Transmission hologram

[agentas]

I got mixt a little bit.Is transmission hologram phase or amplitude hologram?Because holograms can only be phase or amplitude according recording medium.But some holograms depending on recording medium can generate phase and amplitude at the same time.Is it correct. Please help me with this a am getting lost due ti enormal amount of information i am reading.I have exam on friday about holograms and i must be ready.

[Tom B.]

Too late for exam, but a transmission hologram can be either phase or amplitude or both. Amplitude holograms record fringes as bright/dark and absorb energy in the dark parts, Phase holograms just shift the phase,ideally without loss, and so are more efficient (brighter).

[Jeffrey]

An amplitude hologram is black and white, ie. a zone plate or an unbleached silver halide hologram. The black parts modulate the light by cutting the amplitude (blocking).
If you bleach it, the black parts become clear, but of a different refractive index than the gel. The impinging illumination light, rather than absorbing, is phase-shifted as it transmits (in relation to light traveling through gel). Phase, get it. Diffraction happens at all the edges either way, to create the images, but more light is transmitted through a phase hologram, being clear, than an amplitude hologram, being dark.
Probably any hologram that has surface variation as the modulator is a phase hologram, ie. resists or embossed.