Device and method for controlling an acousto-optic component

Abstract

Device for controlling at least one acousto-optic component (1) for influencing light passing through the beam path of a microscope, with at least one radio frequency generator (9) for supplying the acousto-optic component (1) with a radio frequency and a processor (10) upstream of the radio frequency generator (9), wherein temperature-related malfunctions of the acousto-optic component (1) can be compensated by adjusting the radio frequency, The adjustment of the radio frequency, starting from a target radio frequency provided by the processor (10), is carried out depending on the actual temperature that can be determined directly at the acousto-optic component (1), a signal corresponding to the actual temperature at the acousto-optic component (1) can be directly supplied to the radio frequency generator (9), and the compensation coefficient used to adjust the radio frequency can be determined exclusively from the actual temperature of the acousto-optic component (1) and the target radio frequency.

Description

[0001] The invention relates to a device for controlling an acousto-optic component for influencing transmitted light, in particular for influencing the illumination light and / or the detection light in the beam path of a microscope, preferably a confocal laser scanning microscope, with a radio frequency generator for supplying the acousto-optic component with a radio frequency. The invention further relates to a corresponding method as well as uses or applications of both the device and the method.

[0002] This essentially concerns the control of acousto-optic components to influence transmitted light. Such components typically comprise an acousto-optic crystal with an integrated electrical transducer. The transducer usually consists of a piezoelectric material and electrodes positioned above and below it. By electrically applying radio frequencies, typically in the range of 30 MHz to 800 MHz, to the two electrodes, the piezoelectric material is set into vibration, generating an acoustic wave (sound wave) that, due to the transducer's arrangement, travels through the crystal. After passing through the optical interaction region, the sound wave is typically absorbed or reflected away at the opposite side of the crystal.Acousto-optic crystals, such as those used in the acousto-optic elements discussed here, are characterized by the fact that the resulting sound wave alters the optical properties of the crystal. The sound induces an optical grating or a comparable optically active structure, for example, in the form of a hologram. Light passing through the crystal is diffracted by this optical grating, and the light is directed in different diffraction orders or directions.

[0003] The acousto-optic components under discussion here can be divided into those that influence all incident light more or less independently of the wavelength (e.g., AOM, AOD, and Frequency Shifter) and those that selectively affect individual wavelengths depending on, for example, irradiated radio frequencies (e.g., AOTFs).

[0004] Acousto-optic elements often consist of birefringent crystals, such as tellurium dioxide, where the position of the crystal axis relative to the plane of incidence of the light and its polarization determines the optical properties of the acousto-optic element.

[0005] In specific applications, either the light unaffected by diffraction, the light deflected into different diffraction orders, or both the unaffected and the deflected light are used.

[0006] In conventional acousto-optic components, the radio frequency is typically fed to the component via a coaxial cable. There, impedance matching takes place on an electronic circuit board, ensuring that no RF reflections occur. The goal is to deliver as much RF power as possible to the crystal, which usually has a different impedance than the RF cable. From the circuit board, the radio frequency is transmitted to the transducer on the crystal, where the acoustic wave is generated.

[0007] In the past, the acousto-optic components discussed here, especially in AOTFs, were primarily used to adjust and regulate light intensity. More recently, there has been a need to use such components to "cut out" specific portions of light from a more or less spectrally broadband light source. For example, reference is made to DE 101 15 488 A1.

[0008] The acousto-optic components discussed here are primarily used, within the context of the applications mentioned above, to isolate specific spectral components from a continuous or broadband light source for illumination purposes. Examples of their use include white lasers, broadband lasers, ultrashort pulse lasers, superluminescent LEDs or other superluminescent light sources, ASE light sources, incandescent bulbs, point-source LEDs and other LEDs, sunlight, starlight, etc. These optical components are also used to isolate specific spectral light components for detection purposes, for example, for use in programmable spectral filters. The use of acousto-optic components within a programmable array beam splitter (AOBS) is also significant.

[0009] It is also known from practical experience that the acousto-optic components in question change their behavior with temperature, primarily due to changes in the speed of sound within the crystal. If the acousto-optic component is to be used at varying temperatures, compensation for the temperature-induced behavior is necessary. Corresponding compensation methods are already known. These methods propose heating or cooling the crystal exposed to temperature fluctuations to stabilize its temperature. A special temperature control system is provided for this purpose. In this respect, reference should also be made to EP 0 834 762 A2, which describes a type of dummy radio frequency that is applied whenever the actual radio frequency is switched off, ensuring that the same amount of heat is always deposited in the crystal via a heater.

[0010] As an alternative to the method mentioned above, the radio frequency is adjusted according to a measured temperature change as described in DE 198 27 140 C2. However, it has been assumed up to now that the relevant compensation parameter, as well as the radio frequency itself, which is necessary for operating the acousto-optic component, depends on countless parameters, such as the wavelength of the light to be deflected, the angle of incidence of the light on the crystal, the crystal's installation conditions, etc. Therefore, the magnitude of the frequency change has been determined iteratively through experimentation, or tables for the compensation parameters have been created as a function of the wavelength and apparatus conditions. This has required determining the compensation parameters individually for each device. In this respect, particular reference is made to section

[0014] of DE 198 27 140 C2.

[0011] The effort required for error compensation according to the documented state of the art is considerable, as specific correction parameters must be stored and managed for each laser wavelength used and, if applicable, for each system employed. Furthermore, the driver electronics must be supplied with information to define the specific laser wavelength and experimental parameters in order to apply the corresponding compensation parameter. Consequently, according to the documented state of the art, temperature compensation cannot be performed directly by the radio frequency generator but must be supported by, or even entirely performed by, a higher-level control system, since all necessary system information must be readily available for temperature compensation.This hinders the system's ease of use and rapid temperature stabilization on short timescales. For example, a confocal microscope requires a higher software layer that possesses information about which laser wavelengths are currently being deflected from the crystal. This layer provides the necessary compensation parameters for the radio frequency generator, enabling it to correctly track the frequency. Accordingly, in the current state of the art, temperature compensation is not performed by the radio frequency generator itself, but by the controlling computer, which provides the generator with pre-set, temperature-compensated radio frequency setpoints – usually unchangeable. This results in enormous complexity and increased susceptibility to errors in the entire system.

[0012] From US patent 2004 / 0105485 A1, a device for compensating temperature changes in an acousto-optic assembly is known. A temperature sensor is arranged in thermal contact with a substrate of the acousto-optic assembly. The temperature sensor generates an electrical signal corresponding to the temperature measured on the substrate. This electrical signal is fed to a processor, which generates a control signal from it to drive an oscillator. In addition to temperature, other system parameters are also taken into account in the temperature compensation described in this patent.

[0013] Document US 4,272,825 A describes a method for measuring temperature effects on the tuning curves of an AOTF. A photodetector provides a signal representing the light intensity at the optical output of the AOTF. The radio frequency is then varied based on this signal.

[0014] Documents DE 101 37 154 A1, DE 101 37 155 A1 and DE 103 24 331 A1 describe methods for controlling acousto-optic components depending on the temperature.

[0015] In light of the foregoing, the present invention aims to design and further develop a device and a method of the generic type in such a way that error-free automatic operation is possible with a simple system configuration even under changing temperatures. Furthermore, the user should not have to make any decisions regarding any settings or parameters for temperature-dependent error compensation.

[0016] The foregoing problem is solved by the features of dependent claims 1 and 11, namely firstly with regard to the device according to the invention and secondly with regard to the method according to the invention.

[0017] According to the invention, it has been discovered that temperature-fluctuation-related malfunctions of the acousto-optic component can be compensated for in a simple and ideal manner by adjusting the radio frequency. This finding is surprising to experts, considering the effort involved in the relevant prior art. It is particularly surprising that the compensation parameter (in kHz / °C) required for radio frequency tracking only appears to depend arbitrarily on all possible system parameters, such as the wavelength of the light to be deflected, the angle of incidence of the light on the crystal, the crystal's installation conditions, etc. Despite the aforementioned dependencies, it is possible to link the compensation parameters directly and solely to the radio frequency to be set, the radio frequency itself actually depending on numerous parameters in a complex manner.The underlying link here is to the specification of a . The appropriate compensation parameter follows an extremely simple, essentially linear mathematical relationship except for small corrections.

[0018] The aforementioned finding of the invention has very significant consequences with regard to the claimed device and the claimed method. According to the invention, it is possible to determine the corresponding compensation value (in kHz / °C) directly from the radio frequency provided for the radio frequency generator. In other words, the radio frequency generator can be adjusted according to the temperature at the acousto-optic component simply by knowing the output radio frequency.

[0019] The insight underlying the invention represents a significant advantage for the user, as they no longer need to concern themselves with the temperature prevailing in the area of ​​the acousto-optic component, particularly the crystal temperature, when operating the respective system. Even the calibration of the system to the correct radio frequencies for operating the respective acousto-optic components can also be performed under the conditions of the temperature compensation according to the invention, so that the user always sets the correct radio frequencies relative to a defined standard temperature, regardless of the actual temperature present at the acousto-optic component at the time of calibration.

[0020] The mathematical relationship between the desired radio frequency at a defined temperature and the associated compensation coefficient is advantageously expressed as follows: Compensation coefficient (kHz / °C)=a0+a1*RF+a2+RF2+a3*RF3+…+an*RFn.

[0021] Typically, n can be chosen to be very small (preferably n<5, but even n=1 provides excellent temperature compensation). Often, a0 is even close to 0, so this coefficient can also be omitted, and in extreme cases, only a single coefficient needs to be stored in the radio frequency generator. Generally, one to a maximum of five coefficients is sufficient. This is also significantly simpler in terms of data volume than the individually calibrated tables required by established technical standards.

[0022] Advantageously, the radio frequency is adjusted, starting from a target radio frequency, depending on the temperature directly measurable at the acousto-optic component. Assuming that the acousto-optic component comprises a crystal with variable optical properties, it is a significant advantage to include a temperature sensor that allows the temperature to be determined directly at the crystal. Accordingly, a signal corresponding to the actual temperature at the acousto-optic component is fed to the radio frequency generator, enabling temperature compensation directly at the generator based on a simple linear relationship between the desired radio frequency and the actual temperature.

[0023] As mentioned previously, the device according to the invention offers the enormous advantage that the compensation coefficient used to adjust the radio frequency can be determined solely based on the temperature of the acousto-optic component and the target radio frequency. This allows the actual temperature of the acousto-optic component to be continuously determined. It is conceivable that a signal corresponding to the actual temperature is fed directly to the radio frequency generator or an upstream processor. If the actual temperature is fed to an upstream processor, this processor generates a control signal for the radio frequency generator. Consequently, the control signal provided by the processor is used to generate a radio frequency based on the respective temperature of the acousto-optic component.

[0024] It is also possible, in a particularly simple way, to feed the continuously measured temperature of the acousto-optic component directly to the radio frequency generator as a control signal. This signal enables the generator to produce the appropriate radio frequency based on the respective temperature of the acousto-optic component. The radio frequency generator is only supplied with digital information via the processor, with the actual compensation taking place within the generator itself. In this case, the processor communicates exclusively with the radio frequency generator, which receives data from the temperature sensor and delivers the required, adjusted radio frequency to the crystal of the acousto-optic component.

[0025] As mentioned previously, the device according to the invention can be used to control several acousto-optic components, in which case radio frequency generators are provided according to the number of acousto-optic components. These generators are supplied with control signals via a common processor to generate radio frequencies based on the temperature of the respective acousto-optic component. Accordingly, it is conceivable that different acousto-optic components are provided in the system, wherein the acousto-optic component can be an AOTF (acousto-optical tunable filter), an AOD (acousto-optical deflector), an AOM (acousto-optical modulator), a component within a programmable beam splitter (i.e., within an AOTF), a frequency shifter, or the like.

[0026] Within a merge module, beam merging and an AOTF can be used for intensity control, with the components potentially housed in a single enclosure. Alternatively, two or more acousto-optic components can be combined into an AOBS (programmable beam splitter) within a single enclosure.

[0027] According to the features mentioned above, devices according to the invention can be operated, in particular taking into account the claimed process steps.

[0028] There are no limits to the possible uses of the device according to the invention. For example, the device according to the invention can be used for temperature compensation in a confocal laser scanning microscope. An illumination beam could be guided through a first acousto-optic component with temperature compensation according to the invention, preferably an AOTF. The control unit of the confocal microscope controls not only the confocal microscope itself but also one or more radio frequency generators, which supply the acousto-optic components with the necessary radio frequencies. The light deflected and selected in the first acousto-optic component is preferably guided via an optical fiber to the scan head of the laser scanning microscope, where it serves as illumination.

[0029] In a particularly advantageous manner, the light is coupled into the microscope via an optical switch, i.e., via an acousto-optic beam splitter (AOBS). The optical switch can also include the temperature compensation according to the invention, which is performed accordingly via the radio frequency generator.

[0030] Other applications include optical coherence tomography, white light interferometry, optical tweezers in lithography, distance measurement, etc.

[0031] There are now various ways to advantageously elaborate and further develop the teaching of the present invention. For this purpose, reference should be made, on the one hand, to the claims subordinate to claim 1 and, on the other hand, to the following explanation of a preferred embodiment of the invention with reference to the drawing. In conjunction with the explanation of the preferred embodiment of the invention with reference to the drawing, generally preferred embodiments and further developments of the teaching are also explained. The drawing shows Fig. 1. In a schematic view, the basic structure of an acousto-optic component and Fig. 2 in a schematic diagram the application of the device according to the invention using the example of a confocal microscope, wherein a total of three acousto-optic components are used.

[0032] Fig. Figure 1 shows a schematic view of the basic structure of an acousto-optic component 1, which is controlled by the device according to the invention in a temperature-compensating manner. The acousto-optic component 1 comprises an acousto-optic crystal 2, which is arranged on a crystal holder 3. A temperature sensor 4, preferably equipped with a digital output, is provided directly on the crystal holder 3. A transducer 5 for coupling the high frequency into the crystal 2 is provided on the side of the acousto-optic crystal 2 facing away from the crystal holder 3.

[0033] Fig. Figure 2 shows in a schematic diagram the application of a device according to the invention for controlling a total of three acousto-optic components 1, wherein two of the acousto-optic components 1 form an AOBS 6 and wherein a further acousto-optic component 1 is arranged in a merge module 7. Within the merge module 7, the beam merging and the AOTF serve to control the intensity of the laser light coming from three laser light sources 8 in a common housing.

[0034] A total of three radio frequency generators 9 are provided for controlling the acousto-optic components 1, which are controlled by a processor 10 or computer with a control signal.

[0035] The radio frequency generators 9 receive control signals via the computer 10 on the one hand and temperature-specific signals via the temperature sensors 4 assigned to the acousto-optic components 1 or the crystals 2 therein, so that an adjustment of the radio frequency for temperature compensation can take place in the respective radio frequency generator 9.

[0036] At the in Fig.In the embodiment shown in Figure 2, the compensation for the temperature-fluctuation-related malfunction of the acousto-optic component 1 in the respective radio frequency generator 9 is carried out exclusively by taking into account the respective temperature at the acousto-optic component 1, taking into account the target radio frequency provided by the computer 10, based on a defined standard temperature at the radio frequency generator 10. The actual temperature is continuously determined by the temperature sensors 4 and sent to the radio frequency generator 9. This continuously calculates new values ​​for the radio frequencies and sends them to the associated acousto-optic component 1 or the crystal 2 located therein.

[0037] Finally, it should be noted that the embodiment discussed above serves only as an example to illustrate the claimed teaching, but does not limit it to that embodiment. Reference symbol list 1 acousto-optic component 2 acousto-optic crystal 3 Crystal holder 4 Temperature sensor 5 Transducers 6 AOBS 7 Merge Module 8 Laser light source 9 Radio frequency generator 10 Processor, Computer

Claims

[1] Device for controlling at least one acousto-optic component (1) for influencing light passing through the beam path of a microscope, comprising at least one radio frequency generator (9) for supplying the acousto-optic component (1) with a radio frequency and a processor (10) upstream of the radio frequency generator (9), wherein temperature-related malfunctions of the acousto-optic component (1) can be compensated by adjusting the radio frequency, The adjustment of the radio frequency, starting from a target radio frequency provided by the processor (10), is carried out depending on the actual temperature that can be determined directly at the acousto-optic component (1), a signal corresponding to the actual temperature at the acousto-optic component (1) can be directly supplied to the radio frequency generator (9), and the compensation coefficient used to adjust the radio frequency can be determined exclusively from the actual temperature of the acousto-optic component (1) and the target radio frequency. [2] Device according to claim 1, wherein the acousto-optic component (1) comprises a crystal (2) whose optical properties can be modified, characterized by , that a temperature sensor (4) is provided, via which the temperature can be determined directly at the crystal (2). [3] Device according to claim 1 or 2, characterized by , that the actual temperature of the acousto-optic component (1) is continuously determined and a control signal corresponding to the actual temperature is supplied to the radio frequency generator (9) to generate a radio frequency based on the respective temperature of the acousto-optic component (1). [4] Device according to any one of claims 1 to 3, characterized by, that several acousto-optic components (1) are provided in the beam path and that radio frequency generators (9) are provided according to the number of acousto-optic components (1), which are supplied with control signals via the common processor (10) to generate radio frequencies based on the temperature at the respective acousto-optic component (1). [5] Device according to any one of claims 1 to 4, characterized by , that the acousto-optic component (1) is an acousto-optic adjustable filter. [6] Device according to any one of claims 1 to 5, characterized by , that the acousto-optic component (1) is an acousto-optic deflector. [7] Device according to any one of claims 1 to 6, characterized by , that the acousto-optic component (1) is an acousto-optic modulator. [8] Device according to any one of claims 1 to 7, characterized by, that the acousto-optic component (1) is a component within a programmable beam splitter. [9] Device according to any one of claims 1 to 8, characterized by , that the acousto-optic component (1) is a frequency shifter. [10] Device according to any one of claims 1 to 9, characterized by , that the device for controlling the at least one acousto-optic component (1) is designed to influence the illumination light and / or the detection light in the beam path of a confocal laser scanning microscope. [11] Method for controlling at least one acousto-optic component (1) for influencing light passing through it in the beam path of a microscope, wherein at least one radio frequency generator (9) is provided for supplying the acousto-optic component (1) with a radio frequency, in particular for use in a device according to one of claims 1 to 10, wherein temperature-fluctuating malfunctions of the acousto-optic component (1) are compensated by adjusting the radio frequency, The adjustment of the radio frequency, starting from a target radio frequency provided by a processor (10) upstream of the radio frequency generator (9), is carried out depending on the actual temperature that can be determined directly at the acousto-optic component (1), a signal corresponding to the actual temperature at the acousto-optic component (1) is fed directly to the radio frequency generator (9), and The compensation coefficient used to adjust the radio frequency is determined exclusively from the actual temperature of the acousto-optic component (1) and the target radio frequency. [12] Method according to claim 11, wherein the acousto-optic component (1) comprises a crystal (2) whose optical properties can be modified, characterized by , that a temperature sensor (4) is provided, via which the temperature is determined directly at the crystal (2). [13] Method according to claim 11 or 12, characterized by , that the actual temperature of the acousto-optic component (1) is continuously determined and a control signal corresponding to the actual temperature is supplied to the radio frequency generator (9) to generate a radio frequency based on the respective actual temperature of the acousto-optic component (1). [14] Method according to any one of claims 11 to 13, characterized by, that several acousto-optic components (1) are provided in the beam path and that radio frequency generators (9) are provided according to the number of acousto-optic components (1), which are supplied via the common processor with control signals for the generation of radio frequencies based on the actual temperature at the respective acousto-optic component (1). [15] Method according to any one of claims 11 to 14, characterized by , that the acousto-optic component (1) is controlled to influence the illumination light and / or the detection light in the beam path of a confocal laser scanning microscope. [16] Use of a device according to any one of claims 1 to 10, using a method according to any one of claims 11 to 15 in optical coherence tomography. [17] Use of a device according to any one of claims 1 to 10, using a method according to any one of claims 11 to 15 in white light interferometry. [18] Use of a device according to any one of claims 1 to 10, using a method according to any one of claims 11 to 15 in optical tweezers in lithography [19] Use of a device according to any one of claims 1 to 10, using a method according to any one of claims 11 to 15 in distance measurement.

Images