JPH0228980A - Laser light source - Google Patents

Abstract

PURPOSE:To improve efficiency at a time when the sum-frequency laser beams and/or difference-frequency laser beams of first and second laser beams are generated remarkably by arranging a nonlinear type optical crystal element into the resonator of first laser beams while satisfying the conditions of external resonance to second laser beams by the resonator. CONSTITUTION:Laser beams L4 for converting a wavelength emitted from a second semiconductor laser 12 for converting the wavelength are projected to a beam splitter 11 through an objective 13, and a nonlinear type optical crystal element 7 is selected at a specified azimuth phi=68-73[deg] to the oscillation laser beams L2 of an Nd:YAG laser 6 projected and the laser beams L4 for converting the wavelength emitted from the semiconductor laser 12 for converting the wavelength. Accordingly, the light intensity of the second laser beams L4 projected to the nonlinear type optical crystal element 7 can be increased remarkably, thus acquiring sum-frequency laser beams L5 and differential-frequency laser beams with high efficiency.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Overview of the invention C. Prior art (Fig. 13) D. Problem to be solved by the invention (Fig. 13) E. Means for solving the problem (Fig. 1) 2. Effect ( (Figure 1) G Embodiment (Figures 1 to 12) H Effects of the Invention A Industrial Application Field The present invention relates to a laser light source, for example, a laser light source that efficiently generates short wavelength visible light. It is suitable for application.

B Summary of the Invention The present invention provides a laser light source that generates a sum frequency laser beam and/or a difference frequency laser beam of first and second laser beams by phase matching of the nonlinear optical crystal element. The light intensity of the second laser beam incident on the nonlinear optical crystal element can be reduced by placing the laser beam inside the resonator and making the resonator satisfy the external resonance conditions for the second laser beam. It is thus possible to generate a sum frequency laser beam and/or a difference frequency laser beam with significantly higher efficiency than in the past.

C. Prior Art Conventionally, this type of laser light source combines a first laser beam obtained from a solid-state laser and a second laser beam obtained from a semiconductor laser by phase matching in a nonlinear optical crystal element. A system has been proposed in which a sum frequency light component obtained from a nonlinear optical crystal element is emitted as an output laser light (Appl, Ph.
ys, Lett, 52(2), 11 January
198885 pages).

That is, as shown in FIG. 13, this laser light source 1 is first emitted from a semiconductor laser 2 and has a wavelength λ1 of 804 (n
The first laser beam L1 consisting of
Inside the AV, for example, Nd: Y AG (neodya
+iua+:yttrium aluminum ga
rnet) is focused on a solid-state laser 6.

As a result, the Nd:YAG laser 6 is excited to emit a second laser beam L having a wavelength λ2 of 1060 (nm).
2, and this oscillated laser light Lt resonates inside the resonator CAV.

Here, inside the resonator CAV, the first mirror 4 and Nd:
For example, KTP (KTi
A nonlinear optical crystal element 7 consisting of OP 04) is arranged, and due to the phase matching of this KTPT, the sum frequency light of the first laser light and the oscillation laser light L2 becomes A third laser beam L3 having a wavelength λ of 457 nm is generated, and is transmitted through the second mirror 5 and output.

D Problems to be Solved by the Invention By the way, in the laser light source 1 having such a configuration, the KTP
7 is arranged inside the resonator CAM of the Nd:YAG laser 6, the oscillation laser beam L2 passes through KTP7 every time it goes back and forth inside the resonator CAV, and as a result, the oscillation laser beam L2 is phase-matched by KTP7. Sufficient light density (ie, light intensity) can be obtained as the light L2.

However, on the other hand, the first laser beam L1 emitted from the semiconductor laser 2 passes through the KTP 7 once and then passes through the N
d: Y A G laser 6 is excited and most of the Nd: Y
The light is absorbed by the AG laser 6, and as a result, sufficient light density (that is, light intensity) cannot be obtained as the first laser light L1 to be phase matched by the KTP7.

In practice, the first laser beam and the oscillation laser beam L2 are
The generation efficiency when phase matching is performed at TP7 to obtain the third laser beam consisting of sum frequency light is as follows: The light intensity of the oscillation laser beam Lz, the first and third laser beams, and L3 is
, ll and ■, it is given by the following equation, I, ccdt I+ It (d is a nonlinear constant) (2).

Therefore, even if sufficient light intensity is obtained as the oscillation laser light L2, if sufficient light intensity is not obtained as the first laser light LI, efficient (third laser light) cannot be obtained,
In practice, due to the problem of the output limit of the semiconductor laser 2, there was a problem in that the output power of the third laser beam could only be about 20 [μ-].

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a laser light source that can obtain sum frequency laser light with significantly higher efficiency than conventional ones.

Means for Solving Problem E To solve this problem, in the present invention, the first and second signals obtained from the first and second lasers 6 and 12 are Laser light L
In the laser light source 10 that generates sum frequency laser light and/or difference frequency laser light of 2 and L4, the nonlinear optical crystal element 7 is placed inside the resonator CAM of the first laser light Lt obtained from the first laser 6. At the same time, the resonator CAV is made to satisfy external resonance conditions for the second laser beam L4 obtained from the second laser 12.

The F-action nonlinear optical crystal element 7 is disposed inside the resonator CAV of the first laser beam Lx obtained from the first laser 6, and the resonator CAV is arranged inside the resonator CAV of the second laser beam Lx obtained from the second laser 12. By making L4 satisfy the external resonance condition, it is possible to significantly increase the light intensity of the second laser beam L4 incident on the nonlinear optical crystal element 7, thereby achieving high efficiency. Sum frequency laser light and/or difference frequency laser light can be obtained.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. 13 are given the same reference numerals, 10 indicates a laser light source as a whole, and the first semiconductor laser 2 is used to excite the Nd:YAG laser 6. .

In this laser light source 10, excitation laser light emitted from the excitation semiconductor laser 2.

However, a polarizing beam splitter 11 is inserted in the optical path leading to the resonator CAV via the objective lens 3.

This beam splitter 11 includes a wavelength conversion laser beam L4 emitted from a second semiconductor laser 12 for wavelength conversion.
is incident through the objective lens 13, and thus the wavelength conversion laser beam L4 is bent by the beam splitter 11 in the traveling direction of the optical path of the excitation laser beam LL, so that it enters the KTPT inside the resonator CAV. is being done.

The wavelength λ8 of the excitation laser beam is N as shown in FIG.
d: Considering the wavelength absorption characteristics of the YAG laser 6,
In particular, the wavelength λ = 808 (nm) with a high wavelength absorption coefficient was selected, so that it was efficiently absorbed by the Nd:YAG laser 6 and effectively excited the Nd:YAG laser 6. There is.

On the other hand, the wavelength λ4 of the wavelength conversion laser beam L4 is
Based on the wavelength absorption coefficient K, the wavelength λ4 = 840 (nm), for example, is selected from the wavelengths 826 to 840 [nII] that are hardly absorbed by the Nd:YAG laser 6, and thereby the first and second mirrors Even if the resonator CAV composed of 4 and 5 is used as the external resonator CAVI for the wavelength conversion laser beam L4, the wavelength conversion laser beam L4 will not be absorbed by the Nd: Y A G laser 6 and will cause external resonance. first and second mirrors 4 and 5 inside the vessel CAV 1;
It is designed so that it can be reflected and reciprocated many times.

In reality, KTP7 is composed of incident Nd, as shown in FIG.
: It is arranged to have a predetermined azimuth angle φ with respect to the oscillation laser beam L2 of the YAG laser 6 and the wavelength conversion laser beam L4 emitted from the wavelength conversion semiconductor laser 12, and in this case, the azimuth angle φ is selected to be, for example, the azimuth angle φ=68 to 73 (deg) based on the wavelength 826 to 840 (nm) of the wavelength conversion laser beam L4 shown in FIG. As described above, TYPE II phase matching is performed to obtain oscillation laser light and sum frequency laser light of the wavelength conversion laser light L4.

In equation (3), λ is the wavelength of the laser beam, n
ai is the extraordinary ray refractive index with respect to the wavelength of the laser beam Li, n
0i is laser light L! is the ordinary ray refractive index for the wavelength of .

Here, the first mirror 4 is Nd as shown in FIG.
: Excitation laser light LI that excites the YAG laser 6
It has a transmittance of almost 100% for the wavelength λ = 808 (nm) of the wavelength conversion laser beam L4, and a transmittance of several % for the wavelength λ4 = 840 (nm) of the wavelength conversion laser beam L4. : It is coated to have a reflectance of approximately 100% for the wavelength λg=1060 (nm) of the oscillation laser beam L2 obtained from the YAG laser 6.

Further, as shown in FIG. 6, the second mirror has the wavelength λ==840 (nm) of the wavelength conversion laser beam L4 and Nd:
It has a reflectance of almost 100% for the wavelength λ==1060 (nm) of the oscillation laser light L8 obtained from the YAG laser, and the wavelength λ5-470 of the sum frequency laser light LS obtained by phase matching of TYPEn. (nm) to have a transmittance of approximately 100%.

In this way, the first and second mirrors 4 and 5 are connected to the Nd:YAG laser 6 disposed inside as in the conventional case.
For the oscillation laser light obtained from the internal resonator C
In addition to configuring the AV, an external resonator CAVI is configured for the wavelength conversion laser beam L4 obtained from the external wavelength conversion semiconductor laser 12.

Note that the reflectance of the first mirror 4 with respect to the wavelength λ, =840 (nm) of the wavelength converting laser beam L4 obtained from the wavelength converting semiconductor laser 12 is denoted by R, and the reflectance of the second mirror 5 is denoted by R2. At the same time, if the internal transmittance is To, then the light intensity of the incident wavelength conversion laser beam L4 is . The ratio of the optical intensity IK+ inside the external resonator CAV1 is given by the following formula:
...... (4) It is expressed as follows. Here, the angle δ is the phase difference that occurs when the wavelength conversion laser beam L4 makes one round trip through the external resonator CAV1 having the cavity length, and this phase difference δ is expressed by the following formula, (m is an integer)... ...When the relationship expressed by (5) is satisfied, it becomes a Fabry-Perot resonance condition, and at this time, the wavelength λ of the wavelength conversion laser beam L4
4=840 (nn+) reflectance R1 of the first mirror 4, reflectance R8 of the second mirror 5, and internal transmittance T
0 as the following formula, R, = 0.9 RZ = 0.99 To "" 0.95 ...... (6) From formula (4), the incident intensity of the wavelength conversion laser beam L4 is Internal strength IKI in IXO and external resonator CAVl
The O ratio is expressed by the following formula, where I is 0. Inside the external resonator CAV 1, the light intensity IK is about 10 times the light intensity ■7° of the incident wavelength conversion laser beam L4. Laser light L for wavelength conversion
You can get 4.

Thus, as described above for equation (2), KTP7
By increasing the light intensity ■□ of the wavelength conversion laser beam L4 incident on the laser light source 10 by approximately 10 times compared to the conventional one.
As a whole, the optical intensity of the sum frequency laser beam of the wavelength conversion laser beam L4 and the oscillation laser beam Lt obtained by phase matching of TYPEn can be increased about 10 times.

Note that in order to satisfy equation (5) above, it is necessary to adjust the resonator length of the external resonator CAV1 in units of the wavelength of light, but in reality, it is necessary to adjust the resonator length of the external resonator CAV1 by the temperature change of the resonator CAV (CAVl). In order to avoid the possibility that the resonance conditions may shift, in this embodiment, by controlling the current value that drives the wavelength conversion semiconductor laser 12, the cavity length within the semiconductor laser 12 is effectively controlled to change the wavelength conversion semiconductor laser 12. Laser light L4
The wavelength of the laser beam is finely adjusted to maintain optimal resonance conditions at all times.

Further, in the case of this embodiment, the resonator length of the resonator CAV (CAVl) is set to an integral multiple of the effective cavity length of the wavelength conversion semiconductor laser 12, so that the semiconductor laser 12 oscillates in multiple modes. In this case, the resonance condition described above regarding equation (5) can be satisfied for all modes.

According to the above configuration, the oscillation laser beam L! obtained from the Nd:YAG laser 6 is generated by phase matching of TYPEn of KTP7. In the laser light source 10 configured to generate a sum frequency laser beam of the wavelength conversion laser beam L4 obtained from the wavelength conversion semiconductor laser 12, the KT
By arranging P7 inside the resonator CAV of the Nd:YAG laser 6 and making the resonator CAV satisfy the external resonance condition for the wavelength conversion laser beam L4, the Thus, it is possible to realize a laser light source 10 that can obtain sum frequency laser light with significantly high efficiency.

Furthermore, according to the above embodiment, the wavelength conversion laser beam L4
By using a semiconductor laser 12 and controlling the current value for driving this semiconductor laser 12 to effectively change the cavity length and finely adjust the wavelength of the wavelength conversion laser beam L4, Adjustment can be easily made to satisfy external resonance conditions without using a complicated mechanism or the like.

Note that in the above embodiment, Nd is used as the first laser.
: Although the case has been described in which a solid-state laser consisting of the YAG laser 6 is used, other solid-state lasers may be used instead of this, or a gas laser such as a He-Ne laser may be used. A laser with relatively high laser intensity may be used. Incidentally, in this case, the light source for excitation is not limited to the semiconductor laser 2, and other excitation means such as a flash lamp may be used.

In the above embodiment, a case was described in which KTP (KTiOP Oa) 7 was used as the nonlinear optical crystal element, but the nonlinear optical crystal element is not limited to this, and for example, BBO (β-BaB a 04) A nonlinear optical crystal element having an optical wavelength conversion function by equilocated phase matching may be used.

In the above-described embodiment, the wavelength of the wavelength conversion laser beam L4 is finely adjusted by controlling the current value for driving the wavelength conversion semiconductor laser 12, and the external part of the resonator CAV for the wavelength conversion laser beam L4 is Although the case where the resonance condition is adjusted has been described, the present invention instead of adjusting the resonance condition, for example, the first
As shown in FIG. 7, in which parts corresponding to the figures are given the same reference numerals, a piezoelectric element 20 is provided behind one mirror 5 of the resonator CAVIO, and a predetermined control voltage is applied to this piezoelectric element 20. The mirror 5 may be controlled to move in the optical axis direction indicated by arrow a, thereby varying the actual resonator length.

Further, as shown in FIG. 8, in which parts corresponding to those in FIG. By applying the voltage, the effective optical path length between the mirrors 4 and 5 of the resonator CAV20 may be variably controlled, thereby making the resonator length variable.

In the above-mentioned embodiment, when the excitation laser beam L1 and the wavelength conversion laser beam L4 are combined, the polarizing beam splitter 11 is used to combine two polarized beams that are orthogonal to each other. Instead, for example, as shown in FIG. 9, in which parts corresponding to those in FIG. 1 are given the same reference numerals,
The dichroic prism 40 may be used to synthesize the excitation laser light and the wavelength conversion laser light L4 by utilizing the difference in wavelength.

Similarly, as shown in FIG. 10, in which parts corresponding to those in FIG. It is also possible to synthesize them.

Furthermore, in addition to this, as shown in FIG. 11, in which parts corresponding to those in FIG. 1 are given the same reference numerals, the wavelength conversion laser beam L4
is incident from the second mirror 5 side, and a sum frequency laser beam is emitted,
may be taken out through the dichroic prism 40, and the same effect as in the above embodiment can be achieved using various methods.

Note that in the above embodiment, the first and second mirrors 4
The case has been described in which the nonlinear optical crystal element 7 and the solid-state laser 6 are arranged inside the resonator CAV sandwiched between As shown in FIG. 12, a predetermined mirror coding 50 (and or 5
The resonator CAV30 may be configured by performing 1).

In the above embodiment, the present invention is applied to a laser light source that can efficiently generate a sum frequency laser beam of the first and second laser beams, but the present invention is not limited to this. The present invention is also suitable for application to a laser light source that can efficiently generate a difference frequency laser beam between the first and second laser beams.

Effects of the Invention As described above, according to the present invention, the nonlinear optical crystal element is arranged inside the resonator for the first laser beam, and the resonator satisfies the external resonance condition for the second laser beam. By doing so, the light intensity of the second laser beam incident on the nonlinear optical crystal element can be significantly increased,
Thus, by phase matching the nonlinear optical crystal element, it is possible to realize a laser light source that can significantly improve efficiency in generating sum frequency laser light and/or difference frequency laser light of the first and second laser lights.

[Brief explanation of the drawing]

Figure 1 is a line diagram showing an embodiment of the present invention, Figure 2 is a characteristic curve diagram showing the wavelength absorption characteristics of the Nd:YAG laser, and Figure 3 is a line diagram for explaining phase matching of KTP. Figure 4 is a characteristic curve diagram showing the relationship between the azimuth angle and wavelength, Figures 5 and 6 are characteristic curve diagrams showing the transmission characteristics of the first and second mirrors, respectively, and Figures 7 and 8 are The figure is a line system diagram showing other control methods of the resonator length, Figures 9 to 11.
The figure is a systematic diagram showing another method of synthesizing laser light.
Figure 2 is a line diagram showing another embodiment of the resonator, No. 13.
The figure is a schematic diagram showing a conventional laser light source. 1.10...Laser light source, 2...Semiconductor laser for excitation, 3.13...Objective lens, 4
．． 5...Mirror, 6...Nd: Y
A G laser, 7...KTP. 12... Semiconductor laser for wavelength conversion, CAV, C
AV1, CAV10 to CAV30...Resonator,
L. ...Excitation laser light, L2...Oscillation laser light, L3, LS...Sum frequency laser light, L4
・・・・・・Laser light for wavelength conversion. 10 Red light

Claims (1)

[Claims] A sum frequency laser beam and/or a difference frequency laser beam of the first and second laser beams obtained from the first and second lasers is generated by phase matching of a nonlinear optical crystal element. In the laser light source, the nonlinear optical crystal element is arranged inside a resonator of the first laser beam obtained from the first laser, and
A laser light source characterized in that the resonator satisfies an external resonance condition for the second laser light obtained from the second laser.