Diacetone acrylamide-based non-toxic holographic photopolymer

A new low-toxicity diacetone acrylamide-based photopolymer is developed and characterized. The environmentally-compatible photopolymer has been modified with the inclusion of glycerol. The incorporation of glycerol results in a uniform maximum refractive index modulation for recording intensities in the range of 1-20 mW/cm2. This may be attributed to glycerol’s nature as a plasticizer, which allows for faster diffusion of un-reacted monomer within the grating during holographic recording. An optimum recording intensity of 0.5 mW/cm2 is observed for exposure energies of 20-60 mW/cm2. The modified photopolymer achieves a refractive index modulation of 2.2x10-3, with diffraction efficiencies up to 90 % in 100 µm layers. The photopolymer layers containing glycerol have improved stability and optical quality

Electronic Speckle Pattern Shearing Interferometry using Photopolymer Diffractive Optical Elements for Vibration Measurements

Electronic speckle pattern shearing interferometry (ESPSI) is superior to Electronic speckle pattern interferometry (ESPI) when strain distribution, arising from object deformation or vibration, need to be measured. This is because shearography provides data directly related to the spatial derivatives of the displacement. Further development of ESPSI systems could be beneficial for wider application to the measurement of mechanical characteristics of vibrating objects. Two electronic speckle pattern shearing interferometers (ESPSI) suitable for vibration measurements are presented. In both ESPSI systems photopolymer holographic gratings are used to shear the images and to control the size of the shear. The holographic gratings are recorded using an acrylamide-based photopolymer material. Since the polymerisation process occurs during recording, the holograms are produced without any development or processing. The ESPSI systems with photopolymer holographic gratings are simple and compact. Introducing photopolymer holographic gratings in ESPSI gives the advantage of using high aperture optical elements at relatively low cost. It is demonstrated that both ESPSI system can be used for vibration measurements. The results obtained are promising for future applications of the systems for modal analysis

Investigation of the Photoinduced Surface Relief Modulation in Acrylamide-based Photopolymer

A surface relief diffraction grating is inscribed in acrylamide photopolymer by holographic recording with spatial frequency below 300 l/mm. The periodic surface modulation appears in addition to a volume phase holographic grating. Due to the nature of the presented photopolymerisable material the gratings are induced by light only and no post-processing is required. An investigation of the dependance of the amplitude of the photoinduced relief modulation on spatial frequency of recording and on sample thickness has been carried out utilising white light interferometry. A model of the mechanism of surface relief formation is proposed on the basis of the measured dependencies. The possibility for inscription of surface relief modulation implies different applications of the photopolymer: fabrication of diffractive optical elements, recording of computer generated holograms and biosensors

Comparison of Three Electronic Speckle Pattern Shearing Interferometers using Photopolymer Holographic Optical Elements.

Three electronic speckle pattern shearing interferometers (ESPSI) using photopolymer holographic gratings to produce the sheared image are presented. In the first ESPSI system two holographic gratings are used. The gratings are placed between the object and an imaging lens in front of the CCD camera. In the second ESPSI system one grating is used in combination with a sheet of ground glass. The sheared images on the ground glass are further imaged onto a CCD camera. In the third ESPSI system only one grating is used - it is placed in front of the object. The image and the sheared image are imaged onto the CCD camera, whose optical axis coincides with the normal to the object surface. The introduction of photopolymer holographic gratings in ESPSI systems gives the advantage of using high aperture optical elements at relatively low price. The systems are compared in terms of flexibility in their adjustment, sensitivity, suitability and limitations for different applications

Simple Electronic Speckle Pattern Shearing Interferometer with a Holographic Grating as a Shearing Element

An optical set-up for electronic speckle pattern shearing interferometry (ESPSI) using a photopolymer diffractive optical element as a shearing element, is presented. A laser beam illuminates the object at an angle to the normal to the object surface. The holographic diffraction grating is placed in front of the object. The zero and the first order of diffraction form the image and the sheared image of the object. The images are imaged onto the CCD camera, whose optical axis coincides with the normal to the object surface. The field of view is limited only by the dimensions of the photopolymer plate. The photopolymer diffractive element is characterised by low level of light scatter and diffraction efficiency of 60%. The simplicity of the proposed new shearing interferometer is manifested by the extremely small number of components required – a coherent light source, a holographic optical element and a CCD camera

Application of a Photopolymer Material in Speckle Pattern Shearing Interferometry

A new application of a photopolymer diffractive optical element in electronic speckle pattern shearing interferometer (ESPSI) is presented. In the first stage a holographic grating is recorded using an acrylamide based photopolymer material. Since the polymerisation process occurs during recording, the holograms are produced without any development or processing. In the second stage the holographic grating is used to produce the two sheared images in an ESPSI configuration. A ground glass screen following the grating serves the purpose of eliminating unwanted diffraction orders. The distance between the grating and the ground glass can be used to control the amount of the shear. The sheared images on the ground glass are further imaged onto a CCD camera. The proposed system is simple and flexible

Determination of the polymerisation rate of a low-toxicity diacetone acrylamide-based holographic photopolymer using Raman spectroscopy

The polymerisation rate of a low-toxicity Diacetone Acrylamide (DA)-based photopolymer has been measured for the first time using Raman spectroscopy. A value for the polymerisation rate of 0.020 s−1 has been obtained for the DA photopolymer by modelling the polymerisation reaction dynamics as a stretched exponential or Kohlrausch decay function. This is significantly lower than the polymerisation rate of 0.100 s−1 measured for the well known Acrylamide (AA)-based photopolymer composition. The effect of the additive glycerol on the polymerisation rate of the DA-based photopolymer has also been investigated. The inclusion of glycerol is observed to increase the rate of polymerisation of the DA photopolymer by up to 60%. It is also observed that the polymerisation rate of the DA photopolymer is less dependent on the recording intensity when glycerol is present

Research on Holographic Sensors and Novel Photopolymers at the Centre for Industrial and Egnineering Optics

The recent resurgence of interest in photopolymers for commercial holograms is a strong incentive for development of photopolymers that are as environmentally friendly as possible. Photopolymer materials consist of a light-sensitive film which is exposed during production to form the hologram, thereby offering versatility well beyond that of current security holograms, which are mass produced from a master using a foil stamping processes

Application of Photopolymer Holographic Gratings

Two optical set-ups for electronic speckle pattern shearing interferometry (ESPSI) using photopolymer diffractive optical elements are presented. Holographic gratings are recorded using an acrylamide based photopolymer material. Since the polymerisation process occurs during recording, the holograms are produced without any development or processing. In both ESPSI systems the photopolymer gratings are used to shear the image. In the first ESPSI system only one grating is used in combination with a sheet of ground glass. The distance between the grating and the ground glass can be used to control the amount of the shear. The sheared images on the ground glass are further imaged onto a CCD camera. In the second ESPSI system two gratings are used to shear the image. The gratings are placed between the object and an imaging lens in front of the CCD camera. The distance between the two gratings controls the size of the shear. The ESPSI system with two photopolymer holographic gratings is compact and suitable for industrial applications. Introducing photopolymer holographic gratings in ESPSI gives the advantage of using high aperture optical elements at relatively low price. Both of these interferometric systems are simple and flexible

Research on Holographic Sensors and Novel Photopolymers at the Centre for Industrial and Engineering Optics

The recent resurgence of interest in photopolymers for commercial holograms is a strong incentive for development of photopolymers that are as environmentally friendly as possible. Photopolymer materials consist of a light-sensitive film which is exposed during production to form the hologram, thereby offering versatility well beyond that of current security holograms, which are mass produced from a master using a foil stamping processes