DE1204747B - Amplifiers or transmitters working according to the principle of stimulated emission, in particular light amplifiers working with a semiconductor - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

HOIs

German class: 2If-90

Number: 1204 747

File number: S 76176 VIII c / 21 f

Filing date: October 4, 1961

Opening day: November 11, 1965

The invention relates to the principle of stimulated Emission-working amplifiers with an atomic or molecular system that is controlled by a external energy source, in particular in pulses, can be excited.

This excitation determines the occupation ratio in the atomic or molecular system terms optically combined with one another changed in such a way that energetically higher terms are stronger and energetically lower terms are less occupied than it corresponds to the state of equilibrium which the system adjusts itself in the absence of the excitation energy. They start already during the excitation excited terms to emit a short-wave, in particular optical radiation.

The atomic system, in particular a semiconductor provided with suitable dopants, e.g. B. a ruby, is generally provided with two plane-parallel, opposing mirrored surfaces, between which the radiation emanating from the terms is constantly reflected back and forth. As a result of this multiple reflection, the radiation in the system is amplified into a sharply focused, high-power beam. When it hits the reflective surface parts of the system, a portion (ε _Γ ) of the beam energy emerges from the system through a hole in one of the reflective surfaces and is emitted. Another part (e _A ) of the incoming beam energy is absorbed in the mirror coating. The remainder of the beam is reflected and again amplified on its way to the opposite, plane-parallel mirrored surface.

Provision is made for the amplifier according to the invention to allow the radiation to exit the system through one or more weakly permeable, reflective surfaces known per se in a proportion ε _τ.

In amplifiers, e.g. B. with well-cut, mirrored ruby crystals, which were stimulated by strong photo flash lamps to a light amplification of the type described, it has now been found that the amplitude of the emitted beam during the duration of the excitation of the photo flash, which was about 10-3 seconds, very was violently and clearly anharmonic "modulated" with a frequency of about 10 ^{6 Hz.}

When transmitting messages using optical, in particular infrared, amplifiers or - The impulse mode has proven itself very well for transmitters; above all, this is the impulsive excitation of the amplifier very easy to achieve high transmission power

Amplifiers or transmitters working according to the principle of stimulated emission, in particular light amplifier working with a semiconductor

Addition to registration: S 75744 VIII c / 21 f - Auslegeschrift 1191041

Applicant:

Siemens & Halske Aktiengesellschaft, Berlin and Munich,
Munich 2, Witteisbacherplatz 2

Named as inventor:

Dr. rer. nat. Hans Rother, Munich

wishes. Here, however, the aforementioned "modulation" of the emitted radiation is particularly disruptive. For this reason, this "modulation" in the amplifier must be brought to decay as quickly as possible, with a decay time that is short compared to the pulse duration.
On the basis of detailed considerations, this object of the invention is in an optical amplifier or transmitter with stimulated radiation in an atomic or molecular, selectively fluorescent medium, in particular a solid body that is stimulated in pulses by an external energy source and in which an extremely short-wave, in particular Optical radiation is amplified as a result of multiple reflections in an optical resonator to a sharply focused beam of high power, especially in an optical amplifier in which, according to the main patent application, German Auslegeschrift 1191 041, a portion of the beam running inside a crystal at one point of Crystal surface, on which this beam strikes at an angle corresponding to total reflection, emerges from the crystal by tunnel effect in that the reflection point is opposite at a very small, preferably adjustable distance, the size of which is at most approximately equal to 5 to 10 f achen the wavelength of the emitted radiation, a for

509 737/147

the exiting beam is arranged permeable body, achieved in that the means that cause the exit of the beam from the optical amplifier are dimensioned so that the portion (ε _Γ ) of the radiation impinging on the S exit surface exiting from the optical amplifier so it is small that the intensity of the emitted radiation ^{assumes a constant value during the - in particular up to about 10 ~ 2} seconds - lasting excitation pulse, ίο

Under "optical amplifier or transmitter" in the sense of the invention are those in the Anglo-Saxon To understand literature as a »burl« and in particular the arrangements called »lasers«, which are sometimes referred to as quantum mechanical amplifiers or transmitters. Under »optical Resonator «is to be understood as a resonator as it is known for maser or laser is used.

The effect of this rule is surprising, because despite the weakening of the percentage of radiation exiting the system (ε _τ ) caused by the measure according to the invention, the intensity of the emitted radiation is only changed insignificantly. However, the great advantage is achieved that after the excitation, the beam is emitted with a practically always constant size. As has been found through detailed investigations and considerations, the intensity of the emitted beam is proportional to the

haltnis ^^ where ε _τ indicates the portion of the radiation energy emerging from the system on the exit surface of the system and ε _Α indicates the absorption losses occurring in the mirrored end surfaces; on the other hand, the decay time of the “modulation” mentioned is proportional to the sum of these two values (ε _Α + ε _τ ). By reducing the component ε _τ according to the invention, the decay time of the "modulation" can be made sufficiently short without the intensity dropping too significantly.

With the mentioned amplifiers with ruby as medium and other similar amplifiers with solid medium, systems that are evenly mirrored on both sides have been used up to now, i. H. the two mirrored, plane-parallel surfaces of the ruby were partially permeable. Will however according to the further invention worked only on one side with transparent mirrored systems, while the other plane-parallel opposite surface is opaque mirrored, so is the Speed at which a constant intensity is established after the start of the excitation pulse,

and the intensity increased by a factor of about 2. _t ^B

It has proven to be particularly useful to work with a system in which the mirroring is completely omitted and the beam is totally reflected on the surface of the system, as suggested in the main patent application, German Auslegeschrift 1191 041, and in the example in Fig. 2 is described. In this case, the absorption losses have become ε ^ = zero. In order that the "modulation" decays during the excitation time and then remains constant without "modulation" for the duration of the external excitation, the inequality c · ε < L (S + A) is decisive, as detailed investigations have shown.

In this equation, c denotes the speed of light, ε the sum of the value formed from the absorption ε _Α and the component ε _τ , L the length of the path of the bundled beam in the system between two emissions, S the probability that the external energy source generates the excitable atoms of the system are raised from their ground state (E ₀ ) to the excited higher energy state (E ₁ ) and A the probability of spontaneous emission by return of the atoms brought into the excited state E ₁ by the external light source to the ground state E ₀ ; To further explain these variables S + A, let us explain: The external energy source lifts n _o -S atoms per second and cubic centimeter from the ground state E ₀ to the excited state E ₁ , where n _{0 is} the number of atoms · cm ^-3 which are in the ground state E ₀ before the excitation and can be brought into the excited state E ₁ by the external energy source (stimulable atoms), the excited state E ₁ goes with a probability A (see " ¹ ) with spontaneous light emission of the frequency

** = "V ^{again m the} basic state E ₀ over.

The inequality given above can therefore be fulfilled if the ε in it, ie the sum of the proportions of the beam energy that is lost during emission and reflection from the incoming beam due to _{emission and absorption} , is kept sufficiently small. Due to the total reflection proposed in the main patent application, the absorption ε ^? »O is made, ie only scatter reflection losses occur as a result of an imperfectly polished surface; In addition, according to the present invention, the ε _{τ must} be kept sufficiently small by making the tunnel path (see d in FIG. 2) sufficiently long. The "modulation" of the emitted radiation then dies away during the brief excitation pulse.

The ratio of the line width v _{0 of} the emitted, sharply bundled beam to the transition probability A divided by the number N of stimulable atoms cm- ³ has an atomic value for each basic material of the atomic system at a given operating temperature, namely the concentration of the stimulable atoms in the atomic System should be chosen so high that the broadening of the line width v ₀ , which is dependent on the mutual interaction of the stimulable atoms, just does not cause a disturbing

take the expression

with increasing N

when such amplifiers place value on a narrow line width of the emitted beam. It is therefore important, depending on the atomic or molecular system used, to make the number of stimulable atoms so large that the emitted beam has the line width v ₀ that is just allowed.

Further details of the invention can be found in the following description and in FIGS and FIG. 2 shown embodiments.

In Fig. 1, 1 is a ruby crystal, which is impermeable on side 2 and permeable on side 3

is mirrored. The sharply bundled bundle of rays (see the solid arrow 4) only emerges from the ruby 1 in one direction, namely through the transparent mirror coating 3. Inside the amplifier, a beam with the energy E hits the transparent mirror coating on. Part of this energy (ε _Α ) is absorbed in the mirror coating 3. Another part (ε _τ ) see the dashed arrow 5) emerges from the crystal and is emitted so that the beam reflected by the mirror coating 3 only has the energy content Ε— (ε _Α + ε _Γ ) . The material and the thickness of the mirror coating 3 are chosen so that ε _{τ is} greater than or at most = ε _Α . As explained above, the "modulation" of the radiation 4 then dies away during the excitation pulse by which the stimulable atoms of the crystal are raised to their higher energy level. However, it is possible to make the decay time significantly shorter, in particular less than 10 ^-3 seconds, so that the emission 4 has reached its constant value at the end of the excitation pulse only in the case of very short excitation pulses. Nevertheless, due to this relatively low radiation ε _τ due to the low permeability of the layer 3, as provided according to the invention, the intensity of the emitted beam 4 is reduced to approximately half of the maximum possible.

In Fig. 2 shows an optical amplifier according to the main patent application. The beam (see the dashed line) which circulates the stimulable atoms in the single crystal after the excitation is reflected completely and practically without loss on the three planar but not mirrored surfaces 11, 12, 13 (except for scattered reflection on the poorly polished surface). Opposite the surface 14, which is also ground flat and not mirrored, on which the beam is also totally reflected, a glass body 15 is provided for coupling-out, which faces the surface 14 of the single crystal 1 at an adjustable distance d. The beam impinging on the surface 14 with the energy E emits the energy ε _τ into the glass body 15 through the tunnel effect, from which this beam emerges sharply bundled in the direction of the arrow 4. The beam reflected back into the single crystal 1 by the surface 14 initially only has the energy E - ε _τ , but is then amplified again to the energy E in the course of its dashed path, etc. According to the invention, the distance d is now selected to be so large that the "modulation" of the emitted beam 4 already decays during the duration of the excitation pulse. Since no absorption losses ε _Α occur in the exemplary embodiment in FIG. 2, this condition can therefore easily be met with a sufficiently well-polished surface. In order to reduce the emitted energy component ε _τ , the distance d between the exit surface 14 of the single crystal for the beam and the surface of the glass body 15 opposite it must accordingly be made correspondingly large.

In all cases of the invention it is essential that the component ε _{τ is} not reduced unnecessarily. It is therefore important to make it just so small that the "modulation" of the emitted beam decays at least during the excitation pulse and the emitted beam thus assumes its constant value during the excitation pulse. Since, however, especially in the embodiment of FIG. 1 with permeable, playful surfaces, the emitted power is essentially dependent on the component ε _τ , it is recommended, on the other hand, not to make the component ε _τ smaller than is absolutely necessary to meet the stated condition correspond to. In the case of FIG. 1, in order not to reduce the intensity of the emitted beam unnecessarily strong, the coupled-out power ε _{τ is made} approximately equal to the power ε _Α absorbed when it exits.

Claims (6)

Patent claims: 1. Optical amplifier or transmitter with stimulated radiation in an atomic or molecular, selectively fluorescent medium, in particular a solid body, which is stimulated in pulses by an external energy source and in which an extremely short-wave, especially optical radiation as a result of multiple reflections in an optical resonator is amplified to a sharply focused beam of high power, in particular an optical amplifier, in which, according to the main patent application S 75744 VIIIc / 21 f, (German Auslegeschrift 1191 041) a portion of the beam running inside a crystal at a point on the crystal surface at which this beam impinges at an angle corresponding to total reflection, exits the crystal by tunnel effect, in that the reflection point opposite at a very small, preferably adjustable distance, the size of which is at most about 5 to 10 times the wavelength of the exiting radiation, one for the exiting beam is arranged permeable body, characterized in that the means which cause the exit of the beam from the optical amplifier are dimensioned so that the portion (ε _τ ) of the radiation impinging on the exit surface exiting from the optical amplifier is so small is that the intensity of the emitted radiation assumes a constant value during the excitation pulse. 2. Amplifier according to claim 1, the surface of which is at least partially reflective to the exit of a portion of the incident rays, characterized by such a permeability of the reflective coating that of the rays impinging on the reflective coating of the amplifier only about as much (ε _τ ) of the incoming rays Radiant energy passes through for emission, as is lost through absorption or scattering (ε ^) during reflection. 3. Amplifier according to claim 1, characterized in that of the mirrored surfaces of the amplifier only one is provided with a mirror coating that is partially permeable to the beam is. 4. Amplifier according to claim 1, in which the beam according to the main patent application (German Auslegeschrift 1191041) is decoupled from the optical amplifier on a totally reflective surface by means of tunnel effect, characterized in that the tunnel path, that is, the distance between the opposing surfaces, so large and the decoupled portion (ε _τ ) of the incident rays is so small that during 7 8 of the excitation pulse the emitted Strah-Elektro Welt, 1960, vol. 5, no. 5, edition C, development reaches a constant value. P. 124; 1961, vol. 6, No. 95, specialist edition, pp. 124/125. Publications Considered: Older Patents Considered: U.S. Patent No. 2,929,922; 5 German Patent No. 1151 601. 1 sheet of drawings 509 737/147 11.65 © Bundesdruckerei Berlin