JP4945934B2 - Optical system, inspection device, processing device and measuring device - Google Patents

Description

  The present invention relates to a resonator, an optical system, an inspection device, a processing device, and a measuring device, and is suitable for application to, for example, high output or high-efficiency wavelength conversion of a single frequency and linearly polarized laser by coherent addition of laser light. It is a thing.

  There are several methods for increasing the output of a single frequency and linearly polarized laser as follows. One method is to increase the oscillation output by increasing the input excitation power of the laser itself. This is the simplest method, but there is a problem that if the output exceeds a certain level, the laser itself becomes large and it becomes difficult to control the oscillation frequency and polarization. In another method, as shown in FIG. 15, a small single frequency and linearly polarized laser is used as a seed laser (main laser) 5101, and a laser beam 5102 emitted from the seed laser 5101 is excited. And amplifying the output of the original laser beam 5102 by stimulated emission in the amplification medium 5103. This method has the advantage that if the amplification medium 5103 is modularized, it can be easily powered up by arranging the amplification medium 5103 in a multistage cascade, but there is a drawback that the lateral mode control is difficult. Further, when the seed laser 5101 starts from low power, it is difficult to optically saturate the amplification medium 5103. Therefore, a method of using a plurality of stages of amplification medium 5103 or passing laser light 5102 through the same amplification medium 5103 multiple times is available. Although generally taken, efficiency is not so good. In addition, amplification by the multistage cascade arrangement of the amplification media 5103 has a limit value limited by the damage threshold of the amplification media 5103.

  Recently, development of amplification technology using a fiber amplifier, which is a kind of this method, has been advanced. In this method, as shown in FIG. 16, the laser light 5102 emitted from the seed laser 5101 is passed through a fiber amplifier 5105 excited by the excitation module 5104 to amplify the output of the original laser light 5102.

  Next, as a method for easily optically saturating the amplification medium 5103 with the low-power seed laser 5101, there is an injection locking method in which the amplification medium 5103 itself has a resonator structure. In this method, as shown in FIG. 17, laser light 5102 emitted from a seed laser 5101 is incident on an input coupler (internal coupling element) 5106, and the laser light 5102 that has passed through the input coupler 5106 is passed through an amplification medium 5103. Then, the light is sequentially reflected by the high reflection mirrors 5107, 5108, and 5109 to enter the input coupler 5106, and the amplified laser beam 5102 is taken out from the input coupler 5106. Here, the input coupler 5106 is generally a partial reflector (partial reflecting mirror) having a transmittance of several percent. In this method, a high gain can be expected with only one amplification module, but in order to control the frequency by forcibly injecting specific light from the outside into the self-oscillating seed laser 5101, The point is that high-accuracy resonator length control is necessary.

On the other hand, there is a method called coherent addition which is different from the method based on the stimulated emission control of light (for example, see Non-Patent Document 1). This is basically a method in which the amplification module is placed in each optical path of a Mach-Zehnder interferometer, and the phases of the two optical paths are matched to perform interference addition. It is a feature that can be simply added. An example is shown in FIG. As shown in FIG. 18, the laser beam 5102 emitted from the seed laser 5101 is incident on the half mirror 5110 and divided into laser beams 5102a and 5102b. The laser beam 5102a transmitted through the half mirror 5110 is passed through the amplification module 5111, reflected by the folding mirror 5112, then incident on the half mirror 5113 and reflected, and the laser beam 5102b reflected by the half mirror 5110 is sent to the amplification module 5114. Then, the light is reflected by the folding mirror 5115 and then incident on the half mirror 5113 to be transmitted. In this case, the folding mirror 5115 is placed on the actuator 5116 and is actively controlled, so that the phase of the optical path passing through the amplification module 5111 and the optical path passing through the amplification module 5114 are matched to perform interference addition.
Appl.Opt. 30 (1991), 317

By the way, since the oscillation wavelength of many lasers is near the near infrared, a light source having a visible or ultraviolet wavelength can be made using a special optical crystal called a nonlinear optical crystal. Nonlinear optical crystals include LN (LiNbO ₃ ), KTP (KTiOPO ₄ ), LBO (LiTaO ₃ ), BBO (β-BaB ₂ O ₄ ), and LT (LiTaO ₃ ), and these have wavelengths near the near infrared. Can be converted into short wavelength laser light. In addition, the efficiency of wavelength conversion is improved by using special devices such as Periodically Polarized Inversion (PP) LN (PPLN), PPKTP, and Periodically Polarized Stoichiometric (PPS) LT (PPSLN). Is also underway. In nonlinear conversion, the efficiency of conversion improves nonlinearly as input power increases. Also, the higher the excitation of the nonlinear optical crystal, the higher the conversion efficiency.

  In order to improve the conversion efficiency, a method using an external resonator is often used. In this method, an external resonator inputs laser light extracted from an original light source to a high finesse resonator to confine the light. An example is shown in FIG. As shown in FIG. 19, in this method, the laser light 5102 emitted from the seed laser 5101 is amplified through the amplification module 5117 and then incident on the input coupler 5106. The laser light 5102 that has passed through the input coupler 5106 is The light is sequentially reflected by the high reflection mirrors 5107, 5108, and 5109 to confine light in the resonator. In this case, since the confined light circulates around the inside of the resonator about several times the finesse of the resonator, the laser light intensity on the optical path (path) inside the resonator can be made extremely strong. Therefore, if conversion by an external resonator is used, wavelength conversion can be realized with high conversion efficiency by inserting the nonlinear optical crystal 5118 on the optical path inside the resonator as shown in FIG. In general, the light confined in the resonator is dissipated by the loss (absorption / scattering) in the resonator while circulating around the resonator, or leaks out of the resonator as a minute transmitted light of the mirror constituting the resonator. Go. In the case of wavelength conversion by an external resonator, the energy used at the conversion wavelength can be considered as included in the loss in the resonator.

となるよう設定することにより、位相条件（共振器長ロッキング）が満たされ、モードマッチングが得られた条件で共振器への１００％の結合（入射）が実現できる。上記の条件で外部共振器内の光強度は最大になり、最も効率よく外部共振器内の損失要素（ロスエレメント）で消費されることになる。例えば、外部共振器を使った波長変換の場合、外部共振器内の損失は主に吸収・散乱などの線形損失と非線形波長変換のエネルギー変換に伴う非線形損失とで構成されるが、上記のインピーダンスマッチング条件の下で非線形変換により発生する短波長光パワーが最大となる。これにより外部共振器内のパワーＰ_circは入力パワーをＰ_inとして、

で表される。 The light to the resonator is coupled (incident) through the input coupler. Since the input coupler has a transmittance of several percent, most of the light is normally reflected by the input coupler. However, according to the impedance matching theory of the external resonator, if the sum of all losses inside the resonator is Δ, the transmittance T of the input coupler is

By setting so that 100% coupling (incident) to the resonator can be realized under the condition that the phase condition (resonator length locking) is satisfied and mode matching is obtained. Under the above conditions, the light intensity in the external resonator is maximized, and is most efficiently consumed by the loss element in the external resonator. For example, in the case of wavelength conversion using an external resonator, the loss in the external resonator is mainly composed of linear loss such as absorption / scattering and nonlinear loss due to energy conversion of nonlinear wavelength conversion. Under the matching conditions, the short wavelength optical power generated by the nonlinear conversion is maximized. As a result, the power P _circ in the external resonator is defined as the input power P _in

It is represented by

Note that a solid-state laser has been proposed that achieves frequency synchronization by injecting light in the reverse circulation direction generated inside the resonator of the external resonator type laser light source into another laser light source (see, for example, Patent Document 1). .) Further, a method has been proposed in which a laser beam having a sum frequency of 198 nm is generated by a double resonant of a laser beam having a wavelength of 1064 nm and a laser beam having a wavelength of 780 nm (see, for example, Patent Document 2). Further, a scattered foreign matter inspection apparatus using laser light has been proposed (see, for example, Patent Document 3). In addition, a circuit pattern inspection apparatus (review station) using laser light has been proposed (see, for example, Patent Document 4). Further, it has been proposed that phase modulation for locking an external resonator having a wavelength of 266 nm is performed simultaneously with the phase modulation of the 532 nm external resonator on the 532 nm phase modulator before generation of laser light having a wavelength of 266 nm (for example, patents). Reference 5).
US Pat. No. 5,068,546 JP 2002-99007 A US Pat. No. 4,898,471 JP 2000-352507 A Japanese Patent Laid-Open No. 2002-311467

As described above, coherent addition using a resonator can be given as a method for increasing the output of a laser. However, as a coherent addition system, only one input coupler is provided in the resonator so far. However, with this coherent addition system, it has been difficult to increase the output power of the laser and perform high-efficiency wavelength conversion.
Accordingly, the problem to be solved by the present invention is to provide a resonator capable of performing high-power laser conversion and high-efficiency wavelength conversion, a high-performance optical system using the same, an inspection device, a processing device, and a measuring device. Is to provide.

  The inventors of the present invention have conducted intensive research to solve the above-mentioned problems of the conventional technology, and confine light in a resonator (external resonator) to realize high output of the laser and efficient wavelength conversion. In order to achieve this, it has been noted that it is effective to provide a plurality of input couplers in the resonator and combine a plurality of laser beams of the same frequency (wavelength) separately. The design procedure of the resonator has not been clear so far. In particular, unless the impedance matching condition of the resonator is satisfied, the laser light incident on the resonator cannot be consumed efficiently inside the resonator, and highly efficient wavelength conversion cannot be realized. Therefore, as a result of various studies, the optimum transmittance of each input coupler is obtained as a design solution based on the impedance matching theory described later, and a method for realizing efficient coupling has been found and the present invention has been devised.

That is, in order to solve the above problem, the first invention
A resonator composed of two or more mirrors,
Two of the plurality of mirrors are constituted by a first input coupler and a second input coupler for coupling the first laser beam and the second laser beam having the same frequency, respectively. It is characterized by this.

The second invention is
With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively divided into the first input coupler and The optical system is coupled to the second input coupler.

In the first and second inventions, from the viewpoint of maximizing the coupling efficiency between the laser beam and the resonator, the total transmittance of the first input coupler and the second input coupler is preferably the resonator. And the transmittance of the first input coupler is a value proportional to the power of the first laser beam, and the transmittance of the second input coupler is equal to the power of the second laser beam. Make it a proportional value. In particular, when the power of the first laser beam and the power of the second laser beam are substantially equal to each other, by making the transmittance of the first input coupler and the transmittance of the second input coupler substantially equal to each other, The coupling efficiency between the laser beam and the resonator can be maximized.
Here, as described above, the input coupler is generally a partial reflector having a transmittance of several percent, but is another element having a similar function, such as a diffraction grating. Also good.
The resonator includes various types such as a ring resonator and a linear resonator (standing wave type).
The first laser light and the second laser light include those in a wide wavelength (frequency) band such as infrared light, visible light, and ultraviolet light.

In the second invention, for example, a laser beam emitted from a seed laser (main laser) is divided into a first laser beam and a second laser beam by a half mirror or the like, and the first laser beam and the second laser beam are divided. Are amplified and coupled to the first input coupler and the second input coupler. Alternatively, after the laser light emitted from the seed laser is amplified, it is divided into a first laser light and a second laser light, and after one of these first laser light and second laser light is amplified, these The first laser beam and the second laser beam are coupled to the first input coupler and the second input coupler. Alternatively, the laser light emitted from the seed laser is divided into the first laser light and the second laser light, and the first input coupler is subjected to wavelength conversion of the first laser light and the second laser light, respectively. And a second input coupler. Alternatively, wavelength conversion is performed by arranging a nonlinear optical crystal in the resonator.
This optical system can be used, for example, to increase the output of a single-frequency, linearly polarized laser, for example, a near-infrared laser light source, and a high-power visible light source or a high-power depth by nonlinear wavelength conversion using a nonlinear optical crystal. It can be used to obtain an ultraviolet light source.

The third invention is
A resonator composed of a plurality of mirrors of three or more,
Three mirrors of the plurality of mirrors are a first input coupler and a second input for coupling the first laser beam, the second laser beam, and the third laser beam having the same frequency, respectively. It is characterized by comprising a coupler and a third input coupler.

The fourth invention is:
With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. The third laser beam is coupled to the first input coupler, the second input coupler, and the third input coupler, respectively.

  In the third and fourth inventions, preferably, the first input coupler, the second input coupler, and the third input coupler are transmitted from the viewpoint of maximizing the coupling efficiency between the laser beam and the resonator. The sum of the rates is approximately equal to the total internal loss of the resonator, the transmittance of the first input coupler is a value proportional to the power of the first laser beam, and the transmittance of the second input coupler is the second. The transmittance of the third input coupler is set to be a value proportional to the power of the third laser light. In particular, when the power of the first laser beam, the power of the second laser beam, and the power of the third laser beam are substantially equal to each other, the transmittance of the first input coupler and the transmittance of the second input coupler are By making the transmittance of the third input coupler substantially equal to each other, the coupling efficiency between the laser beam and the resonator can be maximized.

In the fourth invention, for example, the laser beam emitted from the seed laser is divided into a first laser beam, a second laser beam, and a third laser beam, and these first laser beam and second laser beam are divided. The light and the third laser light are respectively amplified and then coupled to the first input coupler, the second input coupler, and the third input coupler. Alternatively, after the laser beam emitted from the seed laser is amplified, it is divided into a first laser beam, a second laser beam, and a third laser beam, and these first laser beam, second laser beam, and third laser beam are separated. After amplifying all, two, or one of the laser beams of the first laser beam, the first laser beam, the second laser beam, and the third laser beam are converted into the first input coupler, the second input coupler, and the second laser beam. Connect to 3 input couplers. Alternatively, the laser beam emitted from the seed laser is divided into a first laser beam, a second laser beam, and a third laser beam, and the first laser beam, the second laser beam, and the third laser beam. The light is wavelength-converted and then coupled to the first input coupler, the second input coupler, and the third input coupler. Alternatively, wavelength conversion can be performed by arranging a nonlinear optical crystal in the resonator.
In the third and fourth inventions, the matters other than the above are explained in relation to the first and second inventions unless they are contrary to the nature.

The fifth invention is:
a resonator composed of a plurality of n (n is an integer of 2 or more) mirrors,
Of the plurality of mirrors, n mirrors are constituted by n input couplers for respectively coupling n laser beams having the same frequency.

The sixth invention is:
With one seed laser,
a resonator composed of n (n is an integer of 2 or more) or more mirrors, and n mirrors of the plurality of mirrors are composed of n input couplers;
The optical system is characterized in that the laser light emitted from the seed laser is divided into n laser beams having the same frequency, and the n laser beams are respectively coupled to the n input couplers.
In the fifth and sixth inventions, what has been described in relation to the first to fourth inventions is valid as long as it is not contrary to the nature thereof.

The seventh invention
In an inspection device using a light source,
As the light source,
With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively divided into the first input coupler and An optical system coupled to the second input coupler is used.

The eighth invention
In a processing apparatus using a light source,
As the light source,
With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively divided into the first input coupler and An optical system coupled to the second input coupler is used.

The ninth invention
In a measuring device using a light source,
As the light source,
With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively divided into the first input coupler and An optical system coupled to the second input coupler is used.

The tenth invention is
In an inspection device using a light source,
As the light source,
With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. And an optical system that couples the three laser beams to the first input coupler, the second input coupler, and the third input coupler, respectively.

The eleventh invention is
In a processing apparatus using a light source,
As the light source,
With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. And an optical system that couples the three laser beams to the first input coupler, the second input coupler, and the third input coupler, respectively.

The twelfth invention
In a measuring device using a light source,
As the light source,
With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. And an optical system that couples the three laser beams to the first input coupler, the second input coupler, and the third input coupler, respectively.

  In the seventh to twelfth inventions, the inspection device, the processing device, and the measurement device include any device as long as it uses laser light. Specifically, the inspection apparatus is an apparatus that inspects, for example, foreign matters and circuit patterns on the surface of a semiconductor wafer, and the processing apparatus performs various processes such as heat treatment, processing, and surface modification of various substrates and materials. The measuring device is a device that performs various measurements using a laser beam.

  In the present invention configured as described above, a plurality of laser beams having the same frequency can be coupled to the same resonator with high coupling efficiency by using coherent addition. For this reason, for example, even when the output of the amplification module is limited, it is possible to simply scale up the laser. In particular, the method according to the present invention is very effective when the amplification module has an output limitation of light intensity and serial amplification is not possible. Further, since the coupling portion to the external resonator can be allocated, it is effective in improving the reliability when the input coupler becomes a problem as a deterioration point.

  According to the present invention, since a plurality of laser beams having the same frequency can be coupled to the same resonator with high coupling efficiency, a high-performance optical system capable of performing high-power laser conversion and high-efficiency wavelength conversion. A system can be obtained, and by using this optical system as a light source, a high-performance inspection device, processing device, and measuring device can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or corresponding parts are denoted by the same reference numerals, and repeated description will be omitted as appropriate.
First, a first embodiment of the present invention will be described.
In the first embodiment, a description will be given of a bow tie type ring resonator constituted by four mirrors in which two of the four mirrors are constituted by an input coupler.

FIG. 1 shows a bow-tie ring resonator according to the first embodiment.
As shown in FIG. 1, this bow tie ring resonator is composed of four mirrors, two of which are input couplers M1 and M3, and the remaining two are high reflection mirrors M2 and M4. . These input couplers M1 and M3 have a predetermined transmittance, which will be described later, through which laser light can be taken into the resonator from the outside. Here, it is assumed that there is a loss in the resonator. Here, it is assumed that the high reflection mirror M4 out of the high reflection mirrors M2 and M4 that are not configured by the input coupler has a predetermined transmittance, and the high reflection mirror M4 is used as a resonator. Assume that the light stored inside leaks outside. In other words, output laser light is extracted from the high reflection mirror M4 to the outside. It is assumed that the transmittance of the high reflection mirror M2 is zero. As a loss element inside the resonator, in addition to the case where the mirror (here, the high reflection mirror M4) has a transmittance (output coupler) as in this example, the nonlinearity for the purpose of nonlinear wavelength conversion of the external resonator type Absorption / scattering of the crystal and nonlinear loss when the optical crystal is arranged in the resonator can also be assumed.

高反射ミラーＭ２、Ｍ４については、振幅反射率ｒ_m2 ,ｒ_m4を以下のように定める。

上述のように高反射ミラーＭ４は所定の透過率を有するが、その強度透過率をΔとして表記する。計算上、この高反射ミラーＭ４の透過による漏れは共振器内の別コンポーネントで発生する損失に置き換えて考えることも可能であり、結果的に共振器内に分布したいくつかの損失要素の合計として考えることもできる。例えば、共振器内部に非線形光学結晶を配置した場合、この非線形光学結晶の吸収散乱などの損失のほか、非線形変換に消費されるエネルギー分も考慮した損失の合計として考えればよい。 Let r ₁ , t ₁ , r ₃ , and t ₃ be the amplitude reflectance and amplitude transmittance of the input couplers M1 and M3, respectively. Further, the intensity reflectance and the intensity transmittance of the input couplers M1 and M3 are R ₁ , T ₁ , R ₃ and T ₃ , respectively. Assuming no absorption during transmission, the following equation holds:

For the high reflection mirrors M2 and M4, the amplitude reflectances r _m2 and r _m4 are determined as follows.

As described above, the high reflection mirror M4 has a predetermined transmittance, and its intensity transmittance is expressed as Δ. In calculation, the leakage due to the transmission of the high reflection mirror M4 can be considered as a loss generated in another component in the resonator, and as a result, the sum of several loss elements distributed in the resonator is obtained. You can also think about it. For example, when a nonlinear optical crystal is arranged inside the resonator, it can be considered as the total loss considering the energy consumed for nonlinear conversion in addition to the loss such as absorption scattering of the nonlinear optical crystal.

と表示する。式中δは、シードレーザーから放出されるレーザー光を分割して最終的に共振器に入射させるまでの光路差から生じる位相差を表す。また、インプットカプラーＭ１、Ｍ３による反射光電場振幅をＥ_out1, Ｅ_out3とする。一方、共振器内では、図１中インプットカプラーＭ１、Ｍ３による反射直後の電場をそれぞれＥ_circ1 、Ｅ_circ3 とする。これらの電場は以下の連立方程式で表される。

共振器内の電場Ｅ_circ1 , Ｅ_circ3 は、それぞれ外部からインプットカプラーＭ１、Ｍ３を透過したレーザー光と、共振器内を周回してインプットカプラーＭ１、Ｍ３および高反射ミラーＭ２、Ｍ４により反射される反射光との和で表される。インプットカプラーＭ１、Ｍ３で反射された電場Ｅ_out1, Ｅ_out3については、共振器を周回し、これらのインプットカプラーＭ１、Ｍ３を透過して外部に取り出される光と、これらのインプットカプラーＭ１、Ｍ３による反射光との和で表される。インプットカプラーＭ１、Ｍ３を透過する際に位相回転項として虚数ｉが付加されていることに注意すべきである。また、上式でφ₁ ，φ₂ はそれぞれ共振器内の光路Ｍ１−Ｍ４−Ｍ３と光路Ｍ３−Ｍ２−Ｍ１とから計算される位相項である。周回の位相はφ₁ ＋φ₂ で表される。（式６）の連立方程式を解くと、それぞれ以下の式が導かれる。

Well, here the input coupler M1, M3 respectively an electric field amplitude of the incident laser light E _in1, E _in3. These incident laser lights are obtained by dividing and amplifying the laser light emitted from one seed laser so as to have the same frequency ω.

Is displayed. In the equation, δ represents a phase difference resulting from an optical path difference between splitting the laser light emitted from the seed laser and finally entering the laser. Also, the reflected photoelectric field amplitudes by the input couplers M1 and M3 are assumed to be E _out1 and E _out3 . On the other hand, in the resonator, electric fields immediately after reflection by the input couplers M1 and M3 in FIG. 1 are _denoted as E _circ1 and E _circ3 , respectively. These electric fields are expressed by the following simultaneous equations.

The electric fields E _circ1 and E _circ3 in the resonator are _reflected from the laser beam that has passed through the input couplers M1 and M3 from the outside and the input couplers M1 and M3 and the high-reflection mirrors M2 and M4, respectively, that circulate in the resonator. It is expressed as the sum of the reflected light. The electric fields E _out1 and E _out3 reflected by the input couplers M1 and M3 circulate around the resonator, pass through these input couplers M1 and M3, and are extracted to the outside, and by these input couplers M1 and M3 It is expressed as the sum of the reflected light. It should be noted that an imaginary number i is added as a phase rotation term when passing through the input couplers M1 and M3. In the above equation, φ ₁ and φ ₂ are phase terms calculated from the optical paths M1-M4-M3 and the optical paths M3-M2-M1 in the resonator, respectively. The phase of the circulation is represented by φ ₁ + φ ₂ . Solving the simultaneous equations of (Expression 6) leads to the following expressions, respectively.

FIG. 2 shows a basic configuration of an optical system according to the second embodiment of the present invention.
As shown in FIG. 2, in this optical system, a bow tie ring resonator 10 is constituted by two input couplers M1 and M3 and two high reflection mirrors M2 and M4. In this case, the nonlinear optical crystal 11 is arranged on the optical path in the bow tie ring resonator 10. The configuration of the bow tie ring resonator 10 is the same as that of the bow tie ring resonator according to the first embodiment except that the nonlinear optical crystal 11 is disposed inside. This optical system has a single seed laser 12. The laser beam 13 emitted from the seed laser 12 is divided into a laser beam 13a and a laser beam 13b by the half mirror 14, and the laser beam 13a is amplified by the amplification module 15 and then incident on the input coupler M1. At the same time, the laser beam 13b is reflected by the folding mirror 17 placed on the actuator 16, is amplified by the amplification module 18, and then enters the input coupler M3. The laser beams 13a and 13b are respectively input couplers. The resonator is coupled to the resonator via M1 and M3. Output laser light is extracted from the high reflection mirror M4 to the outside. In this case, since the nonlinear optical crystal 11 is arranged inside the bow tie ring resonator 10, higher-order harmonics can be generated, and according to what is used as the nonlinear optical crystal 11, the seed laser 12 It is possible to extract output laser light having a short wavelength such as ½ of the wavelength of the laser light 13 emitted from the laser.

で表される。さらに、コヒレント加算を行う場合、二つに分けられた光路間の位相差が一致している必要がある。これに関しては、二つの支光路のうち一方に含まれる折り返しミラー１７をアクチュエーター１６で波長距離程度移動させることで位相差を調整できる。具体的には、レーザー光１３ａ、１３ｂ間の位相差δが

となるよう折り返しミラー１７の位置を調整することにより、レーザー光１３ａ、１３ｂのボウタイ型リング共振器１０への同時結合が可能となる。 In this optical system, if the incident laser beams 13a and 13b exactly match the resonance frequency of the bow tie ring resonator 10, the laser beams 13a entering the resonator from the outside via the input couplers M1 and M3, 13b interferes and accumulates inside the resonator so as to strengthen each other. In order to synchronize the frequency of the incident laser beams 13a and 13b and the resonance frequency of the resonator, one mirror of the resonator, here a high reflection mirror M2 is placed on the actuator 19, and the frequency of the input light Actively control to synchronize with. In particular, a high-accuracy frequency locking method such as the Pound Drever Hall method is often used for this synchronization. The resonator length synchronization condition for the seed laser 12 is expressed by (Equation 7)

It is represented by Further, when performing coherent addition, the phase difference between the two optical paths needs to match. In this regard, the phase difference can be adjusted by moving the folding mirror 17 included in one of the two optical paths by the actuator 16 by a wavelength distance. Specifically, the phase difference δ between the laser beams 13a and 13b is

By adjusting the position of the folding mirror 17 such that the laser beams 13a and 13b are simultaneously coupled to the bow-tie ring resonator 10.

の場合、インプットカプラーＭ１、Ｍ３の振幅反射率ｒ₁ , ｒ₃ は、

と表される。 Next, optimization (impedance matching) of the coupling efficiency between the outside and inside of the resonator will be described. The impedance matching is designed by optimizing the transmittance of the input couplers M1 and M3 with respect to the loss in the resonator and efficiently consuming the laser beams 13a and 13b incident on the resonator inside the resonator. is there. Specifically, the transmittances of the input couplers M1 and M3 may be selected so that the reflected photoelectric field amplitudes _Eout1 and _Eout3 by the input couplers M1 and M3 in (Expression 7) become zero. For example, let β be a constant (intensity ratio between two incident laser beams 13a and 13b).

In this case, the amplitude reflectances r ₁ and r ₃ of the input couplers M1 and M3 are

It is expressed.

が導かれる。この条件のとき、共振器の内部パワーが最大になることを、Ｅ_circ1 , Ｅ_circ3 の値から確認することができる。さらにここで、共振器内部損失Δが十分小さい条件に限定して考えた場合、（式１２）をテイラー展開することで、

という式が求まり、インプットカプラーＭ１、Ｍ３の透過率は入力するレーザー光１３ａ、１３ｂのパワーの比で表されることがわかる。（式１３）より、インプットカプラーＭ１、Ｍ３の透過率の合計は、共振器内部の合計損失にほぼ等しくなる。

また、特に入射させるレーザー光１３ａ、１３ｂが同程度のパワーである場合、

が、インピーダンスマッチングを実現する最適な条件となる。 (Equation 4) and R ₁ = r ₁ ² , R ₃ = r ₃ ² ,

Is guided. It can be confirmed from the values of E _circ1 and E _circ3 that the internal power of the resonator is maximized under this condition. Further, here, when considering that the internal loss Δ of the resonator is limited to a sufficiently small condition,

It can be seen that the transmittance of the input couplers M1 and M3 is expressed by the ratio of the power of the input laser beams 13a and 13b. From (Equation 13), the total transmittance of the input couplers M1 and M3 is approximately equal to the total loss inside the resonator.

In particular, when the incident laser beams 13a and 13b have the same level of power,

However, this is the optimum condition for realizing impedance matching.

When the resonator internal loss is large, it is considered that there is a possibility of practical application as a coherent addition technique that also serves as a mode cleaner, for example. Further, in the limit case, when the internal loss is maximum (Δ = 100%), the laser beams 13a and 13b incident on the resonator are no longer circulated in the resonator and are immediately consumed by the internal loss element. The optimum condition in this case is R ₃ = 0% (that is, the input coupler M3 is coated with antireflection (AR) or the input coupler M3 itself is removed) and R ₁ = 50% (β = 1) ), Which is consistent with the conventional example of coherent addition. On the other hand, assuming that the internal loss Δ of the resonator is several percent and considering the limit where β = 0, T ₁ = Δ and T ₃ = 0, and the conventional single laser beam is coupled to the external resonator. It corresponds to.
As described above, according to the second embodiment, a high-performance optical system capable of performing highly efficient wavelength conversion can be realized.

In order to obtain sufficient gain in the amplification modules 15 and 18, a certain amount of power is required as the input seed laser 12, but the seed laser 12 alone cannot cover the seed power of the two amplification modules 15 and 18. There is. Next, optical systems according to third and fourth embodiments of the present invention that are suitable for such cases will be described.
That is, in the optical system according to the third embodiment, as shown in FIG. 3, an amplification module 20 is disposed between the seed laser 12 and the half mirror 14, and the laser light 13 emitted from the seed laser 20 is emitted. After being amplified by the amplification module 20, it is divided into laser beams 13a and 13b by the half mirror 14. By doing so, the power of the laser beams 13a and 13b can be sufficiently increased, so that the seed power of the amplification modules 15 and 18 can be sufficiently covered.
Other than the above are the same as in the second embodiment.
According to the third embodiment, the same advantages as those of the second embodiment can be obtained.

In the optical system according to the fourth embodiment, as shown in FIG. 4, after the laser beam 13 emitted from the seed laser 12 is once amplified by the amplification module 20, a part of the laser beam 13 is converted into the laser beam 13b by the partial mirror 21. This is further amplified by the amplification module 18 and then incident on the input coupler M3, and the remainder is extracted as laser light 13a and incident on the input coupler M1 as it is, so that the total number of amplification modules is reduced to two. However, the desired number of laser beams (in this case, two laser beams 13a and 13b) can be secured.
According to the fourth embodiment, the same advantages as those of the second embodiment can be obtained.

In the first to fourth embodiments, the case where the bow tie type ring resonator 10 is used has been described. However, the resonator is not limited to this, and other types of ring resonators as well as linear resonators are used. It may be. Next, an optical system according to a fifth embodiment of the present invention using a linear resonator will be described.
That is, in the optical system according to the fifth embodiment, as shown in FIG. 5, the laser beam 13 emitted from the seed laser 12 is divided into the laser beam 13a and the laser beam 13b by the half mirror 14, Among them, the laser beam 13 a is reflected by the folding mirror 22, amplified by the amplification module 15 and then incident on the half mirror 23, and the laser beam 13 b is reflected by the folding mirror 17 placed on the actuator 16, and is amplified by the amplification module 18. After being amplified, the light enters the half mirror 23. In this case, the half mirror 23 corresponds to the input couplers M1 and M3 in the first to fourth embodiments, and the half mirror 23 and the high reflection mirrors M2 and M4 constitute a linear resonator 24. The laser beams 13a and 13b are coupled to the linear resonator 24 through the half mirror 23 corresponding to the input couplers M1 and M3. The output laser light is taken out from the high reflection mirror M4.
According to the fifth embodiment, an optical system capable of obtaining a high-power laser beam can be realized.

Next explained is an optical system according to the sixth embodiment of the invention.
In the optical system according to the sixth embodiment, as shown in FIG. 6, the linear resonator 24 has a high reflection mirror 25 disposed so as to face the high reflection mirror M <b> 4 and is transmitted through the half mirror 23. The non-linear optical crystal 11 is arranged on the optical path of the laser beam that has been reflected by the high reflection mirror M4 toward the high reflection mirror 25. Since the nonlinear optical crystal 11 is arranged inside the linear resonator 24 as described above, high-order harmonics can be generated. Depending on what is used as the nonlinear optical crystal 11, the seed laser 12 An output laser beam having a short wavelength such as ½ of the wavelength of the emitted laser beam 13 can be extracted.

Next explained is an optical system according to the seventh embodiment of the invention. In this optical system, two bowtie ring resonators for wavelength conversion are inserted between the seed laser 12 and a bowtie ring resonator 10 capable of wavelength conversion, and higher-order harmonics are obtained by two-stage wavelength conversion. Generate. Since the phase relationship of light is maintained at the time of wavelength conversion, a bow tie type ring resonator for wavelength conversion can be inserted by the same method as that for inserting an amplification module.
That is, in the optical system according to the seventh embodiment, as shown in FIG. 7, two bow tie ring resonators 26 and 27 are arranged in front of the bow tie ring resonator 10. The bow tie ring resonator 10 includes input couplers M1 and M3 and high reflection mirrors M2 and M4, and a fourth harmonic generation (FHG) crystal 28 is disposed therein. The bow tie ring resonator 26 includes an input coupler M5 and three high reflection mirrors M6, M7, and M8, and a second harmonic generation (SHG) crystal 29 is disposed therein. The high reflection mirror M6 is placed on the actuator 30. The high reflection mirror M8 has a predetermined transmittance, and the transmittances of the high reflection mirrors M6 and M7 are zero. The bow tie ring resonator 27 includes an input coupler M9 and three high reflection mirrors M10, M11, and M12, and an SHG crystal 31 is disposed therein. The high reflection mirror M12 is placed on the actuator 32. The high reflection mirror M10 has a predetermined transmittance, and the transmittances of the high reflection mirrors M11 and M12 are zero.

  In this optical system, the laser beam 13 emitted from the seed laser 12 is amplified by the amplification module 20, and then a part thereof is extracted as the laser beam 13 b by the partial mirror 21, reflected by the folding mirror 17, and amplified by the amplification module 18. After that, the light is incident on the input coupler M9 of the bow tie ring resonator 27, and the remainder is taken out as laser light 13a and directly incident on the input coupler M5 of the bow tie ring resonator 26. Then, the laser light extracted from the high reflection mirror M8 of the bow tie ring resonator 26 is sequentially reflected by the folding mirrors 33 and 34 and then incident on the input coupler M1 of the bow tie ring resonator 10, and the bow tie ring resonance. The laser light extracted from the high reflection mirror M10 of the device 27 is sequentially reflected by the folding mirrors 35 and 36 and then incident on the input coupler M3 of the bow tie ring resonator 10. The folding mirror 35 is placed on the actuator 37.

In this optical system, the laser beams 13a and 13b obtained by branching the laser beam 13 emitted from the seed laser 12 are respectively made incident on the input couplers M5 and M9 of the bow-tie ring resonators 26 and 27, respectively. The wavelength can be converted to ¼ wavelength by converting the wavelength to / 2 wavelength and making these wavelength-converted laser lights enter the input couplers M1 and M3 of the bow-tie ring resonator 10 in the subsequent stage. By doing so, it is possible to extract from the long-wavelength laser beam 13 an extremely short-wavelength laser beam having a quarter wavelength.
According to the seventh embodiment, a high-performance optical system capable of performing highly efficient wavelength conversion can be realized.

Next explained is a ring resonator according to the eighth embodiment of the invention. In this ring resonator, three input couplers are used.
FIG. 8 shows this ring resonator.
As shown in FIG. 8, this ring resonator is composed of four mirrors, three of which are input couplers M1, M2 ', M3 and the remaining one is a high reflection mirror M4. These input couplers M1, M2 ′, and M3 have a predetermined transmittance, which will be described later, through which laser light can be taken into the resonator from the outside. It is assumed that there is a loss in the resonator, and here, the high reflection mirror M4 not constituted by the input coupler has a predetermined transmittance, and the light stored inside the resonator leaks to the outside from the high reflection mirror M4. And In other words, output laser light is extracted from the high reflection mirror M4 to the outside.

これをもとに、２本のレーザー光を用いる場合と同様に適当な洞察により、以下の解がインピーダンスマッチングを満たすことが確認できる。

この式は、α＝０もしくはβ＝０とおくことで、２本のレーザー光を用いる第１の実施形態の場合と一致することが簡単に確認できる。この場合においても、第２の実施形態において導いた（式１１）と同様に共振器損失が小さい場合について

が導ける。さらに、同様に三つのインプットカプラーＭ１、Ｍ２´、Ｍ３の透過率の合計は、次式のように共振器内部の合計損失にほぼ等しくなる。

Assume that the amplitude reflectance and amplitude transmittance of the input coupler M2 ′ are r ₂ and t ₂ , and the intensity reflectance and intensity transmittance are R ₂ and T ₂ , respectively. The electric field of the laser beam incident on the input coupler M2 ′ is E _in2 , the electric field reflected by the input coupler _M2 ′ is E _out2 , and the electric field in the resonator is E _circ2 .
Similar to the first embodiment, assuming that all laser beams coupled to the resonator have the same frequency, the electric field amplitude is expressed as follows.

Based on this, it can be confirmed that the following solution satisfies the impedance matching by appropriate insight as in the case of using two laser beams.

By setting this equation to α = 0 or β = 0, it can be easily confirmed that it matches the case of the first embodiment using two laser beams. Even in this case, as in the case of (Equation 11) derived in the second embodiment, the resonator loss is small.

Can guide. Further, similarly, the total transmittance of the three input couplers M1, M2 ′, and M3 is substantially equal to the total loss inside the resonator as shown in the following equation.

From (Equation 18) and (Equation 19), it can be seen that the impedance matching condition is a value that distributes the transmittance equal to the resonator loss according to the power ratios incident on the input couplers M1, M2 ′, and M3. In particular, when the intensity of each laser beam incident on the resonator is equal, the optimum design is to make the transmittance of each of the input couplers M1, M2 ′, M3 equal as follows.

FIG. 9 shows a basic configuration of an optical system according to the ninth embodiment of the present invention.
As shown in FIG. 9, in this optical system, a ring resonator 40 is constituted by three input couplers M1, M2 ′, M3 and three high reflection mirrors M41, M42, M43. In this case, the high reflection mirrors M41, M42, and M43 correspond to the high reflection mirror M4 of the ring resonator according to the eighth embodiment, and the ring resonator 40 is substantially the same as the ring resonator according to the eighth embodiment. belongs to. The high reflection mirror M41 is placed on the actuator 41. This optical system has a single seed laser 12. Then, after the laser beam 13 emitted from the seed laser 12 is amplified by the amplification module 20, a part thereof is taken out as a laser beam 13 c by the partial mirror 21 and reflected by the folding mirror 17 placed on the actuator 16. The remainder is taken out as laser light 13a and is directly incident on the input coupler M1. After the laser beam 13c reflected by the folding mirror 17 is amplified by the amplification module 18, a part of the laser beam 13c is taken out by the partial mirror 42 as the laser beam 13d, reflected by the folding mirror 44 placed on the actuator 43, and further amplified. After being amplified by the module 45, the light is incident on the input coupler M2 ′. The laser beam 13b transmitted through the partial mirror 42 is incident on the input coupler M3 as it is.
In this optical system, one of the high reflection mirrors M42 and M43 has a predetermined transmittance, and the other has a transmittance of zero, so that the output laser light is emitted from the high reflection mirror having the predetermined transmittance to the outside. It is taken out.

In the second to seventh and ninth embodiments described above, the case where the laser light emitted from one seed laser 12 is separated and amplified and coupled to the same resonator has been described. A light source may be used, and laser light emitted from these laser light sources may be coupled to the same resonator. Then, next, an optical system according to a tenth embodiment of the present invention suitable for this case will be described.
That is, in the optical system according to the tenth embodiment, as shown in FIG. 10, the bow tie ring resonator 10 is constituted by two input couplers M1 and M3 and two high reflection mirrors M2 and M4. ing. In this case, the nonlinear optical crystal 11 is arranged on the optical path in the bow tie ring resonator 10. The configuration of the bow tie ring resonator 10 is the same as that of the bow tie ring resonator according to the first embodiment except that the nonlinear optical crystal 11 is disposed inside. This optical system has a single seed laser 12, an isolator 51, and a slave laser 52. Then, the laser beam 13 emitted from the seed laser 12 passes through the isolator 51 and enters the input coupler M1. On the other hand, the laser beam 53 emitted from the slave laser 52 enters the input coupler M3. In this case, the laser beam 54 in the reverse circulation direction caused by reflection from the end face of the nonlinear optical crystal 11 inside the bow tie ring resonator 10 leaks out of the bow tie ring resonator 10 and is slave laser 52. As a result of the light injection, frequency synchronization with the seed laser 12 occurs (see, for example, Patent Document 1).

Next, an eleventh embodiment of the present invention will be described.
In the eleventh embodiment, a more specific configuration of the optical system according to the second embodiment will be described.
FIG. 11 shows this embodied optical system.
As shown in FIG. 11, in this optical system, as the seed laser 12, for example, a laser having an oscillation wavelength of 780 nm and an output of 12 mW is used. As the half mirror 14, for example, a mirror having a transmittance of 50% with respect to light having a wavelength of 780 nm is used. For example, a piezo actuator is used as the actuator 16. As the folding mirror 17, for example, a high reflection mirror for light having a wavelength of 780 nm is used. As the amplification modules 15 and 18, for example, a taper amplifier having an output of 1 W is used. As the input couplers M1 and M3, for example, those having a transmittance of 0.5% with respect to light having a wavelength of 780 nm are used. As the high reflection mirrors M2 and M4, for example, high reflection mirrors for light having a wavelength of 780 nm are used. As the nonlinear optical crystal 11, for example, an LBO crystal that is an SHG crystal is used.

  The laser beam 13 a divided by the half mirror 14 is sent to the amplification module 15 via an electro-optic phase modulator (EOM) 60. Laser light emitted to the outside from the input couplers M1 and M3 is detected by photodetectors 61 and 62, respectively. The signal obtained from the photodetector 61 is mixed in the RF mixer 63 with the signal from the transmitter 64 whose oscillation frequency is 10 MHz. The output signal of the RF mixer 63 is sent to the actuator 19 composed of a piezo actuator by the feedback circuit 65, and the actuator 19 is controlled. On the other hand, a signal obtained from the photodetector 62 is sent to the actuator 16 formed of a piezo actuator by the feedback circuit 66, and the actuator 16 is controlled.

Next explained is an optical system according to the twelfth embodiment of the invention.
In the twelfth embodiment, an optical system capable of obtaining a laser beam having a wavelength of 198 nm using a laser light source having an oscillation wavelength of 1064 nm and a laser light source having an oscillation wavelength of 780 nm will be described.
FIG. 12 shows this optical system.
As shown in FIG. 12, this optical system includes a second harmonic generation resonator 71, a fourth harmonic generation resonator 72, a sum frequency generation 266nm resonator 73, and a sum frequency generation 780nm resonator. 74, and a laser beam 75 having a wavelength of 198 nm using a laser beam having a wavelength of 266 nm emitted from the 266 nm resonator 73 for generating the sum frequency and a laser beam having a wavelength of 780 nm emitted from the resonator 780 nm for generating the sum frequency. Is generated.

  A 1064 nm non-planar ring oscillator (NPRO) 100 is used as a laser light source with an oscillation wavelength of 1064 nm. Laser light emitted from the 1064 nm non-planar ring oscillator 100 is amplified by a fiber amplifier 200 (excitation module is omitted) via an electro-optic phase modulator 2000, and then sequentially reflected by folding mirrors 3000, 3001, and 3002. It enters the second harmonic generation resonator 71. The second harmonic generation resonator 71 includes a 1064 nm input coupler (T = 5%) 1000, a dichroic mirror (1064 nm high reflection, 532 nm high transmission) 1001, and two 1064 nm high reflection mirrors 1002 and 1003. The LBO crystal 300 is disposed inside. The LBO crystal 300 is converted into a wavelength of ½ wavelength, that is, a wavelength of 532 nm by passing a laser beam. The electro-optic phase modulator 2000 is supplied with a signal from the RF generator 2001 and is controlled. A signal from the RF generator 2001 is sent to the RF mixer 2002 and mixed with a signal obtained by detecting the laser beam emitted from the 1064 nm input coupler 1000 by the photodetector 2003. The output signal of the RF mixer 2002 is sent via a feedback circuit 2005 to a PZT actuator 2004 on which a 1064 nm high reflection mirror 1003 is mounted, and the PZT actuator 2004 is controlled.

  Laser light having a wavelength of 532 nm extracted outside from the dichroic mirror 1001 of the second harmonic generation resonator 71 passes through the electro-optic phase modulator 2010 and is sequentially reflected by the folding mirrors 3003 and 3004 to be the fourth harmonic. The light enters the wave generating resonator 72. The fourth harmonic generation resonator 72 includes a 532 nm input coupler (T = 2%) 1100, a dichroic mirror (532 nm high reflection, 266 nm high transmission) 1101, and two 532 nm high reflection mirrors 1102, 1103. The BBO crystal 310 is disposed inside. When the BBO crystal 310 passes through the laser beam, the wavelength is converted to ½ wavelength, that is, 266 nm. A signal is sent from the RF generator 2011 to the electro-optic phase modulator 2010 to be controlled. A signal from the RF generator 2011 is sent to the RF mixer 2012 and mixed with a signal obtained by detecting the laser beam emitted from the 532 nm input coupler 1100 with the photodetector 2013. The output signal of the RF mixer 2012 is sent to the PZT actuator 2014 on which the 532 nm high reflection mirror 1103 is mounted via the feedback circuit 2015, and the PZT actuator 2014 is controlled.

  Laser light with a wavelength of 266 nm extracted from the dichroic mirror 1101 of the fourth harmonic generation resonator 72 is sequentially reflected by the folding mirrors 3005 and 3006 and enters the sum frequency generation 266 nm resonator 73. The 266 nm resonator 73 for generating the sum frequency is composed of a 266 nm input coupler (T = 2%) 1200 and three 266 nm high reflection mirrors 1201, 1202 and 1203. A signal is also sent from the RF generator 2021 to the electro-optic phase modulator 2010 for control. A signal from the RF generator 2021 is sent to the RF mixer 2022 and mixed with a signal obtained by detecting the laser beam emitted from the 266 nm input coupler 1200 by the photodetector 2023. The output signal of the RF mixer 2022 is sent to the PZT actuator 2024 on which the 266 nm high reflection mirror 1202 is mounted via the feedback circuit 2025, and the PZT actuator 2024 is controlled.

On the other hand, as a laser light source with an oscillation wavelength of 780 nm, for example, a Littman diffraction grating feedback external resonator semiconductor laser 400 is used. The laser light emitted from the Littman diffraction grating feedback external resonator semiconductor laser 400 passes through the electro-optic phase modulator 2200, is sequentially reflected by the folding mirrors 3100 and 3101, is amplified by the semiconductor taper amplifier 421, and is a partial reflector. A part is extracted at (T = 2%) 3106, reflected by the folding mirror 3103, and incident on the 780 nm resonator 74 for generating the sum frequency. The 780 nm resonator 74 for generating the sum frequency is composed of a 780 nm input coupler (T = 1%) 1300, two 780 nm high reflection mirrors 1301, 1302 and a 780 nm input coupler (T = 0.5%) 1304. . A signal is sent from the RF generator 2201 to the electro-optic phase modulator 2200 for control. A signal from the RF generator 2201 is sent to the RF mixer 2202 and mixed with a signal obtained by detecting the laser beam emitted from the 780 nm input coupler 1300 with the photodetector 2203. The output signal of the RF mixer 2202 is sent to the PZT actuator 2204 on which the 780 nm high reflection mirror 1302 is mounted via the feedback circuit 2205, and the PZT actuator 2204 is controlled. The laser light transmitted through the partial reflector 3106 is sequentially reflected by the folding mirrors 3110 and 3111, amplified by the semiconductor taper amplifier 422, reflected by the folding mirror 3112, and incident on the 780 nm input coupler (T = 0.5%) 1304. To do. A signal obtained by detecting the laser beam emitted from the 780 nm input coupler 1304 to the outside by the photodetector 2213 is sent to the PZT actuator 2214 on which the 780 nm high reflection mirror 3112 is mounted via the feedback circuit 2215. The PZT actuator 2214 is controlled.
In addition, illustration and description of a condensing lens including a relay lens, a collimator lens, a mode matching lens, and the like are omitted.

  The laser beam having a wavelength of 266 nm generated inside the sum frequency generating 266 nm resonator 73 and the laser beam having a wavelength of 780 nm generated inside the sum frequency generating 780 nm resonator 74 are simultaneously formed on the Brewster cut BBO crystal 320. Incident light is extracted, and laser light having an angular frequency that is the sum of the angular frequencies of these laser lights, that is, laser light having a wavelength of 198 nm is extracted (for example, see Patent Document 2).

Next, an optical system according to a thirteenth embodiment of the present invention is described.
In the thirteenth embodiment, an optical system capable of obtaining laser light having a wavelength of 198 nm using a laser light source having an oscillation wavelength of 1064 nm and a laser light source having an oscillation wavelength of 1.56 μm (1560 nm) will be described.
FIG. 13 shows this optical system.
As shown in FIG. 13, in this optical system, a 1.56 μm Bragg grating type single frequency fiber laser 401 is used as a laser light source having an oscillation wavelength of 1.56 μm (1560 nm). The laser light emitted from the 1.56 μm Bragg grating type single frequency fiber laser 401 is amplified by a 1.56 μm fiber laser 411 (excitation module is omitted) through an in-line phase modulator 402, and a partial reflector (T = 2%) 3106 is partly taken out, reflected by the folding mirror 3103, passed through the polarization-reversed LN crystal 330, converted to a half wavelength, that is, 780 nm, sequentially reflected by the folding mirrors 3104 and 3105, and sum frequency The light enters the 780 nm input coupler 1300 of the generation 780 nm resonator 74. The laser light transmitted through the partial reflector 3106 is amplified by a 1.56 μm fiber laser 412 (excitation module is omitted), is sequentially reflected by folding mirrors 3110 and 3111, passes through the polarization-reversed LN crystal 331, and has a half wavelength, that is, The wavelength is converted to 780 nm, is sequentially reflected by the folding mirrors 3113, 3114, and 3112 and enters the 780 nm input coupler 1304 of the 780 nm resonator 74 for generating the sum frequency.
Other than the above are the same as in the twelfth embodiment.

Next, an optical system according to a fourteenth embodiment of the present invention is described.
In the fourteenth embodiment, an optical system capable of obtaining laser light having a wavelength of 198 nm using a laser light source having an oscillation wavelength of 1064 nm and a laser light source having an oscillation wavelength of 1.56 μm (1560 nm) will be described.
FIG. 14 shows this optical system.
As shown in FIG. 14, in this optical system, a part of the laser light having a wavelength of 1064 nm emitted from the fiber amplifier 200 is extracted by a partial reflector (T = 2%) 3007, and the rest is directed to the folding mirror 3001. . A part of the laser light that has passed through the partial reflector 3007 passes through the electro-optic phase modulator 2100, is amplified by the fiber amplifier 201 (excitation module is omitted), and then is sequentially reflected by the folding mirrors 3001, 3011, and 3012. It enters the second harmonic generation resonator 81. The second harmonic generation resonator 81 includes a 1064 nm input coupler (T = 5%) 1010, a dichroic mirror (1064 nm high reflection, 532 nm high transmission) 1011 and two 1064 nm high reflection mirrors 1012, 1013. The LBO crystal 301 is disposed inside. The LBO crystal 301 is wavelength-converted to a half wavelength, that is, a wavelength of 532 nm by passing a laser beam having a wavelength of 1064 nm. A signal is sent from the RF generator 2101 to the electro-optic phase modulator 2100 for control. The signal from the RF generator 2101 is sent to the RF mixer 2102 and mixed with the signal obtained by detecting the laser beam emitted from the 1064 nm input coupler 1010 with the photodetector 2103. The output signal of the RF mixer 2102 is sent via a feedback circuit 2105 to a PZT actuator 2104 on which a 1064 nm high reflection mirror 1013 is mounted, and the PZT actuator 2104 is controlled.

  The laser beam having a wavelength of 532 nm extracted outside from the dichroic mirror 1011 of the second harmonic generation resonator 81 passes through the electro-optic phase modulator 2110, and is sequentially reflected by the folding mirrors 3013 and 3014 to be the fourth harmonic. The light enters the wave generating resonator 82. The fourth harmonic generation resonator 82 includes a 532 nm input coupler (T = 2%) 1110, a dichroic mirror (532 nm high reflection, 266 nm high transmission) 1111, and two 532 nm high reflection mirrors 1112, 1113. The BBO crystal 311 is arranged inside. The BBO crystal 311 is wavelength-converted to a half wavelength, that is, a wavelength of 266 nm by passing a laser beam having a wavelength of 532 nm.

Laser light having a wavelength of 266 nm extracted from the dichroic mirror 1111 of the second harmonic generation resonator 82 is sequentially reflected by the return mirrors 3015, 3016, and 3017 and is incident on the 266 nm resonator 73 for generating the sum frequency. In this case, the 266 nm resonator 73 for generating the sum frequency is composed of two 266 nm high reflection mirrors 1201 and 1202 and a 266 nm input coupler (T = 1%) 1204 and 1205. A signal obtained by detecting the laser beam emitted from the 780 nm input coupler 1204 of the 266 nm resonator 73 for generating the sum frequency by the photodetector 2123 passes through the feedback circuit 2125 and passes through the high reflection mirror 3017 at 780 nm. The PZT actuator 2124 is sent to the PZT actuator 2124, and the PZT actuator 2124 is controlled.
The sum frequency generation 780 nm resonator 74 is composed of two 780 nm high reflection mirrors 1301 and 1302 and a 780 nm input coupler (T = 0.5%) 1304 and 1305.
Other than the above are the same as in the twelfth and thirteenth embodiments.

  The optical systems according to the second to seventh and ninth to fourteenth embodiments described above are suitable for use as light sources for various devices. As an example of such an apparatus, there is a scattered foreign substance inspection apparatus (for details, see, for example, Patent Document 3). This scattered foreign substance inspection apparatus is an apparatus for finding minute foreign substances on a semiconductor wafer (a wafer subjected to planarization processing), and is generally used in semiconductor factories. Information such as the position of the foreign matter on the semiconductor wafer is obtained by scattering the laser beam applied to the foreign matter. The size of the foreign matter is reduced with the progress of semiconductor technology (circuit pattern miniaturization technology), and is smaller than the wavelength of the laser light used, so that scattering by the foreign matter becomes Rayleigh scattering. In order to increase the scattering intensity of a laser beam by a foreign substance, it is currently required to prepare a laser light source with a very high power or a short wavelength laser capable of obtaining a sufficient scattering intensity. At present, laser light with a wavelength of 355 nm or 266 nm has begun to be used in the most advanced devices, but it is considered that a laser light source with a wavelength of 198 nm will be used in the next generation at the development level of semiconductor devices. The optical systems according to the above twelfth to fourteenth embodiments are suitable as a laser light source having a wavelength of 198 nm for such a scattered particle inspection apparatus.

  On the other hand, as an example of an inspection apparatus using an optical microscope for a semiconductor wafer with a circuit pattern, there is one called a review station (see, for example, Patent Document 3 for details of this inspection apparatus). This inspection apparatus copes with the progress of miniaturization of circuit patterns by shortening the wavelength of the microscope light source. Similar to the above-described scattered foreign substance inspection apparatus, a laser light source having a wavelength of 198 nm is desired as a next-generation microscope light source. It is also suitable as a laser light source having a wavelength of 198 nm.

As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.
For example, the numerical values, configurations, constituent elements, and the like given in the above-described embodiments are merely examples, and different numerical values, configurations, constituent elements, and the like may be used as necessary.
Specifically, in the first to fourteenth embodiments described above, the resonator using two or three input couplers and the optical system using the resonator have been described. The present invention can be similarly applied to a resonator using this input coupler and an optical system using the resonator.
In the twelfth embodiment described above, a Littrow diffraction grating feedback external resonator semiconductor laser, a DFB semiconductor laser, or the like may be used instead of the Littman diffraction grating feedback external resonator semiconductor laser 400.
The same technical idea as that of the present invention can be generally established for electromagnetic waves of various wavelength bands including laser light.

1 is a schematic diagram showing a bow tie ring resonator according to a first embodiment of the present invention. It is a basic diagram which shows the optical system by the 2nd Embodiment of this invention. It is a basic diagram which shows the optical system by the 3rd Embodiment of this invention. It is a basic diagram which shows the optical system by the 4th Embodiment of this invention. It is a basic diagram which shows the optical system by the 5th Embodiment of this invention. It is a basic diagram which shows the optical system by the 6th Embodiment of this invention. It is a basic diagram which shows the optical system by 7th Embodiment of this invention. It is an approximate line figure showing a bow tie type ring resonator by an 8th embodiment of this invention. It is a basic diagram which shows the optical system by 9th Embodiment of this invention. It is a basic diagram which shows the optical system by 10th Embodiment of this invention. It is a basic diagram which shows the optical system by 11th Embodiment of this invention. It is a basic diagram which shows the optical system by 12th Embodiment of this invention. It is a basic diagram which shows the optical system by 13th Embodiment of this invention. It is a basic diagram which shows the optical system by 14th Embodiment of this invention. It is a basic diagram which shows the 1st example of the conventional optical system. It is a basic diagram which shows the 2nd example of the conventional optical system. It is a basic diagram which shows the 3rd example of the conventional optical system. It is a basic diagram which shows the 4th example of the conventional optical system. It is a basic diagram which shows the 5th example of the conventional optical system. It is a basic diagram which shows the 6th example of the conventional optical system.

Explanation of symbols

M1, M3, M2 ′, 1204, 1205, 1300, 1304, 1305... Input coupler, M2, M3, 1201, 1202, 1301, 1302... High reflection mirror, 10... Bow-tie ring resonator, 11. 12 ... Seed laser, 13, 13a, 13b, 13c, 13d ... Laser light

Claims (18)

With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively separated from the first laser beam of the resonator. To the input coupler and the second input coupler,
The first laser beam and the second laser beam, which are coupled to the resonator and circulate in the resonator, are incident on the first input coupler and the second input coupler from the outside, respectively. Equal to the frequency of
The total transmittance of the first input coupler and the second input coupler is substantially equal to the total loss inside the resonator, and the transmittance of the first input coupler is the power of the first laser beam. An optical system in which the transmittance of the second input coupler is a value proportional to the power of the second laser beam. The power of the first laser beam and the power of the second laser beam are substantially equal to each other, and the transmittance of the first input coupler and the transmittance of the second input coupler are approximately equal to each other. The optical system according to 1. The laser light emitted from the seed laser is divided into the first laser light and the second laser light, and the first input coupler is amplified after the first laser light and the second laser light are respectively amplified. The optical system of claim 1 coupled to the second input coupler. After amplifying the laser light emitted from the seed laser, it is divided into the first laser light and the second laser light, and after amplifying one of the first laser light and the second laser light 2. The optical system according to claim 1, wherein the first laser beam and the second laser beam are coupled to the first input coupler and the second input coupler. The laser light emitted from the seed laser is divided into the first laser light and the second laser light, and the first input after the wavelength conversion of the first laser light and the second laser light, respectively. 2. The optical system of claim 1 coupled to a coupler and the second input coupler. The optical system according to claim 1, wherein wavelength conversion is performed by arranging a nonlinear optical crystal in the resonator. With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. 3 laser beams are respectively coupled to the first input coupler, the second input coupler, and the third input coupler,
The first laser beam that is coupled to the resonator and circulates in the resonator has an external frequency incident on the first input coupler, the second input coupler, and the third input coupler, respectively. , Equal to the frequency of the second laser light and the third laser light,
The total transmittance of the first input coupler, the second input coupler, and the third input coupler is approximately equal to the total loss inside the resonator, and the transmittance of the first input coupler is The value is proportional to the power of the first laser beam, the transmittance of the second input coupler is a value proportional to the power of the second laser beam, and the transmittance of the third input coupler is the value described above. An optical system having a value proportional to the power of the third laser beam. The power of the first laser light, the power of the second laser light, and the power of the third laser light are substantially equal to each other, and the transmittance of the first input coupler and the power of the second input coupler are 8. The optical system according to claim 7, wherein the transmittance and the transmittance of the third input coupler are substantially equal to each other. The laser light emitted from the seed laser is divided into the first laser light, the second laser light, and the third laser light, and the first laser light, the second laser light, and the third laser light. 8. The optical system according to claim 7, wherein each of the first and second input couplers is coupled to the first input coupler, the second input coupler, and the third input coupler after being amplified. After amplifying the laser light emitted from the seed laser, the laser light is divided into the first laser light, the second laser light, and the third laser light, and the first laser light, the second laser light, and After amplifying all, two or one of the third laser beams, the first laser beam, the second laser beam, and the third laser beam are converted into the first input coupler, 8. The optical system of claim 7 coupled to two input couplers and the third input coupler. The laser light emitted from the seed laser is divided into the first laser light, the second laser light, and the third laser light, and the first laser light, the second laser light, and the third laser light. 8. The optical system according to claim 7, wherein the laser beams are respectively wavelength-converted and then coupled to the first input coupler, the second input coupler, and the third input coupler. With one seed laser,
a resonator composed of n (n is an integer of 2 or more) or more mirrors, and n mirrors of the plurality of mirrors are composed of n input couplers;
Dividing the laser light emitted from the seed laser into n laser beams having the same frequency, and coupling the n laser beams to the n input couplers,
The frequency of the light coupled to the resonator and circulating inside the resonator is equal to the frequency of the n laser beams incident on the n input couplers from the outside,
The total transmittance of the n input couplers is approximately equal to the total loss inside the resonator, and the transmittance of each of the n input couplers is proportional to the power of each of the n laser beams. The optical system that is value. With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively divided into the first input coupler and Coupled to the second input coupler,
The first laser beam and the second laser beam, which are coupled to the resonator and circulate in the resonator, are incident on the first input coupler and the second input coupler from the outside, respectively. Equal to the frequency of
The total transmittance of the first input coupler and the second input coupler is substantially equal to the total loss inside the resonator, and the transmittance of the first input coupler is the power of the first laser beam. An optical system in which the transmittance of the second input coupler is a value proportional to the power of the second laser beam.
Inspection device using as a light source. With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively divided into the first input coupler and Coupled to the second input coupler,
The first laser beam and the second laser beam, which are coupled to the resonator and circulate in the resonator, are incident on the first input coupler and the second input coupler from the outside, respectively. Equal to the frequency of
The total transmittance of the first input coupler and the second input coupler is substantially equal to the total loss inside the resonator, and the transmittance of the first input coupler is the power of the first laser beam. An optical system in which the transmittance of the second input coupler is a value proportional to the power of the second laser beam.
The processing device using as a light source. With one seed laser,
A plurality of mirrors, and two of the plurality of mirrors have a first input coupler and a second input coupler, and a resonator.
The laser beam emitted from the seed laser is divided into a first laser beam and a second laser beam having the same frequency, and the first laser beam and the second laser beam are respectively divided into the first input coupler and Coupled to the second input coupler,
The frequency of the light that is coupled to the resonator and circulates inside the resonator is that of the first laser light and the second laser light incident on the first input coupler and the second input coupler from the outside, respectively. Equal to the frequency,
The total transmittance of the first input coupler and the second input coupler is substantially equal to the total loss inside the resonator, and the transmittance of the first input coupler is the power of the first laser beam. An optical system in which the transmittance of the second input coupler is a value proportional to the power of the second laser beam.
Measuring device using as a light source. With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. 3 laser beams are respectively coupled to the first input coupler, the second input coupler, and the third input coupler,
The first laser beam that is coupled to the resonator and circulates in the resonator has an external frequency incident on the first input coupler, the second input coupler, and the third input coupler, respectively. , Equal to the frequency of the second laser light and the third laser light,
The total transmittance of the first input coupler, the second input coupler, and the third input coupler is approximately equal to the total loss inside the resonator, and the transmittance of the first input coupler is The value is proportional to the power of the first laser beam, the transmittance of the second input coupler is a value proportional to the power of the second laser beam, and the transmittance of the third input coupler is the value described above. An optical system whose value is proportional to the power of the third laser beam
Inspection device using as a light source. With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. 3 laser beams are respectively coupled to the first input coupler, the second input coupler, and the third input coupler,
The first laser beam that is coupled to the resonator and circulates in the resonator has an external frequency incident on the first input coupler, the second input coupler, and the third input coupler, respectively. , Equal to the frequency of the second laser light and the third laser light,
The total transmittance of the first input coupler, the second input coupler, and the third input coupler is approximately equal to the total loss inside the resonator, and the transmittance of the first input coupler is The value is proportional to the power of the first laser beam, the transmittance of the second input coupler is a value proportional to the power of the second laser beam, and the transmittance of the third input coupler is the value described above. An optical system whose value is proportional to the power of the third laser beam
The processing device using as a light source. With one seed laser,
A resonator including three or more mirrors, and three of the plurality of mirrors including a first input coupler, a second input coupler, and a third input coupler. And
The laser light emitted from the seed laser is divided into a first laser light, a second laser light, and a third laser light having the same frequency, and the first laser light, the second laser light, and the first laser light. 3 laser beams are respectively coupled to the first input coupler, the second input coupler, and the third input coupler,
The first laser beam that is coupled to the resonator and circulates in the resonator has an external frequency incident on the first input coupler, the second input coupler, and the third input coupler, respectively. , Equal to the frequency of the second laser light and the third laser light,
The total transmittance of the first input coupler, the second input coupler, and the third input coupler is approximately equal to the total loss inside the resonator, and the transmittance of the first input coupler is The value is proportional to the power of the first laser beam, the transmittance of the second input coupler is a value proportional to the power of the second laser beam, and the transmittance of the third input coupler is the value described above. An optical system whose value is proportional to the power of the third laser beam
Measuring device using as a light source.

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