Study On The Improvement Of Reconstructed Images In Digital Holography And Its Applications

Digital holography(DH),as an advanced technique to quantitatively and dynamically obtain the amplitude and phase information of an object wave with the characteristics of non-contact,full field and high precision,has been wildly applied in many fields,such as non-destructive testing,flow field analysis,material stress and strain analysis,combustion analysis,vibration analysis.Moreover,DH plays an important role not only in visible light,but also in terahertz waves and infrared range.Usually,the measurement results are determined by the reconstructed images in DH,and how to improve the reconstructed images in DH is getting more attentions.This thesis combines digital and physical techniques in DH for improving the reconstructed images in near infrared range.The internal structure and thermal effect pumping by laser in semiconductor devices are measured with the help of reconstructed images improved DH.Besides that,we introduce some applications in DH.The main work of this thesis are as follows:(1)We suppress the zero-order and twin images with the help of phase-shifting technique to obtain a better reconstructed results in DH,and discuss the influence of phase-shifting errors and noise for the reconstructed results.We combine a tubular piezoelectric transducer(PZT)and a single-mode fiber to make an all-fiber variable phase shifter,and calibrate the relationship between voltage and phase shift.The configuration of DH based on the all-fiber variable phase shifter is constructed and different staircase structures on a silicon wafer are measured as samples,two configurations are presented based on different phase-shifting implementations: one is a slight off-axis two-step phase shift and the other is an in-line four-step phase shift.(2)We introduce the short-coherence infrared light source in DH to suppress the noise and quantitatively measure the weak thermal effect in silicon wafer under visible laser pumping.We compare the differences of long-coherence and short-coherence light sources in DH.The conditions of off-axis hologram recording and the optimal coherence length range in the proposed configuration is given.Meanwhile,we measure the weak thermal effect in silicon pumped by two different approaches of a continuous visible laser with different powers.(3)We propose a short-coherence in-line phase-shifting digital holographic microscopy to measure internal structure in silicon.In the configuration,a short-coherence infrared laser is used as the light source in order to suppress the noise and the in-line phase-shifting configuration is introduced to overcome the problem of poor resolution and large pixel size of the infrared camera and improve the space bandwidth product of the system.A specimen with staircase structure is measured by using the proposed configuration and the 3D shape distribution are given to verify the effectiveness and accuracy of the method.(4)We introduce a high-speed camera in DH to measure the fast event with a temporal resolution of 10 μs.We design and construct an interferometry based on DH and monitor the thermal effect of liquid crystal(LC)device under high-power laser irradiation by using digital holographic interferometry with the characteristics of non-contact,full field,and dynamic measurement.And then,we experimentally investigate the premixed ethylene and oxygen flame that is burning in a narrow channel and the propagation of weak compression wave,finger flame,tulip flame and shock wave generated in the narrow channel are all observed.(5)We present a single-exposure lensless in-line digital holography(LIDH)with double field of view.Two different wavelengths laser beams with a small angle are used to project on different areas of the sample and the wavelength-multiplexed hologram is captured by a color charge coupled device(CCD).By separating the two wavelength channels and eliminating the crosstalk,two independent holograms contain the respective information of two projected areas can be extracted from the single-shot wavelength-multiplexed hologram,which greatly expands the recording area of LIDH without resolution losing.