Photorefractive digital holographic microscopy: an application in the microdevices surfaces

Abstract

Abstract-In this work, we present a Photorefractive Digital Holographic Microscopy (PRDHM) technique based on the writing-reading holographic process in photorefractive Bi 12 TiO 20 (BTO) crystal using the numerical reconstruction of the phase and amplitude image performed by a Digital Holographic Microscopy (DHM) method. We demonstrate that a holographic reconstructed image by diffraction process in photorefractive BTO crystal can be combined with a second reference beam to form a hologram in CCD plane in a DHM setup. The experimental results in a glass slide resolution target and thin film structure was obtained, where, amplitude, phase and 3D phase images are calculated performing digital reconstruction. This technique presents potentials possibilities to obtain 3D phase image of the microdevices for dynamic holography applications.Index Terms-holography; microscopy; non-destructive testing; photorefractive materials. I. INTRODUCTIONPhotorefractive holography is increasingly being used for quantitative measurements of the amplitude and phase of the objects waves in static and dynamic process [1][2][3][4][5][6][7]. In the photorefractive holography, the holographic recording medium is a photorefractive (PR) material. In PR crystals the holographic grating recording are characterized by following light-induced mechanisms: photorefractive (PR) effect, thermo-optic refractive index modulation or photochromic effect [1]. The PR effect consists on the refractive index modulation through charge carriers photo-induction and linear electro-optic effect; the refractive index modulation by thermo-optic effects is due to temperature gradients on the crystal surface; and the photochromic effect is caused by absorption coefficient modulation for high light intensities. These holographic recording materials present advantages like in situ self-processing of recording medium, indefinite reusability, high resolution and low response time. Moreover, PRCs do not present fatigue in dynamic and reversible processes. In Digital Holography by calculating the complex optical field of an image, the amplitude and phase of the optical field are available for direct manipulation [8][9][10][11][12]. The applications of digital holography to microscopy are particularly advantageous because a single hologram records the information of a three-dimensional object space. These advantages have been noted since early in the development of digital holography and applied to imaging analysis of microstructures and biological microscopy [9-12] using CCD sensor as holographic detector. In off-axis holography the angle of incidence of the reference beam is chosen so that when the hologram is reconstructed, the zero order light may be spatially separated from the diffracted holographic reconstruction. The method of offaxis holography involves a high spatial-frequency fringe pattern that must be sufficiently sampled by the CCD, the spatial resolution of the CCD is an important parameter.Recently, some works present the combination of the photorefractiv...

Algoritmos simplificados de hologramas computacionais: I – para geração de imagens 3D

“…Atualmente, as técnicas holográficas podem ser classificadas de acordo com o processo de registro e/ou processo de reconstrução, como em: holografia analógica (convencional ou clássica) e holografia computacional (numérica, digital ou eletrônica) [4,5,[7][8][9][10][11][12][13][14][15][16][17][18].…”

“…Na holografia clássica ou analógica, usando luz coerente (laser) e elementos ópticos tradicionais, o processo de registro e reconstrução é feito a partir de meios de registro holográfico convencionais: filmes de haleto de prata, fototermoplásticos, materiais fotossensíveis ou cristais fotorrefrativos [4,5,12,13]. Na verdade, a invenção do laser revolucionou a holografia com a possibilidade de hologramas de alta qualidade, que atraiu a atenção dos cientistas, engenheiros, artistas e meios de comunicação [6].…”

“…Isto se deve aos recentes avanços, nas tecnologias baseadas em semicondutores (microeletrônica e optoeletrônica) e, também, ao aumento da capacidade de processamento e armazenamento de dados dos atuais microcomputadores. Procedimentos aprimorados têm sido empregados, abrindo caminho para a holografia computacional que podemos classificar em hologramas gerados por computador (HGCs), quando o processo de registro é numérico-computacional e o processo de reconstrução é óptico-experimental; ou, em holografia digital (HD), quando o processo de registro é ópticoexperimental e o processo de reconstrução é numéricocomputacional [5,[7][8][9][10][11][12][14][15][16][17][18]. Nestes casos, dispositivos como câmeras CCDs (Charge Couple Devices) e os moduladores espaciais de luz SLMs (Spatial Light Modulators) que são baseados em cristal líquido (LC/LCoS) ou micro-espelhos (DMDs), a intensidade e fase das ondas podem ser registradas, armazenadas, transmitidas e aplicadas em simulações controladas por computador [5].…”

Algoritmos simplificados de hologramas computacionais: II – para geração de feixes e vórtices ópticos

“…O desenvolvimento de dispositivos optoeletrônicos cada vez mais rápidos e de alta resolução, como: as câmeras CMOS e CCD (Coupled Charge Device) e os moduladores espaciais de luz (SLMs), baseados em cristal liquido (LCDs) ou micro-espelhos (DMDs); fontes lasers eficientes, sistemas ópticos e opto-mecânicos de excelente qualidade e estáveis. Estes vêm possibilitando, cada vez mais, a implementação experimental de sistemas holográficos de registro e reconstrução numérica e/ou óptica de ondas ópticas de objetos e formas e feixes ópticos [31,32,[34][35][36][37]. Bem como, outros meios de registro holográfico, materiais fotossensíveis, fotorrefrativos e metasuperfícies holográficas [38][39][40][41][42].…”

Dynamic Digital Holography for recording and reconstruction of 3D images using optoelectronic devices

“…Subsequently, materials that dispensed the chemical processing emerged: the photorefractive crystals, which are used as recording medium in Photorefractive Holography [6,7]. This technique has been broadly applied in surface contouring and in phase-shifting real time interferometry [8,9,10,11,12,13,14], as well as in microscopy [15,16].…”