CN204515222U - Long-pupil-distance short-wave infrared spectrum imaging objective lens - Google Patents

Abstract

The utility model discloses a short-wave infrared spectrum imaging objective lens with long pupil distance. The objective lens includes five lenses, which are sequentially arranged on the system optical axis from the diaphragm to the image plane. The first three lenses are achromatic glass pairs with positive, negative and positive focal powers. The combination of fluoride glass and heavy flint glass has good achromatic ability in the short-wave infrared range and good spectral transmission. Overrate. The fourth lens is used to balance the astigmatism and field curvature of the system to increase the field of view capability of the imaging objective lens, and the fifth lens is used to further compensate the astigmatism of the objective lens and meet the image telecentricity requirements of the imaging objective lens; Finally, the requirements of long interpupillary distance and achromatism in the short-wave infrared band can be realized.

Description

A Long Pupil Distance Shortwave Infrared Spectral Imaging Objective Lens

Technical field:

The utility model relates to an optical imaging objective lens, in particular to a long-distance short-wave infrared imaging objective lens for spectrum imaging.

Background technique:

Spectral imaging is an imaging detection method that integrates images and spectra. The obtained image data is generally a data cube that contains two-dimensional spatial information and one-dimensional spectral information.

There are three main types of spectral imaging technologies commonly used at present:

The first type of spectral imaging technology uses optical filter technology to obtain spectral data of images;

The second type of spectral imaging technology uses dispersion technology to obtain the spectral data of an image;

The third category is the interference spectral imaging technology using Fourier transform spectroscopy technology.

In particular, the third type of interference spectroscopy imaging technology has attracted more and more attention due to its typical advantages of high throughput, and is currently a hot technology in international research.

The optical objective lens used for static interference spectral imaging is very different from the conventional imaging objective lens. Ultra-precision interferometer components should be placed in the optical path of this type of imaging objective lens. Therefore, in practical applications, the interferometer should be minimized. Size, in order to reduce the size of the interferometer, the entrance pupil of the imaging objective lens is often placed in the middle of the interferometer components, and at the same time, in order to achieve a good imaging spectrum, the objective lens is often required to achieve image telecentricity, and the method of realizing image square telecentricity is generally adopted Place the diaphragm outside and on the front focus of the objective lens.

For the imaging objective lens with an external diaphragm, the entrance pupil distance refers to the position from the first surface of the optical system to the diaphragm. Usually, the transmission imaging objective lens is composed of multiple lenses in order to correct the aberration, which makes the objective lens The front focus position is often less than double the focal length, and the interferometer based on short-wave infrared often has a very long optical path, so the imaging objective lens must have a long entrance pupil distance to match the size and optical path requirements of the interferometer, and at the same time Realize image telecentricity to meet the requirements of spectral imaging.

Short-wave infrared usually refers to electromagnetic radiation with a wavelength of 1000nm to 2500nm. There are many important detection requirements in this wavelength band, which are often realized by means of spectral imaging. The transmissive optical system can all adopt the spherical shape and has the characteristics of simple processing technology, easy assembly and adjustment, high degree of engineering realization and low cost, so that it has a wide range of applications. To realize the transmission spectral imaging system in this wavelength band, the chromatic aberration of the optical system must be well corrected, and the optical material must have good transmittance in this spectral band.

One of the important means of correcting the chromatic aberration of the optical system is to use the different dispersion properties of the optical material to distribute the focal power reasonably. Usually, the transmissive optical system is composed of several lenses with positive and negative focal powers. When performing chromatic aberration correction in the short-wave infrared band, the crown glass with small dispersion is often used as the positive lens, and the flint glass with large dispersion is used as the negative lens. However, the dispersion characteristics of these two types of glasses change in the short-wave infrared band. Realize the correction of chromatic aberration. This method cannot effectively correct chromatic aberration. At the same time, the transmittance of crown glass also decreases between 2200nm and 2500nm, which cannot meet the performance requirements of the optical system. The infrared spectral band must be matched with suitable optical materials and a reasonable structure to achieve chromatic aberration correction in this band.

Utility model content:

The utility model designs a long-pupillary distance short-wave infrared spectrum imaging objective lens, which can meet the long-pupillary distance and the achromatic requirements in the short-wave infrared band.

The technical scheme of the utility model is as follows:

The long-pupillary distance short-wave infrared spectrum imaging objective lens includes five lenses arranged sequentially on the optical path from the diaphragm to the image plane; wherein the first lens, the second lens and the third lens are biconvex lenses, curved toward the diaphragm, respectively. Lunar lens and biconvex lens constitute an achromatic glass pair with positive, negative and positive refractive powers, which is a combination of fluoride glass and heavy flint glass as a whole; the fourth lens and the fifth lens are both of negative refractive power Infrared quartz glass meniscus mirror curved towards the diaphragm.

The distance between the diaphragm and the first lens is 1.8 times the focal length of the system.

The above-mentioned fluoride glass can be selected from CaF ₂ and BaF ₂ , and heavy flint glass can be selected from ZF series and Schott materials SF series.

The preferred material configuration of the first three lenses is as follows: the material of the first lens is CaF ₂ , the material of the second lens is SF ₆ , and the material of the third lens is CaF ₂ .

The utility model has the following technical effects:

The first three lenses are achromatic glass pairs with positive, negative and positive focal powers. The combination of fluoride glass and heavy flint glass has good achromatic ability in the short-wave infrared range and good spectral transmission. Overrate. The fourth lens is used to balance the astigmatism and field curvature of the system to increase the field of view capability of the imaging objective lens, and the fifth lens is used to further compensate the astigmatism of the objective lens and meet the image telecentricity requirements of the imaging objective lens. Finally, the requirements of long interpupillary distance and achromatism in the short-wave infrared band can be realized.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the imaging objective lens of the present invention.

Fig. 2 is the MTF curve of the objective lens when the normalized focal length is 100 mm in this embodiment.

Detailed ways:

As shown in Figure 1, the imaging objective lens includes a diaphragm and lenses 1-5, which are sequentially arranged on the system optical axis oo' together with the image plane (imaging detector).

The diaphragm is placed in front of the system at a distance of 1.8 times the focal length from the first lens element. the

Lens 1 is a biconvex lens with positive refractive power, the material used is CaF ₂ , lens 2 is a meniscus lens with negative refractive power that bends toward the diaphragm, and the material used is SF6, and lens 3 is a biconvex lens with positive refractive power. Convex lens, the material used is CaF ₂ ;

CaF ₂ and BaF ₂ can be used for lenses with positive refractive power, and ZF or SF series can be used for lenses with negative refractive power, so lenses 1, 2, and 3 can be combined in three ways, namely positive-negative-positive , negative-positive-positive, positive-positive-negative combinations.

Lens 4 is a thick meniscus lens with a negative refractive power that bends toward the diaphragm with an diameter-thickness ratio less than 2. The material used is infrared quartz glass, and lens 5 is a meniscus lens that bends toward the diaphragm with negative refractive power. The material used is infrared quartz glass.

As shown in FIG. 2 , the MTF curve of the objective lens in this embodiment when the normalized focal length is 100 mm. The image space telecentric imaging objective lens of the pre-diaphragm has a long entrance pupil distance of 1.8 times the focal length, a field angle of 10°, a relative aperture of F#5, and is well corrected in a wide spectral range of wavelengths from 900 to 2500nm The chromatic aberration is eliminated, and when the focal length of the objective lens is 100mm, the imaging quality reaches and approaches the diffraction limit in the entire field of view.

Claims (3)

1. a long-pupillary distance short-wave infrared spectrum imaging objective lens is characterized in that: comprise five lenses that are arranged successively on the optical path from diaphragm to image plane; Wherein the first lens, the second lens and the third lens are biconvex respectively The lens, the meniscus lens and the biconvex lens that are bent to the diaphragm constitute an achromatic glass pair with positive, negative and positive refractive powers, and the whole is a combination of fluoride glass and heavy flint glass; the fourth lens and the fifth The lenses are infrared quartz glass meniscus lenses with negative power that are bent towards the diaphragm. 2. The long-pupillary distance short-wave infrared spectrum imaging objective lens according to claim 1, characterized in that: the distance between the diaphragm and the first lens is 1.8 times the system focal length. 3. The long-pupillary distance short-wave infrared spectrum imaging objective lens according to claim 1, characterized in that: the first lens is CaF ₂ glass, the second lens is SF ₆ glass, and the third lens is CaF ₂ glass.