Advantages_and_Disadvantages_of_Holographic_Interferometry

3.5 Advantages and Disadvantages of Holographic Interferometry

Interferometric methods for transparent objects offer, in comparison with other experimental methods, the following advantages:

• Holographic interferometry makes it possible to record the whole thermal or concentration field by using holographic interferometer.
• The observed area is not disrupted by sensors or sensing heads to detect the local values in the measuring space.
• Light beams can be considered totally free from inertia which enables to record the immediate events.
• Holographic interferometry allows to visualise the distribution of thermal and concentration fields in shape-complex objects (Rezníček, 1980).
• The holographic interferometer is cheaper than the classical interferometer because it does not put high requests on the optical components (lenses and mirrors) quality.

Advantages of the holographic-interference methods in the research of the diffusively reflecting objects can be summarised into the following paragraphs:

• Interferometric measurements enable the non-contact measurements; the deformation process is conditioned exclusively by the object characteristics, its embedding (fastening) and its loading.
• Holographic interferometry does not overtax the quality of the recorded object surface, therefore we can carry on measurements on the investigated object whereas it is not necessary to produce any physically similar models.
• Through the methods of holographic interferometry we can compare the shapes of already non-existing objects and analyse them.
• An advantageous property of holography is the possibility to obtain a three-dimensional display of the object, which allows to determine three components of the displacement vector from one holographic plate.
• The observed area is not disturbed by sensors or sensing heads to detect local displacements.

Interferometric methods for transparent and diffusively reflecting objects have besides their advantages, also disadvantages that are not negligible:

• The equipment for holographic interferometry is rather complex, expensive (cheaper than in classical interferometers) and limited by laboratory conditions.
• Dimensions of the investigated object are limited by the size of the objective viewing field.
• Larger deformations lead to formation of a non-distinguishable interference structure.
• The method of holographic interferometry is possible to apply mainly in laboratories – to ensure the stability of the holographic equipment (with the exception of the holographic interferometry in the impulse mode).
• The experimental equipment for the object investigation must satisfy the specifications of a holographic interferometer respecting its dimensions and construction.
• If we use a real interferometric equipment we must keep in view the deviation from the ideal interferometric system and rectify it by using corrections.
• When looking through a hologram it is not possible to tell if the phase difference is positive or negative (for example it is not possible to find out if the heat is transmitting from the side of the plate to the potential flow or vice versa). In the interpretation of a holographic interferogram it is necessary to measure the value at the edges by sensors or determine them from the experiment character. That is also the case of holographic interferometry of diffusively reflecting objects interpretation, i.e. the loading force direction is not possible to determine.
• During the interpretation of a holographic interferogram of diffusively reflecting objects larger deformations lead to formation of a non-distinguishable interference structure.