RU2495467C2 - Method of limiting intensity of laser radiation - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to a method of limiting powerful pulse-periodic laser radiation and can be used to protect visual organs and sensitive radiation detectors from the destructive action of high-intensity incident radiation. The method is implemented by a limiter based on suspensions of nanoparticles having nonlinear optical properties, in transparent liquid matrices containing a surfactant. Pulse-periodic laser radiation is limited with repetition frequency of up to 10 Hz, wherein the ratio of viscosity (η) to molecular mass (M) of the liquid component of the limiter is defined by the empirical formula γ = Kη/M for values 1 < γ < 10 and K=10 D/P.

EFFECT: using a method of limiting laser radiation without change in optical parameters of the limiter under the effect of powerful laser radiation.

Description

The invention relates to intensity limiters for pulsed and repetitively pulsed laser radiation with a repetition rate of up to 10 Hz and can be used to protect organs of vision and sensitive radiation detectors from the damaging effects of high-intensity incident radiation.

Laser radiation limiters differ both in the design of the device and in the working material, which consists of a transparent matrix and active components, which are nanoparticles with nonlinear optical properties [1, 2].

Modern requirements for the working materials of the limiters (limiters) of the intensity of high-power laser radiation are as follows:

- High initial transmittance of radiation T (λ) and broad-band linear transmission of the limiter in the working region of the spectrum, which provides neutral coloring of the field of view of optical devices.

- High speed limiter, the so-called speed.

- A high degree (multiplicity) of attenuation of the intensity of the input radiation (limitation), which is understood as the ratio of the intensity of the incident radiation to the intensity of the radiation transmitted through the limiting device.

The specified requirements are met by limiters whose active components are carbon nanoparticles, multilayer and single-walled nanotubes, carbon nanofibres, gold and silver nanoparticles, “semiconductor-metal and dielectric-metal nanostructures” [1].

The active components of the working material can be enclosed in a solid-state transparent matrix, as well as a suspension of nanoparticles in various solvents.

The main mechanisms for limiting high-power laser radiation are nonlinear scattering, multiphoton absorption, RSA (reversible saturated absorption), and other optical nonlinear processes [1].

Thus, limiters are known based on solid-state polymer matrices containing gold and silver nanoparticles [2]. Such solid-state devices along with ease of use meet the basic criteria of limiters, but they have significant disadvantages. Such disadvantages include the low radiation strength of the polymer matrix in which the nanoparticles are distributed, which, in essence, determines the difficulty of using them in a pulse-periodic mode. So, in [3] it is noted that solid-state “limiters”, in which the mechanism of “healing” of the laser exposure zone does not work, are less durable than liquid ones.

Laser radiation limiters, in which the working material is a suspension of the active component in various solvents, are characterized [4-6] by the fact that the destruction of the working material, in contrast to solid-state, is a reversible process, and along with high performance of the limiter could have advantages over solid state limiters.

However, liquid limiters have drawbacks characterized by the bleaching of the material in the light channel along the laser beam with a gradual restoration of the initial state of the suspension [1]. Enlightenment of a nonlinear optical medium can be associated with the removal (or sublimation) of nanoparticles from the laser beam propagation region. For a nonlinear optical medium placed in a confocal system, it is permissible to use liquid limiters in a pulse-periodic mode if the pulse repetition rate does not exceed 3 Hz. Such behavior of liquid limiters sharply limits their use in a pulse-periodic regime of laser radiation.

There is evidence [7] regarding the limitation of high-power laser radiation by a suspension of amorphous carbon nanoparticles placed in a viscous polymer matrix based on epoxy resins or aqueous gelatin gel. The authors note the possibility of using limiters in a pulse-periodic mode. However, the limitation of laser radiation with a power of 100 MW / cm to such systems is possible at a laser pulse repetition rate of 0.5-2.0 Hz.

The closest in technical solution is the method of limiting high-power laser radiation proposed in [6]. As a matrix, distilled water or an organic solvent is used. The finely dispersed carbon medium is a multilayer carbon nanotube. A surfactant may be used to impart stability to the suspension. This technical solution provides a high initial transmittance of the radiation T (λ) and a broadband linear transmission of the limiter in the working region of the spectrum, a high switching speed of the limiter (speed) and a high degree of attenuation of the input laser radiation intensity.

However, the disadvantage of such a limiter is the impossibility of using it to limit powerful laser radiation in a pulse-periodic mode [1] at repetition frequencies of more than 3 Hz.

The aim of the present invention is the possibility of limiting high-power laser radiation based on a suspension of nanoparticles having nonlinear optical properties in a pulse-periodic mode to 10 Hz.

This goal is achieved by the fact that in the claimed method of limiting high-power laser radiation, the polymers selected from a number of complex compounds, esters, aromatic hydrocarbons, higher alcohols, higher alkanes, and also mixtures thereof are used as the liquid component of the limiter. In the inventive method for limiting high-power laser radiation, carbon nanoparticles can be used as an active component of a limiter, namely, single-layer and multilayer nanotubes, carbon nanofibers, amorphous carbon particles, astralen, nanoshells, and other polyhedral multilayer carbon nanostructures of fulleroid type.

A distinctive feature of the liquid media of the limiters according to the claimed method of limiting the radiation intensity is the correspondence of the value of γ, determined by the following empirical formula, to a certain range:

γ = Kη / M,

where K is the coefficient of proportionality, η is the viscosity of the liquid component of the limiter, M is the molecular weight of the liquid component of the limiter.

The use of the limiter in a pulse-periodic mode with a repetition rate of up to 10 Hz without changing the nonlinear optical properties of the working material of the limiter is carried out in the range η from 1 to 10. In this case, the possible values of viscosity η and molecular weight of the liquid component of the limiter M are shown in the examples given in the table one:

Table 1. Examples of the properties of solvents for limiters with nonlinear optical properties in a pulse-periodic mode up to 10 Hz.

(K = 10 Da / Pz).

γ η, cPz M Yes one twenty 20000 2 twenty 10,000 four twenty 5000 5 one hundred 20000 10 twenty 2000 10 one hundred 10,000

At molecular weight and viscosity values of the liquid component of the limiter, the ratio between which leads to values of γ that fall outside the range of 1-10, undesirable changes in the properties of the limiter are observed.

So, in the range of molecular masses M of the liquid component of the limiter 20000-2000 Yes:

- at M = 20,000 and η <20 cPs, a precipitation of nanoparticles and a weakening of the nonlinear optical properties of the limiter are observed;

- at M = 2000 and η> 20, the gaseous products of the action of powerful laser radiation on the material of the limiter do not have time to dissipate, as a result of which the recovery time of the optical properties of the limiter becomes too long, which does not allow it to limit the laser radiation in a pulse-periodic mode to 10 Hz.

Literature

1. I.M. Belousova, O. B. Danilov, A. I. Sidorov. Optical Journal, vol. 76, No. 4, 2009, p. 71.

2. S. Dengler, G. Riit, B. Eberle, Proc. of SPIE. V.7481, 74810T-1.

3. T.N. Kopylova, A.P. Lugovitsky et al. Quantum Electronics, vol. 36, No. 3, 2006, p. 274.

4. Pat. RF №2238577, Non-linear optical element to limit the flow of electromagnetic radiation.

5. K.M. Nashold, D.P. Walter, J. Opt. Soc. B / Vol. 12, No. 7, 1995.

6. L. Vivien, P. Lancon, D. Riehl, F. Hache, E. Anglaret, Carbon. V.40, 1.10, 2002. P.1789.

7. S. E. Zeiensky, J. V. Copyshinsky et al. Semiconductor Physics, Quantum Electronics. V.13, No. 1. P.70

Claims (1)

1. A method of limiting the intensity of high-power laser radiation by a limiter based on suspensions of nanoparticles having nonlinear optical properties in transparent liquid matrices containing a surfactant, characterized in that the limitation of pulse-periodic laser radiation is performed with a repetition rate of up to 10 Hz, at the ratio of viscosity (η) and molecular weight (M) of the liquid component of the limiter is determined by the empirical formula γ = Kη / M with a value of 1 <γ <10 and K = 10 Da / Pz.