DE2638943A1 - METHOD AND DEVICE FOR CONVERTING COHERENT LIGHT OF DIFFERENT WAVELENGTHS INTO COAERENT LIGHT OF ONE WAVELENGTH - Google Patents

Description

DR. KARL · TH. HEGEL DIPL.-ING. KLAUS DICKEL

.. i. ο ο 9 y η 4

P A T El N T A N W A L T B

HAMBURG BO GROSSE BERGSTRASSE 223 8 MUNICH 6O JULIUS-KREIS-STRASSE 33 POST BOX Β006Θ2 TELEFON (O40) 39 62 95 TELEPHONE (O 89) 886210

Telegram address i Doellnerpateiit Munich

Your reference: Our reference: H 2610 8OOO Munich, Aug. 24, 1976

Exxon Research and Engineering Company LINDEN, New Jersey 07036 V. St. A.

Method and apparatus for converting coherent Light of different wavelengths into coherent light of one wavelength

The invention relates to a method and a device for converting coherent light of different wavelengths into coherent light of one wavelength using a Laser delegation. In particular, a coherent one

. 709817/0672

Postal checking account: Hamburg 2612 20-20B. Bank: Dresdner Bank AG. Hamburg, account no. 3 813 897

'Radiation with different wavelengths effective in one essentially monochromatic coherent radiation implemented who

The conversion of optical information from a first j beam with a first frequency to a second beam with
another frequency is known. Describes in particular
the American patent 3 731 223 an optical cavity with a laser operating simultaneously on two or more
Wavelengths works, and an organic color solution that
the radiation of the shorter wavelength absorbs and fluoresces the [longer wavelength. With this arrangement! the dye are located within the optical resonator, ί so that accordingly the laser material does not work with the maximum efficiency. I. E. the color changes the gain distribution of the overall combination. With this distribution
change, the pump laser works below the efficiency with which it alone in the optical resonator
whose normal resonance wavelengths would work.

According to another known arrangement, color lasers are used, only the wavelength of the incident coherent; to change the radiation. For example, after the
American patent 3 371 265 a Raman-active cell j with a coherent radiation of a first wavelength applied; shine. The Raman cell absorbs the incident energy and
it emits in a different wavelength. The frequency of the
Output radiation is determined by the frequency of the excitation radiation; changed by an amount directly related to the j Raman active stationary energy levels of the particular in the j

[Cell material used stands. I.

·

; In this arrangement, the energy source is monochromatic. ί

The invention is based on the object in an effective Way to convert the entire output energy of a source of coherent light with different wavelengths into radiation energy of a single wavelength.

According to the invention, a. first laser material is pumped to produce spontaneous light emissions in two or more wavelengths. An optical resonator is applied to the first laser material in order to effect an optical feedback, so that the first laser material emits stimulated emissions of coherent light of those wavelengths. The optical resonator has a partially transparent reflective surface which part of the stimulated coherent light of different Wavelengths is emitted. A second laser material is irradiated through the output of the resonator. That The second laser material preferentially absorbs the light of all incident wavelengths with one exception, this exception the unabsorbed wavelength in the fluorescent Band of the second laser material lies. The light irradiation of the second laser material causes it to be stimulated emits coherent light with the one unabsorbed wavelength.

Essentially, the absorption of the multi-wave output of the first laser by the second laser material serves to to pump the latter (i.e. to produce an inverted population density) and the only output of the unabsorbed The wavelength of the first laser material stimulates the inverted second laser material and amplifies the non-absorbed white len length. The multi-wave pump radiation for the second laser, material must be spatially and temporally synchronous with the non-absorbed stimulating radiation.

I Various exemplary embodiments of the invention are to be ! explained in more detail with reference to the accompanying drawings will. It shows in detail:

ι Figure 1 is a schematic representation of a preferred embodiment the invention,

Figure 2 shows the laser output energy at two wavelengths,

FIG. 3 shows the absorption and emission spectra of a color laser at two wavelengths,

Figure 4 illustrates an optical delay that can be used where the optical outputs of the do not enter the first laser at the same time,

Figure 5 is a schematic representation of a second embodiment of the invention and

FIG. 6 shows the energy spectrum in the embodiment according to FIG. 5.

! In Figure 1, a first laser material 1 is shown at . which can be any laser material, capable of giving off spontaneous light emissions at different wavelengths. In one embodiment of the invention acted the laser material 1 is copper vapor obtained by discharge dissociation of copper-halogen vapor and which is enclosed in a suitable transparent container 3.

The laser medium 1 is pumped by means of electrodes 5, which (not shown) to a corresponding voltage source are connected to an electrical discharge within the '· container 3 carried out. With copper halogen vapor as laser I

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material 1 requires two electrical discharges. j The first electrical discharge disassociates the copper from ^: the halogen; the second electrical charge pumps the copper,

to achieve an inverted population density.

Although Figure 1, a copper vapor laser is pumped by an electrical discharge in accordance with the embodiment, any laser material is suitable that is capable of producing stimulated emission at two or more wavelengths _o Examples of other suitable laser materials are lead vapor and manganese vapor. In addition, any arrangements for pumping this laser material can also be used. Other possible pumping arrangements are, for example, flash tubes and other lasers.

Although most laser materials that are capable of at the same time radiation with more than one wavelength increases emit, can be used, the present invention works best when the first laser material has a high Able to generate energy density in the dye.

The laser material is enclosed by an optical resonator 7. The optical reso. nator 7 consists of a 'totally reflective mirror 9 and a partially reflective Mirror 11 and provides an optical feedback for the spontaneously emitted light of the laser material 1, whereby this one coherent light radiation at the wavelengths emitted, which are generated spontaneously under the pumping action of the electrical charge arrangement 5. The optical resonator 7 is preferably arranged so that the laser material 1 outgoing radiation has the same mode overall.

The Lasr shown in Figure 1 generates two wavelengths of stimulated coherent light: Λ ₁ and Λ ₂ · Λ ^ is a shorter wavelength than An · In addition, the characteristic

-? Q9S17 / O672 ■■ · "". ■

ka of the optical resonator 7 and the "pumping" by elec- I

tric discharge set so that the total energy output j is optimized and it is ensured that the output / L i and / ^ 2 from a common volume of excited materials; is produced. The latter condition leads to the spatial
Overlapping of the output of the laser 1 into the laser material 2
into it. This optimal condition can be obtained by ^: experimentally changing parameters such as pump intensity, cavity tuning and mirror reflection using conventional methods. In particular, in the case of a copper vapor laser, in which the pumping is carried out by electrical discharge, the variable parameters are discharge voltage, discharge current density, current rise time and pulse width. the
Setting the parameters of the reinforcement material such as
Copper vapor pressure and the inert gas environment can also be changed in order to achieve an optimized total energy output; keep·

The radiation penetrating the partially reflecting mirror 11; is collected by means of a lens 13 in order to concentrate the radiation on a: small volume so that a high energy density is generated. A second laser material 15 is arranged at the focal point of the lens 13. The second laser material 15; should be able to absorb j all of the wavelengths generated by the laser material 1 with one exception for the most economical mode of operation. In addition, the non-absorbed _; Wavelength in the fluorescent band of the laser material 15 ] . If these conditions are met, the laser material 15 emits stimulated coherent light of the unabsorbed wavelength with a large proportion of the total multi-wave energy which the laser material 1 imitates.

Finally, it is extremely important that the laser material 15 at
, outshining the energy density with which it is irradiated

j is. That is, the combination of the energy output

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of the laser material 1 and the lens 13 in the laser material 15 generates an energy density which is sufficient to generate a sufficiently large inverted population density so that the Laser material 15 has a large ratio of increased spontaneous emission to spontaneous emission ("super radiation") has unabsorbed wavelength. In practice this requirement means that the laser material 15 has a simple transition gain of normally over ten db.

Another consequence of the physical properties of the laser : materials 2 is that the denser the emitted by laser 1 Wavelengths are, the greater the efficiency of the laser material 15 is.

Since the optical resonator 7, which causes the emission of the stimulated coherent light emitted by the laser material 1,

has the same mode, the pump ^{wavelengths (the:} wavelengths that are absorbed by the laser material 15,)

not completely absorbers inside the spatial volume of the ί <bierten wavelength, thereby causing stimulated emission. Thus, wherever photons are in the laser material | 15 are pumped, this also stimulates to emit light coherently * and synchronously with the output wavelength.

In addition, according to the preferred embodiment, an arrangement for focusing the output of the laser material 15 is provided. In detail, this arrangement is shown schematically by the lens 17 in FIG. The lens 17 focuses the slightly divergent output of the laser material 15 to infinity, d. H. the rays leaving the lens 17 run parallel.

Although those skilled in the art will be able to identify numerous systems within To build up the parameters given above, the following example should be given. The laser material 1 is a

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Copper chloride vapor in a suitable container. An electrical discharge is created to remove the copper chloride
dissociate and pump the dissociated copper vapor into an excited state so that stimulated light emission occurs. The laser material 15 is a cell of rhodamine-6G-

—4
Dye in solution of 10

neither methanol nor ethanol.

—4 5
Dye in solution of 10 to 10 mol per liter of

j The following theoretical derivation explains the invention; proper operation and in particular the example mentioned above. It should be assumed that the laser material 1 generates a plurality of wavelengths, N ie / \ <, ^ p, ..., -. / WI ^f Ä N ° ^D ^ ^"e 9 ^ESAM th output energy (E) of Laser material corresponds to the sum of the output energies at each wavelength, ie

O / 1 "/ Ϊ" / Im-I / Im

The dye material 15 is used - as described above - to generate the energy E, which is normally applied to the N wavelengths
distributed, as indicated in equation (I), are distributed into a single wavelength of interest, i.e. H · / \ „i to implement. ·

As a special example, the output of a copper vapor laser is to be assumed. There are two operating _{wavelengths at / ^ 1} - 5106 X and A ₂ ⁼ 5782 % . Assuming further that the laser is operating under optimal conditions, the output energy at 5106 A ₁ E \ is three times that

greater than the energy output at 5782 ft . _f E \. I. E.

A ₁

3E. (H)

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shown.

Inserting equation (II) into equation (III) results in ¹

! 1. The wavelength ^ ₁ is near the tip of the absorbing

[tion band of the dye,

1 2. the wavelength / \ ₂ is close to the tip of the fluores

ί decorative tape of the dye

! and

\ 3. the dye has a high fluorescence efficiency.

09817/067 2

The output energy and the wavelength under consideration of the copper vapor laser is shown in FIG. "i.." - "

ι The ratio ^^ of the output energy Ελ to the total output energy E is given by _;

^! '"7E" - E _n V (Ev + E.). (III7!

_{Zf 1} -1/4 (IV)

i This shows that a quarter of the total output energy is at about the wavelength / V.

; The dye converter amplifies this ratio (the maximum is of course the unit). The dye is due selected from the following criteria:

- ίο -

The absorption and fluorescence bands of a selected color ^; material are shown in FIG. ■

The incident radiation at) ^, which is absorbed by the dye solution, "pumps" the dye molecules of the basic stage into a first excited electron stage. Would just ) i,. are present, the excited dye molecules would fluoresce spontaneously over the entire fluorescent band shown in FIG.

—9
sometimes 10 seconds, generally resume the basic stage.

The simultaneous presence of the laser output in / ^ p within the dye does not stimulate the excited _molecules: - to mimic over the entire spontaneous Fluoreszensband, but only at exactly the same wavelength, the same \ Charaktaristika in the incident radiation at ^ ₂ vorlie-! gen. Accordingly, the laser output at, ^ ab-; sorbed energy at /) p ^m ^^ emitted ^the same characteristic a (ζ. B. direction and polarization) _? like the incident radiation from the laser at ^ _2.

; As mentioned earlier, the extremely fast leads spontaneously; ; Fluorescence speed of the excited dye molecules

■ 8 —1 '

\ (10 see) for the system to two requirements to the order ^; To optimize conversion efficiency. The first requirement;

^! lies in the fact that the radiation at ^ ^ and } \ ₂ is to be focused into the dye cell in order to achieve the greatest pumping speeds in the excited state of the dye and the greatest stimulated emission rate out of the excited state of the dye. The second requirement is that there must be a temporal overlap of the laser output at ^ ^ and / ^ _{2 in} order to ensure that essentially all molecules through / ^ ₁ in the

! stimulated status are pumped in order to become stimulated

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Emission at ^ \ _{2 to} contribute. If the laser output occurs at and ^ "in a chronological sequence, optical delay arrangements must be provided outside the laser before the radiation is focused into the dye converter.

j -

j Figure 4 shows a device that can be used j when the laser outputs at ^ ₄ . and ^ ₂ i "occur in a time sequence. In FIG. 4, parts that are already shown in FIG. 1 are provided with the same reference numerals. In the following example, it should be assumed that the laser output at,? Laser output occurs at f \ * ^{. Accordingly, it is necessary to} delay the ^ - output relative to the ^ \ ₂ -output. For this purpose a dichronic beam splitter 30 is provided at the output j of laser 1, which is the ( ^ ,, - output and the ^ ₂ -OuS-j output from one another. The ^ ,, - output is fed to an optical delay zone 32 (for example a white cell or another suitable delay arrangement), where it is passed for a sufficiently long time is delayed in order to ensure the temporal overlap, if it is ^{reunited with the ^ 2 "" AuS (} 3 ^to 9 via a dichronic mirror 34 or a similar arrangement, as shown schematically, the ^ "output can be the dichronic mirror 34 via the reflectors 35 and 36, which cause only a negligible delay due to the longer propagation path, are fed back. The beam from the mirror 34, which contains the ^ ₁ and } \ ^ components at the same time, is again transmitted to the lens 13 in order to bring about a focusing, as was explained above in connection with FIG.

The total energy conversion efficiency # _c can be expressed as

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where ff _{d is} the fluorescence efficiency of the dye. For the example, If _d = 1 should be selected. Then applies

^ c * fil ^ 2

and for the copper vapor laser, in which ^ ₁ = 5106 8 and »5782 % , applies

0.88 (V)

The ratio h ~ of the output energy at ^ _? using the dye converter to calculate the total output energy of the

: Laser E applies
ο ^y

In the specially chosen example, in which E ^ = 3 E \ (see equation II), equation VI applies

and from equation V, since yj = 0.88 results

η ₂ m 0.91.

Thus the laser dye converter combination for our example leads to 91% of the laser output in ^ ₂ · In contrast to this! there is only a ratio of 25% with equation IV without the converter.

In the following the embodiment according to FIGS. 5 and are explained in more detail.

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Often times, the main pump laser material creates some widely spaced ones Wavelengths. If this distance is too great, it can (A single dye laser does not work in an effective way [convert these frequencies into a single frequency. This disadvantage is caused by the embodiment shown in FIG is fixed.

In FIG. 5, three laser materials are used according to the invention, namely a main pump material and two laser transducer materials. If necessary, more laser materials can also be used according to the invention. To simplify: folding number, the features illustrated in Figure 5 are connected to the - 'is provided the same reference numerals as the corresponding features \ in FIG. 1

Accordingly, the laser 1 is enclosed by an optical resonator Τι »The output of the laser 1 is by means of the lens

13 focused in a first dye laser material 19 and the : The output of the laser material 19 is turned into a by means of the lens 21 Second dye laser material 23 focused. The lens 25 directs I the slightly diverging output of the laser material 23 in ■ f parallel outgoing rays around.

\ The dye of the laser material 19 is selected so that the -energy is converted this pair "of the shortest wavelength pair to that of the j longest wavelength in similar;!. 1icher, the dye of the laser material 23 is exclusively selected so that the! Energy of the now shortest wavelength-I pair is converted to the longer wavelength of this pair -i.

i · .- ■■ "

If accordingly, for example, the Laswr 1 has three wavelengths pL and f \ _o and / L in an increasing! Wavelength generated, the laser material 19 would be the energy

70 9 817/087 2

as ^) ₂ ^unc * the laser material 23 only decreases the energy at 3 ~

radiate, with which most of the energy of the shorter waves-i 'length is converted into the longest wavelength'. ■ j

Each of the laser converting materials can have more than one. ^; j Convert the wavelength into a longer wavelength. In a similar way, additional laser materials can be added to convert the energy of pairs of wavelengths into a single wavelength. '. '

FIG. 6 is a graphic representation of the energy conversion of the embodiment according to FIG. 5. The left shows
Curve the absorption band of the laser 19, the middle solid curve the fluorescence band of the laser 19, the middle one
dashed curve the absorption band of the laser 23 and the
right curve the fluorescence band of the laser 23.

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Claims (3)

PATENT CLAIMS Process for converting coherent light from different Wavelengths in coherent light of one wavelength, characterized in that one first uses a laser for spontaneous Emission of coherent light components at a number of wavelengths and then pumps by means of these coherent light components irradiate a laser medium that has at least one, but not all of these wavelengths absorbed and has a fluorescent band that is within at least one of the unabsorbed wavelengths j wherein the unabsorbed wavelength of the fluorescent band allows the laser material to emit coherent light the unabsorbed wavelength stimulates. 2. Device for converting coherent light of different Wavelengths in coherent light of one wavelength for carrying out the method according to claim 1, characterized by a first laser (1) for the simultaneous and spontaneous emission of coherent light of different wavelengths as well as a laser material (15) irradiated by the coherent light of this laser (1), the at least one, however does not absorb all wavelengths and has a fluorescent bandwidth within which the unabsorbed Wavelengths lie, with the unabsorbed wavelengths within the fluorescent bandwidth the laser material (15) can be stimulated to emit coherent light of the non-absorbed wavelength. 3. Device according to claim 2, characterized in that the laser (1) consists of a pumped by electric discharge copper vapor laser, wherein the laser material of a cell Rbodamin 6G in a 10 ~ ⁴ to 10 ~ ⁵ mol per liter 709817/0672 Methanol solution is. ; 4. Device according to claims 2 or 3, characterized thereby; characterized in that a plurality of secondary lasers (19, 23) connected in series are provided, the first of the secondary ^: laser (19) being irradiated by the coherent light emitted by the first laser (1), while each of the following; the laser materials (23) from the preceding; j laser material (19) is irradiated and each of the secondary reader materials (19, 23) connected in series absorbs the light with the respectively shortest wavelength and fluoresces in a longer wavelength with which it is also irradiated. 709817/0672