RU205001U1 - Device for high-intensity longitudinal fiber pumping of solid-state lasers based on Nd: YAG crystals - Google Patents

Abstract

The utility model relates to the field of laser physics and fiber optics and concerns a device for high-intensity longitudinal fiber pumping of solid-state lasers based on Nd: YAG crystals. The device contains a sequentially located radiation source, a radiation initiation system, an optical multimode fiber, the input end of which is located at the focal distance of the radiation initiation system, and a collimating lens located at a collimating lens focus distance from the multimode fiber output end. As a radiation source, a Nd: YAG crystal laser operating in the free-running mode and containing an intracavity frequency doubler was used. A spherical focusing lens is used as a system for generating radiation. An optical multimode fiber with a core diameter of 50 µm to 100 µm and a length of less than or equal to 100 m is used as an optical multimode fiber. The technical result consists in increasing the spatial coherence of the radiation source and increasing the radiation power. 2 dwg, 2 tbl

Description

The utility model relates to the field of laser physics and fiber optics. This useful model can be used as a longitudinal pumping of solid-state lasers based on a crystal of yttrium alumina garnet doped with neodymium ions (Nd: YAG).

The prototype of the proposed utility model can be a well-known solution that uses fiber-output laser diodes as longitudinal fiber pumping of Nd: YAG lasers based on Nd: YAG crystals, described, for example, in the work: N. Kofler, et. al. "Experimental development of a monolithic passively Q-switched diode-pumped Nd: YAG laser" Eur. Phys. J. D 58, 209-218 (2010).

This prototype contains in itself a radiation source - a laser diode emitter connected to a system for introducing radiation into an optical multimode fiber with a diameter of 100 μm or more, an optical multimode fiber connected to a radiation collimation device at the output.

The prototype works as follows: a radiation source - a laser diode emitter forms optical radiation, which, passing through the insertion system into the optical fiber, propagates along the optical multimode fiber and, at the exit from the fiber, enters the collimation system, which compensates for its divergence. Further, this radiation is suitable for longitudinal pumping of solid-state lasers based on Nd: YAG crystals.

The performance of the prototype is achieved by using a radiation source - a laser diode emitter with a central radiation wavelength located near 808 nm, which is due to the intense absorption of active Nd: YAG crystals in the vicinity of this wavelength (the absorption peak is indicated in Fig. 1).

The main disadvantage of the prototype is the low spatial coherence of the radiation source - a laser diode emitter and, as a consequence, the limited radiation power at the output of an optical multimode fiber with a core diameter of 100 microns does not exceed 100 W. Low spatial coherence of radiation makes it necessary to develop rather complex systems for introducing radiation into optical fibers, such as: US 5127068 A, US 6666590 B2, and with an increase in the output radiation power, the diameter of the used fiber has to be increased, as powerful (more than 100 W) fiber sources use optical multimode fibers with a core diameter of more than 400 μm, but the use of optical fibers with a large core diameter limits the pump radiation intensity, which, in the case of fiber pumping, can be estimated as the ratio of the radiation power to the cross-sectional area of the core of an optical multimode fiber.

The technical result of the utility model in comparison with the prototype is an increase in the spatial coherence of the radiation source and, as a consequence, an increase in the radiation power at the output of an optical multimode fiber with a core diameter from 50 µm to 100 µm to several kilowatts. An increase in the spatial coherence of radiation will make it possible to simplify the system of insertion into optical fibers and, with an increase in the radiation power, use optical fibers with a core diameter not exceeding 100 μm, the use of fibers with a diameter of 100 μm or less allows, accordingly, to increase the radiation intensity at the output.

The technical result is achieved by the fact that a device for high-intensity longitudinal fiber pumping of solid-state lasers based on Nd: YAG crystals containing a sequential radiation source, a radiation initiation system located with a radiation source on one optical axis, an optical multimode fiber, the input end of which is located at the focal distance of the radiation initiation system and lies on the same optical axis with the radiation initiation system; and a collimating lens located with the output end of the optical multimode fiber on the other optical axis and at the focal distance of the collimating lens there is the output end of the optical multimode fiber, the radiation source, the radiation initiation system, the optical multimode fiber and the collimating lens are placed next to each other compactly - right next to one housing and connected to each other by screwing, a laser on an Nd: YAG crystal operating in the free-running mode and containing an intracavity frequency doubler was used as a radiation source, a spherical focusing lens was used as a radiation initiation system, an optical multimode fiber was used as an optical multimode fiber with a core diameter of 50 μm to 100 μm and a length less than or equal to 100 m.

The utility model uses the presence in the absorption spectrum of Nd: YAG crystals of an absorption peak at a wavelength of 532 nm (the absorption peak is indicated in Fig. 1), which can also be used to create an inverse population in Nd: YAG crystals and, as a consequence, generate laser radiation ... Such radiation has a high energy of more than 200 mJ, high spatial coherence, which allows it to be inserted into multimode optical fibers with a core diameter (D) with an efficiency of more than 90%, while the condition: 50 μm≤D≤100 μm, using a spherical focusing lens ...

FIG. 1 shows the absorption spectrum of a Nd ³⁺ : YAG crystal.

FIG. 2 shows a block diagram of a device for high-intensity longitudinal pumping of solid-state lasers based on Nd: YAG crystals.

Accepted designations:

1 - radiation source - a pulsed laser on a Nd: YAG crystal, operating in the free-running mode with intracavity frequency doubling;

2 - the system of radiation initiation - a spherical focusing lens installed so that the spherical focusing lens and the input end of the optical multimode fiber are located on the same optical axis and are located relative to each other at a distance from the focal length of the lens;

3 - optical multimode fiber with a core diameter from the minimum possible for optical multimode fibers from 50 microns to 100 microns and a length from the minimum possible for attaching an optical multimode fiber up to 100 m (it is possible to use a longer optical multimode fiber with a power drop to subkilowatt level) ;

4 - collimating lens that collimates radiation at the output of an optical multimode fiber.

Table 1 shows the experimental data on the output radiation power depending on the parameters of the used optical multimode fiber.

Table 2 shows the experimental data on the implementation of the pumping of monolithic Nd, Cr: YAG crystals (one of the possible types of lasers based on Nd: YAG crystals) with a useful model.

The utility model (Fig. 2) contains sequentially located: a radiation source - laser 1 on a Nd: YAG crystal, operating in the free generation mode and containing an intracavity frequency doubler (hereinafter laser), a system of radiation initiation located with it on the same optical axis - a spherical focusing lens 2, mounted so that the spherical focusing lens 2 and the input end of the optical multimode fiber 3 are located on the same optical axis and the input end is located at the focal distance of the spherical focusing lens 2, the optical multimode fiber 3 with a core diameter of 50 μm to 100 μm, and length less than or equal to 100 m (it is also possible to use a longer optical multimode fiber with a power drop to a subkilowatt level) (hereinafter referred to as a fiber), lens 4, collimating radiation at the output of fiber 3, located on another optical axis with the output end of the optical multimode fiber 3 at focal distance of the lens 4. In general, ae the above two optical axes do not coincide, and are not parallel, and do not lie in the same plane. The radiation source 1 is generally located at any distance from the spherical focusing lens 2. The foci of the spherical focusing lens 2 and collimating lens 4 are generally different.

As elements of the utility model (Fig. 2) can be applied, for example:

as laser 1 - any pulsed Nd: YAG laser with intracavity frequency doubling and the ability to operate in a free-running mode (for example, with a switched-off Q-switch);

as a spherical focusing lens 2 - any spherical focusing lens, for example, a spherical focusing lens with a focal length of 11 to 12 mm;

as fiber 3 - an optical multimode fiber, for example, an optical multimode fiber with a core diameter of 50 to 100 μm, a numerical aperture of 0.11 to 0.22 and a length of 5 cm (the operability of this utility model is shown for fiber lengths from 10 m (Table 1), which allows us to expect similar results for shorter lengths of optical multimode fibers due to a radical decrease in radiation propagation losses in an optical multimode fiber) up to 100 m (it is possible to use a longer optical multimode fiber with a power drop to a subkilowatt level), If it is necessary to reduce the overall length of the device, the optical multimode fiber can be used, being wound on a spool. When using optical fibers with core diameters different from those presented and tested for this utility model, in particular, fibers with core diameters less than 50 microns, including the case of using single-mode (core diameters less than 10 microns), one should expect a drop in the efficiency of introducing radiation into optical fibers and as a consequence of the general drop in the radiation intensity at the output of the utility model;

as collimating lens 4 - any focusing lens, for example, a focusing lens with a focal length of 4 to 6 mm with an antireflection coating.

All elements of the utility model 1-4 are placed next to each other compactly - end-to-end in one housing (not shown in the figure) and are interconnected by assembly operations, for example, by screwing, joining, gluing, etc.

As a pumping object (Nd: YAG laser cavity), one can use, for example, a monolithic (diffusely bonded Nd, Cr: YAG) crystal with deposited mirrors on the crystal faces.

The utility model (Fig. 2) works as follows.

Laser 1 generates radiation at a wavelength of 532 nm.

The radiation at the output of the laser 1 falls on a spherical focusing lens 2 located with it on the same optical axis, installed so that the spherical focusing lens 2 and the input end of the optical multimode fiber 3 are located on the same optical axis and the input end is located at the focal distance of the spherical focusing lens 2.

Further, the radiation propagates along fiber 3. For example, in the case of using fiber 3 with parameters: length 100 meters, core diameter 100 microns and numerical aperture 0.22 is more than 1 kW (table 1).

The radiation at the output of the fiber 3 hits the lens 4, collimating the radiation at the output of the fiber 3, located on the same optical axis with the output end of the optical multimode fiber 3, at a focus distance.

The collimated radiation at the output of the utility model can be further used for longitudinal pumping of any laser resonator based on an active Nd: YAG crystal with active or passive Q-switching or operating in the free-running mode (Table 2), as well as in a number of other problems of laser physics and fiber optics requiring high-intensity radiation obtained using this utility model.

Experimental confirmation of the efficiency of the proposed utility model has been demonstrated for optical multimode fibers 3 with a length of 10 to 200 meters with the parameters given in Table 1 for the duration of the radiation of laser 1 on a Nd: YAG crystal, operating in the free-running mode with intracavity doubling of the frequency of this laser 1, determined by only the lifetime of the excited state of neodymium ions and for a particular laser 1 does not exceed 200 μs. The high spatial coherence of radiation from a solid-state laser 1 allows radiation to be fed into an optical multimode fiber 3 with an efficiency of more than 90% and, as, for example, can be seen from the data given in Table 1 when using an optical multimode fiber 3 with a numerical aperture of 0.22 with a core diameter of 100 μm and a length of 100 m, the output radiation power is more than 1 kW. The use of optical multimode fibers 3 with a small core diameter (not exceeding 100 μm) makes it possible to radically increase the radiation intensity at the output of this utility model in comparison with the prototype.

As discussed above, in the absorption spectrum (Fig. 1) of the crystals of yttrium aluminum garnet doped with neodymium ions, there is an absorption peak at a wavelength of 532 nm (indicated in Fig. 1). The radiation wavelength of the device is 532 nm, so it can be used to pump solid-state lasers based on Nd: YAG crystals, which was experimentally confirmed by us. For experimental confirmation, a number of monolithic Nd, Cr: YAG crystals were selected (Table 2). The radiation of the utility model at a wavelength of 532 nm, falling into Nd, Cr: YAG, excited lasing in them at a wavelength of 1064 nm with the parameters given in Table 2. Thus, it can be concluded that the utility model can be used for high-intensity pumping of lasers based on yttrium aluminum crystals. garnet doped with neodymium ions.

Thus, the claimed technical result is achieved, namely, an increase in the spatial coherence of the radiation source and, as a consequence, an increase in the radiation power at the output of an optical multimode fiber with a core diameter from 50 μm to 100 μm to several kilowatts.

An increase in the spatial coherence of radiation simplifies the system of insertion into optical fibers 3 and an increase in the radiation power to several kilowatts allows the use of optical fibers 3 with a core diameter of 50 μm to 100 μm and a length of up to 100 m, in addition, the possibility of using such fibers with a length of up to 200 m s has been demonstrated. obtaining subkilowatt power levels.

Claims (1)

A device for high-intensity longitudinal fiber pumping of solid-state lasers based on Nd: YAG crystals, containing a sequentially located radiation source, a radiation initiation system located with a radiation source on one optical axis, an optical multimode fiber, the input end of which is located at the focal distance of the radiation initiation system and lies on one optical axes with emission institution system; and a collimating lens located with the output end of the optical multimode fiber on the other optical axis and at the focal distance of the collimating lens there is the output end of the optical multimode fiber, the radiation source, the radiation initiation system, the optical multimode fiber and the collimating lens are placed next to each other compactly - right next to one housing and connected to each other by screwing, characterized in that a laser on an Nd: YAG crystal, operating in the free generation mode and containing an intracavity frequency doubler, is used as a radiation source, a spherical focusing lens is used as a radiation initiation system, as an optical multimode fiber, an optical multimode fiber with a core diameter of 50 μm to 100 μm and a length of less than or equal to 100 m is used.

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