current flowing through the Peltier element 31.

A nonlinear optical crystal having optical anisotropy is
The phase matching angle changes according to the crystal temperature, and the phase matching angle of the nonlinear optical crystal is changed by controlling the crystal temperature as described above. The crystal temperature is controlled so that the angle matches the phase matching angle.

That is, in the first and second embodiments described above, as a method of adjusting the phase matching condition, the incident angle of the nonlinear optical crystal with respect to the incident laser beam is changed so that the phase matching angle of the nonlinear optical crystal and the phase matching angle are adjusted. Although a method of making the coincidence has been described, in this embodiment, the incident angle of the incident laser light to the crystal is not changed (or used together with the change of the incident angle).
By adjusting the crystal temperature, the phase matching angle is changed to make them match.

For example, as described in the first embodiment,
Two wavelength conversion conditions, namely, a case where a BBO crystal having a crystal length of 10 mm is used as a nonlinear optical crystal and the wavelength of an incident laser wavelength of 532 nm is converted to an output laser wavelength of 266 nm by Type I phase matching, and the same type of BBO crystal is used for Type I phase matching The incident laser wavelength is 420 nm and the output laser wavelength is 210 nm
In the two cases, the relationship between the temperature of the BBO crystal and the phase matching angle was calculated, and the plotted results are shown in FIG. 6 (the above conditions) and FIG. 7 (the above conditions). For example, K.Kato IEEE JOE QE-2
2 1013 1986).

FIG. 6 shows the change of the phase matching angle under the above-mentioned wavelength conversion condition when the crystal temperature of the nonlinear optical crystal BBO is changed from 0 ° C. to 150 ° C. The amount of change of the phase matching angle per 1 ° C. of crystal temperature change is determined to be 0.0017 deg. On the other hand, the angle resolution and the effective adjustment width of the phase matching angle required under these wavelength conversion conditions are 0.001 deg for the angular resolution and 0.15 deg for the effective adjustment width according to the study result of FIG. 2 in the first embodiment. It is.

Therefore, the resolution in the temperature control for satisfying the required angular resolution only needs to be 0.59 ° C. and the effective adjustment width is about 88 ° C., and it is easy to use known temperature adjusting means using the Peltier element. A wavelength converter that makes the phase matching angle coincide with the incident angle of the fundamental laser beam can be configured, and the method can easily adjust and control the phase matching angle.

FIG. 7 shows a nonlinear optical crystal BB similar to FIG.
FIG. 9 shows a change in a phase matching angle under the above-described wavelength conversion condition when the crystal temperature of O is changed from 0 ° C. to 150 ° C. Then, from this calculation result, the crystal temperature change 1 ° C
The amount of change in the phase matching angle per hit is determined to be 0.0055 deg. With respect to this value, the angular resolution and the effective adjustment width of the phase matching angle required under this wavelength conversion condition are 0.001 d in the angular resolution from the examination result of FIG. 3 in the first embodiment.
eg, the effective adjustment width is 0.2 deg.

Therefore, the resolution in the temperature control for satisfying the required angular resolution is 0.18 ° C. and the effective adjustment width is about 36 ° C., and the phase can be easily adjusted using the known temperature adjusting means 30 using the Peltier element. A wavelength converter for matching the matching angle with the incident angle of the fundamental laser light can be configured, and the phase matching angle can be adjusted and controlled.

In the embodiment described above, an example is shown in which the Peltier element 31 is used as the temperature adjusting means 30 for adjusting the temperature of the nonlinear optical crystal, but this temperature adjusting means efficiently converts the nonlinear optical crystal. What is necessary is just to be able to adjust the temperature, and for example, it can be constituted by appropriately using a known heating means such as a heater. Further, the temperature adjusting means may be formed integrally with, for example, a crystal supporting member that arranges and supports the nonlinear optical crystal in the laser optical axis.

Next, the fourth embodiment of the laser wavelength converter according to the present invention will be described.
An embodiment will be described. The laser wavelength converter according to the present embodiment holds the nonlinear optical crystal using the cylindrical orbital member described in the first embodiment as a crystal support member that arranges and supports the nonlinear optical crystal on the laser optical axis. The non-linear optical crystal is provided with a temperature adjusting means for adjusting the crystal temperature, while the holding body to be moved is movably arranged on the track surface. The adjustment of the phase matching condition is performed by adjusting the position of the holder holding the nonlinear optical crystal along the surface of the track member and by adjusting the crystal temperature.

Hereinafter, in the examples of the present embodiment, a case where a BBO crystal is used as the nonlinear optical crystal and the wavelength of the incident fundamental laser beam is 532 nm converted to the output laser wavelength of 266 nm (the first and third embodiments are described below). This corresponds to the first embodiment of the present invention) with reference to FIG. 8 and FIG.

FIG. 8 shows the incident laser light L
FIG. 9 is a sectional view taken along a plane VIII-VIII in FIG. 9 showing a main section cut along a plane that defines the incident angle with respect to the crystal optical axis, including i and the emitted laser light Lo. 2 shows a cross-sectional view taken along a plane orthogonal to FIG.

In this embodiment, the temperature adjusting means 30 for adjusting the temperature of the BBO crystal 10, which is a nonlinear optical crystal, uses a heat source such as aluminum or copper to efficiently and uniformly maintain the entire crystal. It is the same as that already described in the third embodiment except that it has a heat storage member 33 formed so as to wrap the crystal with a material having high conductivity. In addition, 31 in the figure is a Peltier element, and 32 in the figure is a radiator plate.

BBO crystal 10 provided with temperature adjusting means 30
Is fixed to the crystal holder 23 by fixing means (not shown) such as a screw, and is mounted on the cylindrical raceway surface 22a in the same manner as described in the first embodiment.

As shown in a sectional view of FIG. 9, the cylindrical race member 22 has a standing portion 22b that stands upright in a plane having a cylindrical race surface. Therefore, track member 2
2 is formed in an L-shape. The crystal holder 23 also has an upright portion 23b in contact with the upright portion 22b in addition to a surface in contact with the cylindrical raceway surface. The crystal holder 2 is provided on the side end face of the cylindrical track member 22 facing the upright portion 22b (the left side end face of the cylindrical track member 22 in FIG. 9).
A fixing member 24 for pressing the third standing portion 23b against the standing portion 22b is provided. The fixing member 24 is fixed to the track member 22 and the crystal holder 2 by fixing means (not shown) such as screws.
Fixed to 3. Then, the crystal holder 23 is sandwiched and fixed between the fixing member 24 and the standing portion 22b.

Thus, the crystal holder 23 can be moved in the direction of the laser optical axis on the cylindrical orbital surface 22a by loosening the fixing means such as a screw. When the crystal holder 23 is positioned, the standing part 23b of the crystal holder 23 is moved by the fixing means. Standing part 2
2b to fix it.

The crystal holder 23 can be formed integrally with the heat storage member 33, for example. However, the temperature of the nonlinear optical crystal can be made uniform, the power consumption of the input power can be reduced, and other optics including cylindrical orbits can be used. From the viewpoint of suppressing thermal deformation due to heat conduction to the equipment, it is preferable to process a material having a heat insulating property and a low coefficient of linear expansion and use it in combination. Examples of such a material include ceramic and synthetic mica.

By moving the BBO crystal 10 on the cylindrical orbital surface 22a via the crystal holder 23 in such a configuration, or by adjusting the crystal temperature of the BBO crystal, the phase can be adjusted by only one of the methods. Matching conditions can be adjusted. By combining these two, more efficient adjustment can be performed as described below.

First, the Peltier device 3 serving as a temperature adjusting means
1 is supplied with power, the BBO crystal temperature is set to a constant temperature higher than the ambient temperature, for example, about 50 ° C., and the BBO crystal is controlled at a constant temperature at this temperature. Next, the fundamental laser light is incident on the BBO crystal, and the BBO crystal holder 23 is moved and adjusted on the cylindrical orbital surface 22a by, for example, a micrometer (not shown) so that the light intensity of the SHG wave as the output laser light is maximized. (Incident angle adjustment), and the crystal holder 23 is fixed at this incident angle position using the crystal holder fixing member 24. Then, a fine residual between the phase matching angle and the incident angle remaining after the crystal holder 23 is fixed (for example, an adjustment residual at the time of movement adjustment or a minute movement of the crystal position by fixing the crystal holder) is phase-matched by finely adjusting the crystal temperature. The angle is slightly changed to match the incident angle, and the temperature of the crystal is controlled to be constant under the temperature condition at which the obtained SHG wave is maximized.

With such a configuration and control, it is possible to easily and efficiently adjust detailed phase matching conditions. Further, according to the present embodiment, when the incident angle to the wavelength conversion device changes due to, for example, realignment of the peripheral optical device or the like, an appropriate adjustment method can be arbitrarily selected according to the amount of the change and executed. Can be. For example,
When the amount of change is small, phase matching can be performed only by adjusting the temperature of the crystal.

In the laser wavelength converter of such an embodiment, as shown in FIG. 10, for example, a laser output detector is connected to an output section of the laser wavelength converter via a partially reflecting member 150 such as a beam splitter or a chopper. It is preferable to dispose 160 to control the temperature of the nonlinear optical crystal so that the output intensity of the laser beam detected by the laser output detector is maximized.

According to the above configuration, even when the incident angle of the incident laser light to the nonlinear optical crystal slightly fluctuates due to, for example, a change in the positional relationship between the laser oscillator and the wavelength conversion device or a change in the ambient temperature condition, this change is not caused. The wavelength converter can be always operated at the maximum efficiency by self-correcting the fluctuation.

Alternatively, the partial reflection member 150 is disposed so as to be freely inserted into and removed from the laser optical axis. For example, when the laser device is started or at regular intervals of operation, the crystal temperature at which the laser output intensity becomes maximum is obtained. After that, temperature control may be performed at the crystal temperature until the next adjustment.

In the above description of each embodiment, the case where a single-stage BBO or LBO crystal is used as the nonlinear optical crystal to generate the second harmonic is described as an example. The present invention is not limited to this embodiment. For example, the present invention can be similarly configured using other nonlinear optical crystals exemplified above, and can be configured in multiple stages to generate a desired 2n harmonic. Alternatively, it is possible to generate a desired nth harmonic by combining optical parametric generation.

[0076]

According to the above-described method and apparatus, phase matching can be performed without using a large and complicated fine movement stage. Therefore, the laser wavelength converter can be made compact, and there is no problem of contamination caused by lubricants and the like.

A laser wavelength converter is provided with a temperature adjusting means for adjusting the temperature of the nonlinear optical crystal, and the phase matching condition is adjusted by adjusting the temperature of the nonlinear optical crystal. By changing the phase matching angle to match the incident angle.

According to the above-described method and apparatus, it is possible to satisfy the phase matching condition by fixing the nonlinear optical crystal on the optical axis at a fixed arrangement angle without using a mechanical adjustment mechanism such as a fine movement stage. it can. Therefore, it is possible to provide a laser wavelength converter that is small, does not change with time, and does not cause a problem of contamination.

Further, a laser wavelength converter is constituted by combining the above-mentioned constitutions, and the phase matching condition is adjusted by adjusting the nonlinear optical crystal disposed on the orbital plane or the holder for holding the crystal on the orbital plane. Or by adjusting the crystal temperature by the temperature adjusting means together with the position adjustment of the nonlinear optical crystal, and by controlling the temperature adjusting means after setting the incident angle, to adjust the detailed phase matching conditions. Can be performed easily and efficiently. Further, an appropriate adjustment method can be performed according to the amount of change in the phase matching.

The laser wavelength converter having the temperature adjusting means further includes a conversion output detecting means for detecting the intensity of the laser light which is wavelength-converted and output by the wavelength converting crystal. It is preferable that the temperature of the nonlinear optical crystal be controlled so that the intensity of the laser beam detected by the output detecting means is maximized.

According to the above configuration, the laser wavelength converter can always be operated at the maximum efficiency by adjusting the temperature of the nonlinear optical crystal even when the phase matching condition is deviated due to an external factor, for example. Therefore, it is possible to provide a laser wavelength converter that is stable over a long period of time by suppressing changes over time.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a laser wavelength conversion device according to the present invention.

FIG. 2 shows Type I using a BBO crystal as a nonlinear optical crystal.
The fundamental wave laser light of 532nm wavelength is 266nm by phase matching.
7 is a graph showing the phase matching angle dependence of the wavelength conversion efficiency when the wavelength is converted to the SHG wave of FIG.

[FIG. 3] Type I using a BBO crystal as a nonlinear optical crystal
420nm wavelength fundamental laser light 210nm wavelength by phase matching
7 is a graph showing the phase matching angle dependence of the wavelength conversion efficiency when the wavelength is converted to the SHG wave of FIG.

FIG. 4 is a configuration diagram showing a second embodiment of the laser wavelength conversion device according to the present invention.

FIG. 5 is a configuration diagram showing a third embodiment of the laser wavelength conversion device according to the present invention.

FIG. 6: Type I using a BBO crystal as a nonlinear optical crystal
The fundamental wave laser light of 532nm wavelength is 266nm by phase matching.
7 is a graph showing the relationship between the crystal temperature of the BBO crystal and the phase matching angle when the wavelength is converted to the SHG wave of FIG.

FIG. 7: Type I using a BBO crystal as a nonlinear optical crystal
420nm wavelength fundamental laser light 210nm wavelength by phase matching
7 is a graph showing the relationship between the crystal temperature of the BBO crystal and the phase matching angle when the wavelength is converted to the SHG wave of FIG.

FIG. 8 is a main sectional view showing a fourth embodiment of the laser wavelength conversion device according to the present invention.

FIG. 9 is a cross-sectional view of the laser wavelength conversion device in a direction orthogonal to a laser optical axis.

FIG. 10 is an explanatory diagram illustrating an overall configuration of a laser wavelength conversion device according to the present invention.

FIG. 11 is a configuration diagram of a laser microscope which is an example of a laser device configured using the laser wavelength conversion device.

[Explanation of symbols]

Reference Signs List 10 nonlinear optical crystal 20 crystal support member 21 wedge substrate (crystal support member having different inclination angles) 22 cylindrical track member (crystal support member having arc-shaped track surface) 22a cylindrical track surface (arc-shaped curved surface Orbital plane having) 23 crystal holder (holding body for holding crystal) 30 temperature adjusting means 100 laser wavelength converter 160 laser output detector (converted output detecting means)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaki Harada 3-2-3 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (72) Inventor Soichi Yamato 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Stock Company F term in Nikon Corporation (reference) 2K002 AB12 BA01 CA30 DA01 EA24 GA04 GA06 HA18 HA20

Claims (5)

[Claims] 1. An angle phase matching is performed to a predetermined phase matching angle by adjusting an incident angle of an incident laser beam with respect to an optical axis of a nonlinear optical crystal to convert a wavelength of the incident laser beam. In the laser wavelength converter, a crystal supporting member that arranges and supports the nonlinear optical crystal on the optical axis of the incident laser light at the predetermined phase matching angle,
A track surface having an arc-shaped curved surface at least in a plane that defines the incident angle; the nonlinear optical crystal or a holder holding the crystal is movably disposed on the track surface; Is set by adjusting the position of the nonlinear optical crystal or the holder along the track surface. 2. An angle phase matching is performed to a predetermined phase matching angle by adjusting an incident angle of an incident laser beam with respect to an optical axis of a nonlinear optical crystal, thereby converting a wavelength of the incident laser beam. In the laser wavelength converter, a crystal supporting member that arranges and supports the nonlinear optical crystal on the optical axis of the incident laser light at the predetermined phase matching angle,
It comprises a plurality of crystal support members having different inclination angles in a plane defining the incident angle, and the setting of the incident angle is performed by arranging the plurality of crystal support members having the different inclination angles in a selectable manner. A laser wavelength converter characterized by the above-mentioned. 3. A laser wavelength conversion device for causing a laser beam to be incident on a nonlinear optical crystal and converting the wavelength of the incident laser beam, wherein the temperature of the nonlinear optical crystal is adjusted for the nonlinear optical crystal. A temperature adjusting unit that adjusts the temperature of the nonlinear optical crystal to change the phase matching angle of the nonlinear optical crystal so that the incident angle of the laser light matches the phase matching angle. Laser wavelength converter. 4. A laser wavelength conversion device for causing a laser beam to be incident on a nonlinear optical crystal and converting the wavelength of the incident laser beam, wherein the nonlinear optical crystal is positioned on an optical axis of the incident laser beam. Having a crystal support member arranged and supported at a phase matching angle of
The crystal support member includes a track surface having an arc-shaped curved surface at least in a plane that defines the incident angle, and the nonlinear optical crystal or a holder holding the crystal is movably disposed on the track surface. In addition, the nonlinear optical crystal further includes a temperature adjusting unit that adjusts the temperature of the nonlinear optical crystal, and the setting of the incident angle includes setting the nonlinear optical crystal or the crystal disposed on the orbital plane. The position of the holding body to be held is adjusted along the orbital plane, or by adjusting the crystal temperature by the temperature adjusting means together with the position adjustment of the nonlinear optical crystal, and after setting the incident angle, the temperature is adjusted. A laser wavelength converter controlled by adjusting means. 5. The laser wavelength conversion device further comprises a conversion output detecting means for detecting the intensity of the laser light wavelength-converted by the wavelength conversion crystal, wherein the temperature adjusting means detects the intensity by the conversion output detecting means. The laser wavelength converter according to claim 3 or 4, wherein the temperature of the nonlinear optical crystal is controlled so that the intensity of the laser light to be applied is maximized.