DE1282209B - Optical transmitter - Google Patents

Description

The invention relates to an optical transmitter for generating output pulses of high peak power by influencing the quality of the optical resonator (ß-circuit) by placing inside it a medium of variable absorption is used, which after receiving a sufficient amount of energy from the stimulated radiation itself saturates, becomes transparent and thus the path within the optical Resonator releases.

The general theory and operation of optical transmitters (laser devices) is today generally known and has already been described in detail in the literature.

In many cases there is a desire to replace those normally produced by such devices sharp, scattered pulses with relatively low peak power from individual optical pulse transmitters Generate energy pulses with high peak power. A typical application for such sharply defined Impulse is the distance measurement where the beginning of the impulse initiates a timing cycle, which is terminated when the pulse is received that was reflected from the object whose Distance to be measured.

There are several embodiments of devices for generating such individual pulses with known for high peak performance. One of these embodiments uses a cell as one optical shutter for controlling the generation of high peak power pulses. The usage of Kerr cells, however, has the disadvantage that a relatively high peak power for switching the same must be used.

The present invention also relates to devices for generating output pulses high peak power through an optical transmitter, whereby the quality of the optical resonator (ß-circuit) being affected. This is used to generate output pulses with high peak power (sometimes also called "giant" pulses) made use of an optical avalanche technique. At this Technique creates a medium of variable absorption in the transmission path of stimulated radiation placed in the resonator to control the threshold at which the optical transmitter oscillates. That Medium of variable absorption raises the energy threshold at which the oscillation in the optical Transmitter occurs above the threshold at which the optical transmitter occurs in the absence of the absorbing medium would vibrate. The onset of oscillation at this higher threshold The absorbing medium "burns through" and makes it permeable, thereby opening the way within of the optical resonator becomes free.

For an optical transmitter of the type mentioned at the outset, it has already become known, a photochromic Insert glass in the path of the stimulated light beam. The glass is under the action of the stimulated Light beam permeable, while its permeability for light of shorter wavelengths decreases. The present invention shows another generally applicable way of controlling an optical Transmitter without the use of a photochromic glass, which has the disadvantage of being so must be adapted so that it is transparent at a particular wavelength.

It is characteristic of the invention that the absorbent medium is either made of the same substance is like the stimulable medium or consists of a different material, but that is not photochromic glass.

In a preferred embodiment of the invention, the stimulated radiation is through a stimulable medium generated, for example by a solid rod made of crystalline material (e.g. Ruby) or by a gas. The medium arranged within the optical resonator is more variable Absorption absorbs the radiant energy that initially occurs when the stimulable medium is excited is generated by the excitation energy source. As a result of the absorbing effect, the vibration in the stimulable medium does not set in at the normal threshold as the losses in the optical resonator were increased. Since the threshold value of the onset of oscillation in the stimulable medium is increased, the absorbing medium continues its radiation-absorbing Effect continues until it has absorbed enough stimulated radiation to become saturated. That means that of the two energy levels for effective absorption, the higher one is stimulated for so long until there is practically no further absorption. Now the absorbing medium becomes effective transparent to the stimulated radiation, so that the vibration in the stimulable medium can occur. Due to the delay in the onset of oscillation in the stimulable medium, as it is achieved by the absorbent medium, there is an increase in the threshold value the vibration. This results in an increase in the density of the stimulable medium stored energy before the sudden consumption of the same at the time of the becoming permeable absorbent medium. This delay stimulates the peak power of the output pulse Radiation increased.

The optical avalanche technique of the present invention is practical on stimulable media of all types for optical transmitters, namely solid, liquid or gaseous, applicable. The medium too variable absorption can be an appropriately selected solid, liquid or gaseous material. the Optical avalanche technology is particularly advantageous as it enables the generation of higher output pulses Allowing peak performance through the use of an optical shutter effect, which itself is not performance needed from outside. Also, the material used for the absorbent medium is preferable chosen to be reusable, d. that is, it is more stimulated in generating an output pulse Radiation is not destroyed under normal output power conditions.

The invention will now be described with reference to the drawings. It shows

F i g. 1 shows a diagram for the energy build-up and the oscillation conditions in an optical Transmitter without an optical shutter,

F i g. 2 an optical transmitter with a Kerr cell for generating output pulses of high peak power,

F i g. 3 an optical transmitter that uses optical avalanche technology to generate output pulses high peak power used,

F i g. 4A and 4B energy output diagrams of an optical transmitter that uses optical avalanche technology used, and

F i g. 5 an optical transmitter based on optical avalanche technology, in which a gaseous working medium and a gaseous absorbent medium can be used.

There are already some theories to explain the generation of irregular or pointed ones Output pulses of relatively low power developed in an optical pulse transmitter working under normal conditions. While none of these theories completely agree with the observations made with working optical transmitters agree, they all work the problem from the same general point of view. This general point of view fits in with Part of the observations made.

To explain the generation of peak output pulses in a ruby medium, these say various theories that in the vibratory state for some reason the excitation of the stimulable The medium is excited beyond its value in the steady state, while the stimulated Emission temporarily suspends. When the stimulated emission then starts again, the excitation energy supply is reduced below the value of the steady state consumed for the maintenance of the oscillation necessary is. During the time of the exhausting excitation, a radiation pulse is generated generated. The excitation falls off and the energy field disappears with a time constant that is equal to the of the optical resonator approximates. Then the process repeats itself, and during the Time during which the excitation power remains constant, the amplitudes of the pulsating Radiation output is limited essentially to a value that is caused by this relaxation or tilting oscillation is determined.

On the basis of this simple theory it can be shown that one of the necessary conditions for the occurrence of stimulated radiation requires that a frequency be present at which at the same time the gain from the stimulable medium is equal to or greater than the overall system losses based on output couplings , Joule heat at the reflectors, scattering due to imperfections in the medium, diffraction, etc. A second condition requires that the phase shift over a self-closing path including phase shifts at the reflectors is zero. The first of these conditions is the "win" condition, the second the "phase" condition. For the commonly used ruby medium, these conditions are met for many frequencies within a relatively broad band. For example, occur around the center of 4.3 ■ IO ⁵ GHz with a ruby rod of 7 cm length of vibrations according to both 1.2 GHz over a bandwidth of 300 GHz.

The observed behavior in a working Ruby medium differs from the predictions of this simple theory in particular with respect from the 60 zeitpulsierenden type of radiation emitted. There is also an instability resulting in a “peak” modulation of the vibration strength when the energy build-up within the resonator lags behind the gain build-up in the stimulable medium.

The F i g. 1 approximates the behavior of a typical impulse ruby transmitter. At time t = 0 the excitation light (line A) is switched on, and the absorption of the excitation energy by the ruby rod begins to increase the excitation energy reserve of the stimulable medium, namely said ruby rod (line B), towards the oscillation threshold value. The vibration energy density or intensity (line C) does not experience any appreciable increase before point a on line C, the vibration threshold value of the working medium, is reached, whereupon an exponential increase begins. At point b of line C, the vibration energy density has reached a value which, if the phenomenon of relaxation vibration were not present, would be maintained by the excitation. At this point, the rate of increase in excitation energy of the working medium is zero, but the excitation energy reserve is significantly higher than that which could be maintained by excitation without the presence of relaxation oscillations. The vibrational energy density continues to build up and goes beyond stimulation, making the stimulable medium permeable. At this point c, the decay of the energy density field begins as a result of resonator losses. Under normal ruby vibration conditions, the cycle repeats itself according to points a ', b', c ' of FIG. 1. It should be noted that higher threshold values for generating an oscillation are required for larger resonator losses.

From this simple explanation it can be seen that any peak that appears when the medium becomes permeable, tends to consume the energy stored in the medium.

When the starting point or threshold value of the oscillation by introducing a time-independent The limb is increased to consume the energy in the system, so the build-up of the stimulation is prevented, and the excitation energy of the stimulable medium does not go to zero. It follows from this incomplete consumption of energy. If, however, stimulation is prevented, the vibration threshold value can be increased and then by suddenly increasing the quality of the optical Resonator is lowered when the oscillation is about to start, so the emitted in a peak increases Energy by the amount by which the threshold or threshold was increased. This Effect is called ß-switching or control of the quality factor of the optical resonator and can can be used to generate single high peak power pulses.

One way of setting the starting point or threshold value of the vibration of a stimulable medium to control, is to have an influence on the coefficient of relaxation of the resonator and thus to exercise the value of the excitation in the steady state. For example, it can be used to stimulate of a medium can be extended to its oscillation threshold value by the fact that the resonator reflection coefficient is kept at a lower value, resulting in a higher resonator loss means. If this low reflection coefficient is kept constant, the time becomes probably longer between the oscillation pulsations, but the output pulses are in the have essentially the same amplitude.

The reflection coefficient of the resonator is based on

at a low value only until the light excitation or the electrical discharge for the onset of an oscillation at this low excitation, is pulsed or sensed. This kind of However, the required excitation value is reached and then pulsed operation is not as beneficial and the reflection coefficient suddenly changes to a larger one for the reasons already mentioned. It is The value (lower resonator loss) in a line is therefore preferable if the radiation span is increased, which is short compared to the duration, the stimulable medium is continuously stimulated of a pulse, then the stimulable medium possesses, so that under suitable conditions a now a supply of excitation energy, which can be generated over the constant oscillation, lies, who is responsible for overcoming the new, lower The stimulable medium contains in a steadily Losses (higher reflection coefficient) of the vessel io excited state a considerable energy, since would be necessary to generate the vibration. Atoms, ions or molecules move as a result of excitation If after reaching an excitation energy through electromagnetic radiation with suitable Shot are at a higher energy level during the time of the low reflection frequency, coefficient, which is sufficient to make the oscillation from- This stored energy can be converted into a short to solve and the excitation of the working medium about 15 timespan and is much greater than To lower the reflection coefficient of the vessel to zero, the relatively low energy, which is suddenly increased to the stimulus, then the oscillation occurs in the case of a manageable medium through the excitation energy source a higher excitation than it supplied for the higher during an equally short period of time Reflection coefficient would be necessary. Thus becomes will.

the excitation energy supply of the stimulable meter 20 Various devices can be used to control diums far beyond its original for the Schwin of optical transmitters to achieve such can be used with the higher resonator loss (lower pulse operation. Reflection coefficient) required value excited, and there occurs an impulse of short duration and to reach, consists of the effective number of large peak amplitude. The amplitude of these 25 excess excited atoms by means of the Impulse is greater than changing a stimulable Zeeman or Stark effect. this Medium that works under normal conditions without succeeding through a sudden change in the magnet-controlled change in the resonator gain, tables or electric fields, Since the oscillation is caused by an excitation energy, an impulse operation can also be caused by sudden supply is generated which is above the normal change in the resonance frequency of the stimulable wise is required for the oscillation, d. i.e., the medium achieved by the Zeeman or Stark effect Threshold is temporarily increased so that one can be (for example by changing the magnetic or longer time for the vibrational energy of the electric field to build up in the vessel), and there is more energy. A number of the pulsed operation can also be achieved by means of the small output pulses, the first large formation of a locking device, Impulse due to the new low condition, for example, by a rotating reflector or Follow loss in the resonator. '' an electronic arrangement, such as a Kerr cell,

The above-described mode of action can be used as a result of the radiation in the closed path Radiation occlusion can be considered as the resonator is effectively attenuated so that the actually a shutter at a certain time- 40 losses are large enough to open a stimulated oscillation point in order to reduce the optical losses in certain states of the shutter the resonator vessel. To prevent this radiation.

Shutting effect can be achieved by means of a radiation module, generation of running pulses in an optical transmitter as shown in another proposal by the inventor 45 is shown in FIG. 2 shown. This figure shows is described. However, it can also with certain a vessel 401, the interior 402 of which is filled with a geVantage regarding the simplicity of the device by suitable stimulus optical avalanche technology described above, as it is filled with removable media. In Fig. 2 is the stimulus that will be described below. agent for this medium for the sake of simplicity For certain applications it is desirable to have 50 omitted. In the vessel 401 there is an optical transmitter to be operated in such a way that it is running prism 403. A window 404 is at the counter-generating radiation energy pulses. Such pulses are arranged at the end of the vessel 401. A reflective prism 405 similar to the properties of the other will generally have the process signals of a conventional optical transmitter, seen and in the device according to FIG. 2 outside namely narrow band width, almost flat wave form 55 of the vessel 401 attached. There is also the etc. In addition, these impulses will have their energy possibility concentrated on the two reflecting prisms 403 for a very short time. These and 405 either both inside the vessel or time period can be shorter than 10 " ⁸ seconds. Both can be arranged outside the vessel. The length of the pulse can of course be greater certain frames 60 the incident rays, as indicated by the arrows 408, the shape of the pulse, which will all be explained later, on their respective faces Radiation intensity that is noticeable at a different angle, and that is achieved for the prism and similar devices, which are constantly in its vicinity. With this arrangement, the radiation state will work work or not, can of course be reflected inside the prism, while light in pulsed mode is simply applied through it ends, of a different polarity partially outside of that the source of the exciting energy, for example corresponding surfaces 406 and 407 is reflected.

1

Thus, a closed path with low loss is only provided for light of a certain polarity. A Kerr cell 411 is arranged in the closed radiation path so that all radiation passing through this closed path passes through the Kerr cell 411 .

The Kerr cell is electrically excited by a pulse generator and timer 412. As can be seen, the Kerr cell controls the output pulses of radiation and the pulse generator and timer 412 is appropriately sized to produce pulses of the appropriate duration and timing so as to deliver radiation pulses having the characteristics desired in a particular application. The construction of Kerr cells is well known and is therefore not described in detail here. It will suffice to point out that a shape of the Kerr cell of a plurality of conductive plates is (preferably g at an angle of 45 ° to the plane of the paper in F i. 2 is arranged), the electrical conductor 413 to a source of potential, for example the Pulse generator and timer 412 are connected. The spaces between the conductive plates 414 are provided with a (usually liquid) dielectric so that when voltage is applied to the plates 414, an electric field is created in the dielectric which changes the polarization of a plane polarized plane passing through the Kerr cell Wave creates what is commonly known as the Kerre effect.

Prisms 415 are provided at the ends of the Kerr cell 411 so that the rays shown by arrows 408 reach the Kerr cell at an angle with the outer and inner surfaces of the prism 415 which is substantially equal to Brewster's angle; this reduces the reflection on the surfaces of the prism 415 to a minimum, which also reduces the radiation loss as possible as a result of the introduction of the Kerr cell into the system.

Since door radiation of a certain polarization is shown in FIG. 2 an almost undamped, closed path is provided and since radiation of a different polarity is partially reflected out of this closed path, it is understandable that the excitation of the Kerr cell to shift the polarization of the radiation passing through it results in a considerable loss of radiant energy in the closed path caused, for example, by the reflection on the surfaces 406 and 407 of the prisms 403 and 405. The polarization can be changed in various ways by the Kerr cell; it can be converted to a circular polarization or shifted to a new polarization angle that deviates by 90 ° from the original one, or other changes can be made. Every change in polarization results in an attenuation of the light rays, with the maximum attenuation being achieved with a 90 ° change in the angle of the plane of polarization.

Thus, when the Kerr cell 411 is excited, energy losses of the resonator prevent the build-up of an oscillation, although there is an excess occupation in a higher energy level from which a self-sustaining stimulated emission would occur as a result of the transitions to a lower energy level if the conditions of the Energy storage in the system near the

209

Would be optimal. Thus, if the Kerr cell is suddenly switched off under these conditions in order to reduce the energy loss , then the energy embodied by the higher population in the upper energy state will rapidly decrease by stimulated emission, whereby a light energy pulse is generated in the resonance light amplifier.

An output signal can be obtained from the optical transmitter as shown in FIG. 2 can be obtained by making the surface 407 of the prism 405 partially reflective. This is done for example by using a partially reflective coating or could be done by rotating the prism 405 about an axis perpendicular to the plane of the paper so that the rays indicated by the arrows 408 are not exactly at the Brewster angle, but at a slight angle changed angle, which results in a partial reflection from the surface 407 of the prism 405 , whereby output rays arise as indicated by arrows 409.

The in F i g. The apparatus shown in FIG. 2 and described above is particularly advantageous in that the Kerr cell can be actuated at time intervals which are only 10 ^-9 seconds.

In the device according to FIG. 2, the peak power pulse intensity is significantly higher than the intensity obtainable from a non-pulsing or keyed optical transmitter. The increase in power results from the fact that considerable energy is stored in the interior 402 of the enhancer vessel 401 when the stimulable medium therein is kept in an excited state. This energy can be emitted in a very short pulse by means of the Kerr cell 411 , which results in a very high peak power pulse intensity. The foregoing has dealt with the form of degradation of the resonator using a Kerr cell.

While the Kerr cell device described above is successful for the generation of desired high Peak power output pulses can be used by means of a radiation shutter effect, suffers this Ausluhrungsform at the disadvantage that a relatively large peak power for actuation the cell must be expended. In some cases, this performance is comparable to that achieved at the Exciting the optical transmitter itself is required.

The F i g. Figure 3 illustrates an apparatus using an optical avalanche technique to generate momentary high peak power output pulses through a radiation shutter effect. The device has a stimulable medium 10, which in this example is a rod made of ruby crystal. The rod 10, which has the length L ₁ and the cross-sectional area A ₁ , is surrounded by a conventional excitation lamp 15 which is supplied by a suitable external power source (not shown). The lamp 15 can be of any suitable type and, as usual, serves to reverse the population distribution, inversion, in the stimulable medium. If ruby is used as a stimulable medium, a krypton or xenon lamp can be used. If desired, the excitation lamp 15 can be enclosed within a suitable vessel 16 , the inner surfaces of which are designed to be wholly or partially reflective, in order to reflect the excitation light onto the rod 10.

909523/78

1

One end of the ruby rod 10 is covered with a partially radiolucent and reflective material coated, for example it is a semi-reflective mirror 18. The generated in the rod 10 stimulated Radiation is partially reflected off mirror surface 18 and the output of the ruby becomes also generated at this end. The other end 20 of the rod 10 is transparent to the stimulated radiation. This interface and others can be in the Device to be arranged at the Brewster angle in order to keep the reflection losses as small as possible.

The stimulated light beam emerging through the end 20 of the rod 10 passes through a lens system 22, where its cross-section is reduced, d. That is, it is focused by a biconvex lens 23 to a smaller beam, while a diverging biconcave lens 24 the output beam of the Lens 23 collimated. It goes without saying that the lens system 22 can be replaced in whole or in part by equivalent reflector or other optical means can be, as they are known to the person skilled in the art.

The collimated narrow bundle on the right side of the biconcave diverging lens 24 is directed onto an absorbent medium 25 which is formed by a rod of length L ₂ and a cross-sectional area A ₂ . In the embodiment described, the absorbent medium 25, like the stimulable medium 10, is also a ruby crystal. In this case, the light generated by the rod 10 has precisely the frequency that is required to stimulate an electron transfer from one state of the atoms in the absorbing medium 25 to the other. This takes place in the same way as the electron transfer in the stimulable medium 10.

The absorbing rod 25 is not excited, and its two ends are transparent to the stimulated light beam of the rod 10. A mirror 27 is near the right end of the absorbing medium 25 to complete the resonator appropriate. The light from the stimulated rod 10 is thus reduced by the lens system 22 and passed through the non-excited absorber medium 25 to be reflected by mirror 27. That reflected light travels through the absorbing medium 25 and the lens system 22 back into the Rod 10 through its transparent end 20. This light is in turn reflected in part by the semi-transparent mirror 18.

The mode of operation of the device according to FIG. 3 is as follows: When the excitation energy lamp S is switched on, the excitation in the stimulated laser crystal 10 grows until the threshold value condition for an oscillation is reached. This threshold condition is determined by both the Loss due to the reflection at the mirrors 18 and 27 as well as the loss due to the absorption of the radiation in the unexcited one Crystal 25. When the threshold condition is reached, the stimulated radiation begins, and the The supply of excitation energy in this crystal is used up. At the same time there is also the loss in that reduced non-excited crystal rod 25, as a result of the removal of the atoms from the absorbing ground state as a result of the absorption of the Radiation from the rod 10. When the excitation energy supply in the crystal 10 and the loss in the crystal 25 be reduced to the same extent as the

209

If the intensity of the optical radiation were the same in both crystals, then this will be the case optical field only decay from its value at the threshold value oscillation. On the other hand, if the loss in crystal 25 subsides faster than the supply of excitation energy, as would be the case if the intensity of the optical radiation were in the unexcited shutter crystal 25 would be larger than in the stimulated crystal 10, then that will build up optical field in the crystal 10 from an initial value to a peak value and then rapidly decrease when both the excitation energy reserve and the absorption loss decrease.

The latter condition actually prevails because the light output from crystal 10 is through the Lens system 22 is reduced in size in order to generate a beam of greater light intensity in the absorbing medium 25 than in the stimulated crystal 10. In order to obtain a sufficiently intense pulse from the crystal 10, the absorbing crystal 25 is made permeable to lower the energy stored in the excited crystal 10. Since the sudden decrease in energy due to the presence of the absorbing crystal 25 at If the threshold value is higher than normal, the output pulse has a relatively high one Top performance. The duration of the output pulse is relatively short because of the absorbing medium 25 switches extremely quickly from an absorbent to a permeable state. As in the case of the Kerr cell lock, subsequent output pulses after the first "giant" pulse can be suppressed.

The mathematical description of the mode of operation of the device according to FIG. 3 is as follows: If the energy density in the stimulated crystal 10 is designated P ₁ and that in the non-excited absorbing crystal 25 is designated P ₂ , then the total energy E in the resonator results as

E = P ₁ Zl ₁ L ₁ + P ₂ Zi ₂ L ₂ , (1)

where A _i and L _{i are} the area and length of the i-th crystal and L ₁ and L ₂ and A _i and A _{2 are} the lengths and cross-sectional areas of crystals 10 and 25. From the conservation of energy arises

P ₁ A ₁ = P ₂ A ₂ . (2)

The change in energy per time in the resonator, dE

-yy-, results from the sum of three expressions:

a) the rate of decline is due to the finite time

constant τ of the resonator;

b) the growth rate due to the stimulated radiation in the stimulated crystal 10 is in? *) HvBP _l A ₁ L ₁ ;

c) is the rate of decay due to absorption in the absorbent crystal 25

- (n { ²⁾ -n ™) hv BP ₂ A ₂ L ₂ ,

where njjl is the population density in the, / th energy level in the i-th crystal. For the sake of simplicity, only two non-degenerate energy levels 1 and 2 should be considered, with «ι + ⁿ 2 = N = constant, h ν is the energy of a photon of the stimulated radiation, B is Einstein's fl coefficient.

Adding these rates of change gives

d £
dr

(HVB) L ₁ + L ₂

£ ([nj »-“ <»] L ₁ -W ^2, -ni ² »] L ₂ ).

The change in the population density in the excited crystal 10 with respect to time is determined by the interaction between optical excitation and stimulated and spontaneous emission:

f _t W ^l) - - "H = <2p".

■ IAnl ¹¹ )

[«J ¹ '-n / ¹ '] Bp ₁

(4)

where ρ is the speed of excitation and A is the rate or change of spontaneous emission. The change in the population density in the absorbing crystal 25 with respect to time is determined by the interaction of absorption and spontaneous emission:

[»I ^2, -« i ⁽²⁾ ] = 2 Uu - [; j ₂ ⁽²¹

'2 ■

(5)

The introduction of the absorbing crystal 25 has the effect that the threshold value of the stimulated medium is increased by a factor of 1 + α.

The next question arises, what condition, if the threshold is reached, d £

d. h "if = 0 , the energy field of his

The initial value E _{0 can} increase, so that due to the loss in the crystal 25 its second derivative

-jp-> 0 falls faster than the excitation energy reserve in the crystal 10. After differentiating equation (3) and inserting equations (5) and (6)

d £

and after evaluating for -37 = 0 you get the

/ d ² E \

Condition that the second derivative [- ^ pJ is greater than zero if

After the threshold condition is achieved for the system (^ - = Sj, the energy and the population distribution in the equations (4) and (5) the slight influence of the members for exciting change in the two crystals as a result of stimulated radiation rapidly Thus. and the spontaneous emission can be neglected in comparison to the terms of the stimulated radiation. Using the relationship according to equation (2) one obtains:

A ₁

> 1

(H)

(«2

(U.

Ili ⁱ ')

L ₁ + L ₂

L ₁ + L ₇

A ₁

When the threshold is

d £
df

A,

0 and

- ■ (7)

(2)

N ^a> , 0,

£ = E ₀ ;

the equation (3) can be written:

L ₁ + L ₂

hvBrL,

whereby

= 1 + a,

h VBtL ₂ N ^w L ₁ + L ₂

(8th)

(9)

(10)

40

Thus, the amount of reduction in the light beam depends on the stimulable medium Achieve an automatic closure effect from the amount by which the threshold for a Vibration was increased by inserting the absorbent crystal. At a small magnification a large reduction is required for the threshold value, and vice versa.

The form of the pulsation of the optical transmitter according to FIG. 3 can be determined by integrating the three differential equations (3), (6) and (7) subject to the initial conditions. At the threshold we get:

d £
German

nj ² >

E ₀ , 0,

N ^a> , 0,

[L ₁ TL ₂ ]

HvBtL _x

TU ■

60

From equation (9) it follows that the quantity has the meaning that in the absence of the absorbing crystal 25 = 0 and the threshold value Inj ^u -n / ^u ] is given by

(L ₁ -L ₂ )

From equations (6) and (7) one can

(nj ^f) -n / °) as a function - (nf -n, ^<0 ). To

Inserting into equation (3) the time integral can be calculated directly, and E results as a function of the densities [^ ¹ '-n / ¹ *] and [nj ² ' -n / ²⁾ ]. This can be converted into a function of only (nj "- n / ¹ ') by the relationship

Ν ,.

Uni ^u - «/ ¹ W A ₂ '

ItvBrL _i

which results from the ratio of equations (6) and (7) to one another and through integration over the inverse population density. Since E as a function

of (n] ¹ '- η / ¹ ') is now known, equation (6) can be integrated and it results

(L ₁ + L ₂ ) A ₁ B.

dx

xE (x) '

(nJ "-«, "'Jru

(13)

whereby

E (x) = E ₀ + ßlnx + γ (1 -χ) + d (l ~ ^x ~ f)

η κ ■ ^{2 (14)} and where

γ = IivA _i L _x (nj "-» / ") ™, δ = hv A ₂ L ₂ N ⁱ² K

Equation (13) can easily be evaluated numerically.

Fig. 4A shows E as a function of * ^and Fig. 4B shows

this is the reshuffle normalized to the threshold, also as a function of

for a stimulated ruby radiation and a absorbent with the following parameters defined above:

A ₂

-9- = ίο,

A ₁ L ₁ L ₂

π 2

7 cm, 7th

cm,

The time constant of the resonator is given as

1 -ν + Ci _s (L ^ L ₂ ) C '

whereby

L = length of the resonator = 20 cm, r = radius of the resonator = 0.9 cm, a, = scattering coefficient = 0.05 cm ^-1 , c = speed of light = 3 · ¹⁰ cm / sec.

Similar curves can be drawn for other systems that use other stimulable media and use absorbent media and / or other resonator time constants.

The way in which a stimulated ruby beam works with an absorbing medium has given rise to the above theoretical considerations. In one case, a ruby staff 10 was made with with a diameter of 1 cm and with a 90 ° orientation in a suitable resonator vessel.

The rear surface 18 of the rod was 100% silver-plated and the front surface 20 was coated _{with MgF 2 to reduce reflection.} The other mirror 27 of the Fabry-Perot was approximately 40 cm from the surface 20 of the ruby that was coated with the anti-reflective agent and consisted of a dielectric half mirror with 10% transmittance. Between the outer Fabry-Perot mirror 27 and the one with the anti-reflective agent

On the coated surface 20 of the ruby rod 10, a Kepler telescope was provided, which the lens arrangement 22 according to FIG. 3 corresponded. An absorbing medium 25 made of a 0.04% chromium-doped ruby rod with a cross-sectional area of ^{1 cm 2} and 57 ° orientation was placed near the focal point of the telescope. The absorbent Rubin 25 has been rotated so that it stimulated light generated by the oriented by 90 ° stimulated ruby rod 10 ^- was maximal coupled.

When 750 electrical joules of excitation energy were supplied to the system, oscillation occurred in a single sharp point after about 590 (Asec on; without the absorbing ruby would be the oscillation occurred approximately after 400 μβεϋ.

Thus, the threshold value of the vibration became due to the use of the absorbent medium elevated.

Although the embodiment of the invention using the optical avalanche technique for a Ruby medium and a ruby absorbent medium have been described, it is evident that the Principles of the invention are not limited thereto. For example, any suitable stimulable medium in solid, liquid or gas shaped form can be used. Many such Substances are already known to be useful for generating stimulated radiation when the appropriate type of excitation energy is supplied. Accordingly, the fabric of the absorbent Medium 25 either solid, liquid or gaseous be. In general, the absorbent medium is chosen so that it can be reused, to generate many output pulses; especially so that it is sufficiently resistant to thermal Shock effects is to withstand the high peak power output pulses of the optical transmitter to be able to.

Although it is simple and convenient for the stimulable medium and the absorbing medium Using the same material can be done with a different absorber medium in certain cases Be an advantage. While the use of the same substance for the stimulable medium and the absorbent medium ensures that the stimulable Medium generates light of suitable frequency, which is the transition of electrons in the atoms of the absorbent medium to bring the latter into a permeable state, so can but appropriately chosen, different fabrics for the absorbent medium and the stimulable Medium can be used with equal success. For example, a solid, liquid or gaseous stimulable medium can be combined with a different gaseous absorbing medium Find use. It is well known that certain gases, especially molecular gases, have numerous absorption lines with a relatively large bandwidth, and there is therefore a high probability

that they are useful for a given stimulable medium. The absorption band can also a gas used as an absorbing medium within certain limits by increasing the Pressure of the gas can be broadened.

The F i g. Figure 5 shows the principles of optical avalanche technology applied to a gaseous stimulable medium. A vacuum sealed fused tube 50 contains a quantity of a suitable gaseous stimulable medium 52 useful for generating stimulated radiation. The excitation energy is supplied from a suitable radio-frequency energy source 54 to two electrodes 55 which are capacitively coupled to the tube 50 . The rear end of the tube has a semi-transparent mirror 57, while the front end has a transparent surface 59 which is arranged at Brewster's angle. The gaseous stimulable medium operates in a conventional manner, the electrons of the gas being excited by the radio-frequency energy to produce an output pulse which would normally be continuously emitted by the mirror 57 in the absence of an absorbing medium 25.

The absorbent medium 25 is arranged near the transparent surface 59 and is designed as a vacuum-tight tube 60 with two permeable surfaces 61 and 62 . These surfaces are also arranged at Brewster's angle. The tube 60 contains a certain amount of the gas, which acts as an absorbent in a manner similar to that already in the absorbent medium according to FIG. 3 has been described. A reflective mirror 27 is positioned near surface 62 to complete the optical resonator.

In the embodiment according to FIG. 5 , no optical system for converging the beam is arranged between the stimulable medium and the absorbing medium 25. Such an optical system can of course be provided if necessary. If the absorbing medium is made of the same material as the stimulable medium, then it needs a higher light energy density than the stimulable medium in order that its saturation rate becomes fast enough to lower the energy of the stimulable medium. Where the stimulable medium and the absorbent medium are of the same fabric, an optical system is required for a necessary downsizing. This has already been explained with reference to equations (10) and (11). If the stimulable medium and the absorbent medium are not the same, downsizing may be unnecessary because an absorbent which saturates faster than the stimulable medium can be used. In this case, no optical system is required for downsizing.

As already stated above, the same or different gases can be used for the stimulable medium and the absorbing medium. In general, a few millimeters are sufficient for the thickness of the absorbing gas at or above atmospheric pressure in order to achieve a corresponding absorption for the closure effect, as described in connection with FIG. 3 was described to generate. It should be noted that FIG. 5 is not drawn to scale as the relatively small required thickness

of the absorbing gas would be displayed. As pointed out earlier, the bandwidth can the absorption or spectral lines of the gaseous absorbent medium by increasing the gas pressure can be widened. The thickness of the absorbing gas can also be changed, to control the vibration threshold of the optical transmitter.

If different gases are used for the stimulable medium and the absorbing medium, see above Molecular gases are preferable for the absorbing medium. With molecular gases you can do a lot easily a coincidence between the absorption band of the absorbing gas and the frequency of the output light of the stimulated medium. Iodine and bromine are especially considered to be absorbent Suitable for gases. Molecular gases as an absorbing medium that dissociate and thereby promote the effect of the absorbent medium are beneficial. Of course, others can too appropriate molecular gases, whether dissociable or not, are used. Also an atomic gas other than the stimulable medium can be used where appropriate random coincidence of the spectral lines occurs. .

The mode of operation of the gaseous optical transmitter according to FIG. 5 corresponds to that according to FIG. 3. Excitation of the gaseous stimulable medium 52 generates stimulated light which exits through the permeable surface 59 into the absorbing medium 25. The absorbing gas 25 is excited by the absorbed stimulated light reflected back into the tube 50 by the mirror 27. At a predetermined light output threshold of the stimulated medium, the absorbing gas will "burn through" and become practically permeable. This makes it possible to achieve a larger stored energy supply in the stimulable medium at a higher threshold value than is normally achievable without the absorbing medium, and thus an output pulse at the end 57 with a relatively high peak power is produced.

It can thus be seen that the optical avalanche technique described has various advantages. before above all, the light shutter effect is passive, and there are no additional output power and associated therewith Power supplies are required for the operation of the absorbing medium. Also will the absorbing medium is not necessarily destroyed every time an output pulse is generated. The pulse effect can be controlled so that single high peak power output pulses are achievable.

The optical avalanche technique described above can also be used for the selection of a special one Natural oscillation of the stimulated radiation from several generated transverse natural oscillations Find application. As is well known, the vibration of a stimulated medium is sometimes through it characterized in that it occurs in more than one natural oscillation. Will be the output of the stimulated When the light is shown on a screen, the natural oscillations of a transverse kind appear as separate ones Light pattern at a distance from the optical axis of the resonator. To select the natural vibrations different techniques are already used; an easy way is to

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Claims (7)

1 to use a lens and a pinhole collimator which are inserted into the light path of the resonator and only allow the passage of light with the desired natural oscillation. F i g. 6 shows a system for the selection of the natural oscillation by means of the optical avalanche technique. A semi-transparent mirror 71 is disposed near the rear surface of either solid, liquid, or gaseous stimulable medium 70. The excitation power source and other accessories] 0 are of conventional design and have been omitted for clarity. Likewise, the Brewster angular interfaces have been omitted which can be used if desired. The front surface of the medium is transparent and the stimulated light appears on one surface of a biconvex lens 73, the focus of which is located within the boundaries of the absorbing medium 25. As has already been explained, the absorbing medium can consist of solid, liquid or gaseous substance and can be the same or different from the stimulable medium. Another biconvex lens 74 is arranged between the absorbing medium 25 and the mirror 27. Other suitable optical systems can optionally be used for the downsizing. The optical lenses 73 and 74 are physically arranged so that they together with the reflectors 27 and 31 form the optical resonator. The optical resonator can easily be dimensioned so that a certain transverse natural oscillation prevails; this is usually always the case. As can be seen from the basic optical principles, there is only one focal point in the absorber for each transverse natural oscillation (or each direction of the stimulated radiation). The cones, which represent the volume of the absorbing medium through which a certain natural oscillation flows, can be made sufficiently small that there is little or no overlap between adjacent transverse natural oscillations. Thus, a certain double-cone-like part of the volume of the absorbing medium 25 receives light energy density almost exclusively from a certain predominant natural oscillation and hardly from all other natural oscillations. As a result of its higher energy density, the light of a desired natural oscillation will "burn through" the absorbing medium in this small double-cone-like volume part (make it permeable) before the light energy of the other natural oscillations can achieve this with the same result for their corresponding volume parts. This means that the energy stored in the stimulable medium is used for a desired natural oscillation and is thus withdrawn from the other natural oscillations. Optical avalanche technology thus generates a selection of the natural oscillation in such a way that only the stored excitation energy is used up for the prevailing natural oscillation. This is completely different from the other natural oscillation selection systems in which the consumption of the excitation energy is coupled with a desired direction of propagation, which may or may not represent a predominant natural oscillation, while other directions are blocked. It will be understood that the peak output power of the selected natural oscillation can be increased at the same time by raising the oscillation threshold value as a result of the use of an absorbing medium in the manner previously described. Patent claims: 1. Optical transmitter for generating output pulses of high peak power by means of influencing the quality of the optical resonator (ß-circuit) by having a medium inside it variable absorption is used, which is achieved after receiving a sufficient amount of energy the stimulated radiation saturates itself, becomes transparent and thus the way within of the optical resonator releases, characterized in that the absorbing Medium (25) is either made of the same substance as the stimulable medium or made of consists of a different material, but which is not a photochromic glass. 2. Optical transmitter according to claim 1, characterized in that an optical system (23, 24) between the stimulable medium (10) and the absorbing medium (25) is arranged to generate a concentrated incidence of the stimulated light bundle on the absorbing medium, which a cross-sectional limitation of the parallel beam in the absorbing medium (25) allows. 3. Optical transmitter according to claim 2, characterized in that the optical system focuses a predominant natural oscillation of the stimulated light beam on the absorbing medium, whereby said predominant natural oscillation makes the absorbing medium relatively permeable before the corresponding threshold values for the other natural oscillations are reached. 4. Optical transmitter according to one or more of claims 1 to 3, characterized in that the absorbing medium is gaseous or vaporous. 5. Optical transmitter according to claim 4, characterized in that the gas of the absorbing medium is atomic. 6. Optical transmitter according to claim 4, characterized in that the gas of the absorbing medium is molecular. 7. Optical transmitter according to claim 6, characterized in that the molecular gas of the absorbing medium is iodine or bromine. 1 sheet of drawings