rus
Issue #8/2024
A. N. Melnikov
Controlling Mirror Mutual Arrangement in Three-Mirror Telescopes Using Computer-Generated Hologram Optical Elements
Controlling Mirror Mutual Arrangement in Three-Mirror Telescopes Using Computer-Generated Hologram Optical Elements
DOI: 10.22184/1993-7296.FRos.2024.18.8.630.638
A solution to the precision control issue of mirror mutual arrangement in centered three-mirror telescopes is proposed based on the application of axial computer-generated hologram optical elements (CGHOE) both at the stage of telescope assembly and adjustment and during operation to ensure their regular additional adjustment.
A solution to the precision control issue of mirror mutual arrangement in centered three-mirror telescopes is proposed based on the application of axial computer-generated hologram optical elements (CGHOE) both at the stage of telescope assembly and adjustment and during operation to ensure their regular additional adjustment.
Теги: adjustment assembly centered three-mirror telescope circular axial computer-generated hologram optical element cylindrical axial computer-generated hologram optical element laser-holographic control of mirror mutual arrangement radial-sector axial computer-generated hologram optical elemen regular additional adjustment круговой осевой синтезированный голограммный оптический элемент лазерно-голографический контроль взаиморасположения зеркал радиально-секторный осевой синтезированный голограммный оптичес регулярная подъюстировка сборка центрированный трехзеркальный телескоп цилиндрический осевой синтезированный голограммный оптический эл юстировка
Controlling Mirror Mutual Arrangement in Three-Mirror Telescopes Using Computer-Generated Hologram Optical Elements
A. N. Melnikov
JSC Scientific and Production Association “State Institute of Applied Optics”, Kazan, Tatarstan, Russia
A solution to the precision control issue of mirror mutual arrangement in centered three-mirror telescopes is proposed based on the application of axial computer-generated hologram optical elements (CGHOE) both at the stage of telescope assembly and adjustment and during operation to ensure their regular additional adjustment.
Keywords: centered three-mirror telescope, assembly, adjustment, regular additional adjustment, laser-holographic control of mirror mutual arrangement, circular axial computer-generated hologram optical element, radial-sector axial computer-generated hologram optical element, cylindrical axial computer-generated hologram optical element
Article received: 31.10.2024
Article accepted: 20.11.2024
Introduction
In order to perform regular monitoring of extraterrestrial space, solve big issues of cosmology, protect the planet against dangerous space debris and asteroids, and conduct remote sensing of the Earth’s surface, it shall be necessary to constantly increase the number of optical telescopes being developed and generated, both ground-based and space-based, including the spaceborne telescopes (ST) installed on board the small spacecrafts [1–4].
The analysis shows as follows: in order to solve the remote sensing issues of the Earth’s surface, the most preferred options of the optical systems for the ST development among the existing toolkit of technical solutions shall include the centered three-mirror systems (CTMS), mainly with the aspherical working surfaces, without any additional lens adjusters [5–10].
The main advantages of the ST CTMS shall be noted: they allow operation within a wide spectral range (the integral transmission coefficient of the entire CTMS is determined only by the operating spectral range of the reflective coatings); they have an increased field of view compared to the classical Ritchey-Chretien and Cassegrain arrangements; there are no additional problems with the selection of materials for the lens adjustors that ensure stability of specifications over the entire range of operating temperatures; when using the lightweight mirrors, it is possible to achieve a reduction in the overall ST weight [7, 11].
It is well-known [1, 12, 13] that if the adjustment processes in the workshop conditions and regular additional adjustment in the space conditions even for the centered dual-mirror ST systems cause significant difficulties and are characterized by high labor intensity, then it shall be obvious that for the ST CTMS such adjustment difficulties and labor intensity are enhanced due to the increased degrees of freedom of the mirrors being adjusted and possible variations in their mutual arrangement. Therefore, the search for new approaches in the field of adjustment control in the production and operational conditions for the ST CTMS shall be relevant.
Existing technical solutions
and approaches
Among a number of methods to assembly and adjust the centered dual-mirror systems (CDMS) currently applied in the workshop conditions [13], in particular by using the coordinate measurement systems, with the mirror center adjustment in the frames, with the transfer of axes to an additional base with due regard to their practical constraints, only the precision method based on the axial CGHOE and specified by the interferometric accuracy and possible operation within a wide spectrum of electromagnetic waves is the most promising for development and application during the CTMS assembly and adjustment control. This laser-holographic approach based on an axial CGHOE on a flat substrate in the transmitted light was partially applied in the Offner scheme for the assembly and adjustment of the mutual arrangement of only two mirrors (namely, the primary and tertiary) in the absence of a secondary mirror in the scheme [10]. Then the secondary mirror was precisely installed by three actuators in relation to the adjusted pair of the “primary mirror – tertiary mirror”. Moreover, if we consider our earlier technical proposals [12] on the possible applicability of holographic control devices (HCD) based on a system of axial CGHOEs as the wavefront sensors in the space conditions for the ST CDMS, then the development of these proposals shall be an alternative to the available practical generation of ST service systems in terms of automatic adjustment and automatic focusing systems based, in particular, on the use of systems consisting of the flat auxiliary reflectors, autocollimators, mirror-like rhombuses, corner-cube prisms and position-sensitive (quadrant) photodetectors [11, 14] that are less accurate compared to the interferometric wavefront sensors.
Main provisions
of the proposed solution
Since the HCDs capable of monitoring the mutual arrangement of mirrors both in the workshop conditions and in the operating conditions with their regular additional adjustment are of significant practical interest for the ST CTMS, then the HCD construction can be conceptually implemented within the framework of three main options for the beam paths in its object branch:
1st – with the autocollimation beam path in the transmitted light (Figure 1a);
2nd – with the autocollimation beam path in the reflected light (Figure 1b);
3rd – with the quasi-autocollimation beam path and wavefront reversal (Figure 1c).
The following designations are used in Figure 1: 1 – point source of laser radiation; 1′– image of the point source of laser radiation 1 generated by the optical system “axial CGHOE 5 (5′) “plus” the mirror 2 in the transmitted light (mirror 2′ in the reflected light) “plus” the concave surface of mirror 4″; 1″ – image of the point source of laser radiation 1 generated by the optical system “axial CGHOE 6 (6′) “plus” the mirror 2 in the transmitted light (mirror 2′ in the reflected light) “plus” the concave surface of mirror 3″; 1‴– autocollimation image of the point source of laser radiation 1 generated by the axial CGHOE 7 (7′); 2 – axial aspherical mirror on a plano-convex substrate made of the optically transparent material with a semi-transparent optical coating applied to the convex surface; 2′ – axial aspherical mirror on a plano-convex substrate made of the optically opaque material and/or with weight reduction; 3 and 4 – off-axis aspherical mirrors on the plano-concave substrates; 5 (5′) – circular (cylindrical or radial-sector) axial CGHOE to control the mutual arrangement of the mirror 4; 6 (6′) – circular (cylindrical or radial-sector) axial CGHOE to control the mutual arrangement of the mirror 3; 7 (7′) – autocollimation circular (cylindrical) axial CGHOE; 8 – diaphragm in the form of a truncated cone, made at the apex of the convex surface of the mirror 2′, wherein the geometric axis of the diaphragm 8 coincides with the optical axes of the mirror 2′ and the entire CTMS; OO′– optical axis of the system being adjusted; O1 – center of the flat rear surface of the mirror 2; O2 – apex of the convex surface of the mirror 2 (2′); O3 – apex of the “parent” concave surface of the mirror 3; O4 – apex of the “parent” concave surface of the mirror 4; the parameters O1, O2, O3, O4, 1, 1′, 1″and 1‴ are located on the optical axis OO′. In Figures 1g and 1i, the axial CGHOEs 5′, 6′, 7′ are made in the form of radial-sector (segment) apertures in the convex surface edge zone of the mirror 2′.
The implementation of the 1st option shall be possible only when the substrate of the base mirror 2 is solid, without any weight reduction and made of an optically transparent material. The optical material of the substrate and its polished front and rear surfaces shall correspond to the strict tolerances for optical parameters, and a semi-transparent optical coating shall be applied to the front surface of this mirror. For the STs where the substrate of the base mirror 2′ is made with weight reduction and / or of the optically opaque materials (metals, metal alloys, composite materials), the HCD construction is possible only on the basis of the 2nd or 3rd options. However, these HCD construction options are rather cross-functional and can be implemented based on the use of the base mirror 2 with a substrate made of an optically transparent material, in a solid form without any weight reduction.
The operating principle of the HCDs as the wavefront sensors, shown in Figures 1a, 1b, 1c, is similar to the CDMS adjustment control device [12] and consists of obtaining, recording and analyzing the interference fringe patterns specifying the linear and angular mutual arrangement of the mirrors 2 (2′)–4 relative to each other, the point source of laser radiation 1 and the optical axis of the system OO′, where the flat rear surface of the mirror 2 (Figure 1a) or the convex front surface of the mirror 2′ (Figures 1b, 1c) can be taken as the base surface on which the system of axial CGHOEs 5–7 (5’–7’) is formed.
It shall be proposed to include the considered HCDs as the feedback components in the standard ST automatic adjustment systems with the servo drivers in the form of high-precision actuators that control the linear and angular positions of each of the three mirrors, achieving their design locations within the given optical system.
When calculating the spatial frequency characteristics (SFC) of the axial CGHOEs 5 (5′) and 6 (6′), it shall be necessary to consider the wavelength λк of the probing laser radiation, equations of the meridional section profiles of the “parent” surfaces of the mirror 4 and mirror 3, accordingly, and the design arrangement parameters of these mirrors with due regard to the double transit of the probing radiation through the substrate of the mirror 2 (for Figure 1a, the SFC calculation method of the axial CGHOEs 5 (5′) and 6 (6′) is similar to that given in [14]) or reflection of this radiation from the front surface of the mirror 2′ (for Figure 1b, the SFC calculation method of the axial CGHOEs 5 (5′) and 6 (6′) corresponds to that described in [12], and for Figure 1c, to that proposed in [15]). The spatial frequency characteristics of the autocollimation axial CGHOE 7 (7′) shall be obtained as a design result for the zone plate of the required focal length at a given wavelength λк.
The production of axial CGHOEs 5–7 (Figures 1d, 1f) and axial CGHOEs 5–6 (Figure 1h) in the form of circular apertures, as well as the axial CGHOEs 5’–7’ (Figure 1g) and axial CGHOEs 5’–6’ (Figure 1i) in the form of radial-sector (segment) apertures shall be possible with the optical diameters of up to 500–600 mm on circular ruling engines (MDA and MDG types) using special diamond cutters [16] or with an aperture record area of up to 300 mm using circular laser recording systems [17].
Since during the axial CGHOE production process their centering is performed with high accuracy, for example, along the common base cylindrical surface of the mirror 2 (2′), the optical axes of these CGHOEs shall be aligned with the optical axis of the mirror 2 (2′) with the smallest possible error (almost no more than one micrometer) [18]. Moreover, their centering with the mirror 2 (2′) shall be obviously remain unchanged in the future during the CTMS operation. This feature shall also increase the adjustment control reliability by the proposed HCD both in the workshop conditions and in the operating mode.
It can be additionally noted that the axial CGHOEs can be manufactured for application at a wavelength shorter than the wavelength of the short-wave limit of the spectral operating range of the CTMS being adjusted. Therefore, the stroked structures of axial CGHOEs (Figures 1f, 1g, 1h, 1i) can be applied in any part of the light zone of the reflective front surface of the mirror 2′ without causing negative effect on the ST image generation at the operating wavelengths.
The proposed approaches to the HCD generation for the mutual arrangement of mirrors for high-aperture and wide-angle large ground- and space-based telescopes with the CTMS [6] are of particular practical interest. In these CTMS, it shall be proposed to implement the HCD for the mutual arrangement of large-sized mirrors, the diameters of which can be within the range from one meter to several meters, not on the basis of circular or radial-sector axial CGHOEs, the production of which on the large-size mirror substrates is almost impossible due to the lack of the appropriate process equipment, but only by using the cylindrical axial CGHOE (CACGHOE). It shall be proposed to produce the CACGHOEs with a width of 10 to 20 mm. This approach with the CACGHOE applications and its implementation methods shall become a development of the proposal previously provided by the author in [19]. It shall be noted that the CACGHOE is to be made primarily in the form of amplitude computer-generated holograms that makes it possible to almost eliminate the dependence of the CACGHOE diffraction efficiency on the incidence angle of the beams from a monochromatic point source of radiation used in the HCD in various areas of its optical diameter, thereby ensuring the constant visibility of the interference fringes of the obtained interferograms within the controlled light field.
A conventional form of the possible CACGHOE implementation is shown in Figure 1e. In this case, the autocollimation CACGHOE 7′ shall be a system of two cylindrical holograms made orthogonal to each other to ensure more accurate and reliable alignment of the point source of laser radiation 1 with its autocollimation image 1‴. Similarly, the CACGHOE with the SFCs equal to those of the circular or radial-sector axial CGHOEs conventionally shown in Figures 1f, 1g, 1h, 1i, can be possibly applied to the convex front surface of the mirror 2′.
The estimates confirm that the laser-holographic control of the mutual arrangement of mirrors in the considered CTMS using the system of axial CGHOEs of the proposed HCDs can be performed with an error not exceeding 0.01 λк, where λк is the wavelength of the probing laser radiation, and this parameter shall be used when selecting the dimensions and resolution of the position-sensitive system to record the resulting interference fringe pattern.
Conclusion
Since the CTMS are currently arousing heightened interest of the ST developers, then the proposed approach to develop the HCD for the mutual arrangement of mirrors in the considered CTMS based on the application of axial CGHOEs shall be relevant. This approach shall be a development of the proposals published in [12, 15, 16] and confirmed by the results of physical modeling on the example of the CDMS prototype assembly and adjustment control [20]. Moreover, it shall open up the possibility to solve the problem of implementing laser-holographic monitoring of the ST CTMS assembly and adjustment both in the workshop conditions and during the regular additional adjustment in the operating space conditions. The CACGHOE application in the proposed HCDs in order to control the assembly and adjustment of high-aperture and wide-angle large-sized STs shall be of special relevance and potential. According to this approach, the following advantages are obvious in the HCD construction, namely interferometric accuracy, reliability and efficiency of the control functions, minimization of weight and dimensional parameters, as well as the energy consumption.
In order to perform comprehensive works on the generation, development and testing of the proposed HCDs for the mutual arrangement of mirrors, including the development of up-to-date high-precision process equipment for the CGHOE production, it shall be necessary to determine and conduct he comprehensive R&D in cooperation with the developers of STs and high-precision equipment.
AUTHOR
Andrei Melnikov, Cand. of Tech. Sc., Associate Professor; e-mail mr.melnikov@bk.ru; Research interests: Optical instruments and systems for Civilian optical products; Head of Department, JSC “Scientific and Production Association “State Institute of Applied Optics”, e-mail gipo@shvabe.com; Kazan, Tatarstan, Russia
ORCID: 0000-0002-3318-9853
A. N. Melnikov
JSC Scientific and Production Association “State Institute of Applied Optics”, Kazan, Tatarstan, Russia
A solution to the precision control issue of mirror mutual arrangement in centered three-mirror telescopes is proposed based on the application of axial computer-generated hologram optical elements (CGHOE) both at the stage of telescope assembly and adjustment and during operation to ensure their regular additional adjustment.
Keywords: centered three-mirror telescope, assembly, adjustment, regular additional adjustment, laser-holographic control of mirror mutual arrangement, circular axial computer-generated hologram optical element, radial-sector axial computer-generated hologram optical element, cylindrical axial computer-generated hologram optical element
Article received: 31.10.2024
Article accepted: 20.11.2024
Introduction
In order to perform regular monitoring of extraterrestrial space, solve big issues of cosmology, protect the planet against dangerous space debris and asteroids, and conduct remote sensing of the Earth’s surface, it shall be necessary to constantly increase the number of optical telescopes being developed and generated, both ground-based and space-based, including the spaceborne telescopes (ST) installed on board the small spacecrafts [1–4].
The analysis shows as follows: in order to solve the remote sensing issues of the Earth’s surface, the most preferred options of the optical systems for the ST development among the existing toolkit of technical solutions shall include the centered three-mirror systems (CTMS), mainly with the aspherical working surfaces, without any additional lens adjusters [5–10].
The main advantages of the ST CTMS shall be noted: they allow operation within a wide spectral range (the integral transmission coefficient of the entire CTMS is determined only by the operating spectral range of the reflective coatings); they have an increased field of view compared to the classical Ritchey-Chretien and Cassegrain arrangements; there are no additional problems with the selection of materials for the lens adjustors that ensure stability of specifications over the entire range of operating temperatures; when using the lightweight mirrors, it is possible to achieve a reduction in the overall ST weight [7, 11].
It is well-known [1, 12, 13] that if the adjustment processes in the workshop conditions and regular additional adjustment in the space conditions even for the centered dual-mirror ST systems cause significant difficulties and are characterized by high labor intensity, then it shall be obvious that for the ST CTMS such adjustment difficulties and labor intensity are enhanced due to the increased degrees of freedom of the mirrors being adjusted and possible variations in their mutual arrangement. Therefore, the search for new approaches in the field of adjustment control in the production and operational conditions for the ST CTMS shall be relevant.
Existing technical solutions
and approaches
Among a number of methods to assembly and adjust the centered dual-mirror systems (CDMS) currently applied in the workshop conditions [13], in particular by using the coordinate measurement systems, with the mirror center adjustment in the frames, with the transfer of axes to an additional base with due regard to their practical constraints, only the precision method based on the axial CGHOE and specified by the interferometric accuracy and possible operation within a wide spectrum of electromagnetic waves is the most promising for development and application during the CTMS assembly and adjustment control. This laser-holographic approach based on an axial CGHOE on a flat substrate in the transmitted light was partially applied in the Offner scheme for the assembly and adjustment of the mutual arrangement of only two mirrors (namely, the primary and tertiary) in the absence of a secondary mirror in the scheme [10]. Then the secondary mirror was precisely installed by three actuators in relation to the adjusted pair of the “primary mirror – tertiary mirror”. Moreover, if we consider our earlier technical proposals [12] on the possible applicability of holographic control devices (HCD) based on a system of axial CGHOEs as the wavefront sensors in the space conditions for the ST CDMS, then the development of these proposals shall be an alternative to the available practical generation of ST service systems in terms of automatic adjustment and automatic focusing systems based, in particular, on the use of systems consisting of the flat auxiliary reflectors, autocollimators, mirror-like rhombuses, corner-cube prisms and position-sensitive (quadrant) photodetectors [11, 14] that are less accurate compared to the interferometric wavefront sensors.
Main provisions
of the proposed solution
Since the HCDs capable of monitoring the mutual arrangement of mirrors both in the workshop conditions and in the operating conditions with their regular additional adjustment are of significant practical interest for the ST CTMS, then the HCD construction can be conceptually implemented within the framework of three main options for the beam paths in its object branch:
1st – with the autocollimation beam path in the transmitted light (Figure 1a);
2nd – with the autocollimation beam path in the reflected light (Figure 1b);
3rd – with the quasi-autocollimation beam path and wavefront reversal (Figure 1c).
The following designations are used in Figure 1: 1 – point source of laser radiation; 1′– image of the point source of laser radiation 1 generated by the optical system “axial CGHOE 5 (5′) “plus” the mirror 2 in the transmitted light (mirror 2′ in the reflected light) “plus” the concave surface of mirror 4″; 1″ – image of the point source of laser radiation 1 generated by the optical system “axial CGHOE 6 (6′) “plus” the mirror 2 in the transmitted light (mirror 2′ in the reflected light) “plus” the concave surface of mirror 3″; 1‴– autocollimation image of the point source of laser radiation 1 generated by the axial CGHOE 7 (7′); 2 – axial aspherical mirror on a plano-convex substrate made of the optically transparent material with a semi-transparent optical coating applied to the convex surface; 2′ – axial aspherical mirror on a plano-convex substrate made of the optically opaque material and/or with weight reduction; 3 and 4 – off-axis aspherical mirrors on the plano-concave substrates; 5 (5′) – circular (cylindrical or radial-sector) axial CGHOE to control the mutual arrangement of the mirror 4; 6 (6′) – circular (cylindrical or radial-sector) axial CGHOE to control the mutual arrangement of the mirror 3; 7 (7′) – autocollimation circular (cylindrical) axial CGHOE; 8 – diaphragm in the form of a truncated cone, made at the apex of the convex surface of the mirror 2′, wherein the geometric axis of the diaphragm 8 coincides with the optical axes of the mirror 2′ and the entire CTMS; OO′– optical axis of the system being adjusted; O1 – center of the flat rear surface of the mirror 2; O2 – apex of the convex surface of the mirror 2 (2′); O3 – apex of the “parent” concave surface of the mirror 3; O4 – apex of the “parent” concave surface of the mirror 4; the parameters O1, O2, O3, O4, 1, 1′, 1″and 1‴ are located on the optical axis OO′. In Figures 1g and 1i, the axial CGHOEs 5′, 6′, 7′ are made in the form of radial-sector (segment) apertures in the convex surface edge zone of the mirror 2′.
The implementation of the 1st option shall be possible only when the substrate of the base mirror 2 is solid, without any weight reduction and made of an optically transparent material. The optical material of the substrate and its polished front and rear surfaces shall correspond to the strict tolerances for optical parameters, and a semi-transparent optical coating shall be applied to the front surface of this mirror. For the STs where the substrate of the base mirror 2′ is made with weight reduction and / or of the optically opaque materials (metals, metal alloys, composite materials), the HCD construction is possible only on the basis of the 2nd or 3rd options. However, these HCD construction options are rather cross-functional and can be implemented based on the use of the base mirror 2 with a substrate made of an optically transparent material, in a solid form without any weight reduction.
The operating principle of the HCDs as the wavefront sensors, shown in Figures 1a, 1b, 1c, is similar to the CDMS adjustment control device [12] and consists of obtaining, recording and analyzing the interference fringe patterns specifying the linear and angular mutual arrangement of the mirrors 2 (2′)–4 relative to each other, the point source of laser radiation 1 and the optical axis of the system OO′, where the flat rear surface of the mirror 2 (Figure 1a) or the convex front surface of the mirror 2′ (Figures 1b, 1c) can be taken as the base surface on which the system of axial CGHOEs 5–7 (5’–7’) is formed.
It shall be proposed to include the considered HCDs as the feedback components in the standard ST automatic adjustment systems with the servo drivers in the form of high-precision actuators that control the linear and angular positions of each of the three mirrors, achieving their design locations within the given optical system.
When calculating the spatial frequency characteristics (SFC) of the axial CGHOEs 5 (5′) and 6 (6′), it shall be necessary to consider the wavelength λк of the probing laser radiation, equations of the meridional section profiles of the “parent” surfaces of the mirror 4 and mirror 3, accordingly, and the design arrangement parameters of these mirrors with due regard to the double transit of the probing radiation through the substrate of the mirror 2 (for Figure 1a, the SFC calculation method of the axial CGHOEs 5 (5′) and 6 (6′) is similar to that given in [14]) or reflection of this radiation from the front surface of the mirror 2′ (for Figure 1b, the SFC calculation method of the axial CGHOEs 5 (5′) and 6 (6′) corresponds to that described in [12], and for Figure 1c, to that proposed in [15]). The spatial frequency characteristics of the autocollimation axial CGHOE 7 (7′) shall be obtained as a design result for the zone plate of the required focal length at a given wavelength λк.
The production of axial CGHOEs 5–7 (Figures 1d, 1f) and axial CGHOEs 5–6 (Figure 1h) in the form of circular apertures, as well as the axial CGHOEs 5’–7’ (Figure 1g) and axial CGHOEs 5’–6’ (Figure 1i) in the form of radial-sector (segment) apertures shall be possible with the optical diameters of up to 500–600 mm on circular ruling engines (MDA and MDG types) using special diamond cutters [16] or with an aperture record area of up to 300 mm using circular laser recording systems [17].
Since during the axial CGHOE production process their centering is performed with high accuracy, for example, along the common base cylindrical surface of the mirror 2 (2′), the optical axes of these CGHOEs shall be aligned with the optical axis of the mirror 2 (2′) with the smallest possible error (almost no more than one micrometer) [18]. Moreover, their centering with the mirror 2 (2′) shall be obviously remain unchanged in the future during the CTMS operation. This feature shall also increase the adjustment control reliability by the proposed HCD both in the workshop conditions and in the operating mode.
It can be additionally noted that the axial CGHOEs can be manufactured for application at a wavelength shorter than the wavelength of the short-wave limit of the spectral operating range of the CTMS being adjusted. Therefore, the stroked structures of axial CGHOEs (Figures 1f, 1g, 1h, 1i) can be applied in any part of the light zone of the reflective front surface of the mirror 2′ without causing negative effect on the ST image generation at the operating wavelengths.
The proposed approaches to the HCD generation for the mutual arrangement of mirrors for high-aperture and wide-angle large ground- and space-based telescopes with the CTMS [6] are of particular practical interest. In these CTMS, it shall be proposed to implement the HCD for the mutual arrangement of large-sized mirrors, the diameters of which can be within the range from one meter to several meters, not on the basis of circular or radial-sector axial CGHOEs, the production of which on the large-size mirror substrates is almost impossible due to the lack of the appropriate process equipment, but only by using the cylindrical axial CGHOE (CACGHOE). It shall be proposed to produce the CACGHOEs with a width of 10 to 20 mm. This approach with the CACGHOE applications and its implementation methods shall become a development of the proposal previously provided by the author in [19]. It shall be noted that the CACGHOE is to be made primarily in the form of amplitude computer-generated holograms that makes it possible to almost eliminate the dependence of the CACGHOE diffraction efficiency on the incidence angle of the beams from a monochromatic point source of radiation used in the HCD in various areas of its optical diameter, thereby ensuring the constant visibility of the interference fringes of the obtained interferograms within the controlled light field.
A conventional form of the possible CACGHOE implementation is shown in Figure 1e. In this case, the autocollimation CACGHOE 7′ shall be a system of two cylindrical holograms made orthogonal to each other to ensure more accurate and reliable alignment of the point source of laser radiation 1 with its autocollimation image 1‴. Similarly, the CACGHOE with the SFCs equal to those of the circular or radial-sector axial CGHOEs conventionally shown in Figures 1f, 1g, 1h, 1i, can be possibly applied to the convex front surface of the mirror 2′.
The estimates confirm that the laser-holographic control of the mutual arrangement of mirrors in the considered CTMS using the system of axial CGHOEs of the proposed HCDs can be performed with an error not exceeding 0.01 λк, where λк is the wavelength of the probing laser radiation, and this parameter shall be used when selecting the dimensions and resolution of the position-sensitive system to record the resulting interference fringe pattern.
Conclusion
Since the CTMS are currently arousing heightened interest of the ST developers, then the proposed approach to develop the HCD for the mutual arrangement of mirrors in the considered CTMS based on the application of axial CGHOEs shall be relevant. This approach shall be a development of the proposals published in [12, 15, 16] and confirmed by the results of physical modeling on the example of the CDMS prototype assembly and adjustment control [20]. Moreover, it shall open up the possibility to solve the problem of implementing laser-holographic monitoring of the ST CTMS assembly and adjustment both in the workshop conditions and during the regular additional adjustment in the operating space conditions. The CACGHOE application in the proposed HCDs in order to control the assembly and adjustment of high-aperture and wide-angle large-sized STs shall be of special relevance and potential. According to this approach, the following advantages are obvious in the HCD construction, namely interferometric accuracy, reliability and efficiency of the control functions, minimization of weight and dimensional parameters, as well as the energy consumption.
In order to perform comprehensive works on the generation, development and testing of the proposed HCDs for the mutual arrangement of mirrors, including the development of up-to-date high-precision process equipment for the CGHOE production, it shall be necessary to determine and conduct he comprehensive R&D in cooperation with the developers of STs and high-precision equipment.
AUTHOR
Andrei Melnikov, Cand. of Tech. Sc., Associate Professor; e-mail mr.melnikov@bk.ru; Research interests: Optical instruments and systems for Civilian optical products; Head of Department, JSC “Scientific and Production Association “State Institute of Applied Optics”, e-mail gipo@shvabe.com; Kazan, Tatarstan, Russia
ORCID: 0000-0002-3318-9853
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