Description :: Our patents

The proposed invention falls into field of laser technique, and is more concrete to field of high-power lasers with high – quality radiation.

Is known the device [1] - the high-power laser with stable - unstable resonator, including laser active medium, stable-unstable resonator, having a plane of stability and perpendicular to it a plane of instability, while the axis of the cavity transits through active medium, drawn in a direction of cavity axis, which fills a caustic of the cavity both in a plane of stability and in a plane of instability of the cavity. One or more mirrors of such cavity are aspherical, (cylindrical or toroidal), creating effect of astigmatism.

At a particular ratio between radiuses of mirrors curvature and distance between them in each of above evocative planes is possible the execution or failure of stability condition.

In a plane of stability are implemented the cross modes of Gauss – Hermit, from which with the help of a diaphragm it is easily possible to select a high Gaussian mode zero-order. In a plane of instability, during each pass of the cavity, the radiation increments its cross size in M times, where M - coefficient of cavity magnification.

The outlet of radiation in such cavity is possible in a plane of instability both outside of cavity smaller mirror, and with the help of a special lead-out mirror, posed before one of end mirrors. The lead-out mirror throws away exterior in relation to an axis a part of radiation, falling on the above mentioned end mirror laterally from cavity axis. Usually a lead-out mirror represents a flat or spherical mirror with a rectangular bore, which sides coincide with stable and accordingly unstable planes.

Generally speaking, the output radiation has in its cross-section two spots, disjointed among themselves by gap, peer to a size of small end mirror or size of a bore in lead-out mirror in a plane of instability.

Edges of a bore in lead-out mirror in a plane of stability are a diaphragm. If the size of this bore in a plane of stability is small enough, about 1,5 diameters of basic mode, measured on a level 1 / e², such diaphragm selects a Gaussian mode zero-order.

The misalignment of the cavity in a plane of instability brings to that the power of one of output beams grows, thus the power of other output beam reduces. Even in case of enough major misalignment, when the cavity axis transits near edge of output mirror (bore in a lead-out mirror) in a plane of instability, power of the second output beam remains enough major (about 10 %). Thus the quality of an output beam is noticeably aggravated at the expense of radiation diffraction reflection from mirror edge in counter convergent wave of unstable resonator.

In spite of the fact that the quality of radiation in a plane of stability can be very high (single-mode), quality of radiation in a plane of instability is high only in case of major values of magnification coefficient - M. If M on the order of 1, that is in case of major gap between output beams in relation to the cross size (in a plane of instability), the quality of output beam radiation is much lower.

Really, the divergence of output radiation q in a plane of instability will be defined by the cross size l in a plane of instability q = l / l = l / b (M-1), where l - wave length of laser radiation, 2b- the size of an output mirror (bore in a lead-out mirror) in a plane of instability. A diffraction divergence of continuous beam with the size d

q _dif.=l / d = l / Mb. Coefficient of radiation quality K=q _dif. / q = (M-1) /M. It is visible, that in case of M® 1, quality of output radiation K® 0.

Let's mark, that losses of stable-unstable resonator for complete light passing around of the cavity t=1-1/M® 0 in case of M® 1.

In many high-power lasers there is an active medium, extended (except an axis) still in one direction and rather restricted in perpendicular to it direction. Besides, frequently in such lasers active medium has a small amplification coefficient, for example, in gas lasers with high pressure of active gases mixture, therefore with the purpose of reaching high efficiency it has to use the cavity with small output losses. That is the cavity with small value of magnification coefficient M. While the quality of output radiation is reduced. Thus, in this case there is a technical conflict between necessity of efficiency magnification of a laser with low amplification coefficient of active medium and quality of output radiation of this laser. At M = 2 the output losses of stable-unstable resonator are made up 50 %, and the quality of radiation is reduced approximately in 2 times.

Problem of the invention is the improvement of radiation quality, efficiency magnification and laser output power. This problem becomes most actual at small magnification coefficients

1 < M < 2.

The problem is solved in such a manner. In high-power laser with stable-unstable resonator with the help of special construction lead-out mirror both output beams in parallel come nearer to each other down to their merging in one compact beam. Thus, as the cross size of output radiation diminishes at maintenance of a divergence, the quality of radiation is incremented.

In that case, when active medium of the laser, for example high-power CO₂ - laser, is rarefied gas, is applied the output transparent window, for example, KCL or ZnSe, to separate active medium from an atmosphere. A problem is the fact, that at major powers of laser radiation absorbed in a window power part brings to thermodeformations of radiation, transiting through a window, and even to a damage of the window. This effect restricts application of a solid-state window from transparent material at a level of laser power, about 5 kW. It is known, that this limiting power, passed by a window, does not depend almost on the size of a beam and is defined by quality of window material (its absorption constant and mechanical properties).

In order to solve a problem of laser radiation outlet, according to claim 2 of the invention formula, we offer at first to output from the laser two strongly distant beams separately. It must be done through two windows, or through one major window, but with conductive enveloping of each beam with separate cooling through both edge surfaces.

The construction of guessed invention is illustrated on fig. 1, 2, 3.

In fig.1 there is a variant, in which stable-unstable resonator is formed with the help of end concave spherical mirror 2, convex cylindrical mirror 1. Lead-out mirror consists of inserted in each other interior (formed by two mirrors 3) and exterior 4 parallel reflecting prisms, which in parallel shift both output beams, down to their tangency on an axis 5. Thus in a plane of instability one compact beam 6, having bell-shaped lateral view of intensity 6.1 is gained. In a plane of stability intensity distribution 6.2 is Gaussian.

On fig. 2 is given a variant, when a lead-out mirror consists of two parallel mirrors 4 and 5. Their planes are displaced from each other on some distance h. In such a manner when reflected from such mirror, one of beams comes in parallel nearer to other beam on distance x=2hsin, where θ - angle of laser beam falling on a lead-out mirror. It is obvious, that if the equality x=2h*sinθ = b (where b – a distance between output beams, equal to a cross size of small (output) mirror or a size of lead-out mirror bore in a plane of instability) is fulfilled, both output beams are closed in one beam 6.1.

It is possible a variant of the invention, when, according to claim 2, the lead-out compressing mirror is posed after an output window on a beam.

On fig. 3 is figured the lead-out mirror with a step-shaped surface. Such mirror is possible to make with the help of the machine tool with diamond turning (milling) for one installation.

Such mirror can be composite, consisting from two mirrors, and one of them (smaller) 4 has parallel back and forward surfaces and lays on optical contact on the first (greater) mirror 3.

An approach of output beams can be carried out also with the help of a window, consisting of two wedge-shaped output windows, with independent conductive cooling. Thus on laser output there are two approaching beams. That these two beams would be focalized in one point with the help of a lens, is necessary the inverse transformation by others two wedges, but posed bases out. Thus these two wedges can be combined with their lenses.

In all evocative variants of parallel beams approach between beams there is a phase shift F , depending on quantity of a step h and on an angle of laser beam falling on a lead-out mirror - q .

F = 2kh/cos q ,

where k = 2p / l , l - wave length of laser radiation.

The maximum quality of radiation will be at F = 2p n, and minimum - at F = p n.

There are different techniques to provide the necessary relation of phases between beams.

Variation of angular declination of a mirror relatively a beam axis.
D F = 2kh (sinq / cos² q ) D q
Temperature variation of a lead-out step–shaped mirror. At variation of a mirror temperature a step quantity in a lead-out step-shaped mirror varies
D h = a hD T,

where D T - variation of a mirror temperature, a - the coefficient of mirror material thermal expansion, thus varies a difference in phase on quantity D F .

D F = 2kD h / cosq = 2ka hD T / cosq
An absorbed part of radiation power, falling on a mirror, also will give a warming -up of a mirror and a variation of phase difference between adjacent beams.
It is possible to adjust this phase difference F with the help of a drawing of an absorb coat on a mirror on a driving radiation wavelength l _dr ¹ l , and to illuminate a mirror by a light on this driving wavelength l _dr.
In case of two separate mirrors it is also possible to vary the indicated phase relation with the help of a piezoceramic drive unit or with the help of a micrometer screw in a direction, perpendicular to a mirror surface.
A prompt variation of a phase difference at the expense of oscillations of a one half mirror plane relatively another with the help of a drive unit brings to periodic with major frequency modulation of radiation quality without variation of an output power level. This phenomenon can appear useful at operations of laser welding, cutting and piercing of bores.

Thus, at usage in high-power laser stable-unstable resonator with a two-sided radiation output and at usage of a lead-out mirror of a special construction, circumscribed above, it is possible to decide a conflict between security of high efficiency in lasers with low strengthening active medium and security of radiation excellence.

What is claimed is:

A high-power laser with stable-unstable resonator, including extended active medium, stable-unstable resonator, having a plane of stability and perpendicular to it a plane of instability, while outlet of radiation is carried out with the help of a lead-out mirror; characterized in that in a plane of instability the resonator has a coefficient of magnification M, 1 < M < 2, and the lead-out mirror is fulfilled with an opportunity to pull together output beams at maintenance of their parallelism.
A high-power laser with the stable-unstable resonator according to claim1, wherein an evocative lead-out mirror consists of two flat mirrors, each of which reflects an output beam, relevant to it, the planes of mirrors reflective surfaces are parallel and biased from each other.
A high-power laser with stable-unstable resonator according to each of claims 1, 2, wherein an evocative lead-out mirror is canted to an axis of the resonator; it is step-shaped and has two parallel reflecting surfaces, displaced from each other on distance h=2bsinq , where b - distance between output beams of stable-unstable resonator, q - a slope angle of a lead-out mirror to a resonator axis.
A high-power laser with stable-unstable resonator according to each claim1, 2 and 3, wherein a phase shift F = 2kh / cos q between output beams, resulting after reflection from a lead-out step-shaped mirror, is equal 0 or is multiple 2p , where k=2 p / l ,
l - wave length of laser radiation.
A high-power laser with stable-unstable resonator according to claim 4, wherein an evocative value of phase shift is ensured with variation of a lead-out mirror temperature.
A high-power laser with stable-unstable resonator according to each claim1, 2, 3, 4, wherein at any rate one of mirrors of a composite lead-out mirror has a drive unit of transposition in a direction, perpendicular to a mirror surface.