Optical Design And Experimental Study Of Chromatic Confocal Microscopy

Increasingly demanding of processing technology puts forward higher requirements on measurement accuracy and speed.The traditional laser confocal has the advantage of high precision while is hardly to meet the speed demand of production line detection.Compared with traditional laser confocal,chromatic confocal has the advantage of non-axial scanning,and is more suitable for the measurement of higher speed demand of micrometer precision.The axis measurement range and axis measurement accuracy of chromatic confocal system is mainly decided by numerical aperture and axial dispersion ability of chromatic dispersion objective.In order to increase the axis precision,larger the numerical aperture dispersive objective is commonly adopt,however,objective with large numerical aperture will have smaller axial dispersion range.Commonly,dispersion objective should be specifically designed to meet the needs of different measurement situation,when developing a chromatic confocal system for diversity measurement requirement,the repeating design of different dispersion lens will cause extra expense.In order to solve this problem,proposing a design of dispersive objective which could easily switch axis dispersion range is significant meaningful for developing common chromatic confocal system.The complexity problem of developing common chromatic confocal system is studied,in order to realize switching the measurement performance of system,the optical design of chromatic confocal system and experimental studying was proposed in this paper,the main studies including are as follows:(1)A dispersion lens are designed which can be effectively separate the dispersion function and focus function.The focusing ability of measurement system can be changed by changing the NA of objective lens.Thus,the modulation of measurement range and measurement accuracy is achieved.Through the compartment between refraction and diffractive modes,pure spherical refraction lens was chosen to design the dispersion tube.In the visible region,axial linear chromatic dispersion better than230 mm can be obtained by ZEMAX simulation and the actual axial linear dispersion range can be up to 160 mm.(2)A chromatic confocal experimental system was constructed,by combining dispersive lens and focusing lens,when switching objective the different axis dispersion range were achieved.With objective lens of 4x magnification(NA=0.1),measurement ranges of 1300?m and 2?m axis accuracy were achieved.When objective lens of 10 x magnification(NA=0.3)was adopted,measurement ranges of225?m and 0.4?m axis accuracy were achieved.The experimental results proven the proposed design could easily switching measurement range from millimeter to micrometer by changing focusing objective.(3)Based on the design of dispersion objective,the chromatic confocal measurement system was constructed with 10 times(NA=0.3)objective lens to realize the axial measurement function.The algorithm of wavelength extraction of the center spectral signal was analyzed and the method of suppressing noise interference was studied.Thus,the axial measurement performance of the system was improved.