JP2005150365A - Green laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a high-power visible light laser by controlling the Q value of an optical resonator in the present invention, because the oscillation efficiency of a desired wavelength is lowered due to oscillation other than the desired wavelength in a laser device. An object is to provide a green laser device obtained at low cost.
A green laser device of the present invention includes an excitation light source, praseodymium ions (Pr ^3+).
) And ytterbium ions (Yb ³⁺ ), and an optical resonator in which the laser medium is excited when light from the pumping light source is incident. Is the wavelength transmission of the resonant mirror in which the Q value of the optical resonator is arranged on the incident side and the output side of the optical resonator so that the Q value near the wavelength of 520 nm is high and the Q value near the wavelength of 635 nm is low. It is controlled by the characteristics or by a filter provided in the optical resonator.
[Selection] Figure 1

Description

The present invention relates to a green laser device that can be used as a light source for a display device or a recording device.

Conventionally, praseodymium ions (Pr ³⁺ ) and ytterbium ions (
Yb ³⁺ ) is added, up-conversion excitation is performed with excitation light having a wavelength of 780 to 900 nm, and an apparatus for obtaining laser light with a wavelength of 490 to 720 nm has been proposed.

For example, in Patent Document 1, by controlling the characteristics of a resonator mirror or by placing a wavelength variable element inside the resonator, the vicinity of 490 nm (blue wavelength), 520 nm (green wavelength), 605 nm (orange wavelength), An example in which oscillation at around 635 nm (red wavelength), around 715 nm (infrared wavelength), etc. is described.

All of these emissions are excitation order ³ P ₀ or excitation order ³ P _{1 that} is thermally connected to ³ P _0.
This occurs when electrons are deexcited from the light source, and if a wavelength other than the desired wavelength oscillates, the oscillation efficiency of the desired wavelength deteriorates. However, if the desired wavelength is made highly reflective and the others are made low reflective as in Patent Document 1, a burden is imposed on the fabrication of the resonator. For example, if the reflecting element is made of a dielectric mirror, the wavelength band that you do not want to oscillate is wide, so if you make all low reflection and make only the desired wavelength highly reflective, the film layer of the dielectric film will also be thick and complicated For this reason, the loss of the mirror itself increases, and the manufacturing cost also increases.
US Pat. No. 5,805,631

As described above, since the resonator characteristics for suppressing oscillation other than the desired wavelength are not clear in the conventional laser device, the resonator characteristics have characteristics more than necessary, and the oscillation efficiency of the desired wavelength is also high. There is a problem that it is not sufficient and the manufacturing cost is increased.

Therefore, an object of the present invention is to provide a green laser device that can obtain a high-power visible light laser efficiently and at low cost by controlling the Q value of the optical resonator.

The green laser device according to the first aspect of the present invention includes an excitation light source, praseodymium ions (Pr).
³⁺ ) and a ytterbium ion (Yb ³⁺ ) co-doped with a laser medium, and comprising an optical resonator that excites the laser medium when light from the excitation light source is incident thereon,
The optical resonator has a high Q value near a wavelength of 520 nm and a low Q value near a wavelength of 635 nm.

The Q value of the optical resonator is controlled by the wavelength transmission characteristics of the resonant mirrors arranged on the incident side and the outgoing side of the optical resonator, or by a filter provided in the optical resonator.

According to a ninth aspect of the present invention, there is provided a green laser device according to the present invention, wherein a semiconductor laser light source, and praseodymium ions (Pr ³⁺ ) and ytterbium ions (Yb ³⁺ ) are co-added to a core portion, An optical fiber including the resonance mirror disposed on the incident side and the emission side of the optical fiber, and the optical fiber in which the core portion is excited by being incident,
The incident-side resonant mirror increases the reflectance at a wavelength near 520 nm so that the optical resonator has a high Q value near a wavelength of 520 nm and a low Q value near a wavelength of 635 nm. The resonating mirror on the exit side has a characteristic of lowering the reflectance at a wavelength near 635 nm and partially reflecting the wavelength near 520 nm.

Furthermore, the green laser device of the present invention according to claim 10 is characterized in that a semiconductor laser light source, and praseodymium ions (Pr ³⁺ ) and ytterbium ions (Yb ³⁺ ) are co-added to the core portion, An optical fiber in which the core part is excited by being incident, and an optical resonator including a resonant mirror disposed on an incident side and an output side of the optical fiber,
The optical resonator is provided with a filter in the optical resonator so that the Q value near the wavelength of 520 nm is high and the Q value near the wavelength of 635 nm is low, and this filter is provided near 520 nm and 780 to 900 nm.
The wavelength is substantially transmitted, has a high reflection characteristic with respect to a wavelength of 635 nm, and is characterized by being installed obliquely with respect to the optical axis in the optical resonator.

According to the present invention, there is an advantage that a high-efficiency high-power green laser can be obtained by controlling the Q value of the resonator.

  Hereinafter, a green laser device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the green laser device of the present invention. In the following drawings, the same components are denoted by the same reference numerals. In FIG. 1, reference numeral 11 denotes an optical fiber, which is composed of a core portion and a clad disposed outside the core portion, and is composed of co-added praseodymium ions (Pr ³⁺ ) and ytterbium ions (Yb ³⁺ ). For example, it is made of a fluoride fiber having a small phonon energy. The concentration of Pr ³⁺ / Yb ³⁺ added is 3000
/ 20000ppm by wt.

Reference numerals 12 and 13 denote reflection elements (mirrors) installed on the incident-side end face and the emission-side end face of the optical fiber 11, which are composed of, for example, dielectric mirrors and constitute resonator mirrors. Reference numeral 14 denotes an excitation light source that excites Pr ³⁺ / Yb ³⁺ added to the optical fiber 11, and includes a semiconductor laser that emits a wavelength in the vicinity of 780 nm to 900 nm. Reference numeral 15 denotes excitation light output from the excitation light source 14, and reference numeral 16 denotes an optical system (lens) for making the excitation light incident on the optical fiber 11. Reference numeral 17 denotes a laser beam output from the output-side reflecting element 13 and has a wavelength of around 520 nm (hereinafter referred to as 520 nm).

Next, the characteristics of the resonator mirrors 12 and 13 and the operation of the green laser device will be described. FIG. 2 is an energy level diagram of Pr ³⁺ and Yb ³⁺ , and FIGS. 3 and 4 are examples of transmission characteristics of the resonator mirrors 12 and 13, where the horizontal axis represents wavelength and the vertical axis represents transmittance.

First, pumping light is emitted from the semiconductor laser light source 14, and the pumping light 15 enters the optical fiber 11 through the optical system 16. Excitation light incident on the optical fiber 11 is absorbed by the Yb ³⁺ added to the optical fiber 11, then, the resonator mirror optical wavelength 520nm generated from Pr ³⁺ that is energy transfer excited to Pr ³⁺ The laser light 17 having a green wavelength of 520 nm can be obtained by repeating reflection amplification at 12 and 13 and extracted from the resonator mirror 13.

The state of excitation and the principle of oscillation at a wavelength of 520 nm will be described in detail with reference to the energy level diagram of FIG. 2 and the transmission characteristics of the resonator mirrors 12 and 13 of FIGS.

In FIG. 2, an electron in the ground state ² F _7/2 of Yb ³⁺ absorbs, for example, excitation light in the vicinity of a wavelength of 830 nm and is excited to the rank ² F _5/2 . The electrons excited to this level are the excitation order ¹ G ₄ of Pr ^3+.
Energy transferred to. Furthermore, ¹ G ₄ electrons again absorb around the excitation light of 830 nm, and Pr ³⁺
Excited to the ³ P ₁ level. When transitioning from here to excitation order ³ H ₅ , green light of 520 nm is generated.

In order to oscillate the 520 nm light, it is necessary to form a so-called inversion distribution state of electrons between the upper level ³ P ₁ and the lower level ³ H ₅ . However, since the inversion than the inversion distribution between levels of thermally connected with level ³ P ₀ lower level ³ F ₂ easily occurs, 520 nm
Instead, the red wavelength around 635 nm (hereinafter referred to as 635 nm) oscillates first.

Therefore, in the present invention, in order to oscillate a green stable laser beam, the transmittance of 635 nm in the optical resonator mirror is as low as possible, that is, the reflectance is lowered as much as possible to reduce the Q value of the optical resonator. , 635nm oscillation is inhibited and 520nm light is oscillated.

Here, a specific example of the optical resonator mirror characteristic having a feature that the Q value of the green wavelength 520 nm is increased and the Q value of the red wavelength 635 nm is lowered will be described. FIG. 3 shows mirror characteristics on the incident side, and FIG. 4 shows mirror characteristics on the output side. As shown in FIG. 3, the incident side mirror 12 makes the excitation light a transmittance close to 100%, and the wavelength of 520 nm has a reflectance close to 100%. At this time, in order to lower the Q value of 635 nm, it is desirable to make the wavelength of 635 nm so that the reflectance is as low as possible.

On the other hand, as shown in FIG. 4, the output side mirror 13 is similarly configured to reduce the Q value at 635 nm.
The wavelength of nm is made so that the reflectance is as low as possible. The reflectance at a wavelength of 520 nm is partially reflected to obtain a high output. In addition, the wavelength of the excitation light is made so that the utilization efficiency of the excitation light can be increased by making it highly reflective. At this time, when excitation light is incident from both sides, it is clear that the transmittance is close to 100%.

In this way, by increasing the transmittance at a wavelength of 635 nm, the Q value of the resonator is lowered, and the wavelength of 635 nm is reduced.
Oscillation can be inhibited, and thereby the Q value at a wavelength of 520 nm can be increased. In other words, by using a resonator mirror characteristic that inhibits oscillation at a wavelength of 635 nm and oscillates only at a wavelength of 520 nm as in the present invention, it is possible to suppress oscillation at a wavelength that becomes an impediment, so that a high-efficiency, high-output green color is achieved. A laser device is possible.

In the above embodiment, Pr ³⁺ / Yb ³⁺ is added to the optical fiber. However, the present invention is not limited to the fiber, and a bulk crystal or glass may be used. Further, the excitation light source 14 need not be limited to a semiconductor laser, and may be another type of light source.

FIG. 5 is a schematic block diagram for explaining a second embodiment of the present invention. In FIG. 5, reference numerals 18 and 19 denote reflection elements (mirrors) constituting an optical resonator. Reference numeral 20 denotes a filter installed inside the optical resonator, which is composed of, for example, a dielectric multilayer filter.

As described in the first embodiment, in order to oscillate light having a wavelength of 520 nm, the upper level ³ P ₁
It is necessary to form a so-called inversion distribution state of electrons between and the lower level ³ H ₅ . However, inversion for population inversion level ³ P ₀ and the lower level ³ F ₂ just below ³ P ₁ to thermally with ties prone than distribution, red wavelength 635nm comes first among the levels Will oscillate. Therefore, it is necessary to lower the Q value at a wavelength of 635 nm.

In the second embodiment of the present invention, the Q value of a resonator having a wavelength of 635 nm that is not desired to be oscillated is lowered. However, in the second embodiment, means for increasing the loss of these wavelengths is provided as means for lowering the Q value.

That is, 20 is a filter for reducing the Q value.
It is installed so as to be almost transparent for 900 nm and highly reflective for a wavelength of 635 nm and to be reflected obliquely with respect to the optical axis in the resonator. Accordingly, light having a wavelength of 635 nm that is not desired to be oscillated by the filter 20 is not oscillated because it is reflected outside the resonator and the loss increases and the Q value decreases. At this time, the mirrors 18 and 19 for the optical resonator are manufactured so as to increase the Q value of the wavelength of 635 nm, and it is not necessary to particularly treat the wavelength of 520 nm, but the reflectance may be decreased.

FIG. 6 shows a specific example of the structure of the filter 20. A part of the optical fiber 11 is cut obliquely, and a filter element 21 made of a dielectric mirror or the like is directly deposited on one of the cut surfaces. The dielectric mirror 21 is substantially transmitted for wavelengths 520 nm and 780 nm to 900 nm, and has a high reflection characteristic for wavelength 635 nm. As a result, light having a wavelength of 635 nm is reflected outside the resonator.

FIG. 7 shows another example of the structure of the filter 20. A part of the optical fiber 11 is cut, and the light output from one of the cut surfaces is collimated (parallelized) by the lens 22. The optical fiber 1 is input to the lens 24 via 23 and condensed again by the lens 24.
This is input to the other one of the cut surfaces. In this example, the filter element 23 is composed of a dielectric mirror or the like, and the dielectric mirror 23 is substantially transmitted for wavelengths of 520 nm and 780 nm to 900 nm, and has a high reflection characteristic for the wavelength of 635 nm. It is a thing. As a result, light having a wavelength of 635 nm is reflected outside the resonator.

Thus, by installing in the resonator a Q-value control filter that only oscillates between the excitation orders ³ H ₅ and ¹ G ₄ required for oscillation at a wavelength of 520 nm as in the present invention, it is highly efficient and large. A green laser device capable of output can be obtained. Other operations and effects are the same as those described above.

In the first and second embodiments, the optical fiber may be a multimode optical fiber. The excitation light for exciting the laser medium may be a multimode semiconductor laser. By using these together, it becomes possible to take out a high-power green laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram for demonstrating one Embodiment of this invention. (Example 1) The energy level diagram explaining the energy transition of Pr3 ⁺ / Yb3 ⁺ . The characteristic view which shows the transmission characteristic of the input side resonator mirror in this invention. The characteristic view which shows the transmission characteristic of the output side resonator mirror in this invention. The schematic block diagram for demonstrating the other Example of this invention. (Example 2) The block diagram for demonstrating the example of a specific structure of the filter 20 of FIG. The block diagram for demonstrating the other specific structural example of the filter 20 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical fiber 12 Reflective element 13 Reflective element 14 Excitation light source 15 Excitation light 16 Optical system 17 Laser beam 18 Reflective element 19 Reflective element 20 Filter

Claims (10)

An excitation light source;
An optical resonator that includes a laser medium co-doped with praseodymium ions (Pr ³⁺ ) and ytterbium ions (Yb ³⁺ ), and is excited by the incidence of light from the excitation light source. Prepared,
A green laser device characterized in that the optical resonator has a high Q value near a wavelength of 520 nm and a low Q value near a wavelength of 635 nm. 2. The green laser device according to claim 1, wherein the Q value of the optical resonator is controlled by wavelength transmission characteristics of a resonant mirror disposed on an incident side and an output side of the optical resonator. The resonant mirror on the incident side of the optical resonator increases the reflectivity at a wavelength near 520 nm and decreases the reflectivity at a wavelength near 635 nm, and the resonant mirror on the output side increases the reflectivity at a wavelength near 635 nm. 3. The green laser device according to claim 2, wherein the green laser device has a characteristic of being lowered and partially reflecting a wavelength around 520 nm. 2. The green laser device according to claim 1, wherein the Q value of the optical resonator is controlled by a filter provided in the optical resonator. The filter was installed so that the wavelength near 520 nm and wavelengths of 780 to 900 nm were almost transmitted, had a high reflection characteristic with respect to the wavelength of 635 nm, and reflected obliquely with respect to the optical axis in the optical resonator. The green laser device according to claim 4. 2. The green laser device according to claim 1, wherein the excitation light source for exciting the laser medium is a multimode semiconductor laser. 2. The green laser device according to claim 1, wherein the laser medium is a core portion provided in an optical fiber. The laser apparatus according to claim 7, wherein the optical fiber is a multimode optical fiber. A semiconductor laser light source;
An optical fiber in which praseodymium ion (Pr ³⁺ ) and ytterbium ion (Yb ³⁺ ) are co-added to the core portion, and the core portion is excited by the incidence of light from the semiconductor laser light source, and the optical fiber An optical resonator including a resonant mirror disposed on the incident side and the outgoing side of
The incident-side resonant mirror increases the reflectance at a wavelength near 520 nm so that the optical resonator has a high Q value near a wavelength of 520 nm and a low Q value near a wavelength of 635 nm. The green laser device is characterized in that the reflectance mirror of the emission side is lowered, the reflectance of the wavelength near 635 nm is lowered, and the wavelength near 520 nm is partially reflected. A semiconductor laser light source;
An optical fiber in which praseodymium ions (Pr ³⁺ ) and ytterbium ions (Yb ³⁺ ) are co-added to the core portion, and the core portion is excited by the incidence of light from the semiconductor laser; An optical resonator including a resonance mirror disposed on the incident side and the emission side,
The optical resonator is provided with a filter in the optical resonator so that the Q value near the wavelength of 520 nm is high and the Q value near the wavelength of 635 nm is low, and this filter is provided near 520 nm and 780 to 900 nm.
The green laser device is characterized in that it is substantially transmitted, has a high reflection characteristic with respect to a wavelength of 635 nm, and is installed obliquely with respect to the optical axis in the optical resonator.

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