DE102020204022A1 - Sensor and method for detecting at least one measured variable - Google Patents

Abstract

The invention relates to a sensor (1) for detecting at least one measured variable, containing at least one optical resonator (2), at least one first active medium (3) which is arranged in the resonator (2) and is set up to generate an optical gain in a first wavelength range, at least one pump source (5, 51, 52) which is set up to excite the first active medium (3), at least one detector (6) which is set up to detect laser radiation, at least a high-frequency transmitter (7) which is set up to generate electromagnetic radiation which acts on the first active medium (3) and which, depending on the at least one measured variable, stimulates at least one transition between at least two states of the first active medium (3), wherein the sensor furthermore contains at least one second active medium (4) which is arranged in the resonator (2) and is set up to provide an optical gain in to generate a second wavelength range, wherein the first and the second active medium (3, 4) in cooperation with the resonator (2) have a laser threshold, and at least one pump source (5, 51, 52) is set up, the second active To excite medium (3) and wherein the first and the second wavelength range are at least partially identical. The invention also relates to a corresponding method for acquiring at least one measured variable.

Description

The invention relates to a sensor for detecting at least one measured variable, containing at least one optical resonator, at least one first active medium, which is arranged in the resonator and is set up to generate an optical gain in a first wavelength range, at least one pump source which is set up to excite the first active medium, at least one detector, which is set up to detect laser radiation, and at least one radio frequency transmitter, which is set up to generate electromagnetic radiation which acts on the first active medium and which depends on the at least a measured variable stimulates at least one transition between at least two states of the first active medium. The invention also relates to a method for detecting at least one measured variable using such a sensor. Devices and methods of this type can be used, for example, to measure a magnetic field.

From the US 2017/0030982 A1 a sensor of the type mentioned is known. The optical resonator, the first active medium and the pump source form a laser. This uses diamond as the first active medium that contains NV centers. In addition to the pump source, the radiation from the radio frequency source also acts on the active medium. The electromagnetic radiation from the radio frequency source has the effect that the laser threshold varies depending on an external magnetic field. By determining the laser threshold as a function of the frequency of the electromagnetic radiation and / or the laser power at a specific operating point, the acting magnetic field can thus be measured.

This known sensor has the disadvantage of limited sensitivity. In addition, production and use are complex. Proceeding from the prior art, the invention is therefore based on the object of specifying a sensor and a method for detecting at least one measured variable which have an improved sensitivity and / or a simplified production and / or a simplified structure.

The object is achieved according to the invention by a device according to claim 1 and a method according to claim 8. Advantageous further developments of the invention can be found in the subclaims.

According to the invention, a sensor or a quantum sensor for detecting at least one measured variable is proposed. The sensor contains at least one optical resonator. The optical resonator contains at least two mirrors which at least partially delimit a resonance space. At least one of the mirrors can be partially transparent, so that part of the incident photons is reflected and another part is transmitted and in this way can leave the resonance space.

At least one first active medium and at least one second active medium are introduced into the resonance space. The first active medium is set up to generate an optical gain in a first wavelength range. The second active medium is set up to generate an optical gain in a second wavelength range. The first and second wavelength ranges are at least partially identical. As a result, the combined optical gain of the first and the second medium in cooperation with the resonator has a lasing threshold. This means that the first and second active medium each have a plurality of energy levels, between which electronic transitions can be excited by supplying a pump power. Radiant transitions can take place between these energy levels which have an energy which corresponds to at least some eigenmodes of the optical resonator. The laser threshold describes the minimum necessary pump power that must be supplied to the media, so that the optical gain due to the supply of energy on the one hand and the optical loss due to absorption in the active medium, due to parasitic losses, for example on surfaces and due to the coupling out of the generated emission, on the other just equalize. The laser threshold is thus the intensity threshold of the energy emitted by the pump source, above which the laser formed from the active media and the optical resonator begins to work.

For this purpose, the sensor according to the invention furthermore has at least one pump source which is set up to stimulate the first and / or the second active medium to emit light. In some embodiments of the invention, a plurality of pump sources can be present, so that pump light from a plurality of pump sources can be supplied to an active medium. In some embodiments of the invention, at least one associated pump source can each be present for the first active medium and the second active medium. In some embodiments of the invention, an active medium can be optically pumped. In this case, the pump source is set up to generate light which is absorbed in the respective active medium and thereby raises electrons to a higher energy level. The pump source can contain, for example, a laser or a light-emitting diode or a superluminescent diode or another light source. In some embodiments of the invention, the pump source can also use the electrons in at least one active medium stimulate another form, for example by electric pumping.

In the case of optical pumping, in some embodiments of the invention, the pumping light source can contain or consist of at least one diode laser. In some embodiments of the invention, a distributed feedback (DFB) diode laser can be used. In other embodiments of the invention, a diode pumped solid state laser can be used. In some embodiments, fiber-coupled lasers can also be used, either in the form of fiber-coupled diode lasers or fiber lasers. This feature has the effect that a simple, compact and inexpensive sensor can be obtained.

Finally, the sensor proposed according to the invention contains a detector which is set up to detect laser radiation from the resonator with the first and / or the second active medium. In some embodiments of the invention, this detector can be or contain a photomultiplier, a photodiode, a phototransistor, a photoresistor, a CCD or CMOS sensor or another radiation detector known per se.

Finally, the sensor proposed according to the invention contains a radio frequency transmitter which is set up to generate electromagnetic radiation which acts at least on the first active medium and which, depending on the at least one measured variable, transitions between at least two states or energy levels of the first active medium (e.g. electrons -Spin transitions), which cause changes in the optical emission and are changed by the external variable to be measured.

For this purpose, the radio frequency transmitter can emit electromagnetic radiation at a frequency of approximately 1 GHz to approximately 120 GHz. In some embodiments of the invention, the radio frequency transmitter can emit electromagnetic radiation with a frequency between about 2 GHz and about 50 GHz or between about 2.5 GHz and about 40 GHz.

When the sensor is in operation, the optical gain of the first active medium is influenced by the frequency of the electromagnetic radiation from the radio frequency transmitter and the measured variable to be detected. The optical gain of the second active medium acts like an optical amplifier, so that the emission in the first active medium can be detected with greater accuracy. As soon as the first active medium begins to emit radiation, it reaches the second active medium located within the resonance space of the resonator and triggers a stimulated emission in this too. From the change in intensity or the onset of the laser radiation, if the frequency of the radio frequency transmitter is known, it is therefore possible to deduce the measured variable to be detected prevailing at the location of the first active medium. Because of the non-linear relationship between the intensity of the laser radiation and the measured value, this measured variable can therefore be recorded with increased sensitivity and / or higher accuracy.

Alternatively or additionally, the optical gain increased by the second active medium compared to the prior art can be used to provide a lower density of color centers and / or a longer coherence time in the first active medium. In particular, more diamond material with a lower density of color centers can be used, so that a longer coherence time is achieved with the same number of emitters. Any higher material losses can be compensated for by the second medium. This can lead to a significant improvement in sensitivity. In some embodiments of the invention, the increased optical gain due to the second active medium can compensate for greater optical losses. This can reduce the requirements for the material of the first active medium and / or for the detector and / or for the number or quality of the surfaces in the resonator, so that the manufacture and / or the operation of the sensor can be simplified. In some embodiments of the invention, the increased gain in the second medium can increase the coupling-out by one of the two resonator mirrors in order to increase the ratio of coupling-out losses to internal losses and thus to increase the slope of the laser and the signal at the detector. This allows the sensitivity to be optimized on the basis of the variation in the output mirror.

In some embodiments of the invention, the first active medium can be a solid or contain a solid which contains color centers. In some embodiments of the invention, the solid of the first active medium can be diamond or contain diamond which contains NV centers. The NV center consists of a single nitrogen atom on a lattice site of the diamond lattice in connection with a nearest neighbor defect in the carbon lattice of the diamond. In the ground state, the electrons of the NV center form a triplet state with a total spin of 0 or +1 or -1. In the absence of a magnetic field, the two states with spin ± 1 are energetically degenerate and thus indistinguishable. The application of an external magnetic field leads to the energetic splitting of the states with spin +1 and -1. The size of this split is dependent on the strength of the magnetic field prevailing at the location of the NV center, so that the NV centers in diamond are basically suitable for measuring an external magnetic field. In the same way, magnetic fields or other measured variables can be determined by other color centers in other solids. Since individual quantum states are manipulated and used to measure an external field, the sensor and the method are located in the field of quantum sensors.

In some embodiments of the invention, the solid body and the color center contained therein is selected so that optically detected magnetic resonance (ODMR) is possible, i.e. the optical gain of the first active medium is varied by applied radio frequency radiation, the resonance frequency being dependent on the external variable to be measured depends. The NV center in diamond can be used in this way to determine temperature, pressure, magnetic field or electrical fields. Cerium in yttrium-aluminum-garnet (YAG) also shows ODMR and can also be used as the first active medium to measure a magnetic field. Further examples of other possible color centers in diamond are the silicon vacancy center, the germanium vacancy center or the ST1 center. Examples of other color centers in other solids are vacancy centers, doping atom vacancy centers or other color centers in silicon carbide or point defects in group III nitrides such as AlN, GaN and BN.

In some embodiments of the invention, the second active medium may include or consist of an optically pumped semiconductor laser. In some embodiments of the invention, the second active medium can contain or consist of at least one semiconductor disk laser and / or at least one semiconductor membrane laser. In some embodiments of the invention, the second active medium can contain or consist of at least one electrically pumped diode laser. Such a semiconductor laser can be designed as a semiconductor heterostructure in which active layers and barrier layers alternate in order to form a quantum well structure in this way. Here, the number of active layers indicates the possible optical gain or the possible amplification by the second active medium. The band gap of the active layers defines the emission wavelength, so that the wavelength range of the radiation emitted by the second active medium can be adapted to the wavelength range of the radiation emitted by the first active medium. In one embodiment of the invention, the optical gain of these quantum well structures is in the range from about 630 nm to about 800 nm. In a further embodiment of the invention, the semiconductor heterostructure is produced from the AlGaInP material system. Finally, the absorption behavior of the pumped light in the second active medium can be adjusted through the thickness of the barrier layers. This is particularly helpful when the sensor is operated with only a single pump source which pumps both active media, in particular when the pump light passes through the second active medium first.

In some embodiments of the invention, the first active medium can have a first side and an opposing second side and the second active medium can have a first side and an opposing second side, the second side of the first medium being in contact with the first side of the second medium Contact is available. This form of contact can be present over the entire area or in a partial area. The contact can be made with a form fit or material fit. This feature has the effect that the first active medium is not only used to determine the desired measured variable, but at the same time acts as a heat spreader in order to dissipate heat from the second active medium. An intermediate layer, for example made of a metal or an alloy or a polymer, can be arranged between the first side of the second active medium and the second side of the first active medium. The intermediate layer can reduce the heat transfer resistance and / or improve the adhesive strength.

In some embodiments of the invention, the first mirror of the optical resonator can be arranged on the first side of the first active medium. In other embodiments of the invention, the second mirror can be arranged on the second side of the second active medium. In still other embodiments of the invention, both mirrors can be arranged on opposite sides of the first and second active medium, respectively. In this way, a mechanically robust, stable and geometrically compact structure can be achieved, which can have a positive effect on operational safety.

In some embodiments of the invention, the detector can be in contact with the first mirror, the detector and the first active medium being arranged on opposite sides of the mirror. In some cases, at least one optical element and / or a bonding layer can be arranged between the mirror and the detector. This can reduce coupling losses between the resonator and the detector.

When the device is in operation, the frequency of the electromagnetic radiation generated by the radio frequency transmitter can be varied. In some embodiments of the invention, this Frequency variation are cycled through. In some embodiments of the invention, the frequency profile can correspond to a sawtooth function, ie the frequency increases linearly from a minimum to a maximum value, this profile being repeated cyclically. In some embodiments of the invention, electromagnetic radiation can be detected as a function of the frequency or the intensity of the electromagnetic radiation generated by the radio frequency transmitter in order to detect the measured variable.

In some embodiments of the invention, the power of the pump source can be varied. In some embodiments of the invention, this variation can be periodic. In some embodiments of the invention, the power curve of the pump source can correspond to a sawtooth function, i.e. the power increases linearly from a minimum to a maximum value, this curve being repeated cyclically.

In some embodiments of the invention, the power of the pump source can be set at a fixed operating point and kept constant there. This operating point can be determined as follows: Adjustment of the optical gain in the second active medium such that about 85% to about 110% or that about 90% to about 105% or that about 90% to about 100% of the total losses of the optical resonator are compensated and adjusting the optical gain of the second active medium such that the laser formed from the optical resonator and the active media is off in the case of resonance of the electromagnetic radiation or has only a low first power P ₁ near the laser threshold and for all other frequencies of the electromagnetic radiation is ON or has a second power P ₂ which is greater than P ₁ . The setting of the optical gain of the second active medium can take place through the number of quantum well structures, the choice of the composition and / or the thickness of the barrier and / or absorber layers and / or through the regulation of the pump power. The setting of the optical gain of the first active medium can take place through the number of color centers and / or the regulation of the pump power.

In some embodiments of the invention, the frequency of the electromagnetic radiation generated by the radio frequency transmitter can be varied with a first period length and the power of at least one pump source with a second period length. In this case, the first period length can be selected to be shorter than the second period length.

In some embodiments of the invention, the light from the pump source can be coupled into the first and / or second medium through the second mirror. Thus, in some embodiments of the invention, a linear structure of pump source, resonator and detector can be present, which is manufactured and operated in a mechanically robust and compact manner.

• 1 ein Termschema eines erfindungsgemäß verwendbaren Farbzentrums.
• 2 zeigt beispielhafte Ergebnisse einer Messung eines magnetfeldabhängigen Fluoreszenzsignals.
• 3 zeigt einen erfindungsgemäßen Sensor in einer ersten Ausführungsform.
• 4 zeigt einen erfindungsgemäßen Sensor in einer zweiten Ausführungsform.
• 5 zeigt einen erfindungsgemäßen Sensor in einer dritten Ausführungsform.
• 6 zeigt einen erfindungsgemäßen Sensor in einer vierten Ausführungsform.
• 7 zeigt einen erfindungsgemäßen Sensor in einer fünften Ausführungsform.
• 8 zeigt einen erfindungsgemäßen Sensor in einer sechsten Ausführungsform.
• 9 zeigt einen erfindungsgemäßen Sensor in einer siebten Ausführungsform.
• 10 zeigt einen erfindungsgemäßen Sensor in einer achten Ausführungsform.
• 11 zeigt beispielhaft die Durchführung einer erfindungsgemäß vorgeschlagenen Messung.

The invention is to be explained in more detail below with reference to figures without restricting the general inventive concept. It shows

• 1 a term scheme of a color center which can be used according to the invention.
• 2 shows exemplary results of a measurement of a magnetic field-dependent fluorescence signal.
• 3 shows a sensor according to the invention in a first embodiment.
• 4th shows a sensor according to the invention in a second embodiment.
• 5 shows a sensor according to the invention in a third embodiment.
• 6th shows a sensor according to the invention in a fourth embodiment.
• 7th shows a sensor according to the invention in a fifth embodiment.
• 8th shows a sensor according to the invention in a sixth embodiment.
• 9 shows a sensor according to the invention in a seventh embodiment.
• 10 shows a sensor according to the invention in an eighth embodiment.
• 11 shows an example of the implementation of a measurement proposed according to the invention.

1 shows an example of the term diagram of an NV center in diamond. The NV center is an example of a color center that can be used according to the invention in a solid, the term scheme of which can be influenced by a measured variable. By measuring this influence, conclusions can be drawn about the desired measured variable.

The NV center consists of a nitrogen atom, which is built into a lattice site of the diamond instead of a carbon atom, and an adjacent defect in the crystal lattice. It is known from measurements of the electron spin resonance that the NV center has an even number of electrons with a total spin of 1. Both the ground state ³ A and the excited state ³ E thus form a triplet state. The electron spin in this state can assume the values -1, 0 and +1. In the absence of an external magnetic field, the energy levels of state +1 and state -1 are degenerate. The presence of one Magnetic field leads to the splitting of these levels, since the total spin can be aligned parallel or anti-parallel to the field vector. How out 1 As can also be seen, the energy levels of the states with spin ± 1 without an externally applied magnetic field are above the energy level of the state with spin 0.

By supplying pump light 55 Electrons can be raised from the ground state ³ A to the excited state ³ E from a pump source. The pump light used for this purpose can be selected from the green spectral range and, for example, have a wavelength of approximately 532 nm to approximately 550 nm.

The excited state ³ E decays radiantly, emitting red light 8th with a wavelength of about 637 nm to about 800 nm. Alternatively, the excited state with the spin quantum number ± 1 decays via the single states ¹ A and ¹ E into the ground state ³ A.

Within the ground state ³ A, electrons can move out of the ground state with the spin quantum number 0 are excited into the excited state with the spin quantum number ± 1. This can be done using high-frequency radiation 75 a radio frequency transmitter can be used, which has a frequency of about 2.88 GHz. This frequency changes in the presence of an external magnetic field when the degeneracy of the spin states +1 and -1 is canceled. Therefore, according to the prior art, a magnetic field can be determined by continuously pumping light into the active medium 55 fed and fluorescent light 8th is determined while the frequency of electromagnetic radiation 75 will be changed.

The result of such a measurement is in 2 shown. Is shown in 2 the fluorescence signal in arbitrary units on the ordinate and the frequency of the electromagnetic radiation 75 on the abscissa. Four fluorescence signals with increasing magnetic field B are shown.

As 2 shows, the intensity of the fluorescence is always reduced when the electromagnetic radiation 75 can drive the transition from spin 0 to spin +1 (or -1) of the ground state ^{3 A.} Accordingly, the optical gain in diamond doped with NV centers is also reduced precisely when this resonance is hit. This means that a laser characteristic curve (output power versus pump power) of the first active medium has to be recorded in order to measure the magnetic field, the laser threshold being increased when using the electromagnetic radiation 75 the response is met. The following operating mode is therefore proposed for the known LV laser: The LV laser is pumped just so strongly that it is OFF in the case of resonance (below the laser threshold) and for all other frequencies that of the electromagnetic radiation 75 (off-resonance) is ON. Then the frequency of the electromagnetic radiation 75 tuned and the collapse of the laser power at the resonance of the electromagnetic radiation 75 observed. The magnetic field can then be deduced from the resonance frequency.

As 2 shows, the energy levels with spin +1 and -1 are degenerate as long as no magnetic field is present. As the magnetic field increases, the degeneration is reversed and the energetic distance between the two energy levels increases. The magnetic field can be determined from the energetic distance.

The person skilled in the art is of course familiar that the measuring principle shown here for a magnetic field can also be transferred to other measured variables. All that is required is a color center in a solid body, which can be pumped in the manner shown and is sensitive to the respective measured variable.

Based on 3 a first embodiment of the sensor according to the invention is explained. The sensor contains an optical resonator 2 . The optical resonator 2 contains at least a first mirror 21 and at least a second mirror 22nd which at least partially limit a resonance space. In the resonance chamber of the resonator 2 there is at least a first active medium 3 and at least a second active medium 4th . The first active medium 3 can for example be a solid which contains color centers. In some embodiments of the invention, the first active medium can 3 Contain or consist of diamond which contains NV centers.

In some embodiments of the invention, the second active medium can be an optically or electrically pumped semiconductor laser which contains, for example, a semiconductor heterostructure. The semiconductor heterostructure contains a sequence of active layers and barrier layers which form a quantum well structure.

The first active medium 3 is chosen so that it is able to generate an optical gain in a first wavelength range. Correspondingly, the second active medium is 4th chosen so that this can produce an optical gain in a second wavelength range. The first and second wavelength ranges are at least partially identical. This characteristic has the effect that from the first active medium 3 emitted light 8th in the second active medium 4th can trigger a stimulated emission. So through the second active medium 4th amplified light can be in the detector 6th be detected after some of the intensity through the first mirror 21 from the resonator 2 has left. The optical gains of the first and second active medium thus serve together to reach the laser threshold.

In the 3 The first embodiment shown also shows a first pump source 51 which is set up to be the first active medium 3 to pump optically. Furthermore shows 3 a second pump source 52 which is set up for this purpose, the second active medium 4th to pump. This will be in the active media 3 and 4th each generates a light emission, as described above.

Finally shows 3 a radio frequency transmitter 7th , which is set up to generate electromagnetic radiation, which at least on the first active medium 3 acts. The electromagnetic radiation induces at least one transition between at least two states of the first active medium as a function of the at least one measured variable 3 , as above using the in 1 termschemas shown. Provided diamond with NV centers as the first active medium 3 the radio frequency transmitter can be used 7th Emit electromagnetic radiation in a wavelength range from about 2.5 GHz to about 120 GHz in order to ^{stimulate the transition between the spin states 0 and ± 1 of the 3} A ground state.

Based on 4th until 10 further embodiments of the sensor according to the invention are explained. The same components of the invention are provided with the same reference symbols, so that the following description is limited to the essential differences.

So shows 4th a second embodiment of the sensor according to the invention. This differs from the in 3 illustrated first embodiment in that a common pump source 5 is provided which is both the first active medium 3 as well as the second active medium 4th pumps.

Based on 5 a third embodiment of the invention will be explained. This differs from the previous embodiments in that the first active medium 3 a first page 31 and an opposite second side 32 having. In the same way, the second active medium 4th a second page 41 and an opposite side 42 on. The first active medium 3 and the second active medium 4th are connected in such a way that the second side 32 of the first active medium 3 with the first page 41 of the second active medium 4th is in contact. This contact can be designed with a form fit or material fit. Optionally, intermediate layers (not shown) can be present, for example a thermal paste or an adhesive. This characteristic has the effect of being the first active medium 3 Diamond also used the heat spreader in the second active medium 4th can dissipate any power loss.

Based on 6th a fourth embodiment of the invention will be explained. This differs from the third embodiment described above in that the second mirror 22nd of the optical resonator 2 on the second page 42 of the second active medium 4th is arranged. This can be done, for example, by sputtering or thermal vapor deposition of a dielectric coating made of a metal or an alloy. In other embodiments of the invention, the mirror 22nd by gluing or soldering to the second active medium 4th be joined. In yet other embodiments, the mirror is integrated into the semiconductor heterostructure of the second active medium by means of suitable semiconductor layer stacks with different refractive indices.

Based on 7th a fifth embodiment of the invention will be explained. In the fifth embodiment, the first mirror is additionally or alternatively 21 immediately on the first page 31 of the first active medium 3 attached. This first mirror too 21 can be produced by sputtering, vapor deposition, plasma coating or other coating methods known per se or as a discrete component with the first active medium 3 be joined. The integration of one or both mirrors 21 and or 22nd has the effect of reducing coupling losses between the active media 3 and 4th and the mirror 21 and 22nd can be reduced and / or that a compact, stable and mechanically robust structure is created, which also enables additional stability in the optical output and / or also enables reliable measurements of the magnetic field in harsh environmental conditions. In the event that two planar mirrors are used, the laser cavity can be stabilized by using the thermal effects within the active media: By forming a thermal lens in the first and / or the second medium, a stable laser cavity can also be achieved in this case.

Based on 8th a sixth embodiment of the invention will be explained. This differs from the previous embodiments in that the second mirror 22nd is designed as a partially transparent or wavelength-dependent mirror, so that the pump source 5 the pump light through the second mirror 22nd about the second page 42 into the second active medium 4th can couple. From there, the pump light can be over the first page 41 into the first active medium 3 are coupled. This further reduces the installation space required for the sensor. Unless the pump source 5 is designed as a semiconductor light source, for example as a semiconductor laser, light emitting diode or superluminescent diode, this can be directly on the surface of the second mirror 22nd generated or joined with this, so that an even more compact, stable and mechanically more robust structure is created. The order of the second and first active medium can also be interchanged.

Based on 9 and 10 Seventh and eighth embodiments of the invention are explained. These differ from the previous embodiments in that the detector 6th , which can be designed as a photodiode, for example, directly on the first mirror 21 is joined. According to the eighth embodiment shown in 9 shown can be between the detector 6th and the first mirror 21 a bond layer 65 and / or an optical element can be arranged. The optical element can be designed, for example, as a lens to the laser light 8th on the detector 6th to focus. In other embodiments of the invention, dispersive elements or filter elements can be used to remove interference light from the detector 6th keep away.

Based on 11 an alternative of the method according to the invention is explained again. The output signal of the detector is shown 6th , which is the intensity of the laser radiation 8th proves against the time as well as the frequency of the electromagnetic radiation 75 against the time. In the illustrated embodiment, the pump power is the pump source 5 or the pump sources 51 and 52 constant. The pump power is chosen so that the laser formed from the active media and the optical resonator is OFF or shows a low power P ₁ near the threshold when the electromagnetic radiation 75 Transitions between the triplet states 0 and ± 1 of the ground state ³ A resonantly excites. When the frequency of electromagnetic radiation 75 is chosen so that there are no transitions between the triplet states 0 and ± 1 of the ground state ³ A resonant electromagnetic radiation 75 Transitions between the triplet states 0 and ± 1 of the ground state ³ A resonantly excites, the laser is ON or shows a high power P ₂ with P ₂ > P ₁ .

The frequency of the radio frequency transmitter 7th is linearly modulated at time t ₀ starting from the minimum value to its maximum value. When the maximum value is reached, the radio frequency transmitter is switched off and starts again with the lowest frequency. The frequency of the electromagnetic radiation 75 of the radio frequency transmitter 7th is thus modulated with a sawtooth function with a first period.

In each case at time t ₁ , the optical gain of the first active medium has dropped so far that it can no longer be compensated for by the optical gain of the second active medium and the laser goes out, which is caused by the detector 6th can be captured. This means that radio frequency transmitter 7th at this time an electromagnetic radiation 75 emits, which, when the magnetic field is currently applied, electrons with spin 0 in the ground state ³ A in the state with spin 1 raises. From the current frequency of the radio frequency transmitter 7th the size of the splitting of the triplet states 0 and ± 1 of the ground state ³ A and from this the applied magnetic field can be determined, as with the aid of 2 explained.

12th shows a second laser characteristic 82 with resonant excitation of transitions between the triplet states 0 and ± 1 of the ground state ³ A due to the electromagnetic radiation 75 . Furthermore shows 12th shows a first laser characteristic 81 , if transitions between the triplet states 0 and ± 1 of the ground state ³ A due to the electromagnetic radiation 75 not be stimulated. Under a laser characteristic 81 or 82 becomes the ratio of the output power, ie the intensity of the laser radiation 8th , and understood the pump line. The pump power p is shown on the abscissa and the output power I on the ordinate. Like the laser characteristics 81 and 82 can be taken, they each have a laser threshold p1 or P ₂ , above which a stimulated emission and thus a laser operation of the sensor begins.

As in the context of the 11 As can be seen, at time t ₁ the sensor is in a state which is indicated by the second laser characteristic 82 is described. At the other times, the sensor is in a state which is indicated by the first laser characteristic 81 is described.

In operation, the optical gain is in the second active medium 4th adjusted so that about 98% to about 85% or about 95% to about 90% or about 97% to about 90% of the total losses of the laser cavity are compensated. The optical gain can be set by controlling or regulating the pump output. This area is in 12th shown as work area 750.

The absolute value of the necessary pump power or the position of the working area 750 on the abscissa can be determined by the choice of the second active medium when designing the sensor or its material parameters are defined. The material parameters can be selected from the number of quantum wells and / or by the number of barrier layers and / or the length of the second active medium 4th and / or the number of second media 4th . Furthermore, the optical gain of the first active medium can be achieved by controlling or regulating the pump power and / or by the number of NV centers or the volume density of the NV centers and / or the choice of the length of the first active medium or the number of the first active ones Media are influenced.

Of course, the invention is not limited to the embodiments shown. The above description is therefore not to be regarded as restrictive, but rather as explanatory. The following claims are to be understood in such a way that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Insofar as the claims and the above description define “first” and “second” embodiments, this designation serves to distinguish between two similar embodiments without defining an order of precedence.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2017/0030982 A1 [0002]

Claims (12)

Sensor (1) for detecting at least one measured variable, containing at least one optical resonator (2), at least one first active medium (3) which is arranged in the resonator (2) and is set up to provide an optical gain in a first wavelength range generate, at least one pump source (5, 51, 52) which is set up to excite the first active medium (3), at least one detector (6) which is set up to detect laser radiation, at least one radio frequency transmitter (7), which is set up to generate electromagnetic radiation which acts on the first active medium (3) and which, depending on the at least one measured variable, stimulates at least one transition between at least two states of the first active medium (3), characterized in that the sensor furthermore contains at least one second active medium (4) which is arranged in the resonator (2) and is set up to convert an optical gain into a m second wavelength range, wherein the first and the second active medium (3, 4) in cooperation with the resonator (2) have a laser threshold, and at least one pump source (5, 51, 52) is set up, the second active To stimulate the medium (3), the first and the second wavelength range being at least partially identical. Sensor after Claim 1 , characterized in that the first active medium (3) contains or consists of diamond which contains color centers, or that the first active medium (3) contains or consists of diamond which contains NV centers. Sensor after Claim 1 or 2 , characterized in that the second active medium (4) contains or consists of an optically or electrically pumped semiconductor laser, or that the second active medium (4) is a surface-emitting semiconductor laser. Sensor after one of the Claims 1 until 3 , characterized in that the first active medium (3) has a first side (31) and an opposite second side (32) and the second active medium (4) has a first side (41) and an opposite second side (42) wherein the second side (32) of the first medium (3) is in contact with the first side (41) of the second medium (4). Sensor after one of the Claims 1 until 4th , characterized in that the optical resonator (2) has at least one first mirror (21) and at least one second mirror (22) and the first mirror (21) is arranged on the first side (31) of the first medium (3) and / or that the second mirror (22) is arranged on the second side (42) of the second medium (4). Sensor after one of the Claims 1 until 5 , characterized in that the detector (6) is in contact with the first mirror (21) or that the detector (6) is in contact with the second mirror (22). Sensor after one of the Claims 1 until 6th , characterized in that the pump source (5, 51, 52) contains or consists of a diode laser. A method for detecting at least one measured variable, comprising the following steps: providing a device with at least one optical resonator (2), at least one first active medium (3) which is arranged in the resonator (2) and is set up to produce an optical gain in one to generate the first wavelength range, at least one pump source (5, 51, 52), at least one detector (6) and at least one radio frequency transmitter (7), arranging the device (1) at a measurement location so that at least the first active medium (3) is exposed to the measured variable to be detected, with the radio frequency transmitter (7) generating electromagnetic radiation which acts at least on the first active medium (3) and which, depending on the at least one measured variable, at least one transition between at least two states of the first active medium ( 3) stimulates, the first active medium (3, 4) being stimulated to optical emission with at least one pump source (5, 51, 52) d, characterized in that the sensor further contains at least one second active medium (4) which is arranged in the resonator (2) and is set up to generate an optical gain in a second wavelength range, the first and second wavelength ranges at least partially are identical and the first and the second active medium (3, 4) have a laser threshold in cooperation with the resonator (2), the second active medium (3) for optical emission with the at least one pump source (5, 51, 52) is excited, and the at least one detector is used to detect laser radiation, the intensity of which indicates the variable to be measured. Procedure according to Claim 8 , characterized in that the measured variable is a magnetic field or comprises a magnetic field. Method according to one of the Claims 8 or 9 , characterized in that the intensity of the laser light is measured and this intensity is a direct measure of the variable to be measured due to previous calibration. Method according to one of the Claims 8 until 10 , characterized in that the frequency or the intensity of the electromagnetic radiation generated by the radio frequency transmitter (7) varies and the intensity of the laser light is detected via a lock-in method or that the intensity of the generated by the pump source (5, 51), on the first medium incoming pump light varies and the intensity of the laser light is detected via a lock-in process. Method according to one of the Claims 8 until 11 , characterized in that the light from the pump source (5, 51, 52) is coupled into the first and / or second medium (3, 4) through at least one mirror (21, 22).

Images