Preface

The book *Holographic Materials and Optical Systems* comprises three sections and twenty-one book chapters.

The first section has six chapters on volume holographic optical elements (HOE) and sys‐ tems, including novel materials, methods, and applications (Chapter 1), holographic optical elements for solar concentrators (Chapter 2), volume Bragg gratings and their applications in laser beam combining and beam phase transformations (Chapter 3), low spatial frequency volume Bragg grating and holographic optical elements (Chapter 4), holographic optical ele‐ ments and their applications (Chapter 5), and holographic data storage systems using paral‐ lel-aligned liquid crystals on silicon display (Chapter 6). Section 2 is dedicated to applications in holographic imaging and metrology. It has nine chapters focused on micro‐ topography and thickness measurements (Chapter 7), 3D capture and 3D contents genera‐ tion for holographic imaging (Chapter 8), multiwavelength digital holography (DH) and phase-shifting interferometry (Chapter 9), dynamic imaging with x-ray holography (Chap‐ ter 10), indirect off-axis holography for antenna metrology (Chapter 11), surface characteri‐ zation by the use of digital holography (Chapter 12), digital holography for analyzing highdensity gradients in fluid mechanics (Chapter 13), digital holographic microscopy (DHM) for clinical diagnostics (Chapter 14), and unlabeled semen analysis by means of the holo‐ graphic imaging (Chapter 15). Section 3 is dedicated to holographic materials and systems for holographic recording and consists of six chapters describing materials suitable for holo‐ graphic photoalignment for fabrication of twisted nematic liquid crystal gratings (Chapter 16), high-performance photoinitiating system for holographic grating recording (Chapter 17), fluorite crystals with color centers for recording extremely stable holograms (Chapter 18), new photo-thermo-refractive glasses for holographic optical elements (Chapter 19), ma‐ terials for active holography (Chapter 20), and organic-inorganic hybrid structures for dy‐ namic holography (Chapter 21).

The chapters describe a comprehensive review of the historical developments leading to the specific topic under discussion and will provide the reader with useful background informa‐ tion. The following paragraphs give a brief summary of chapters' contents.

"Volume Holography: Novel Materials, Methods, and Applications" provides basics on vol‐ ume holography, specific material requirements for volume holography, and diffractive properties of the different types of volume holographic gratings. The interrelation between function and structure of volume holograms is investigated with a view to research on and develop novel materials, methods, and applications.

"Volume Holographic Optical Elements as Solar Concentrators" investigates holographic so‐ lar concentrator in a new photopolymer material as recording medium. Two different con‐ figurations of holographic lenses (with spherical and cylindrical symmetry) are described in terms of both recording process and optical response characterization. The possibility to use this new photopolymer to realize holographic solar concentrator for space applications is discussed.

"Volume Bragg Gratings: Fundamentals and Applications in Laser Beam Combining and Beam Phase Transformations" outlines the fundamentals of transmission and reflection vol‐ ume gratings and compares their spectral properties. The applications of volume Bragg gra‐ tings for spectral and coherent laser beam combining and as holographic phase masks are demonstrated and discussed.

"Holographically Recorded Low Spatial Frequency Volume Bragg Grating and Holographic Optical Elements" presents examples of focusing elements and off-axis cylindrical lenses finding application for collection of solar energy. Some low spatial frequency diffusive ele‐ ments and beam splitters were shown to illustrate the potential of low spatial frequency holographic elements in beam-shaping applications. The advantages of volume photopoly‐ mer holographic gratings are discussed in the context of existing research.

"Holographic Optical Elements and Their Applications" describes in detail the principles and characteristics of the holographic optical elements (HOE). А few typical holographic op‐ tical element–based applications such as head-mounted display, lens array, and solar con‐ centrator are introduced. It has been demonstrated that the HOE is a much useful and an effective technique especially for simplified optical systems.

"Holographic Data Storage Using Parallel-Aligned Liquid Crystals on Silicon Display" ex‐ plores the implementation of holographic data storage where a parallel-aligned liquid crys‐ tal on silicon microdisplay is utilized as the data entry point for a holographic data storage system. The authors demonstrate holographic data storage in a photopolymer as holograph‐ ic recording material by utilizing a phase-only device as a data pager by using different modulation schemes.

"Microtopography and Thickness Measurements with Digital Holographic Microscopy Highlighting Its Tomographic Capacity" demonstrates the potential of digital holographic microscopy (DHM) by using a Mirau interferometric objective. The authors propose ap‐ proaches for reduction of the noise by utilizing LED light and by performing an averaging process of phase and amplitude images reconstructed at different reconstruction distances. Ringing effect is reduced by using an ideal filter in off-axis digital holography.

"3D Capture and 3D Content Generation for Holographic Imaging" follows the two main tendencies in forming the 3D holographic content—direct feeding of optically recorded digi‐ tal holograms to a holographic display and computer generation of interference fringes from directional, depth, and color information about the 3D objects. The focus is set on important issues that comprise encoding of 3D information for holographic imaging.

"Multiwavelength Digital Holography and Phase-Shifting Interferometry Selectively Ex‐ tracting Wavelength Information: Phase Division Multiplexing of Wavelengths" proposes phase-shifting interferometry selectively extracting wavelength information as a novel type of multiwavelength imaging technique. In this technique, multiwavelength images and also the information of 3D space are simultaneously captured by the combination with hologra‐ phy. The proposed technique is experimentally validated.

"Dynamic Imaging with X-ray Holography" discusses the technical aspects of x-ray hologra‐ phy from an end user perspective, focusing on the requirements for obtaining a high-quality image in a short time. The chapter presents the key challenges of the techniques and gives ideas for their implementation.

figurations of holographic lenses (with spherical and cylindrical symmetry) are described in terms of both recording process and optical response characterization. The possibility to use this new photopolymer to realize holographic solar concentrator for space applications is

"Volume Bragg Gratings: Fundamentals and Applications in Laser Beam Combining and Beam Phase Transformations" outlines the fundamentals of transmission and reflection vol‐ ume gratings and compares their spectral properties. The applications of volume Bragg gra‐ tings for spectral and coherent laser beam combining and as holographic phase masks are

"Holographically Recorded Low Spatial Frequency Volume Bragg Grating and Holographic Optical Elements" presents examples of focusing elements and off-axis cylindrical lenses finding application for collection of solar energy. Some low spatial frequency diffusive ele‐ ments and beam splitters were shown to illustrate the potential of low spatial frequency holographic elements in beam-shaping applications. The advantages of volume photopoly‐

"Holographic Optical Elements and Their Applications" describes in detail the principles and characteristics of the holographic optical elements (HOE). А few typical holographic op‐ tical element–based applications such as head-mounted display, lens array, and solar con‐ centrator are introduced. It has been demonstrated that the HOE is a much useful and an

"Holographic Data Storage Using Parallel-Aligned Liquid Crystals on Silicon Display" ex‐ plores the implementation of holographic data storage where a parallel-aligned liquid crys‐ tal on silicon microdisplay is utilized as the data entry point for a holographic data storage system. The authors demonstrate holographic data storage in a photopolymer as holograph‐ ic recording material by utilizing a phase-only device as a data pager by using different

"Microtopography and Thickness Measurements with Digital Holographic Microscopy Highlighting Its Tomographic Capacity" demonstrates the potential of digital holographic microscopy (DHM) by using a Mirau interferometric objective. The authors propose ap‐ proaches for reduction of the noise by utilizing LED light and by performing an averaging process of phase and amplitude images reconstructed at different reconstruction distances.

"3D Capture and 3D Content Generation for Holographic Imaging" follows the two main tendencies in forming the 3D holographic content—direct feeding of optically recorded digi‐ tal holograms to a holographic display and computer generation of interference fringes from directional, depth, and color information about the 3D objects. The focus is set on important

"Multiwavelength Digital Holography and Phase-Shifting Interferometry Selectively Ex‐ tracting Wavelength Information: Phase Division Multiplexing of Wavelengths" proposes phase-shifting interferometry selectively extracting wavelength information as a novel type of multiwavelength imaging technique. In this technique, multiwavelength images and also the information of 3D space are simultaneously captured by the combination with hologra‐

Ringing effect is reduced by using an ideal filter in off-axis digital holography.

issues that comprise encoding of 3D information for holographic imaging.

phy. The proposed technique is experimentally validated.

mer holographic gratings are discussed in the context of existing research.

effective technique especially for simplified optical systems.

discussed.

X Preface

demonstrated and discussed.

modulation schemes.

"Indirect Off-Axis Holography for Antenna Metrology" studies the use of indirect off-axis holography in preventing the effect of errors related to phase acquisition. The aim is to de‐ velop new, efficient, and robust amplitude-only techniques while allowing for cost and com‐ plexity reduction of the measurement setup for antenna characterization.

"Surface Characterization by the Use of Digital Holography" studies numerical reconstruc‐ tion algorithms and discusses the influence of slightly imperfect collimation of the reference wave in off-axis digital holography (DH). Two DH techniques for surface characterization are described and experimentally validated: (1) by using short coherent length, namely, high-brightness digital holographic microscope (DHM) and (2) by using long coherent length, namely, THz DH.

"Digital Holography Interferometry for Analyzing High-Density Gradients in Fluid Me‐ chanics" presents the analysis of a small supersonic jet through comparison of three different optical techniques: (i) digital Michelson holography, (ii) digital holography using Wollaston prisms, and (iii) digital holography without reference wave. The advantages and challenges related to applying digital holography in analyzing high-density gradients in fluid mechan‐ ics are identified and discussed.

"Holography: The Usefulness of Digital Holographic Microscopy for Clinical Diagnostics" explores the implementation of digital holographic (DH) microscopy as a high-resolution imaging technique with the capacity of quantification of cellular conditions without any staining or labeling of cells. The unique measurable parameters are the cell number, cell area, thickness, and volume, which can be coupled to proliferation, migration, cell cycle analysis, viability, and cell death. The authors have used DH microscopy showing that the technique has the sensitivity to distinguish between different cells and treatments.

"Unlabeled Semen Analysis by Means of the Holographic Imaging" studies the morphology, the motility, and the biochemical structure of the spermatozoon and correlates these param‐ eters with the outcome of in vitro fertilization. The chapter summarizes the recent achieve‐ ments of digital holography as an efficient method for healthy and fertile sperm cell selection, without injuring the specimen, and explores new possible applications of digital holography in this field.

"One-Step Holographic Photoalignment for Twisted Nematic Liquid Crystal Gratings" de‐ scribes an innovative method for fabrication of liquid crystal gratings, in which liquid crys‐ tal molecules are periodically aligned. Liquid crystal gratings are fabricated and characterized experimentally and theoretically. They exhibit potential for application as a diffractive optical element that can simultaneously control amplitude, polarization states, and propagation direction of light.

"Application of High-Performance Photoinitiating System for Holographic Grating Record‐ ing" presents a detailed analysis of widely used photoinitiators for polymerization reaction that takes place during holographic recording. The authors study three different compo‐ nents of photointiator systems and made conclusions about the main influencing factors in order to achieve the highest diffraction efficiency in a particular polymer system.

"Fluorite Crystals with Color Centers: A Medium for Recording Extremely Stable but Broad‐ ly Transformable Holograms" studies both the mechanisms of forming the photochromic color centers in fluorite crystals and the photochromism for recording and transforming of holograms. Possible applications as metrological elements and narrow-band transmission and reflection filters for the mid-IR spectral range based on the additively colored fluorite crystals are discussed.

"New Photo-Thermo-Refractive Glasses for Holographic Optical Elements: Properties and Applications" presents recent achievements of developing new holographic media based on fluoride, chloride, and bromide silicate photo-thermo-refractive glasses used for recording holographic optical elements for improving dramatically the parameters of laser systems of different types. The doping of photo-thermo-refractive glasses with rare earth ions was dis‐ cussed as an opportunity for designing lasers with Bragg reflectors and distributed feedback.

"Active Holography" describes laser-active structures comprising dye-doped layers of cho‐ lesteric liquid crystal and polymer as a laser-active medium exhibiting spatial modulation of lasing controlled by the transversely distributed excitation located in the plane of the photo‐ sensitive layer. The influence of the parameters of the pumping interference pattern on the periodical character of the modulation of intensity of the lasing is studied, and the possible application is discussed.

"Two-Wave Mixing in Organic-Inorganic Hybrid Structures for Dynamic Holography" re‐ views recent progress of two-wave mixing and beam amplification in novel type of hybrid structures that combine photoconductive and photorefractive properties of inorganic crystals together with the high birefringence and anisotropy of LC (or PDLC) layers. The proposed organic-inorganic hybrid structures can control transmission, reflection, and scattering of light and are considered to play essential role in 3D holographic display technologies.

#### **Prof. Izabela Naydenova**

School of Physical and Clinical and Optometric Sciences, Dublin Institute of Technology, Ireland

#### **Dr. Dimana Nazarova**

Institute for Optical Materials and Technologies, Bulgarian Academy of Sciences, Bulgaria

#### **Prof. Tsvetanka Babeva**

Institute for Optical Materials and Technologies, Bulgarian Academy of Sciences, Bulgaria **Volume Holographic Optical Elements and Systems**

"Fluorite Crystals with Color Centers: A Medium for Recording Extremely Stable but Broad‐ ly Transformable Holograms" studies both the mechanisms of forming the photochromic color centers in fluorite crystals and the photochromism for recording and transforming of holograms. Possible applications as metrological elements and narrow-band transmission and reflection filters for the mid-IR spectral range based on the additively colored fluorite

"New Photo-Thermo-Refractive Glasses for Holographic Optical Elements: Properties and Applications" presents recent achievements of developing new holographic media based on fluoride, chloride, and bromide silicate photo-thermo-refractive glasses used for recording holographic optical elements for improving dramatically the parameters of laser systems of different types. The doping of photo-thermo-refractive glasses with rare earth ions was dis‐ cussed as an opportunity for designing lasers with Bragg reflectors and distributed feedback. "Active Holography" describes laser-active structures comprising dye-doped layers of cho‐ lesteric liquid crystal and polymer as a laser-active medium exhibiting spatial modulation of lasing controlled by the transversely distributed excitation located in the plane of the photo‐ sensitive layer. The influence of the parameters of the pumping interference pattern on the periodical character of the modulation of intensity of the lasing is studied, and the possible

"Two-Wave Mixing in Organic-Inorganic Hybrid Structures for Dynamic Holography" re‐ views recent progress of two-wave mixing and beam amplification in novel type of hybrid structures that combine photoconductive and photorefractive properties of inorganic crystals together with the high birefringence and anisotropy of LC (or PDLC) layers. The proposed organic-inorganic hybrid structures can control transmission, reflection, and scattering of

**Prof. Izabela Naydenova**

**Dr. Dimana Nazarova**

**Prof. Tsvetanka Babeva**

Dublin Institute of Technology, Ireland

Bulgarian Academy of Sciences, Bulgaria

Bulgarian Academy of Sciences, Bulgaria

Institute for Optical Materials and Technologies,

Institute for Optical Materials and Technologies,

School of Physical and Clinical and Optometric Sciences,

light and are considered to play essential role in 3D holographic display technologies.

crystals are discussed.

XII Preface

application is discussed.

#### **Volume Holography: Novel Materials, Methods and Applications Volume Holography: Novel Materials, Methods and Applications**

Tina Sabel and Marga C. Lensen Tina Sabel and Marga C. Lensen

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67001

#### **Abstract**

This chapter aims to establish a link between material compositions, analytical methods and advanced applications for volume holography. It provides basics on volume hologra‐ phy, serving as a compendium on volume holographic grating formation, specific mate‐ rial requirements for volume holography and diffractive properties of the different types of volume holographic gratings. The particular significance of three‐dimensional optical structuring for the final optical functionality is highlighted. In this context, the interrela‐ tion between function and structure of volume holograms is investigated with view to research on and development of novel materials, methods and applications. Particular emphasis will be placed on analytical methods, assuming that they provide access for a deeper understanding of volume holographic grating formation, which appears to be prerequisite for the design of novel material systems for advanced applications.

**Keywords:** volume holography, Bragg gratings, photonic crystals, refractive index contrast, photosensitive materials, polymers
