DE102019203930A1 - Sensor device - Google Patents

Abstract

The invention relates to a sensor device (1) with a crystal body (8), in particular a diamond, with a number of color centers, in particular nitrogen defects, a laser cavity (5) defining an optical axis (A) for generating excitation light ( 20), a high-frequency device (7) for irradiating the crystal body with microwaves, and one or more photodetectors (3) which are set up to detect fluorescent light (30) which occurs due to the irradiation of the crystal body (8) by the excitation light (20) and the microwaves are generated, the laser cavity (5) having at least two reflectors (3) and an intermediate laser gain medium (9), wherein the crystal body (8) within the laser cavity (5) between the at least two reflectors (3) is arranged.

Description

The present invention relates to a sensor device.

State of the art

Color centers, such as the negatively charged nitrogen vacancy centers in a crystal body, in particular a diamond lattice, also referred to as NV centers (NV stands for “Nitrogen Vacancy”), can be used, for example, in the field of sensor technology. By exciting such NV centers with light and microwave radiation, a magnetic field-dependent fluorescence can be observed. This fluorescence is recorded and evaluated by means of a sensor device. As a further example of such color centers, reference is made to defect centers in SiC, but also to SiV in diamond.

The negatively charged NV center in diamond can be used in particular for the highly sensitive measurement of magnetic fields, electrical fields, mechanical stresses and temperatures. Such quantum technologies offer decisive advantages over classic sensor principles, which underline the disruptive potential of quantum technology. The NV centers have the following advantages: (i) ultra-high sensitivities, (ii) vector magnetometry (determination of the direction of the magnetic field), (iii) high dynamic measuring range (> 1 Tesla), (iv) linearity (Zeeman effect), (v) no degradation , since the measurement is based on quantum mechanical states. In order to read a sensor based on NV centers, the magnetic resonance of the spin triplet of the ground state is detected optically (ODMR, optically detected magnetic resonance). Fluorescent light which is red-shifted compared to the stimulating light shows a characteristic dip in the energetic position of the electron spin resonance. Due to the Zeeman effect, the position is linearly dependent on the magnetic field. This enables a highly sensitive magnetic field sensor to be constructed.

NV centers in Diamant are so sensitive to magnetic fields that they can be used to improve a wide range of existing products (e.g. search devices for electrical lines in walls or current measurement of vehicle batteries) or to implement new products, such as a contactless person -Machine interface that detects and evaluates currents or control signals from the brain.

The measurement of magnetic fields via a combined excitation of such color centers with light and microwaves has proven to be particularly advantageous. In particular, the excitation with light used here leads to relatively complex and large-sized sensor devices.

The DE 37 42 878 A1 describes, for example, an optical magnetic field sensor in which a crystal is used as a magnetically sensitive optical component. Since only part of the excitation light is absorbed at the color centers, the efficiency of such sensor devices and thus their accuracy is not optimal.

• Ein erster Bestandteil ist ein aktives Medium, auch als Laser-Gain-Medium oder Lasermedium bezeichnet. Im aktiven Medium entstehen durch einen durch Photonen verursachten optischen Übergang angeregter Atome oder Moleküle in einen energetisch günstigeren Zustand weitere Photonen. Die auslösenden und die erzeugten Photonen sind hierbei kohärent. Dieser Effekt wird als stimulierte Emission bezeichnet. Wesentliche Voraussetzung für ein wirksames Lasermedium ist, dass sich eine Besetzungsinversion herstellen lässt. Das bedeutet, dass der obere Zustand des optischen Übergangs mit einer höheren Wahrscheinlichkeit besetzt ist, als der untere. Ein solches Medium muss mindestens über drei Niveaus verfügen und kann gasförmig (z. B. HeNe oder CO₂), flüssig (z. B. Farbstofflösungen) oder fest sein. Als Beispiele fester Laser-Gain-Medien seien neodymdotiertes Yttriumaluminiumgranat (Nd:YAG), Rubinkristall und Halbleitermaterial genannt.

Lasers are known from the prior art. A laser basically consists of three components:

• A first component is an active medium, also referred to as a laser gain medium or laser medium. In the active medium, an optical transition of excited atoms or molecules into an energetically more favorable state is generated by photons. The triggering and the generated photons are coherent. This effect is known as stimulated emission. An essential prerequisite for an effective laser medium is that a population inversion can be produced. This means that the upper state of the optical transition is more likely to be occupied than the lower. Such a medium must have at least three levels and can be gaseous (e.g. HeNe or CO ₂ ), liquid (e.g. dye solutions) or solid. Examples of solid laser gain media include neodymium-doped yttrium aluminum garnet (Nd: YAG), ruby crystal and semiconductor material.

A second component is a pump. In order to bring about a population inversion as described above, energy must be introduced or pumped into the laser medium. So that this pumping process does not compete with the stimulated emission, it must be based on a different quantum mechanical transition. Pumping can bring the atoms or molecules of the laser gain medium into excited states in particular optically (irradiation of light) or electrically (by gas discharge or in the form of electrical current in the case of laser diodes).

A third component is a resonator. In the simplest case, a resonator consists of two parallel mirrors or reflectors, between which the active laser medium is located. Photons whose propagation is perpendicular to the mirrors remain in the resonator and can therefore trigger (stimulate) the emission of further photons in the active medium. A photon produced in this way corresponds in all quantum numbers to the triggering photon. So, as mentioned above, the photons are coherent. Photons that the Leave the resonator, accordingly do not stimulate any emissions. This selection of the resonator leads to narrow-band emission or the high coherence length of laser radiation.

US 2014/0072008 A1 discloses a laser that includes a diamond as a laser gain medium that has color centers. Influenced by microwave rays and optical excitation, fluorescence rays are created. The intensity of the fluorescence radiation is dependent on an applied magnetic field. The output power of the laser can thus be influenced by varying the magnetic field.

One object of the present invention is to miniaturize magnetic field sensor devices and improve energy efficiency.

Disclosure of the invention

According to the invention, a sensor device with the features of the independent patent claim is proposed. Advantageous configurations are the subject of the subclaims and the description below.

Advantages of the invention

According to the invention, a sensor device is proposed with a laser arrangement defining an optical axis for generating excitation light, the laser arrangement having at least two reflectors, an intermediate laser gain medium and a pump for bringing about a population inversion. The sensor device also has a crystal body, in particular a diamond, with a number of color centers, in particular nitrogen defects, the crystal body being arranged within the laser arrangement between the at least two reflectors, and a high-frequency device for irradiating the crystal body with microwaves, and one or more photodetectors that are configured to detect fluorescent light that is generated due to the irradiation of the crystal body by the excitation light and the microwaves. In this case, at least one photodetector is arranged at a radial distance from the optical axis of the laser arrangement.

The essence of the invention is to arrange at least one photodetector at a radial distance from the optical axis of the laser arrangement. As a result, coupling out of the fluorescent light generated in the crystal body by a reflector of the laser arrangement is no longer necessary and is preferably also not provided. Coupling out laser light would be a disadvantage, since this would reduce the available intensity. A high optical intensity, which is necessary for the working principle of the color centers, can be achieved within the laser arrangement and thus also within the crystal body.

The photodetector or photodetectors can surround the optical axis of the laser assembly completely radially (e.g. cylindrical) or e.g. even only on one or two or three sides.

In particular, a color filter which transmits the fluorescent light and reflects the excitation light is arranged between at least one, in particular each photodetector and the optical axis of the laser arrangement. This both prevents overdriving of the photodetectors by excitation light and uses the excitation light for further excitations within the crystal body.

According to a particularly preferred embodiment, for which protection is sought separately, at least one of the reflectors, preferably both reflectors, has a reflection coefficient of greater than 95%, 96%, 97%, 98% or 99%, more preferably greater than 99.5%, more preferably greater than 100%. In this way, neither excitation light nor fluorescent light is coupled out of the laser arrangement by a reflector. The detection of the fluorescent light can thus take place at another point, in particular radially offset from the optical axis of the laser arrangement. This allows a smaller structure and a more efficient arrangement to be implemented.

A reflective side surface is preferably arranged at at least one position, radially offset from the optical axis of the laser arrangement, in order to guide the fluorescent light to one of the photodetectors. Such a reflective side surface can, in particular, surround the optical axis in a cylindrical shape in any direction in which no photodetector is arranged. In this way, the fluorescent light can be effectively directed to the photodetector and detected there. This enables particularly efficient detection of the fluorescence radiation, which further increases the energy efficiency and the sensitivity of the sensor.

The laser gain medium and the crystal body are preferably two separate media. This is advantageous because in this way a greater intensity of the excitation light can be achieved. A neodymium-doped yttrium aluminum organate, which is optically pumped at 808 nm and combined with a frequency-doubling lithium triborate crystal or a semiconductor laser that is electrically pumped, is conceivable as a laser gain medium. In particular, the crystal body is in the direction of the optical axis arranged axially adjacent to the laser gain medium.

Further advantages and configurations of the invention emerge from the description and the accompanying drawing.

The invention is shown schematically in the drawing using an exemplary embodiment and is described below with reference to the drawing.

Figure list

• 1 shows a schematic cross-sectional view of a preferred embodiment of a sensor device according to the invention

Embodiment of the invention

In 1 is shown schematically a cross-sectional view of a preferred embodiment of a sensor device according to the invention and designated as a whole with 1.

The sensor device 1 has a laser arrangement defining an optical axis A. 5 for generating excitation light 20th on. The laser arrangement 5 has two a resonator 41 forming reflectors 40 , an intermediate laser gain medium 9 , as well as a schematically shown pump 91 to bring about a population inversion in the laser gain medium 9 on.

Furthermore is a crystal body 8th , in particular a diamond, with a number of color centers, in particular nitrogen voids, within the laser arrangement 5 between the at least two reflectors 40 arranged. The crystal body 8th is in this embodiment in the direction of the optical axis A axially adjacent to the laser gain medium 9 arranged.

A neodymium-doped yttrium aluminum garnet, which is optically pumped at 808 nm and combined with a frequency-doubling lithium triborate crystal or a semiconductor laser which is electrically pumped, is preferably used as the laser gain meium. When using the nedodymium-doped yttrium aluminum garnet, it is conceivable to additionally arrange a lithium borate crystal between the laser gain medium and the diamond and to make a mirror transparent for the pump wavelength of 808 nm so that the pump light can be coupled into the resonator. By recombination or stimulating emission in the laser gain medium 9 becomes coherent laser light as excitation light 20th generated. The laser gain medium 9 is preferably chosen so that green excitation light 20th is produced. The green excitation light 20th is from the reflectors 40 in the resonator 41 reflected back and forth. When the distance of the reflectors 40 satisfies the resonance condition, the excitation light becomes 20th in the resonator 41 reinforced. This creates a high intensity of the excitation light 20th in the area of the crystal body 8th which, as mentioned, is designed in particular as a diamond with nitrogen vacancies.

In addition, there is a high frequency device 7th for irradiating the crystal body 8th with microwaves 27 intended. The simultaneous irradiation of the crystal body 8th with microwaves 27 and green excitation light 20th causes one of the color centers in the crystal body 8th caused fluorescence. In the case of green excitation light, red fluorescent light is typically produced 30th . This fluorescent light 30th is emitted almost isotropically from the color centers after their optical excitation.

In this embodiment, the sensor device has at least one photodetector 3 on, the one for detecting the fluorescent light 30th is set up. This is radially spaced from the optical axis A of the laser arrangement 5 arranged. Furthermore is between the photodetector 3 and the optical axis A of the laser assembly 5 a color filter 6th arranged that the fluorescent light 30th transmitted and the excitation light 20th reflected. This causes overdrive of the photodetector 3 by excitation light 20th prevented. You can also use the color filter 6th reflected excitation light 20th for further stimulation of color centers or nitrogen vacancies within the crystal body 8th be used.

A reflective side surface is in each case at several positions offset radially to the optical axis A of the laser arrangement 4th arranged. This guides the fluorescent light 30th to the photodetector 3 . Dependent on several reflective side surfaces 4th is in the 1 a reflective side surface 4th in the radial direction opposite the photodetector 3 shown.

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

• DE 3742878 A1 [0006]
• US 2014/0072008 A1 [0010]

Claims (6)

Sensor device (1) with a laser arrangement (5) defining an optical axis (A) for generating excitation light (20), the laser arrangement (5) having at least two reflectors (40), an intermediate laser gain medium ( 9), as well as a pump (91) for bringing about a population inversion in the laser gain medium (9), a crystal body (8), in particular a diamond, with a number of color centers, in particular nitrogen defects, the crystal body (8) is arranged within the laser arrangement (5) between the at least two reflectors (40), a high-frequency device (7) for irradiating the crystal body with microwaves, characterized by one or more photodetectors (3) which are set up to detect Fluorescent light (30) which is generated due to the irradiation of the crystal body (8) by the excitation light (20) and the microwaves (27), at least one photodetector (3) being radially spaced from the r optical axis (A) of the laser arrangement (5) is arranged. Sensor device (1) Claim 1 wherein a color filter (6) which transmits the fluorescent light (30) and reflects the excitation light (20) is arranged between at least one photodetector (3) and the optical axis (A) of the laser arrangement (5). Sensor device (1), in particular according to the preamble of Claim 1 wherein at least one of the reflectors (40), preferably both reflectors (40), has a reflection coefficient of greater than 95%, 96%, 97%, 98% or, more preferably greater than 99.5%, even more preferably 100% or have. Sensor device (1) according to one of the preceding claims, wherein a reflective side surface (4) is arranged at at least one position offset radially to the optical axis (A) of the laser arrangement (5) in order to direct the fluorescent light (30) onto one of the photodetectors ( 3) reflect. Sensor device (1) according to one of the preceding claims, wherein the laser gain medium (9) and the crystal body (8) are designed as separate components. Sensor device (1) Claim 5 wherein the crystal body (8) is arranged axially adjacent to the laser gain medium (9) in the direction of the optical axis (A).

Images