Optical design of an imager with wide field-of-view (FOV) and high-resolution utilizes a monocentric objective lens in conjunction with an array of secondary optical lenses to achieve good performance. An intermediate image with uniform residual aberration throughout a wide FOV is obtained on a curved surface by the monocentric objective lens and then relayed to a sensor array by the secondary optical lenses. In this paper, we focus on the study of the monocentric objective lens and the surface type of its obtained curved image. Firstly, the equation of focal length is determined by ray tracing. The achromatic condition is obtained through first-order aberration theory. Accordingly, the initial configuration of the monocentric objective lens is determined, including the surface radii and reasonable glass combination. Secondly, a detailed calculation of the image positions is performed. The results show that the image surface is spherical when the object distance is much larger than the focal length. But it is aspheric when the object distance is comparable to the focal length. Finally, a mono-centric lens is optimumly designed, with a visible working wavelength band of 480-640nm, a focal length of 100mm, a wide FOV of 140°, and a large f-number of 5. Through imaging simulation and the image performance evaluation with ZEMAX, the theoretical calculations are verified.
The multi-focus image fusion technique is to extract the focus regions from source images and compose them together to form a clear image in the full field of view. In order to further improve the accuracy of focus region detection and ensure its efficiency, a novel multi-focus image fusion method in spatial domain, based on guided filter and mixed focus measure, is proposed in this paper. Firstly, a guided filter is employed as an edge-preserving smoothing operator to process the source images, and the difference operator is used between the filtered images and the source images to extract salient feature. Subsequently, the salient feature maps are measured by the mixed focus measure, combining the sum of energy of edge (SEOE) and the sum of local variance (SLV), to detect the focus regions, and the initial decision map is obtained. For holes of different sizes in the initial decision map, the closing operation and the small area removal strategy are used to fill and connect the truncated regions, and then the opening operation and the guide filter are used to optimize the decision map boundary to obtain the final decision map. Finally, the multi-focus fusion image is obtained by the pixel-wise weighted-averaging rule according to the final decision map. Simulation results demonstrate that the method is superior to some existing fusion methods on both subjective visual perception and objective evaluation metrics.
Target discrimination is of great significance in many applications such as remote sensing, security monitoring, production testing and so on. Nowadays accurate target discrimination is often resorted to spectral imaging technique due to its high-resolution spectral/spatial information acquisition ability as well as plenty of data processing methods. In this paper, hyper-spectral imaging technique together with spectral generalized angle analysis method is used to solve camouflage target discrimination problem. A self-developed visual-band hyper-spectral imaging device is adopted to collect data cubes of certain experimental scene before spectral generalized angle is worked out so as to discriminate abnormal target. Full-band spectral generalized angle is measured to evaluate target discrimination effect visually and quantitatively. This is proved to be an effective tool for target detection task and can be further developed for other imaging techniques beyond spectral imaging.
Anomaly detection is helpful in many applications such as food monitoring, production testing, security surveillance, military countermeasure and so on. Spectral imaging technique is often resorted to for accurate abnormal target discrimination due to its high-resolution spectral/spatial information acquisition ability and a great number of data processing methods. Anomaly detection methods for hyperspectral imagery are contrastively studied in this paper. A self-developed visual-band hyperspectral imaging spectrometer is adopted to collect data cubes of certain experimental scene before two kinds of spectral-domain descriptors are used to execute abnormal camouflage detection. Detection effect of information divergence and generalized angle that are utilized as detection descriptors is visually and quantitatively compared and time consumption is assessed. The study is proved to be of significance to meet the anomaly detection demand that is based on spectral signature comparison and can be developed for further detection descriptor study and other imaging techniques beyond spectral imaging.
Target detection is one of most important applications in remote sensing. Nowadays accurate camouflage target distinction is often resorted to spectral imaging technique due to its high-resolution spectral/spatial information acquisition ability as well as plenty of data processing methods. In this paper, hyper-spectral imaging technique together with spectral information divergence measure method is used to solve camouflage target detection problem. A self-developed visual-band hyper-spectral imaging device is adopted to collect data cubes of certain experimental scene before spectral information divergences are worked out so as to discriminate target camouflage and anomaly. Full-band information divergences are measured to evaluate target detection effect visually and quantitatively. Information divergence measurement is proved to be a low-cost and effective tool for target detection task and can be further developed to other target detection applications beyond spectral imaging technique.
Proc. SPIE. 9685, 8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems; and Smart Structures and Materials
Optical design of a novel optical imaging system is presented. It can overcome the scaling of the aberrations by dividing the imaging task between a single objective lens that achieves a partially corrected intermediate image on a spherical surface, and an array of micro-lens, each of which relays a small portion of the intermediate image to its respective sensor, correcting the residual aberrations. The system is aimed for obtaining large field-of-view without deteriorating its resolution, of which traditionally designed optical imaging systems have met great difficult. This progress not only breaks through the traditional restrictions, but also allows a wider application for optical imaging systems. Firstly, proper configuration, which satisfies both the requirement of compactness and high performance, is determined according to the working principle of the novel system and through the research of the design idea in this paper. Then, a design example is presented with the field-of-view 50°and its resolution 0.2mrad, which remains as the field-of-view scales. But the optimized scalable system is of close packed structure and its dimension is less than 300mm along the ray incidence.
Recent research in the area of image quality assessment has been focusing almost exclusively on greyscale and color images. The advent of technologies such as remote sensing, biomedical and industrial imaging however demands this research to be extended to multi/hyper spectral images. Spectral imaging has more judging essentials than greyscale or color imaging and its image quality assessment task intends to cover up all-around evaluating factors. This paper presents an integrating spectral imaging quality assessment project, in which spectral-based, spatial-based and radiometric-based quality evaluation behavior for one remote-sensing hyperspectral imager are jointly executed. Spectral response function is worked out and spectral performance is further judged according to its FWHM and spectral excursion value. Spatial quality assessment is worked out by MTF computing with an improved slanted edge analysis method. Radiometric response ability of different spectral channels is judged by SNR computing based upon local RMS extraction and statistics method. Improved noise elimination and parameter optimization method are adopted to improve the evaluation fidelity. This work on spectral imaging quality assessment not only has significance in the development of on-ground and in-orbit spectral imaging technique but also takes on reference value for index demonstration and design optimization for spectral instrument development.
The imaging spectro-polarimetry combines the spectral imaging technology and the imaging polarization technology. It assembles the functions of camera, spectrometer and polarimeter. So the optical information quantity is increased and the detection efficiency is improved. But the acquirement of the multi-dimensional information results in the detector complex construction and large volume. The moving part is used in the current method to realize the different polarization states or spectral filtering. The images are difficult for registration and the current method can’t be used to get the motion scene. This paper presents innovative imaging spectro-polarimetry method with no moving parts. The hyper-spectral information, full-Stokes polarization information and one-dimensional spatial information are obtained by the polarization modulating and spectrum dispersing. The designed imaging spectro-polarimeter is composed of two parts, a polarization module and the spectral dispersive module. They are all employed stationary configuration. The polarization module includes two birefringent crystal wave plates and a polarizer. The thickness of the birefringent wave-plates and the polarization axes of each component are optimized and the full-Stokes polarization information is loaded on the spectrum. The polarization information can be restored by the Fourier transform. The concentric Offner configuration is adopted for spectral dispersive module. It is composed of two concave spherical mirrors and a holographic aberration-corrected convex grating. The designed dispersive configuration is compact and aligned simply. And high quality linear dispersion, low distortion spectral image are implemented. The Full-stokes imaging spectro-polarimeter our designed is validated by the model simulation and the laboratory experiment. The mixed hyper-spectral information and accuracy polarization information can be obtained.
A novel snapshot imaging spectrometer with large field-of-view (FOV) up to 100° is achieved by taking the advantages of a multiscale fore-optics and a compact Offner imaging spectrograph. Based on the diffraction imaging theory, the multiscale fore-optics composed of a monocentric spherical lens and multi-channel microlens array is designed, over which panchromatic images with small FOV are of uniform image quality. And identical imaging spectrographs with a dimension less than 30 cubic millimeters and with a high spectral resolution of about 2nm are designed correspondingly. The presented imaging spectrometer works at the visible wavelength range which is from 400nm to 780nm. It is of a fast speed about F/2.4 and a compact configuration of only 200mm×300mm×300mm in dimension. But the smile and keystone distortions are negligible.
The radiometric calibration of imaging spectrometer plays an import role for scientific application of spectral data. The radiometric calibration accuracy is influenced by many factors, such as the stability and uniformity of light source, the transfer precision of radiation standard and so on. But the deviation from the linear response mode and the polarization effect of the imaging spectrometer are always neglected. In this paper, the linear radiometric calibration model is constructed and the radiometric linear response capacity is test by adjusting electric gain, exposure time and radiance level. The linear polarizer and the sine function fitting algorithm are utilized to measure polarization effect. The integrating sphere calibration system is constructed in our Lab and its spectral radiance is calibrated by a well-characterized and extremely stable NIST traceable transfer spectroradiometer. Our manufactured convex grating imaging spectrometer is relative and absolute calibrated based on the integrating sphere calibration system. The relative radiometric calibration data is used to remove or reduce the radiometric response non-uniformity every pixel of imaging spectrometer while the absolute radiometric calibration is used to construct the relationship between the physical radiant of the scene and the digital number of the image. The calibration coefficients are acquired at ten radiance levels. The diffraction noise in the images can be corrected by the calibration coefficients and the uniform radiance image can be got. The calibration result shows that our manufactured imaging spectrometer with convex grating has 3.0% degree of polarization and the uncertainties of the relative and absolute radiometric calibrations are 2.4% and 5.6% respectively.
Advanced optical imaging systems should have high imaging quality and robotic environmental suitability. Such a
near-infrared lens with the Pitzval style is designed and developed. Its operation wavelength is from 0.72μm to 1.0μm
and its relative aperture as high as 1:2. Its passive athermalization design to suit for the wide operation temperature range
from -45°C to 60°C is implemented through optimal selection of its optical glasses and opto-mechamical structure.
Sharp ghost image due to even reflection at optical surfaces is eliminated with our suggested means, and thus stray light
within its image plane is both low and uniform even under backlighting. The Modulation Transfer Function (MTF) of the
designed lens at the Niquest spatial frequency 90 lines/mm of focal plane array detector is higher than 0.6 within its
operation temperature range and its entire field of view. Eighty percent of its diffraction encircled energy is within one
pixel of the detector. Its point source transmittance (PST) when the illuminating off-angle of point source is from 5 to 60
degrees, which is just out of its field of view, is computed through modeling and simulation, and as low as between 10-3
to 10-11. The experimentally measured MTF values and veiling glare index of our developed lens reaches respectively to
0.61 and 0.372% and validates our suggested design in the paper.
The optical compressive spectral imaging method is a novel spectral imaging technique that draws in the inspiration of compressed sensing, which takes on the advantages such as reducing acquisition data amount, realizing snapshot imaging, increasing signal to noise ratio and so on. Considering the influence of the sampling quality on the ultimate imaging quality, researchers match the sampling interval with the modulation interval in former reported imaging system, while the depressed sampling rate leads to the loss on the original spectral resolution. To overcome that technical defect, the demand for the matching between the sampling interval and the modulation interval is disposed of and the spectral channel number of the designed experimental device increases more than threefold comparing to that of the previous method. Imaging experiment is carried out by use of the experiment installation and the spectral data cube of the shooting target is reconstructed with the acquired compressed image by use of the two-step iterative shrinkage/thresholding algorithms. The experimental result indicates that the spectral channel number increases effectively and the reconstructed data stays high-fidelity. The images and spectral curves are able to accurately reflect the spatial and spectral character of the target.
Spectral calibration of imaging spectrometer plays an important role for acquiring target accurate spectrum. There are two spectral calibration types in essence, the wavelength scanning and characteristic line sampling. Only the calibrated pixel is used for the wavelength scanning methods and he spectral response function (SRF) is constructed by the calibrated pixel itself. The different wavelength can be generated by the monochromator. The SRF is constructed by adjacent pixels of the calibrated one for the characteristic line sampling methods. And the pixels are illuminated by the narrow spectrum line and the center wavelength of the spectral line is exactly known. The calibration result comes from scanning method is precise, but it takes much time and data to deal with. The wavelength scanning method cannot be used in field or space environment. The characteristic line sampling method is simple, but the calibration precision is not easy to confirm. The standard spectroscopic lamp is used to calibrate our manufactured convex grating imaging spectrometer which has Offner concentric structure and can supply high resolution and uniform spectral signal. Gaussian fitting algorithm is used to determine the center position and the Full-Width-Half-Maximum（FWHM）of the characteristic spectrum line. The central wavelengths and FWHMs of spectral pixels are calibrated by cubic polynomial fitting. By setting a fitting error thresh hold and abandoning the maximum deviation point, an optimization calculation is achieved. The integrated calibration experiment equipment for spectral calibration is developed to enhance calibration efficiency. The spectral calibration result comes from spectral lamp method are verified by monochromator wavelength scanning calibration technique. The result shows that spectral calibration uncertainty of FWHM and center wavelength are both less than 0.08nm, or 5.2% of spectral FWHM.
Compressive spectral imaging combines traditional spectral imaging method with new concept of compressive sensing thus has the advantages such as reducing acquisition data amount, realizing snapshot imaging for large field of view and increasing image signal-to-noise and its preliminary application effectiveness has been explored by early usage on the occasions such as high-speed imaging and fluorescent imaging. In this paper, the application potentiality for spatial coding compressive spectral imaging technique on rural survey is revealed. The physical model for spatial coding compressive spectral imaging is built on which its data flow procession is analyzed and its data reconstruction issue is concluded. The existing sparse reconstruction methods are reviewed thus specific module based on the two-step iterative shrinkage/thresholding algorithm is built so as to execute the imaging data reconstruction. The simulating imaging experiment based on AVIRIS visible band data of a specific selected rural scene is carried out. The spatial identification and spectral featuring extraction capacity for different ground species are evaluated by visual judgment of both single band image and spectral curve. The data fidelity evaluation parameters (RMSE and PSNR) are put forward so as to verify the data fidelity maintaining ability of this compressive imaging method quantitatively. The application potentiality of spatial coding compressive spectral imaging on rural survey, crop monitoring, vegetation inspection and further agricultural development demand is verified in this paper.
Imaging spectrometer is a promising remote sensing instrument widely used in many filed, such as hazard forecasting,
environmental monitoring and so on. The reliability of the spectral data is the determination to the scientific communities.
The wavelength position at the focal plane of the imaging spectrometer will change as the pressure and temperature vary,
or the mechanical vibration. It is difficult for the onboard calibration instrument itself to keep the spectrum reference
accuracy and it also occupies weight and the volume of the remote sensing platform. Because the spectral images suffer
from the atmospheric effects, the carbon oxide, water vapor, oxygen and solar Fraunhofer line, the onboard wavelength
calibration can be processed by the spectral images themselves. In this paper, wavelength calibration is based on the
modeled and measured atmospheric absorption spectra. The modeled spectra constructed by the atmospheric radiative
transfer code. The spectral angle is used to determine the best spectral similarity between the modeled spectra and
measured spectra and estimates the wavelength position. The smile shape can be obtained when the matching process
across all columns of the data. The present method is successful applied on the Hyperion data. The value of the
wavelength shift is obtained by shape matching of oxygen absorption feature and the characteristics are comparable to
that of the prelaunch measurements.
A star tracker optical imaging system is designed for Polaris detection. System parameters determination and its configuration chosen method are given. Based on Macsutov-Cassegrain configuration, the system is designed imagery tele-centric. It works at 0.6μm~1.1μm waveband and the view field is 0.5 degree. The tube length of the system is 80mm, which is only 8 percent of its focal length. Its MTF reaches diffraction limit and the spot diagrams are quit near a circle. About 80% of the energy is encircled in a CCD pixel. And the distortion is less than 1%. Moreover, it has a perfect thermal adaptability from -40℃ to 60℃.
Hyperspectral imager is now widely used in many regions, such as resource development, environmental monitoring and so on. The reliability of spectral data is based on the instrument calibration. The smile, wavelengths at the center pixels of imaging spectrometer detector array are different from the marginal pixels, is a main factor in the spectral calibration because it can deteriorate the spectral data accuracy. When the spectral resolution is high, little smile can result in obvious signal deviation near weak atmospheric absorption peak. The traditional method of detecting smile is monochromator wavelength scanning which is time consuming and complex and can not be used in the field or at the flying platform. We present a new smile detection method based on the holmium oxide panel which has the rich of absorbed spectral features. The higher spectral resolution spectrometer and the under-test imaging spectrometer acquired the optical signal from the Spectralon panel and the holmium oxide panel respectively. The wavelength absorption peak positions of column pixels are determined by curve fitting method which includes spectral response function sequence model and spectral resampling. The iteration strategy and Pearson coefficient together are used to confirm the correlation between the measured and modeled spectral curve. The present smile detection method is posed on our designed imaging spectrometer and the result shows that it can satisfy precise smile detection requirement of high spectral resolution imaging spectrometer.
Compressive spectral imaging is a kind of novel spectral imaging technique that combines traditional spectral imaging method with new concept of compressive sensing. Spatial coding compressive spectral imaging realizes snapshot imaging and the dimension reduction of the acquisition data cube by successive modulation, dispersion and stacking of the light signal. It reduces acquisition data amount, increases imaging signal-to-noise ratio, realizes snapshot imaging for large field of view and has already been applied in the occasions such as high-speed imaging, fluorescent imaging and so on. In this paper, the physical model for single dispersion spatial coding compressive spectral imaging is reviewed on which the data flow procession is analyzed and its reconstruction issue is concluded. The existing sparse reconstruction methods are investigated and specific module based on the two-step iterative shrinkage/thresholding algorithm is built so as to execute the imaging data reconstruction. A regularizer based on the total-variation form is included in the unconstrained minimization problem so that the smooth extent of the restored data cube can be controlled by altering its tuning parameter. To verify the system modeling and data reconstruction method, a simulation imaging experiment is carried out, for which a specific imaging scenery of both spatial and spectral features is firstly built. The root-mean-square error of the whole-band reconstructed spectral images under different regularization tuning parameters are calculated so that the relation between data fidelity and the tuning parameter is revealed. The imaging quality is also evaluated by visual observation and comparison on resulting image and spectral curve.
Zoom lens with variable focal length is well fit for researching objectives far and near. Design of zoom lens working at mid-wave infrared wavelength (7.7-10.3_m) and its view field 10 degrees is presented. Determination of the initial configuration of the variable and the compensate groups are discussed according to the mechanism compensate curves. The compensate group is determined with positive power. Its focal length changes during a large scope, which is from 300mm to 100mm. And the corresponding F number variables from 3.75 to 1.25. So the residual aberration needs to be carefully corrected. The optimized zoom lens is composed of four group elements, and its performance reaches diffraction limited at each focal position.
Based on the wave aberration theory, a new method of optical design of the planate symmetric Offner
type imaging spectrometer is performed. Astigmatism changing with the diffraction angle of the grating,
the meridional and saggital focusing characters are all studied. Determination of the initial
configurations and optimally design methods of two improved types of Offner imaging spectrometer
are discussed in detailed. A design example with the numerical aperture larger than 0.2, and the
entrance slit 30mm is given. Its spectral resolution is better than 2nm and MTF is above 0.7@20lp/mm.
The smile and keystone are less than 3% and 0.2% of the pixel respectively.
The designed hyperspectral imaging system is composed of three main parts, that is, optical subsystem, electronic
subsystem and capturing subsystem. And a three-dimensional "image cube" can be obtained through push-broom. The
fore-optics is commercial-off-the-shelf with high speed and three continuous zoom ratios. Since the dispersive imaging
part is based on Offner relay configuration with an aberration-corrected convex grating, high power of light collection
and variable view field are obtained. The holographic recording parameters of the convex grating are optimized, and the
aberration of the Offner configuration dispersive system is balanced. The electronic system adopts module design, which
can minimize size, mass, and power consumption. Frame transfer area-array CCD is chosen as the image sensor and the
spectral line can be binned to achieve better SNR and sensitivity without any deterioration in spatial resolution. The
capturing system based on the computer can set the capturing parameters, calibrate the spectrometer, process and display
spectral imaging data. Laboratory calibrations are prerequisite for using precise spectral data. The spatial and spectral
calibration minimize smile and keystone distortion caused by optical system, assembly and so on and fix positions of
spatial and spectral line on the frame area-array CCD. Gases excitation lamp is used in smile calibration and the keystone
calculation is carried out by different viewing field point source created by a series of narrow slit. The laboratory and
field imaging results show that this pushbroom hyperspectral imaging system can acquire high quality spectral images.
The aerospace camera developed is an exclusive functional load of a micro satellite. The
signal-to-noise ratio of the aerospace camera reflects its radiance response and is the parameter that
directly associates with the quality of its acquired images. The traditional way to calculate the
signal-to-noise ratio of a camera is to substitute the related parameters of its subassemblies into the
deduced formulas. This kind of method lacks the focalization on the diversities of its components and
specific application occasions. The result tested by using standard uniform source can certainly be
utilized to evaluate the work performance of the camera, but it ignores its actual orbital atmospheric
condition and consequentially leads to unavoidable data deviation.
The atmospheric transmission model is built and the radiation condition of the aerospace camera
in orbit is simulated by means of MODTRAN. Instead of building the noise model based on electronic
devices of the camera to get theoretical noise data, considering the difference of the noises of the
camera between in-lab and on-orbit condition, we adopt the measured noise data of the CCD camera to
calculate the signal-to-noise ratio so as to make it approach the real value as possible.
The influences of the changes of solar altitude angle, earth surface albedo and weather condition
on the signal-to-noise ratio of the camera are quantitatively determined. The result of the
signal-to-noise ratio can be used as the basis to evaluate the remote sensing imaging quality and to
decide the feasible exposure time.
Imaging spectrometers can provide imagery and spectrum information of objects and form so-called three-dimensional
spectral imagery, two spatial and one spectral dimension. Most of imaging spectrometers use conventional spectroscopic
elements or systems, such as reflective diffraction gratings, prisms, filters, spatial modulated interferometers, and so on.
Here a special imaging spectrometer which is based on a novel cemented Prism-Grating-Prism (PGP) is reported. Its
spectroscopic element PGP consists of two prisms and a holographic transmission volume grating, which is cemented
between these prisms. The two prisms mainly function as beam deviation, the grating as a disperser. In addition to the
high light efficiency of the volume gratings that is required for high spectral resolution, the cementing difficulty when
surface relief gratings are used can be avoided due to its voluminal characteristic. The PGP imaging spectrometer has
advantages of direct vision, dispersion uniform, compactness, low cost, and facility to be used. The principle, structure,
and optimized design of the PGP imaging spectrometer are given in detail. Its front collimation optics and rear focusing
lenses are same so as to reduce its cost further. The spectral coverage, resolution, and track length of the designed system
are respectively visible light from 400nm to 800nm, 1.6nm/pixel, and 85mm. From its performance evaluation, it is
shown that the PGP imaging spectrometer has the potentiality to be used in microscopic hyperspectral imagers and
hyperspectral imaging remote sensors.
The optimized design, alignment and experimental results of a compact convex grating hyper-spectral imager with high
fidelity are reported and evaluated. The imager works in visible wavelength range from 0.4 to 0.78 μm. The numerical
aperture of system is 0.2, and the entrance slit images with -1 magnification and linearly dispersed into 7.5mm in width.
In addition, the spectral sample resolution is 0.76nm/pixel with negligible distortion. In order to get good performance
and facilitate alignment, the optical system is both imagery and objective telecentric. The efficiency of the convex
grating can up to about 40 percents by ion-beam etching. The size is 190mm×180mm×90mm and the mass is less than
1kg. The light weighted compact system is portable, and it is feasible in remote sensing.
The lens, whose image height is proportional to its field view angle through introducing reasonable barrel distortion so as to scan or mark linearly is called F-theta lens. Design of F-theta lens is introduced in the paper. The design idea and method are illustrated in detail through the analysis of two systems with working area of 200×200mm2 and 500×500mm2. They're simple and compact. Both of them are composed of only three spherical lenses with two kinds of common optical glasses. Their tube length (from the front surface of the first lens to the back surface of the last one) is far less than 100mm. Remarkably, such simple lenses are able to obtain diffraction-limited focusing performances and low distortions less than 0.5 percent relative to F-Theta linear relation.
A hyperspectral imaging system composed of a fore-optic and an imaging spectroscope is
designed and presented. The fore-optic is a three-mirror anastigmatic telescope with a 360mm
focal length to match the FPA with 1024×1024 pixels. The imaging spectroscope is based on a
modified Offner 1× relay with a holographic convex grating in the place of the secondary mirror.
The hyperspectral imaging system is designed for the visible-near infrared (VNIR) band with 5nm
spectral and 18m ground spatial resolution from the altitude of 500km. Its many attractive features
such as fast speed (F/2.5), large flat field, wide spectral range, low distortion, and compactness
made it ideally suited for spaceborne remote sensing.
F-Theta lens is different from common photo lenses, and it is usually used in the scanning system to realize linear scanning by means of its linearity. The lens focuses a laser beam and its scanning quality mainly depends on its focusing performance. When the F-Theta lenses used in laser marking systems, as we know, their working area is generally not larger than 300×300mm2 interiorly. In this paper, the design of a kind of F-Theta lens, which has the working area as large as 680mm in diameter, is introduced in detail. Firstly, the first-order optical parameters are determined by its paraxial analysis, flat-field condition, and aberration characteristics. Secondly, the initial structure parameters of the F-Theta lens are obtained through the PW method. And then the optimal F-Theta lens meeting with its required optical performances is gained with some optical design software under practical constrained conditions. The designed system is compact and composed of only four spherical lenses made up of two kinds of common optical glass. Its tube length from the front surface of the first lens to the back surface of the last one is less than 100mm. But the focusing performance of the lens is within diffraction limit on the whole and its distortion relative to the F-Theta linear relation is less than 0.5 percent.