DE1924122C3 - Optical parametric oscillator - Google Patents

Description

3. Parametric oscillator according to claim 2, an oscillator in which both signal and characterized in that its tuning idlers are resonant, the continuous tuning mung the temperature of the optically non-linear 30 of the signal frequency that at least three oscillator crystals (11) is changed and that parameters are changed exactly within. In practice it is of the pump resonator (15, 16, 17) a device, however, it is extremely difficult to make such detailed compliance (27, 28) for Kompeasie en the optical positions, and it is mostly only one Path length in the pump resonator, its change as a variable, e.g. crystal rotation or temperature, to the As a result of the temperature change occurs, before a quasi-continuous adjustment is provided. turns. For an oscillator with the signal and

4. Parametric oscillator according to claim 2, idlers are resonant, there are Abstiinmdiskontinuititäten, characterized in that the pump resonator have the gaps that are up to many times wider (15, 41) and the oscillator's own resonator (21, than the axial waveform frequency spacing of the 22) are designed to have a plurality of adjacent 40 oscillators. (See »Optical Parametric Oscillation to Generate Bartered Idler- Frequencies in LiNbO ₃ * by JA Giordmaine and Robert and a device (42) that produces a C. M i 11 er in Physics of Quantum Electronics, Coupling of the natural vibrations of the idling frequency produced by PL Kelley, B. Lay and PE Tan (idler) frequencies. Nenwald [McGraw-Hill, NY 1966, p. 31].)

5. Parametric oscillator according to Anspmch 1, 45 A very significant one, the simultaneous resonance characterized in that, first, the problem associated with pumping signal and idler is the pulsed radiation via an optical valve (59) power-dependent reflection of the excitation beam nonlinear crystal (61) is supplied that treatment (pump radiation) through the nonlinear Krizweitens this optically nonlinear crystal (61) stall. (See “Nonlinear Optical Effects: An Optical a crystal composed of phase-adaptable material so Power Limiter "by A. E. S i e g m a η, Applied Op. Third, the external tics, vol. 1, no. 6, from November 1962, pp. 739 bis Mirror (63) of the oscillator's own optical receiver 744.) This reflection occurs because the backward sonators (62, 63) mix with each other for the signal radiation still running excitation waves. Which is permeable to power. dependent reflection not only creates an unrelated

55 wanted the parametric oscillator to have an effect on the excitation energy source, but also caused poor overall efficiency. The theoretical maximum efficiency is; 50 * / »and

The invention relates to an optical is obtained when the energy supplied is the four-parametric oscillator, the optical of which is not 60 times the parametric oscillation threshold linear crystal within its own optical value. A stronger excitation only reduces the resonator and means of the coherent efficiency, because the power-dependent reflection th radiation from an optical transmitter (laser) increases more than when PIP, (the ratio of pump radiation is excited, with the pump frequency pump power to threshold power ) is increased, as the sum of the signal and idling (idler) frequency 65 as the signal and idler power increase, and the own optical resonator of the

geln is limited, the frequency-selective dielectric signal and idler frequency is only one Have coatings. single axial pumping waveform a given

<t

^enresen · ^An - ⁵⁵⁶¹¹ S ¹ wW · Its optical resonator on a lH ^tr88e 1 ^{ketae Seltmann} * W ^{by a} "" limited, of the non · ^Kings 2 ^{s but 5} ^ ^{iwea s} **** and "opens ^wd? who either on *? f? ^{Ren P {Wwm an} end face of the nicely shaped crystal itself ⁸ * ^ ¹¹ ^ ¹¹ ^ ⁰ " ¹¹ - * ^or « «*« is arranged in front of it, as well as on the other ^{less energies of} the stimulable laser medium ö by ^{a multitude of} c ^h - a conference-form-selective prism29, which is arranged opposite the spinel 15 so that the basic principle is that the eighth through the stimulable medium runs through the stimulable medium """?

vÄ! lw ° ^ ^{l8naI w} - To enable oscillation form selection among the advantages of real oscillation rait a luminous resonant different axial oscillation forms, agnolsrnd better clarity, increased effectiveness, which are available with the argon LaseV, is a kleikong degree and lack of jerk effect of the oscillator _ner auxiliary or? Partial resonator 20 is provided, which is based on the source of the excitation energy. _{1S through mirrors} j _{16 and 17 on} orthogonal surfaces

Accordingly, the parametric oscillator is formed by a prism 18. The prism 18 can Initially, the species should be melted quartz, in which thread the through characterized in that the oscillator's own op-inclined surface 19 has a partial internal reflection Table resonator to be generated only for one of the two in prism 18 to complete the auxiliary source Frequencies, for example, for the idle *> nators 20 will generate

(Idler) frequency, has high quality, the other Fre- The idler resonator for the parametric oscil-

But quenz, for example the Signalfre μιεηζ, non-lator is coupled out inwardly through the reflector 21 near resonant. _{or at the} opposite of Renektor 15

In the following, the end face of the crystal 11 generated in a non-resonant manner, as well as to the outside by radiation, will relate to the signal, although this is _{axially displaceable in a 5 dep *!} Mirror 22 limited. The mirror 22 is mounted on a piezoelectric ring 23, which refers to the designation of the two, which relate to the radiation generated by a fine-tuning source 24, which in some cases reflects the known conventions. It should also be noted that the change in the axial position of the mirror 22 can be controlled so that, in the case of using a multiple speed, it is possible to control. The mirrors 15, 21 and 22 are multiple Dielekgungsform excitation source the non-resonant Si 30 trikum mirrors, which are designed to have special regnal generated in many waveforms to have flexion properties. The mirror 15 is will; whereas the resonant idler will only be generated in a highly reflective manner for the pump radiation and a single oscillation form if permeable to the signal and idler radiation. Of the Idlerschwingungsformabstand wider than the mirror 21 is for the pump radiation and for the Si twice the spectrum of the Pumpschwingungsfor- gnalstrahlung ^is highly permeable and ^men for the idler 35; . Highly reflective radiation. The mirror 22 is for

In detail, the signal radiation is highly permeable to obtain a non-resonant and at least the idler radiation is highly reflective for the signal and a resonant idler,
The idler furthest away from the pump source. The crystal 11 is in a temperature control unit.

Reflector designed to carry the signal practically in full 40 direction is mounted, which is designed to be the Temständig to let through, or is other means to change the temperature of the crystal 11 controllable to a Removal of the signal radiation from the idler reso coarse tuning of the oscillator phase adjustment generator assigned. State and thus idler and signal frequencies

The invention is to be generated below on the basis of the drawing, the sum of which is equal to the excitation described; it shows 45 or pump frequency must be. Since this temperature

F i g. 1 a schematic representation of an opti- cally tuning the optical path length of the small excitation parametric oscillator, which will change for continuous radiation, is for the purpose of a smear oscillation operation a path length compensator 27, for example, is also well suited

F i g. 2 a modification of the embodiment according to an electro-optical modulator for use in Fig. 1 for the forced waveform coupling of the 50 about 5000 A, in the pump beam path with the z-axis parametric oscillator, in order to generate output pulses aligned parallel to the laser axis, and _w ith the adjustment

Fig. 3 shows an oscillator design in which the voltage source 28 is controlled to make the pump path nonlinear Keep crystal constant outside of the pump laser resol length when the crystal temnator is is arranged, and 55 temperature within the housing 26 changes the

Fig. 4 Diagrams to facilitate the excitation flow can in the crystal 11 with the help Being able to focus on the mode of operation of the optical para a suitable lens 29 or metric oscillator. neither.

The parametric oscillator according to FIG. 1 is suitable for the embodiment according to FIG. 1 can

60 different reflection properties can be used for the mirrors of Irish oscillation with a non-resonant Si 15, 21 and 22 in particular to obtain tunable parameters. The signal beam using a steady excitation that runs out of the crystal 11 to the right can be radiation. _{The nonlinear crystal 11, made of barium sodium niobate (Ba 2} NaNb ₃ O ₁₅ ), for example from the pump resonator at any suitable point, is either absorbed or can be absorbed. For example, the mirror 17 for the signal laser 12, which operates at about 5000 A, could be located within the optical resonator of the excitation «5. Its swin-permeable to be made. The two opposing approaches are excited by the excitation radiation, sets current signal rays can be combined by a beam combiner suitable for example in an argon ion laser 12,

if the signal radiation is to be used. This is achieved by replacing the oscillation in all these cases, the mirrors 15, 21 and 22 shape-selective prism 20 in FIG. 1 by a stay the same. simple mirror for the pump wavelength. Frequent

In order to achieve tunability over a broad band, signals can then be amplified because hold, "earth idler mirrors 21 and 22 are used, which s no signal resonance is available. for wavelengths of 1.0 .mu.m as well as significantly longer Lengths of 0.49 to 0.99 μm are still permeable, optical reflections limited by mirrors 21 and 22 have a wavelength of 0.5 μm. The speaker is not resonant because mirrors 15 and 22 gel IS will have a sharp peak at 03 μΐη, while the signal radiation is not reflective. For example from 0.49 to 0.51 μ «, reflecting, the phases of signal aod idler are always makes that the flow of energy from excitation to signal and

When operating the embodiment of FIG. 1 idler, but never the other way around

the excitation or pump radiation is very effective in signal and idler

Enemy A-Lasers, for example, operated in such a way, i _S performance implemented This point is in Fi g. 4 through

that it represents radiation at 0.5 μα in a single Longi curve 72 quantitatively

tudinalschwifigungsfoffii emitted steadily, like the latter The curves show the efficiency under which

selected by the prismatic partial resonator 20, the excitation power in signal and idler

will. In practice, the exact identity of this service can be shown as a function PlP ₁ , the ratio of train-

Waveform through a feedback system μ guided excitation power to the excitation power

ensure that its signal is implemented by one at the threshold value. The curve 71

Freqaezvergldchskreis 31 derives and the pump shows the corresponding relationship for a para-

resonator tunes, for example, by modifying a metric oscillator with simultaneous signal and

rea the voltage supplied to the compensator ti. Idler resonance. It has a maximum value of 50 * / ·

Alternatively, you can address a manual setting «5 for PtP, = 4.00. In addition, although the

can be made accordingly at the comparison circle 31. Thresholdwe «; for oscillators with non-resonant

The BaNaNbOj crystal 11 is, for example, with a larger signal than for oscillators with a simultaneous optical axis perpendicular to the common resonance, curve 72 that for oscillators with the axis of the two optical resonators in FIG. 1 non -resonant signal at PIP, greater than 2, the We-oriented to a phase adjustment, the pump efficiency can be greater than 50 · / ·. With an Ausgnal- and Idter-StrabJung without birefringence to produce a guide shape similar to that still to be described. But nonetheless this Fig.3 has been found that PIP, greater than 2 easy orientation not to be used. A coarse can be obtained.

The signal frequency is tuned by changing the modified Ausföhnmgsform

the temperature inside the housing 26 has reached 35 F »g-2, the corresponding components are identical

and the Fbvimiang by changing the span reference numbers. The embodiment according to

mmg, which the source 24 to the piezoelectric ring Fig. 2 differs from that of Fig. 1 there-

23 for moving the mirror 22 supplies. To the extent that they are suitable for multiple axial vibration

the temperature of the pump path length in the nonlinear form operation of the exciting laser and for one

Crystal 11 changes, the voltage of the source 28 40 is forcibly coupled operation of the waveform

manuefl is designed around the opposite ande- parametric oscillator.

Raising increase in the length of the pump path in the ekktro-op- gungsfoTm forced coupling occurs through damping

table compensator 27 to produce. The basic modulation of the idler resonator is

half a mean Nonnarvui voltage for the grain oscillation of the optical resonator at the same time

pemator 27 uses «the difference frequency for the» b neighboring har-

In terms of age, the rough tuning could also be achieved by monically occurring vibratory forms of the para Rotation of the crystal 11 can be achieved. metric oscillator is "*" ' Even if the idler is not fine-tuned, the modulator 42 can consist of an electro-optical

Spiegefc 22 will see the overall voting properties. Utfiruintantalatkristall 43 OiTa01 exist, this to the Äfafießficn on Ti.ttMiei be 50 with its optical A && parallel to the common

The crystal 43 is much better oriented along the entire resonator axis

will be controlled », as with the earlier double resonance, there is a voltage source 44 in the resonance

th oscillators, the broad nator base frequency 21 when tuning, for example via the trans-

Have holes, as this previously described parent terminal electrodes 45 operated. the The gaps become smaller from half the 5s. Damping changes as a result of the 'rotation of the

AxialaAwmguiigsfonn ^ frequency spacing of the Oszflla- plane of the direction of polarization and leads to a

^ ⁵ ^ *, ^ _ T- ^. u-. «" _ * c -, .1.

Even these curls can have end faces inclined by distant angles

nnmg can be eliminated. There are therefore only two main features. It is an advantage of the design

Clear parameters required for constant coordination & h, fc Fi g. 2, that the pump range can be raised so higher than the ππ opposite to the three required variable crystal 11 that the band parameters, when signal and idler are simultaneously reso- width of the parametric oscillator many times greater ^than ^ Above the S ^ wingungsbandbrtite of the Pmnplasers

? ■ ^ "" η " ⁰ """ ^ Idter-Resonatoräbrnesunge "the Rf

used who, can you scnwmgnngs- 65 can the Omit selective prism and use the oscillator

a vieuxequent (in many forms of variation _ £ _ - ^ 4 "ine"

sceden) stimulate or pump the laser beam. 2L ~ ' ^iyrta ~

7 8

being; but nevertheless many are admissible, not a suitable object for generating a beaxial idler waveform within the oscillation drive with phase coupling. The reason for this is the availability of bandwidth. In order to ensure that the effective gain curve for such a that the homogeneous saturation characteristic of the crystal oscillator is not a smooth, slowly changing 11 not too many of these waveforms. Instead, there are clusters of axial constrictions, one can have an inhomogeneously saturating vibration waveforms that are at a distance from one another around many axial sorption cells 46 of known design within the waveforms, mount idler resonators near the mirror 22, for which there is a high gain. The i, B. a cell that contains a dye solution for quality * possibility of an oscillator with such a complicated '(switching, if the idler * wavelength io th amplification states (because of the complicated 1) 06 μΓπ. Inhomogeneous saturation is inherent - Resonance) to bring about a phase coupling is not known as an amplification - or absorption measure. For an oscillator with a non-medium that depletes the gain (or resonant signal, such as the oscillator after absorption) at a frequency within the available range. 2, such difficulties do not arise.
It should be understood that other execution (or absorption) at all frequencies within forms of the invention are possible. For example, of the available gain or adsorption, successful attempts have been made to dump at bandwidth. The saturable dye will also lead to a pulse sharpening of the nonlinear crystal outside of the pump. Note that the pending laser resonator was located and provided with mirror cells 46 located outside the pump resonator, which were designed so that it does not interfere with pumping. Idler resonate and the signal without

In any case, it is generated if one more reflection is allowed to pass through. In such an attempt

number of axial idler waveforms to the vibration were a nonlinear LiNbO _s * crystal and one

have been stimulated, the phase-coupling mo- pulsed single waveform-ruby laser pump-

dulator 42 a forced coupling of the vibration »5 source (0.6943 μπι) used. Parametric oscillation

shape, which forces the output radiation, conditions with a supplied pump power of

in pulse pulses at the fundamental idler resonator frequency to "· kilowatts were easily obtained, namely at

appear, the pulse width as a sequence ei », he idler wavelength of 1.04 μπι and a Si

their superposition in inverse relationship to the signal wavelength of 2.08 μπι.

Number of vibrating axial idler vibration forms 3 »For reasons of simple test conditions

men is related. the idler power was about 1.04 μπι after starting

An optical parametric oscillator has norcoupling from the oscillator over a 38 Vo reflective uniform gain. This means animal mirrors measured at 41 kilowatts. From the fact that in continuous operation an oscillator excited by a single-frequency non-resonant signal power at about 2.08 μπι pump source tends, in a $ 5 it can be assumed that it is considerably larger axial waveform of the oscillator. Because the resonant radiation that oscillate here as sonators. A multiple oscillation idler is designated, was measured, may et, beform pump can be more convenient to counter this tendency, in such a case the designation can be used to swap suitable means for conveying signal and idler,
The phase coupling of the numerous axial oscillation forms, which would produce an output, results in a considerable improvement in the output, which consists of a train of ultrashort pulses. The embodiment according to FIG. 3 that would on. In order to promote the phase coupling is based the experiments carried out, a opti possible a intracavity modulator in the see parametric oscillator 60 in which an L-eil frequency of the oscillator resonator is used einzu- 45 non-resonant signal. Build the oscillator. To further aid the pulsing, it is desirable 60 outside the resonator of the pulsed to have a saturable dye cell 46 in the pump laser 51. tudinal and transversal oscillation form-their mode of operation can be understood as follows: stungsimpuls ruby laser 51 with plane mirrors 53 and. The modulator forces the oscillator to oscillate over 50 54. A single waveform excitation radiation of the bandwidth of the modulator, which is chosen because this produces reproducible result pulses that are about as long as nisse are ensured, while with a value the reciprocal of this bandwidth. However, multiple waveform pump sources reached irregular reelectronic circuits which could produce fantastically large results. The laser resonance bandwidth and ultrashort pulses that are desired 55 by the highly reflective plane mirror 53 are not. On the way to this, they can only pass through the partially transparent (about 70%. In order to make the impulses shorter, the non-transparent) mirror 54 is formed. The transverse vibration dye cell 46 is used as a pulse sharpening mechanism shape control narrow achieved by insertion. Alternatively, the dye can be viewed as a 2 mm bean in a 1.6 mm thick rust modulator, which has an exemplary 60 free steel plate 55, and the control of the Longi wide bandwidth. Therefore, the dye is tudmally waveform and the Q-switching is used in the same way as dyes to produce a phase coupling in Nd glass and dye (cryptocyanine in methanol), which is caused by the Q-switch 56 with bleachable, which leads to this ruby laser be used. The modulator Zweck near the adjustable laser needle 52 is simply used to ensure that «5 is placed. The excitation light source 5§ will ied the desired phase coupling takes place. adjusted relative to the dye concentration in such a way that

In contrast to this, a parametric oscillator is produced by a single Q-switched f Ttäpiäs

goal. in which both the signal and the idler become resonant.

The resonator of the parametric oscillator is delimited by mirrors 62 and 63, which are highly permeable for the pump light and highly reflective for the idler. The mirror 63 is highly permeable to the signal, and the mirror 62 can have any reflectivity for the signal, since no signal that travels to the left can be generated. In order to prevent the small reflections from the oscillator mirrors from delivering pump radiation back into the pump resonator, an optical valve M is placed between the pump and the oscillator. This could be formed by a Faraday rotator arranged between crossed polarizers. The oscillator can be tuned by adjusting the crystal, for example by means of an exercise drive 64, by controlling its temperature, by supplying an electric field or by pressure. As shown here, the oscillator will be an effective source of variable radiation pulses. However, by adding a damping modulator and a saturable dye for Iffl pulse sharpening to your oscillator resonator, as has been described for the embodiment of FIG ultra-short im-

S pulse exist.

Obviously there are other embodiments with which the optical parametric oscillator is operated with a non-resonant signal. A Example of another means of obtaining nonreso »

Im nanter signals include the use of a broad spectrum relatively highly reflective mirror together with a signal absorbing device 65, which in the Is arranged inside the resonator. Such a device 65 was used in the case of the invention

reasoned attempts are not used and is only useful »It should mainly be used when the Signal * radiation is not to be used or if the device 65 itself

ao turning device is. It should also be

«■■ ·· stand that part of the resonant idler beam can be decoupled for further use.

For this purpose 4 sheets of drawings

Claims (2)

'The term "optical" here denotes one Claims: Radiation whose wavelength is much smaller than the length of the optically non-linear crystal · ■ " I. Optical parametric oscillator, its and from the ultraviolet to the far infrared S optically non-linear crystal within a proper δ and the short-wave microwave range ₍ , uen optical resonator is arranged and with can. * by means of coherent radiation from an opti- The great interest in obtaining a Scbwin- ti see transmitter (laser) as a pump radiation threshold value results from the technical Ψ is excited, the pump frequency being the sum of literature on optical parametric ^ oscillators. j signal and idler frequency is present and ι »(See, for example, the article» Theory of Pararae- {; Spiegel's own optical resonator is the Oscillator Threshold with Single-Mode Optical ι is limited, the frequency-selective dielectric loading Masers and Observation of Amplification ίο j have stratifications, identified by them- UNbO _s «by GD Boyd and A. Ashkin, The L records that the oszuTatore own optical Physisü Review, Vol. 146, No. 1, pp. 187 to 198, from j Resonator (21, 22 or 61, 62) for only one of i $ 3 June 1966.) This interest is almost on natural two frequencies to be generated, for example, arose because an optical parametric wise for the idler frequency, high quality Irish oscillation threshold difficult to obtain ^, but the other frequency, for example, was sufficient, especially in continuous wave operation. the signal frequency, decoupled in a non-resonant manner. It was believed that simultaneous 2. Parametric oscillator according to claim 1, ao resonance of signal and idler in an optical pad, characterized in that the optically non-rametric device is not only desirable linear crystal (11) within a second be- but a necessary condition for obtaining it ner excitation serving optical resonator, parametric oscillations is (cf.Appl. Phys. des Pumpenresonators (15, 16, 17 or 15, 41), Letters, Vol. 12, No. 9, from May 1, 1968, pp. 308 to 310; is arranged and that at least one resonator as Phys. Rev. Letters, Vol. 14, No. 24, of June 14, 1965, mirror (15) of the pump resonance for the signal p. 973 to 976; B-ill Laboratories Record, Vol. 43, frequency is highly permeable. No. 7, 1965, pp. 310 to 311). Unfortunately required for