CN109029244B

CN109029244B - Multi-wavelength laser interferometer

Info

Publication number: CN109029244B
Application number: CN201810749061.6A
Authority: CN
Inventors: 刘世杰; 鲁棋; 周游; 王圣浩; 倪开灶; 潘靖宇; 邵建达
Original assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Current assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Priority date: 2018-07-10
Filing date: 2018-07-10
Publication date: 2020-08-28
Anticipated expiration: 2038-07-10
Also published as: CN109029244A

Abstract

A multi-wavelength laser interferometer, the apparatus comprising: the device comprises a laser, an aperture diaphragm, a beam expanding secondary mirror, a pinhole diaphragm, a beam splitter prism, a collimation primary mirror, a transmission standard mirror, a piezoelectric ceramic transducer, a to-be-detected plane element, a reflection standard mirror, an imaging lens, a hyperspectral camera and a computer. The collimating primary lens in the device is a three-lens, and the imaging lens and the beam expanding secondary lens have the same parameters and are single lenses; in order to reduce the processing difficulty of the lens in the device and the installation and adjustment difficulty of the whole set of system light path, 1 surface of each of the beam expanding secondary mirror and the collimation primary mirror in the device can be a plane. The invention can measure the transmission wavefront or the reflection wavefront of the planar optical element to be measured within the wavelength range of 600 nm-1600 nm.

Description

Multi-wavelength laser interferometer

Technical Field

The invention relates to a plane optical element, in particular to a multi-wavelength laser interferometer for interference measurement of the plane optical element.

Background

The laser interference technology is an optical metrology method based on the principle of light interference, and is one of the most effective and accurate technical means for detecting the surface quality of optical elements. The working wavelength of the laser interferometer commonly used at home and abroad is single wavelength, and the wavelength is 632.8nm, 1053nm or 1064 nm. However, for some optical elements coated with narrow-band filters, their reflectivity is greater than 99% or transmittance is greater than 99% at 632.8nm, 1053nm or 1064nm, so that the conventional laser interferometers in the market cannot collect the required interference fringes, and thus cannot detect them.

For example, the solar filter is used as an important component in a space laser communication system, can block most wave bands in space and protect components in the communication system from being influenced by sunlight and outer space light radiation, and is used as a filter window in numerous communication projects such as laser remote sensing, laser radar and laser ranging. The common solar filter has both surfaces coated with double bandpass filter films, has very high transmittance at wavelengths of 808nm and 1550nm, and has very high reflectivity at wavebands of 510 nm-780 nm, 835 nm-1500 nm, 600 nm-1700 nm and the like, and the transmitted wavefront quality of the filter particularly affects the imaging performance of a space laser communication system. However, the 632.8nm, 1053nm and 1064nm laser interferometers commonly used at home and abroad cannot realize high-precision detection on the quality of the transmitted wavefront.

As another example, in a system for daytime quantum communication, there is a 864nm narrow band volume holographic grating (VBG) filter (FWHM ═ 0.05nm) that suppresses spontaneous raman scattering and reduces the solar background noise in the system, and its reflected wavefront especially affects the quality of the recovered signal. However, the filter only reflects 864nm, so that 632.8nm, 1053nm and 1064nm laser interferometers commonly used at home and abroad cannot detect the quality of the reflected wavefront (or surface shape error).

If laser interferometers working under different wavelengths are purchased respectively according to the requirements of different detection wavelengths, although relevant parameters including but not limited to the two filters can be measured, a user is required to purchase a plurality of laser interferometers at the same time, and the detection cost is doubled.

In the past, there have been few reports that interferometric detection can be achieved at a plurality of wavelengths in one device and that the operating band is 1000nm or more in wide band. In the invention patent of dual-wavelength Fizeau laser interferometer (CN104315971A), the inventor's device can only work under any two wavelengths between 400nm and 800nm and the wavelength interval is more than 100nm, the characteristic of working under various (three or more) wavelengths cannot be realized, and the light source wave band supported by the system cannot meet the measurement requirements under the infrared wave band (such as 808nm, 852nm, 864nm, 1064nm, 1310nm, 1550nm and the like). In the invention patent of a dual-channel dual-wavelength interference detection device (CN106197258A), the inventor device can work under any two wavelengths, and because two sets of optical systems with one-to-one corresponding wavelength are adopted, the interference measurement of optical elements under various wavelengths is difficult to realize.

Disclosure of Invention

The invention provides a multi-wavelength laser interferometer for solving the defect that most laser interferometers on the market only have one output wavelength. The device can measure the transmitted wave front or the reflected wave front of the plane optical element within the wavelength range of 600 nm-1600 nm, the working wavelength covers 632.8nm, 1053nm and 1064nm, and the defect that the existing single-wavelength laser interferometers with 632.8nm, 1053nm and 1064nm and the like cannot work under other various wavelengths is overcome.

The technical solution of the invention is as follows:

a multi-wavelength laser interferometer, the apparatus comprising: the device comprises a laser, an aperture diaphragm, a beam expanding secondary mirror, a pinhole diaphragm, a beam splitter prism, a collimation primary mirror, a transmission standard mirror, a piezoelectric ceramic transducer, a to-be-detected plane element, a reflection standard mirror, an imaging lens, a hyperspectral camera and a computer; the aperture diaphragm, the beam expanding secondary mirror, the pinhole diaphragm and the beam splitting prism are sequentially arranged along the laser output direction of the laser, the beam splitting prism divides an incident laser beam into a transmission light and a reflection light, a collimation primary mirror, a transmission standard mirror, a piezoelectric ceramic transducer, a to-be-measured plane element and a reflection standard mirror are sequentially arranged in the transmission light direction, and the imaging lens, the hyperspectral camera and the computer are sequentially arranged in the reflection light direction; the piezoelectric ceramic transducer can push the transmission standard mirror back and forth along the optical axis direction in a voltage regulation mode; the output end of the hyperspectral camera is connected with the input end of the computer. The laser is a multi-wavelength beam combining laser, lasers with various wavelengths are combined to output lasers with the wavelength range of 600 nm-1600 nm, and the coherence length under each output wavelength is more than or equal to 1 m; the beam expanding secondary lens and the imaging lens have the same parameters and are single lenses; the collimating primary mirror is a three-lens system; the beam splitter prism is positioned between the secondary beam expanding lens and the primary collimating lens; the hyperspectral camera can detect the light intensity of all output wavelengths of the laser.

When the reflected wave front parameter of the plane element to be measured is measured under a certain wavelength, the laser is started, and the output wavelength of the laser is switched to be the same as the working wavelength of the plane element to be measured; placing the planar element to be tested between the transmission standard mirror and the reflection standard mirror to enable the test light beam to completely cover the area to be tested on the planar element to be tested; adjusting the pitching and deflecting postures of the transmission standard mirror and the plane element to be detected to enable the two beams of light beams reflected on the front surface of the transmission standard mirror and the rear surface of the plane element to be detected to generate interference, and obtaining an interference fringe pattern with clear contrast on a photosensitive surface of the hyperspectral camera; the piezoelectric ceramic transducer is controlled to push the transmission standard mirror back and forth to perform phase shifting operation for more than 4 times, and an interferogram after each phase shifting is obtained on the photosensitive surface of the hyperspectral camera; the computer is used for sorting and phase unwrapping the acquired interference pattern, and a wave front distribution diagram is calculated, namely the reflected wave front parameters of the to-be-detected planar element.

When the transmission wavefront parameter of the planar element to be measured is measured under a certain wavelength, the laser is started, and the output wavelength of the laser is switched to be the same as the working wavelength of the planar element to be measured; placing the planar element to be tested between the transmission standard mirror and the reflection standard mirror to enable the test light beam to completely cover the area to be tested on the planar element to be tested; adjusting the pitching and deflecting postures of the transmission standard mirror and the reflection standard mirror to enable the two beams of light beams reflected on the front surface of the transmission standard mirror and the mirror surface of the reflection standard mirror to generate interference, and obtaining an interference fringe pattern with clear contrast on the photosensitive surface of the hyperspectral camera; the piezoelectric ceramic transducer is controlled to push the transmission standard mirror back and forth to perform phase shifting operation for more than 4 times, and an interferogram after each phase shifting is obtained on the photosensitive surface of the hyperspectral camera; the computer is used for sorting and phase unwrapping the acquired interference pattern, and a wavefront distribution map is calculated, namely the transmission wavefront parameters of the to-be-detected planar element.

The invention has the following technical effects:

1) the invention solves the defect that most of the existing laser interferometers can only work under single working wavelength of 632.8nm, 1053nm or 1064nm and the like, and the multi-wavelength laser interferometer can measure parameters of transmission wavefront or reflection wavefront and the like of a plane optical element with multiple wavelengths.

2) The invention can measure the transmission wavefront or the reflection wavefront of the planar optical element at any wavelength within the range of 600 nm-1600 nm.

3) The invention can detect parameters such as transmission wavefront, reflection wavefront and the like of some optical elements which most laser interferometers can not detect at present. For example, optical elements coated with narrow band filters at specific operating wavelengths (780nm, 785nm, 808nm, 852nm, 864nm, 1064nm, 1310nm, 1550nm, etc.) can be detected, including but not limited to detection of transmitted wavefronts at two wavelengths for 808nm/1550nm dual band-pass filters and detection of reflected wavefronts for 864nm narrow band Volume Bragg Grating (VBG) filters;

4) the parameters of the imaging lens and the secondary beam expanding lens in the device are completely the same and are single lenses, the primary collimating lens is three-separation lens, and 1 surface of each of the secondary beam expanding lens and the primary collimating lens is a plane, so that the processing difficulty of a lens in the device is greatly reduced, and the installation and adjustment difficulty of the whole set of system light path is reduced;

5) the optical elements in the device have large processing and adjusting tolerance range. After tolerance analysis is carried out on the optical element in the device through optical simulation software, the fact that even if machining and adjusting errors exist in the optical element in the system is found, the system can still achieve the designed emergent wavefront quality by moving the primary collimating mirror back and forth along the optical axis under the wavelength of 600 nm-1600 nm, and the adjusting range is not larger than 1/100 of the distance between the secondary beam expanding mirror and the primary collimating mirror.

Drawings

FIG. 1 is a schematic diagram of a multi-wavelength laser interferometer of the present invention

FIG. 2 is a schematic diagram showing the relationship between the height of Marginal ray (Marinal ray) of the outgoing beam of the multi-wavelength laser interferometer having an exit aperture of 130mm and the wavelength of the input laser beam according to embodiment 2 of the multi-wavelength laser interferometer of the present invention

FIG. 3 is a line graph showing the relation between the system design outgoing wavefront PV value and the input laser wavelength of a multi-wavelength laser interferometer with an outgoing aperture of 130mm according to embodiment 2 of the multi-wavelength laser interferometer of the present invention

Detailed Description

The invention is further described below with reference to the figures and examples.

FIG. 1 is a schematic diagram of a multi-wavelength laser interferometer according to the present invention. As can be seen from the figure, the multi-wavelength laser interferometer of the present invention comprises: the device comprises a laser 1, an aperture diaphragm 2, a beam expanding secondary mirror 3, a pinhole diaphragm 4, a beam splitting prism 5, a collimation primary mirror 6, a transmission standard mirror 7, a piezoelectric ceramic transducer 8, a to-be-detected plane element 9, a reflection standard mirror 10, an imaging lens 11, a hyperspectral camera 12 and a computer 13; the aperture diaphragm 2, the secondary beam expanding mirror 3, the pinhole diaphragm 4 and the beam splitter prism 5 are sequentially arranged along the laser output direction of the laser 1, the beam splitter prism 5 divides an incident laser beam into a transmission light and a reflection light, the primary collimating mirror 6, the transmission standard mirror 7, the piezoelectric ceramic transducer 8, the plane element to be measured 9 and the reflection standard mirror 10 are sequentially arranged in the transmission light direction, and the imaging lens 11 and the hyperspectral camera 12 are sequentially arranged in the reflection light direction; the piezoelectric ceramic transducer 8 can push the transmission standard mirror 7 back and forth along the optical axis direction in a voltage regulation mode; the output end of the hyperspectral camera 12 is connected with the input end of the computer 13. The laser 1 is a multi-wavelength beam combining laser, lasers with various wavelengths are combined to output lasers with the wavelength range of 600 nm-1600 nm, and the coherence length under each output wavelength is more than or equal to 1 m; (ii) a The beam expanding secondary lens 3 and the imaging lens 11 have the same parameters and are single lenses; the primary collimating mirror 6 is a three-lens system; the hyperspectral camera 12 can detect the light intensity of all the output wavelengths of the laser 1.

In this embodiment 1, the hyperspectral camera 12 is selected from hyper a660 series of Quest Innovations, the netherlands, and has a detectable spectral range of 400nm to 1700nm and an average spectral resolution of less than 1 nm.

Embodiment 2, fig. 2 is a schematic diagram of a relationship between a Marginal ray (Marginal ray) height of an outgoing beam of a multi-wavelength laser interferometer with an outgoing aperture of 130mm and an input laser wavelength in embodiment 2 of the present invention. As can be seen from the figure, when the output wavelength of the laser 1 is changed within the range of 600nm to 1600nm, the beam expanding secondary mirror 3, the beam splitting prism 5 or the primary collimating mirror 6 in the device do not need to be moved, adjusted or changed, and the device can output collimated beams under each wavelength. In this embodiment, the three lenses in the primary collimating mirror 6 are respectively made of three different glass materials, and a combination of positive, negative, and positive lenses is adopted, so that the Super-achromatic (Super-achromatic) capability is achieved, chromatic aberration introduced into the system by the ultra-wide band can be eliminated to a great extent, and spherical aberration in the system under the ultra-wide band is reduced. The glass materials used by the lenses A, B and C in the collimating primary mirror 6 are both selected from German Schottky (SCHOTT), the rear surface of the lens A is a plane, the glass material used by the lens B has Special dispersion (Special dispersion) performance, and the brand is KZFS series.

Fig. 3 is a line graph of the relationship between the PV value of the emergent wavefront and the input laser wavelength in example 2 of the present invention. As can be seen, the outgoing wave front PV value of the system can be kept within 0.06 lambda in the process of continuously changing the incident laser wavelength from 600nm to 1600 nm. In consideration of the fact that in practical situations, due to the existence of processing errors and adjustment errors of optical elements, the PV value of the worst outgoing wave front of the system under the wavelength of 600 nm-1600 nm may be larger than 0.06 lambda, after tolerance analysis is carried out on the optical elements in the system through optical simulation software, it is found that by moving the collimating primary mirror forward 1.02mm along the optical axis direction, the PV value of the outgoing wave front of the system under the wavelength of 600 nm-1600 nm can be controlled within 0.06 lambda, and good outgoing wave front quality is achieved.

Experiments show that the invention can measure parameters such as transmission wavefront or reflection wavefront of the planar optical element to be measured in the wavelength range of 600 nm-1600 nm.

Claims

1. A multi-wavelength laser interferometer, comprising: the device comprises a laser (1), an aperture diaphragm (2), a beam expanding secondary lens (3), a pinhole diaphragm (4), a beam splitting prism (5), a collimation primary mirror (6), a transmission standard mirror (7), a piezoelectric ceramic transducer (8), a to-be-detected plane element (9), a reflection standard mirror (10), an imaging lens (11), a hyperspectral camera (12) and a computer (13); the aperture diaphragm (2), the beam expanding secondary mirror (3), the pinhole diaphragm (4) and the beam splitter prism (5) are sequentially arranged along the laser output direction of the laser (1), the beam splitter prism (5) divides an incident laser beam into a transmission light and a reflection light, a primary collimating mirror (6), a transmission standard mirror (7), a piezoelectric ceramic transducer (8), a to-be-detected plane element (9) and a reflection standard mirror (10) are sequentially arranged in the transmission light direction, and the imaging lens (11), the hyperspectral camera (12) and the computer (13) are sequentially arranged in the reflection direction of the transmission light; the piezoelectric ceramic transducer (8) can push the transmission standard mirror (7) back and forth along the optical axis direction in a voltage regulation mode; the output end of the hyperspectral camera (12) is connected with the input end of the computer (13); the laser (1) is a multi-wavelength beam combining laser, lasers with various wavelengths are combined to output lasers with the wavelength range of 600 nm-1600 nm, and the coherence length under each output wavelength is more than or equal to 1 m; the parameters of the beam expanding secondary lens (3) and the parameters of the imaging lens (11) are the same and the beam expanding secondary lens is a single lens; the collimation primary mirror (6) is a three-lens; the hyperspectral camera (12) can detect the light intensity of all output wavelengths of the laser (1).