RU2328064C2 - Fiber intracavity-doubled laser (variants) - Google Patents

Fiber intracavity-doubled laser (variants) Download PDF

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RU2328064C2
RU2328064C2 RU2006119198/28A RU2006119198A RU2328064C2 RU 2328064 C2 RU2328064 C2 RU 2328064C2 RU 2006119198/28 A RU2006119198/28 A RU 2006119198/28A RU 2006119198 A RU2006119198 A RU 2006119198A RU 2328064 C2 RU2328064 C2 RU 2328064C2
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fiber
radiation
crystal
characterized
laser
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RU2006119198A (en
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Владимир Александрович Акулов (RU)
Владимир Александрович Акулов
Сергей Алексеевич Бабин (RU)
Сергей Алексеевич Бабин
Сергей Иванович Каблуков (RU)
Сергей Иванович Каблуков
Дмитрий Владимирович Чуркин (RU)
Дмитрий Владимирович Чуркин
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Общество с ограниченной ответственностью "НовоЛазер" ООО "НовоЛазер"
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Abstract

FIELD: physics.
SUBSTANCE: invention concerns laser technics, namely fiber lasers with frequency doubling in the visible spectrum band, and can be applied as emission source in such technological spheres as superdense optic memory (and recording), laser colour printing, laser color displays, biomedical diagnostics, analytical measurement, forensic medical examination etc. Fiber intracavity-doubling laser includes pump source, active optic fiber placed into colour-selective mirror resonator, where the first mirror omits pump emission and reflects basic generated emission. The second colour-sensitive mirror is outriggered out of the optic fiber and reflects both basic emission and the quadratic component. The third colour-sensitive mirror reflects basic emission and omits the quadratic component. Non-linear crystal with second-type synchronism placed between the optic fiber and the second mirror is directed so as to minimise angle of drift for the generated wavelength, and focusing elements. Spectrum selector is fitted between the fiber and the crystal for spectrum reduction and output power stabilisation. The selector comprises Bragg grating directly at the fiber end (of filter or interferometer). The second colour-selective mirror with additional focusing element comprises telescopic reflector sustaining optimal focusing and drift compensation of the crystal.
EFFECT: obtaining of fiber intracavity-doubled laser in the basis of a simple non-polarised scheme with high doubling efficiency.
27 cl, 2 dwg

Description

The invention relates to laser technology, in particular to frequency-doubling fiber lasers that generate in the visible spectrum that can be used as radiation sources for technologies such as super-dense optical memory (as well as recording), color laser printing, color laser displays, biomedical diagnostics (cytometry, DNA decoding), analytical measurements (Raman spectroscopy, spectrofluorometry, confocal microscopy), forensic examination and others.

Fiber lasers are new types of lasers in which the active medium is optical fiber. They have a number of advantages compared to other lasers: high beam quality, compactness, stability of output parameters, reliability, lack of water cooling, ease of operation, relatively low cost, which makes them attractive to consumers. Therefore, in recent years, various schemes of fiber lasers for various applications have been actively developed in the world, mainly continuous and pulsed diode-pumped fiber lasers of various powers based on fibers doped with ytterbium (Yb), neodymium (Nd), erbium (Er) ( including those supplemented by Raman converters) that generate in the wavelength region of more than 1 micron, which in their characteristics already surpass other types of lasers.

To generate in the visible region of the spectrum, in particular, blue-green, it is necessary to double the frequency of the fiber laser radiation, which is not an easy task (especially in the continuous mode) due to the specific polarization and spectral characteristics of fiber lasers. Solving the problem of efficiently doubling the frequency of fiber lasers will make it possible to create continuous fiber laser sources in the visible region of the spectrum: in particular, blue-green lasers with a wavelength of 450-570 nm, generated by doubling the frequency of the most powerful ytterbium and neodymium fiber laser, as well as yellow red lasers 740-810 nm, 550-850 based on erbium and Raman fiber lasers.

Efficient, reliable and compact frequency-doubling fiber lasers will be able to replace argon lasers, which require large energy resources and are difficult to operate, and which are gradually replacing them more efficient than argon, but rather complex and expensive solid-state lasers with frequency doubling for the blue-green region, dye lasers and single-mode diodes for the yellow-red range.

The effective frequency doubling of fiber lasers has been demonstrated for pulsed fiber lasers in a limited wavelength range (around 540 and 780 nm), corresponding to the second harmonic of the strongest ytterbium and erbium fiber lasers, for example, RJThompson, M.Tu, D.C. Aveline, N. Lundblad, L. Maleki, High power single frequency 780-nm laser source generated from frequency doubling of a seeded fiber amplifier in a cascade of PPLN crystals. Optics Express, 11 (14), 1709 (2003) [1].

The second harmonic is generated when radiation passes through an external nonlinear crystal - usually these are special periodically oriented crystals such as PPLN, RRKTR and others, in which the drift effect is periodically compensated, which allows increasing the length of the crystal. For continuous systems in the blue region, the generation efficiency in a single-pass scheme is very small even for long crystals: from 2.7 W of radiation from an ytterbium laser (978 nm) no more than 18 mW of the second harmonic (489 nm) was obtained, which corresponds to a doubling efficiency of ~ 0.7% (D. B.S.Soh, C. Codemard, S. Wang, J. Nilsson, J.K.Sahu, F. Laurell, V.Philippov, Y. Jeong, C.Alegria, S. Baek, A 980- nm Yb-doped fiber MOPA source and its frequency doubling, IEEE Photonics Technology Letters, 16 (4), 1032-1034 (2004)) [2].

Moreover, the design of such a laser is very complicated and expensive: the laser is a source of single-frequency linearly polarized radiation in the MAPA scheme (master laser power amplifier) and an external single-pass frequency doubler based on a periodically oriented crystal (RRKTR in a specific circuit). In the green and red regions, the conversion efficiency may be higher, however, at high power, periodic structures quickly degrade, and they are very expensive.

The scheme of intracavity frequency doubling seems more effective, since it allows one to increase the intensity of the main radiation incident on a nonlinear crystal, and, as a consequence, the conversion efficiency, and also use not only long periodically oriented crystals, but also ordinary nonlinear crystals (KTP, LBO, LiNbO 3 , KN, BBO, BiBO, etc.) of standard length, which allows to simplify and reduce the cost of the system.

Fiber laser radiation is usually randomly (randomly) polarized and has a large spectral width, which is mainly determined by the spectral reflection profile of mirrors (fiber Bragg gratings). The low spectral power density and random polarization complicate the solution of the problem of effective doubling using a standard fiber laser as the source of the main radiation. Nevertheless, patented solution options and real attempts to implement a fiber laser with intracavity frequency doubling are known.

In the description of the invention in RF patent N2269849, priority dated 14.03.2001 (EP 01106261.9) [3], a solution is presented for a Raman (or Raman, according to foreign terminology) frequency-doubling fiber laser, in which it is proposed to generate yellow radiation (589 nm) in nonlinear a crystal (second harmonic generator) located inside the cavity of a Raman fiber laser (1178 nm) formed by an optical fiber and two mirrors: the Bragg grating recorded directly in the optical fiber plays the role of the first mirror not, but the second - a volume mirror, taken outside the fiber. The crystal is placed in the air gap between the fiber and the bulk mirror, a matching lens is placed between the fiber and the fiber to transfer and focus radiation from the fiber into the crystal, and a dichroic plane mirror is used to output the second harmonic from the resonator. At the same time, there are no polarizing and selection elements in the circuit that ensure the generation of polarized radiation with a small spectral width.

Y. Feng, S. Huang, A. Shirakawa, and K. Ueda, Multiple-color cw visible lasers by frequency sum-mixing in a cascading Raman fiber laser. Opt. Express 12, 1843-1847 (2004) [4] describes the practical implementation of this solution. For doubling, an LBO crystal with noncritical phase matching of the first type was used, which was placed in the cavity of a Raman (Raman) fiber laser. The obtained conversion efficiency of the pump radiation of the ytterbium laser into the second harmonic of the Raman laser was ~ 0.1%. At the same time, the output power was saturated and did not exceed the level of 10 mW. One of the reasons for the low doubling efficiency is the small nonlinear coefficient of the LBO crystal - even in the absence of drift in uncritical synchronism, it has an order of magnitude lower conversion efficiency than, for example, a KTP crystal. In addition, with the first type of synchronism, only one linear polarization of the radiation of a fiber Raman laser is doubled, which for a real system with unpolarized (randomly polarized) radiation leads to a decrease in the power of the second harmonic by 4 times. The conversion coefficient is further reduced several times due to the large spectral width of the main radiation (> 1 nm) and suboptimal focusing into the crystal when using a flat mirror.

A solution is known, protected by patent US N5966391, 12.10.1999 [5], which proposes a linearly polarized fiber laser circuit with intracavity frequency doubling. In this embodiment, the laser includes a long doped (Yb, Er, Nd, etc.) optical fiber placed in a resonator from dichroic mirrors. The first transmits pump radiation and reflects the generated radiation (in the region of ~ 1.06 μm) and can be made in the form of an intrafiber Bragg grating. The second dichroic mirror reflects the main radiation (1.06 μm) and transmits the second harmonic radiation (0.53 μm) and is made in the form of a volume mirror. A matching lens and a nonlinear crystal are placed in the gap between the fiber and the output volume mirror, similarly to [3, 4]. Additionally, the controller and the polarization selector, made in the form of fiber or volume elements, are placed in the resonator. As a result, the laser should generate linearly polarized radiation, which, when used to double the frequency of crystals with synchronism of the first type, can increase the power of the second harmonic by 4 times. However, no measures have been taken in this scheme to increase the power spectral density, and in addition, a circuit with selection and control of polarization is much more complicated than the usual one - it includes many additional elements and requires active stabilization of the radiation polarization state.

Thus, the disadvantages of the known solutions for intracavity frequency doubling can be formulated as follows: they did not take measures to increase the spectral power density due to narrowing the spectrum and optimal focusing into the crystal; the use of crystals with the synchronism of the first type (e.g., LBO) or periodically oriented crystals (such as PPLN, PPKTP) requires a linearly polarized main radiation, while the scheme of a fiber laser with selection and control of linear polarization at the fundamental frequency is very complex, and the usual scheme with unpolarized radiation it is simple and reliable, but the doubling efficiency in it is 4 times less, and when using crystals with the second type of synchronism (e.g., KTP), for which it is necessary to have two perpendicular linear polarization (or random polarization, as in a conventional fiber laser), the efficiency is limited by the drift effect, which does not allow to increase the length of the crystal and optimally focus the radiation into the crystal.

The present invention is the creation of a fiber laser with intracavity frequency doubling based on a simple non-polarized circuit, but with high doubling efficiency (no worse than that of a complex polarized circuit).

This problem has been solved by using a special focusing scheme in a crystal with a second type of synchronism (e.g., KTP) and additional spectral selection, which make it possible to increase the spectral density of radiation, use both polarizations of radiation and reduce the drift effect.

This solution allows you to create a simple, reliable and cheap fiber radiation source in the blue-green range with improved technical and operational characteristics compared to analogues, which expands the scope of applications of such lasers.

The essence of the invention lies in the fact that in the known fiber laser with intracavity frequency doubling, including a pump source, an active optical fiber placed in a resonator from dichroic mirrors, the first of which transmits pump radiation and reflects the generated main radiation, the second dichroic mirror is placed behind the optical fiber and reflects the main radiation, a nonlinear crystal placed between the optical fiber and the second mirror, and the first and second focusing elements, in particular the first and second Inza, a second-type synchronism crystal is used, oriented in such a way as to provide the smallest drift angle for the generated second harmonic, the first and second focusing elements focus the transmitted beam approximately in the middle of the nonlinear crystal, a spectral selector is introduced into the gap between the fiber and the crystal to narrow the spectrum and stabilization of the output power, made in the form of a Bragg grating directly at the end of the fiber, filter or interferometer, and the third output dichroic a mirror that reflects the main radiation and transmits the second harmonic, and the second dichroic mirror reflects both the main radiation and the second harmonic and forms an telescopic reflector with an additional third focusing element, which ensures optimal focusing and compensation of the drift effect in the crystal.

This option is optimal; laser options are also proposed aimed at achieving various components of technical effects.

The description of the laser is illustrated in figure 1, which presents the proposed and implemented fiber laser circuit with intracavity frequency doubling.

In the drawing, LD is a diode pump laser, PC is a pump multiplexer, M 1 is a first dichroic mirror, M 2 is a second dichroic mirror, M 3 is a third dichroic mirror, DF is an active (doped) optical fiber, S is a narrow-band spectral selector, focusing elements: L 1 is the first focusing lens, L 2 is the second focusing lens, L 3 is the third additional focusing lens, NC is a nonlinear crystal with a second type of synchronism (e.g., KTP) placed in a T ° thermostat.

Description of the proposed solution

For doubling, a KTP crystal with a high conversion efficiency and the possibility of using both polarizations was taken. The KTP crystal (d eff = 3.88 pm / V) allows the use of nonpolarized (randomly polarized) radiation from a Yb fiber laser even with a generation spectrum width of ~ 1 nm. This is 4 times better in spectral characteristics than for periodically oriented crystals PPLN (d eff = 16 pm / V) and RKTR (d eff = 5.3 pm / V), which require linear polarization for their operation. Although the conversion coefficient of KTP is slightly lower than that of RKKTR (d eff 2 = 15 and 28, respectively), when using unpolarized radiation it is 2 times higher than that of the latter.

Traditionally, a KTP crystal in the wavelength range close to 1 μm is used with the second type of synchronism → → е or ое → о. Moreover, even a small drift of the unusual e-wave significantly reduces the efficiency of second harmonic generation, J.-J. Zondy, Comparative theory of walkoff-limited type-II versus type-I second-harmonic generation with Gaussian beams, Opt. Commun. 81, 427-440 (1991) [6]. The drift value for the traditional wavelength of the Nd laser of 1064 nm is 4 mrad, and for the experimentally realized wavelength of 1085 nm is 10 mrad. To assess the decrease in conversion efficiency, the drift parameter B = ρ (k ω L) l / 2/2 is traditionally used, where ρ is the drift angle, k ω is the wave vector of the main wave in the crystal, and L is the length of the crystal. Parameter B is 0.63 and 1.7 for a crystal 10 mm long for the above drift values, respectively. According to the data given in the above work, the reduction in the conversion coefficient is 2 and ~ 7 times, respectively.

A decrease in the conversion coefficient can be compensated to some extent with an oblique incidence of the pump radiation on the crystal. In this case, the birefringence effect and vector synchronism are used.

The crystal we used was cut out for critical collinear synchronism with a deviation of 3.7 ° from the crystallographic axis (XZ at 60 ° С). The optimal cutting angle can vary in the range from 0 to 20 ° depending on the wavelength (from 1079 to 1110 nm, respectively). At a cut angle of 3.7 ° for λ = 1085 nm, the difference in the synchronism angles for deviation from the normal incidence in one or the other direction was + 3 ° and -17 °, respectively. The recession angles of the orthogonal polarization pump rays were 8.7 and -2.4 mrad, respectively. As a result of a decrease in the scatter of the pump waves, the conversion efficiency is 2 times higher for a larger deviation from the normal incidence on the crystal and amounted to ~ 10 -3 1 / W. According to Z. Ou, S. Pereira, E. Polzik, and H. Kimble, 85% efficiency for cw frequency doubling from 1.08 to 0.54 μn, Opt. Lett. 17, 640-642 (1992) [7], the optimal conversion coefficient in the absence of drift is ~ 2 × 10 -3 1 / W for a 10 mm crystal. Thus, we were able to significantly increase the conversion coefficient.

In addition to reducing the conversion efficiency, drift leads to the formation of two parallel pump beams of orthogonal polarization after passing through the crystal. This circumstance makes it difficult to use the crystal inside the cavity. A standard solution to this problem is to use a flat mirror that returns both beams along the same path (see, for example, [3]). This leads to a shift of the focus point beyond the crystal, which significantly reduces the coefficient of conversion to the second harmonic.

An original “lens-mirror” telescopic reflector was created, which allows one to maintain optimal focusing in the crystal for both polarizations and return both beams along their path strictly back.

The beam path is shown in Fig. 2, where NC is a nonlinear crystal of the second type (for example, KTP), f is the focal length of the lens L, R is the radius of curvature of the mirror M, d is the distance to the waist of the returned beam. The solid and dashed lines indicate the propagation of the extraordinary and ordinary rays, respectively.

In addition, the work of the reflector with Gaussian beams was calculated using the matrix ABCD method. The results showed that an additional useful property of the proposed reflector is that it returns the Gaussian beam back without changing the size and position of the waist. In this case, the distance d to the waist of the returned beam is determined by the parameters of the reflector and does not depend on the size of the beam: d = (f + R) f / R. This allows you to implement a two-pass conversion scheme with optimal matching of the beams of the main radiation and the second harmonic and thereby increase the conversion efficiency by 2 times.

The advantages of a fiber laser (for example, over solid-state ones) include the possibility of smoothly changing the generation frequency in the range of tens of nanometers and obtaining tunable radiation in the second harmonic, for example, in the region of 480-570 nm for an ytterbium fiber laser. From the point of view of frequency tuning, the used crystal orientation has advantages over the noncritical temperature synchronism variant, which has a limited wavelength range: 539-541 nm for a KTP crystal at reasonable temperatures.

Mirrors M 1 , M 2, and M 3 form a resonator, which makes it possible to obtain laser generation for the main radiation with a wavelength in the specified spectral range. The dichroic mirror M 1 transmits pump radiation and reflects the main radiation - it can be formed directly inside the fiber in the form of a fiber Bragg grating with a relatively narrow reflection spectrum (0.03-1 nm) and allowing the wavelength to be tuned by compressing and stretching the fiber section, in which the lattice is recorded.

An additional spectral selector S, which is a narrow-band filter or an interferometer (fiber or volume), can be inserted inside the resonator to narrow the spectrum; in the case of a fiber version, it can be made on the basis of the Bragg grating (s), as an option, it can be integrated with mirror M 1 or M 3 .

The dichroic mirror M 2 is in the form of a bulk optical element with spectral characteristics that provide a high reflection coefficient both at the fundamental frequency and the second harmonic. The output of the second harmonic radiation is output through the output rotary dichroic mirror M 3 , which has a high reflection coefficient at the fundamental frequency but is transparent to the second harmonic - in this case, the power of the second harmonic generated in two passes of intense intracavity radiation through the crystal is summed.

It is possible to combine the mirrors M 2 and M 3 in one element — an output mirror transparent to the second harmonic — then the system will become simpler, but its efficiency will decrease by 2 times.

The orientation of the crystal (for example, KTP) is carried out in such a way as to ensure synchronism of the second type and the smallest drift angle (for example, due to the oblique incidence of radiation on the crystal, as described above) - this allows you to use the entire intensity of the unpolarized (randomly polarized) radiation, which two orthogonal linear polarizations, and thereby increase the efficiency by 4 times, and further increase the conversion coefficient by increasing the length of the crystal, respectively.

To reduce the effect of residual drift and optimize focusing in the crystal, a special lens-mirror telescope scheme (shown in detail in Fig. 1) is used to return both polarizations back to the optical fiber, as well as to better combine the waves generated during forward propagation through the crystal and back. It is also possible KTP with non-critical phase matching for a limited range of wavelengths near 540 nm and the use of other crystals.

In this case, the active fiber can be a standard single-mode fiber with a glass sheath size of 100-400 microns and a core diameter of 3-10 microns (as well as multimode, gradient, microstructured, composite - such as GTW and others), doped with Yb, as well as other rare earths elements (respectively, the working spectral range of the mirrors, selector, and crystal changes). In addition, the core may have an increased mode diameter (10-100 μm), which allows to reduce the loss of radiation input into the fiber by the L 1 and L 2 lens system and use both aspherical, gradient and microlenses, as well as conventional short-focus lenses. In addition, the large beam diameter in the active fiber makes it possible to reduce the intensity of the main radiation locally in the optical fiber and, accordingly, reduce the saturation of the amplifying medium and nonlinear effects (leading to broadening of the spectrum) at a given power level, which makes it possible to increase the conversion efficiency to the second harmonic.

Device operation

The radiation of one or more LD laser pump diodes (generating at wavelengths around 976, 915, or 808 nm) is injected directly or through the PC pump multiplexer into the active optical fiber DF (doped with Yb or Nd, Er) and creates an amplification of the signal propagating through the optical fiber in the wavelength region of the fiber gain band (for ytterbium fiber it is usually 0.97-0.98 and 1.03-1.15 microns, 0.9-1.1 microns for neodymium and 1.48-1.62 microns for Erbium).

An amplified signal with a wavelength in the specified spectral range propagates in the resonator formed by the fiber and mirrors M 1 , M 2 and M 3 through intracavity elements (S selector, L lenses 1-3 and non-linear NC crystal), so that when signal amplification is exceeded in active fiber over the total losses in the cavity, the regime of laser generation of the main radiation is achieved. The selector partially reflects and narrows the spectrum of the main radiation, the lenses L 1 and L 2 focus the transmitted beam approximately in the middle of the nonlinear NC crystal, and then returns (and at the same time focuses again in the middle of the nonlinear NC crystal) using a telescopic reflector formed by the mirror M 2 and lens L 3 . In this case, the second harmonic radiation (in the forward and reverse directions), which leaves the resonator through the mirror M 3 , is generated in the crystal due to the nonlinear conversion of light.

This scheme was implemented for a specific embodiment (figure 2) with a KTP crystal oriented according to the above description. The efficiency of conversion to the second harmonic was ~ 5%, which is an order of magnitude higher than that of the considered analogues. In this case, the output power (obtained up to ~ 0.5 W on the 542 nm line) linearly increased with an increase in the pump power (laser diodes), which allows a further increase in the second harmonic power due to an increase in the pump power.

Information Sources Used

1.RJThompson, M.Tu, DCAveline, N. Lundblad, L. Maleki, High power single frequency 780-nm laser source generated from frequency doubling of a seeded fiber amplifier in a cascade of PPLN crystals, Optics Express, 11 ( 14), 1709 (2003).

2. DBSSoh, C. Codemard, S. Wang, J. Nilsson, JKSahu, F. Laurell, V. Philippov, Y. Jeong, C. Aleria, S.Baek, A 980-nm Yb-doped fiber MOPA source and its frequency doubling, IEEE Photonics Technology Letters, 16 (4), 1032-1034 (2004).

3. D. Bonacchini, V. Hackenberg, High-band narrow-band fiber lasers with an extended wavelength range. RF patent N2269849, priority dated 14.03.2001 (EP 01106261.9).

4. Y. Feng, S. Huang, A. Shirakawa, and K. Ueda, Multiple-color cw visible lasers by frequency sum-mixing in a cascading Roman fiber laser, Opt. Express 12, 1843-1847 (2004).

5. M.S. Zediker, R. A. Rice, Long cavity laser system including frequency doubling long cavity fiber optic laser system, US Patent, N5966391, 12/10/1999.

6. J.-J. Zondy, Comparative theory of walkoff-limited type-II versus type-I second-harmonic generation with Gaussian beams, Opt. Commun. 81, 427-440 (1991).

7. Z. Ou, S. Pereira, E. Polzik, and H. Kimble, 85% efficiency for cw frequency doubling from 1.08 to 0.54 μm, Opt. Lett. 17, 640-642 (1992).

Claims (27)

1. A fiber laser with an intracavity frequency doubling, including a pump source, an active optical fiber placed in a resonator from dichroic mirrors, the first of which transmits pump radiation and reflects the generated main radiation, the second dichroic mirror is placed behind the optical fiber and reflects the main radiation, a nonlinear crystal placed between the optical fiber and the second mirror, and the first and second focusing elements, characterized in that a crystal with a synchronism of the second type is used, allowing which can operate without selection of the polarization of the main radiation, oriented in such a way as to provide the smallest drift angle for the generated second harmonic, the first and second focusing elements focus the transmitted beam approximately in the middle of the nonlinear crystal, and the second dichroic mirror forms a telescopic reflector with an additional third focusing element, providing optimal focusing and compensation of the drift effect in the crystal.
2. The laser according to claim 1, characterized in that a nonlinear crystal with type 2 synchronism (for example, KTP) is used, which is cut out for critical collinear synchronism with a deviation of 0-20 ° from the crystallographic axis depending on the working wavelength.
3. The laser according to claim 1, characterized in that the pump source is the radiation of one or more laser diodes generating at wavelengths around 976, 915 or 808 nm, which is introduced into the optical fiber through a pump multiplexer.
4. The laser according to claim 1, characterized in that the first dichroic mirror transmitting pump radiation and reflecting the main radiation is formed directly inside the fiber in the form of a fiber Bragg grating with a relatively narrow reflection spectrum (0.03-1 nm) and allowing tuning the radiation wavelength by compressing-stretching the portion of the fiber in which the lattice is recorded, or by changing its temperature.
5. The laser according to claim 1, characterized in that the active optical fiber has a core diameter of from 3 to 100 microns.
6. The laser according to claim 1, characterized in that as the focusing elements are used as aspherical, gradient and microlenses, and conventional short-focus lenses.
7. A fiber laser with an intracavity frequency doubling, including a pump source, an active optical fiber placed in a resonator from dichroic mirrors, the first of which transmits pump radiation and reflects the generated main radiation, the second dichroic mirror is placed behind the optical fiber and reflects the main radiation, a nonlinear crystal placed between the optical fiber and the second mirror, and the first and second focusing elements, characterized in that a crystal with a synchronism of the second type is used, allowing which can work without selection of the polarization of the main radiation, oriented in such a way as to provide the smallest drift angle for the generated second harmonic, the first and second focusing elements provide focusing of the transmitted beam approximately in the middle of the nonlinear crystal, and a spectral selector is introduced into the gap between the fiber and the crystal to narrow the spectrum and stabilization of the output power, made in the form of a Bragg grating directly at the end of a fiber, filter or interferometer, and the second is dichroic mirror forms with an additional focusing element telescopic reflector for optimum focusing and compensation for drift effects in the crystal.
8. The laser according to claim 7, characterized in that a nonlinear crystal with type 2 synchronism (for example, KTP) is used, which is cut out for critical collinear synchronism with a deviation of 0-20 ° from the crystallographic axis depending on the operating wavelength.
9. The laser according to claim 7, characterized in that the pump source is the radiation of one or more laser diodes generating at wavelengths around 976, 915 or 808 nm, which is introduced into the optical fiber through a pump multiplexer.
10. The laser according to claim 7, characterized in that the first dichroic mirror transmitting pump radiation and reflecting the main radiation is formed directly inside the fiber in the form of a fiber Bragg grating with a relatively narrow reflection spectrum (0.03-1 nm) and allowing tuning the radiation wavelength by compressing-stretching the portion of the fiber in which the lattice is recorded, or by changing its temperature.
11. The laser according to claim 7, characterized in that the active optical fiber has a core diameter of from 3 to 100 microns.
12. The laser according to claim 7, characterized in that both aspherical, gradient and microlenses and conventional short-focus lenses are used as focusing elements.
13. A fiber laser with an intracavity frequency doubling, including a pump source, an active optical fiber placed in a resonator from dichroic mirrors, the first of which transmits pump radiation and reflects the generated main radiation, the second dichroic mirror is placed behind the optical fiber and reflects the main radiation, a nonlinear crystal placed between the optical fiber and the second mirror, and the first and second focusing elements, characterized in that a crystal with a synchronism of the second type is used, which works without selection of the polarization of the main radiation, oriented in such a way as to provide the smallest drift angle for the generated second harmonic, the first and second focusing elements provide focusing of the transmitted beam approximately in the middle of the nonlinear crystal, the third rotary output dichroic mirror is introduced into the gap between the fiber and the crystal, which reflects the main radiation and transmits the second harmonic, and the second dichroic mirror, reflects both the main radiation and the second harmonic y and with an optional third focusing element forms a telescopic reflector for optimum focusing and compensation for drift effects in the crystal.
14. The laser according to claim 13, characterized in that a nonlinear crystal with type 2 synchronism (for example, KTP) is used, which is cut out for critical collinear synchronism with a deviation of 0-20 ° from the crystallographic axis depending on the working wavelength.
15. The laser according to item 13, wherein an additional focusing element is placed between the rotary output mirror and the crystal.
16. The laser according to item 13, wherein the pump source is the radiation of one or more laser diodes generating at wavelengths around 976, 915 or 808 nm, which is introduced into the optical fiber through a pump multiplexer.
17. The laser according to item 13, wherein the first dichroic mirror, transmitting pump radiation and reflecting the main radiation, is formed directly inside the fiber in the form of a fiber Bragg grating having a relatively narrow reflection spectrum (0.03-1 nm) and allowing tuning the radiation wavelength by compressing-stretching the portion of the fiber in which the lattice is recorded, or by changing its temperature.
18. The laser according to item 13, wherein the active optical fiber has a core diameter of from 3 to 100 microns.
19. The laser according to claim 13, characterized in that both aspherical, gradient and microlenses, and conventional short-focus lenses are used as focusing elements.
20. A fiber laser with intracavity frequency doubling, including a pump source, an active optical fiber placed in a resonator from dichroic mirrors, the first of which transmits pump radiation and reflects the generated main radiation, the second dichroic mirror is placed behind the optical fiber and reflects the main radiation, a nonlinear crystal placed between the optical fiber and the second mirror, and the first and second focusing elements, characterized in that a crystal with a synchronism of the second type is used, In order to provide the smallest drift angle for the generated wavelength, the first and second focusing elements focus the transmitted beam approximately in the middle of the nonlinear crystal; a spectral selector is introduced into the gap between the fiber and the crystal to narrow the spectrum and stabilize the output power, made in the form of a Bragg lattices directly at the end of a fiber, filter or interferometer, and a third output dichroic mirror, which reflects the main radiation and transmits the second harmonic, and the second dichroic mirror reflecting both fundamental radiation and second harmonic, and the third additional focusing element forms a telescopic reflector for optimum focusing and compensation for drift effects in the crystal.
21. The laser according to claim 20, characterized in that a nonlinear crystal with type 2 synchronism (for example, KTP) is used, which is cut out for critical collinear synchronism with a deviation of 0-20 ° from the crystallographic axis depending on the working wavelength.
22. The laser according to claim 20, characterized in that between the rotary output mirror and the crystal placed an additional focusing element.
23. The laser according to claim 20, characterized in that the pump source is the radiation of one or more laser diodes generating at wavelengths around 976, 915 or 808 nm, which is introduced into the optical fiber through a pump multiplexer.
24. The laser according to claim 20, characterized in that the narrowband spectral selector is integrated with the first or third mirror.
25. The laser according to claim 20, characterized in that the first dichroic mirror transmitting pump radiation and reflecting the main radiation is formed directly inside the fiber in the form of a fiber Bragg grating with a relatively narrow reflection spectrum (0.03-1 nm) and allowing tuning the radiation wavelength by compressing-stretching the portion of the fiber in which the lattice is recorded, or by changing its temperature.
26. The laser according to claim 20, characterized in that the active optical fiber has a core diameter of from 3 to 100 microns.
27. The laser according to claim 20, characterized in that both aspherical, gradient and microlenses and conventional short-focus lenses are used as focusing elements.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2548388C1 (en) * 2013-12-30 2015-04-20 Общество с ограниченной ответственностью "Техноскан-Лаб" (ООО "Техноскан-Лаб") Fibre laser with nonlinear radiation frequency conversion in high-q resonator (versions)
RU2589268C2 (en) * 2010-02-24 2016-07-10 Алькон Ленскс, Инк. High-power femtosecond laser with repetition frequency controlled according to scanning speed
RU2589270C2 (en) * 2010-02-24 2016-07-10 Алькон Ленскс, Инк. High-power femtosecond laser with controlled repetition frequency
RU2708811C2 (en) * 2015-03-31 2019-12-11 АйПиДжи Фотоникс Корпорейшен Higher-order raman pumping without priming

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2589268C2 (en) * 2010-02-24 2016-07-10 Алькон Ленскс, Инк. High-power femtosecond laser with repetition frequency controlled according to scanning speed
RU2589270C2 (en) * 2010-02-24 2016-07-10 Алькон Ленскс, Инк. High-power femtosecond laser with controlled repetition frequency
RU2686871C2 (en) * 2010-02-24 2019-05-06 Алькон Ленскс, Инк. High-power femtosecond laser with repetition rate controlled according to scanning speed
RU2548388C1 (en) * 2013-12-30 2015-04-20 Общество с ограниченной ответственностью "Техноскан-Лаб" (ООО "Техноскан-Лаб") Fibre laser with nonlinear radiation frequency conversion in high-q resonator (versions)
WO2015102518A1 (en) * 2013-12-30 2015-07-09 Общество С Ограниченной Ответственностью "Техноскан-Лаб" (Ооо"Техноскан-Лаб") Fiber laser having nonlinear radiation frequency conversion in a high-q resonator (variants)
RU2708811C2 (en) * 2015-03-31 2019-12-11 АйПиДжи Фотоникс Корпорейшен Higher-order raman pumping without priming

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