The optical limiter

 

The invention relates to laser equipment, namely, optical limiters laser radiation. Developed device for limiting the intensity of the laser radiation on the basis of nonlinear effects in semiconductor element. Nonlinear-optical element made of a semiconductor with deep impurity levels or deep defect levels in the band gap energy gap between these levels and the bottom of the conduction band lower photon energy. The concentration of impurities or defects is in the range 1015-1018cm-3. The technical result of the invention is the extension of the range of operating parameters of the limiter, in particular the reduction of the energy threshold emission restrictions. 3 Il.

The invention relates to optics and can be used in laser technology.

Known limiter laser radiation [1, 2], consisting of a semiconductor nonlinear optical element and the diaphragm. Semiconductor nonlinear optical element has a width of forbidden zonegmost of the photon energy hbut smaller double photon energy (h<E<2h

The disadvantages of such a limiter are relatively high threshold emission restrictions and narrow spectral region of operation is to obtain limits the photon energy must lie within Eg/2<h<E.

Known limiter laser radiation, selected as a prototype [3], consisting of two defocusing lenses, aperture, located behind the second lens, and nonlinear optical semiconductor element, with the bandgap Eglarger photon energy hbut smaller double photon energy (h<E<2hlocated in the common focal plane of the lens. The limitation of the radiation intensity is due to samedifference radiation in a semiconductor two-photon absorption [2, 3]. In the two-photon absorption in a semiconductor occurs the generation of nonequilibrium electron-hole pairs, leading to a decrease of the refractive index of the semiconductor in the field of radiation exposure, i.e. to the formation of dynamic negative lens, which is fussing radiation. The drawbacks of such will limit the region of operation - Eg/2<h<Eand what the most effective limitation of radiation can be obtained only in the picosecond range pulse duration of the radiation. The duration of the radiation pulse tens of nanoseconds - microseconds energy threshold limit increases in 10-3-10-4time.

The purpose of this invention is to reduce the energy threshold emission restrictions and extension of spectral and temporal scope of the limiter.

This objective is achieved in that the nonlinear optical limiter element made of a semiconductor with deep impurity levels or deep defect levels in the band gap energy gap between these levels and the bottom of the conduction band lower photon energy, and concentration of impurities or defects is in the range 1015-1018cm-3.

In this case, the main mechanism of generation of nonequilibrium charge carriers is not two-photon absorption of radiation having a high threshold of occurrence, and the impurity-photon absorption, which takes place even when the intensity of the radiation, which tends to zero. This reduces clubline radiation. Since in this case the spectral region restrictions is determined not only by the bandgap of the semiconductor, as in the case of two-photon limit, but also the ionization energy of the impurity (E<E), the spectral region restrictions increases towards lower energies of the photon -E<h<E. Because the process is one-photon and due to the fact that the time of impurity recombination of nonequilibrium charge carriers exceeds the radiative recombination time increases the effectiveness of the restrictions in the nanosecond and microsecond range duration of the radiation pulse.

This solution is new, and the set of distinctive features not follow from the known technical solutions. The significance of the distinctive features is that the limiter radiation is used semiconductor nonlinear optical element with deep impurity levels or levels of defects with ionization energy, lower energy photon.

Specific examples of the invention.

In Fig. 1 shows the design of the limiter radiation. The limiter consists of two defocusing Lin is pacoste lenses and the diaphragm 4, located at a distance L from the second lens and transmits 90% of the incident radiation in the absence of the nonlinear element. As a nonlinear semiconductor element used plate from compensated GaAs (Eg= 1.45 eV), containing deep impurity levels with the energy of ionizationE=0.6-0.7 eV [4], the impurity concentration of 1016cm-3and a thickness of 5 mm or plate of ZnSe (Eg=2.7 eV), with deep levels in the forbidden zone formed by the defects of interstitial zinc and zinc vacancies and selenium withE=0,23, 1,1 and 1.58 eV with a concentration of 1018cm13the thickness of the ZnSe plate - 5 mm

The limiter works as follows. Under the action of the radiation pulse with photon energyE<h<Ein the semiconductor wafer is generated nonequilibrium carriers with deep impurity levels in the conduction band. At low energy of the incident radiation, the generation rate of carriers does not exceed the rate of their recombination, therefore, with increasing energy radiation at the input of the limiter the radiation energy at the output increases linearly. At a certain threshold energieproductie there is a negative lens, leads to defocusing of the radiation, resulting in reduced energy radiation transmitted through the aperture.

In Fig. 2 shows the dependence of the energy radiation output of limiter on the energy of radiation at the input to the nonlinear optical element of GaAs at a wavelength of the incident radiation 1,315 μm (h=0.95 eV) and duration of the radiation pulse=50 NS (curve 1) and=6 μs (curve 2), and nonlinear-optical element of ZnSe for a wavelength of 1.54 μm (h=0.8 eV) and duration of the radiation pulse 20 NS (curve 3). In the first case, F1=25 mm, F2= 15 mm, L=50 mm, in the second and third cases, F1=6 mm, F2=4 mm, L=60 mm, an Energy threshold limits in the first case is equal to 2 PJ, the second 10 CPL and in the third - 60 PJ. The limit is in the range of the input energy for the first case - 210-12-10-8J, in the second case - 10-11-10-3J. and in the third case - 610-11-10-4J. The attenuation of the signal in the restriction mode of the radiation in the first and third slucak equal to 104in the second case is equal to 105.

In Fig. 3 shows the dependent is ementa from ZnSe to radiation in the spectral range of 3.8-4.2 μm and duration of the radiation pulse=250 NS at F1=50 mm, F2=30 mm, L=100 mm In this case also, there is the limitation of radiation with an energy threshold of 500 µj in the range 510-4-0.0025 j.

From the above examples that use to limit the emission of semiconductors with deep levels in the forbidden zone can reduce the threshold limit of radiation in the 10-3-10-4times compared with threshold limit due to two-photon absorption, the proposed prototype, and the reduction of the threshold limit is reached as in the nano - and microsecond range pulse duration of the radiation, thereby expansion of temporary operation of the limiter. From the above examples, it also follows that for ZnSe with deep levels in the band gap spectral region of emission restrictions expanded to 4 μm, while under two-photon absorption limit is possible only in the spectral range from 0.47 to 0.9 μm. Thus, the invention allows to reduce the energy threshold emission restrictions and to extend the spectral and temporal scope of the limiter compared to the prototype.

The invention can be used in priemnik devices from the blinding rays of high intensity and destruction by radiation.

LITERATURE 1. Patent 4.846.561 (USA), 11.07.89.

2. E. W. Van Stryland, Y. Y. Wu, D. J. Hagan, M. J. Soileau, K. Mansour. Optical limiting with semiconductors. J. Opt. Soc. Am. B, V. 5, N9, P. 1980-1988, 1988.

3. T. F. Boggess, A. L. Smirl, S. C. Moss, I. W. Boyd, E. W. Van Stryland. Optical limiting in GaAs. IEEE J. of Quant. Electr., V. QE-21, N5, p. 488-494, 1985.

4. A. Chantre, G. Vincent, D. Bois. Deep-level spectroscopy in GaAs. Physical Review B, V. 23, No. 10, P. 5335-5358, 1981.

Claims

The optical limiter containing optical system with real focus and semiconductor nonlinear optical element, characterized in that the nonlinear optical element made of a semiconductor with deep impurity levels or deep defect levels in the band gap energy gap between these levels and the bottom of the conduction band lower photon energy, and concentration of impurities or defects is in the range 1015-1018cm-3.

 

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