Laser Hologram Principle
A laser holographic principle
Holography and reproducing strategy of the recording process, the hologram recording process proven in Determine 1:
Figure 1 Holographic optical recording
Laser beam by the beam splitter is divided into two beams of sunshine: the light beam is the thing, ie, after the mirror M1, D1 shine on the item beam expander
And then diffuse reflection from the thing to the hologram dry plate on H; bunch is the reference mild, ie, after the mirror M2, D2 beam expander to shine immediately on the hologram dry plate H. Object and reference beams intervene in the hologram dry plate to type interference fringes. These interference fringes of the thing emitted gentle (reflected gentle) of amplitude and phase concurrently fully document all the data that is object wave.
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These interference fringes in shiny stripes and darkish stripes levels of distinction between gentle and dark, depending on the section of the two interfering beams of light depth (amplitude squared), while the density of the interference fringes in addition to where to position the darkish gentle which relies upon two mild beams to interfere the part difference (optical path difference).
When the hologram dry plate growth, the interference sample on the photosensitive medium density variations in the type of Is displayed, the identical place wavefront section density, the place the wavefront part totally different densities weakened. The different densities, ranging from mild and dark interference fringes and the object itself had nothing in widespread, but it contains all the data of the object. The essence of the recording process info with all of the objects stored in the type of interference fringes in the hologram dry plate, the equal of the modulation object wave.
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After completion of the recording course of, the object wave all the information recorded hologram dry plate to get the darkroom for developing, fixing and other therapy, the handled hologram dry plate only dense fringes, the equal of a complex grating. Then after the laser irradiation beam expander this hologram dry plate, shown in Determine 2: for the reproducing light beam diffracted by the grating, will probably be first-order diffracted mild of the original object wave wavefront re reproduced, so we holographic plate, re-see the unique utterly life like three-dimensional hologram images.
When seen from the hologram dry plate on the back (the route of the transmitted mild received) could be seen in the authentic place and has a 3-dimensional digital image of the same unique, and the hologram dry plate relative to mentioned other aspect of the masks at the obtained obtainable conjugate actual image. Saved in the copy process of the interference pattern in a light-weight diffraction methodology was taken out, which is equivalent demodulation process.
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Holographic optical reproduction
Second, the examine have an effect on the success components holographic experiments
Because the laser holography experiments on experimental demanding environmental and experimental conditions, the completion of holographic experiments want by means of a number of links, to make holographic recording success and acquiring increased high quality hologram shouldn't be easy. Since holography experiments for engineering students begin the college year, we continue to review results of laser holography experiments key success components are summarized below
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(A) The steadiness of the experimental outcomes
Because the hologram is recorded on the reference mild and the article mild of the interference fringes, that are very thin stripes within the publicity process, minimal vibration and displacement of the interference fringes will trigger blurred, or the interference fringes cannot be recorded fully down.
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(B). Arrange and alter the optical path taken impact on the experimental hologram results
(1) The reference gentle and the article light of the optical path distinction: the reference mild and the object gentle of the optical path difference shouldn't be too large and can not be higher than the coherence length of the laser, or the two cannot coherent, not interfere with the hologram dry plate obtained stripes.
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(2) the angle between the reference light and the item gentle effects: If the hologram dry plate spacing between interference fringes is d, the sunshine supply wavelength and the reference mild and the object d is the angle between the light ..
It may be seen .. angle the better the interference fringes recorded more thin, dry plate of resolution necessities for the higher angle .. not so much. The angle .. re phenomenon hologram commentary window (angle) influential angle, may be in a wide range images from different angles, quite the opposite, the commentary window is small, so the angle cannot be .. too small.
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(3) the reference gentle and the thing light of the sunshine intensity ratio: hologram object gentle and the reference gentle is a two-beam interferometer. .. one hundred ninety .. For general two-beam interferometer, if I1 = I2, the interference fringes will be obtained maximum distinction, the minimal strength of zero fringe with phase three .. dry plate publicity characteristics of the utmost intensity of 4I, which is usually linear receiving member is suitable. While the hologram recording medium, the publicity amount and the amplitude transmittance attribute curve is nonlinear, odd on each ends of the curve modifications (Figure three), leading to larger order diffracted mild, the diffraction effectivity is reduced. Then again, when the thing reference light depth than light, markings more significant, leading to relatively large halo of light across the zero-order diffracted gentle, decreasing the flux imaging,
Leading to reduced efficiency.
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(C) exposing and growing the experimental outcomes of (1) publicity time results: If the publicity time is simply too brief, not even on the floor shallow stripe, the diffraction grating can't type a fancy, after all, can not be reproduced image. If the publicity time is too lengthy, backplane.
Could also be too dark, the sunshine transmittance decreases. In addition, the longer the publicity time, the tougher to take care of system stability, a sudden noise exposure time sound and vibration will shoot failed.
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(2) The growing time of: the extent of the event is suitable drastically affect the quality of the hologram. If the event time is just too long, the hologram dry plate black, gentle transmittance decreased, can not be reproduced image; creating time is too brief, there are not any streaks and the dry board, can't form a complex diffraction grating, or perhaps a piece of transparent glass, is unable to reproduce the image. These components affect the hologram can't be ignored, we should totally think about the excellent, balanced, we've got all of the above factors are analyzed, discussed later, summed up the following to enhance the success charge of laser holography experiments some particular practices.
Third, enhance the success rate of laser holography experiments particular practices
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(A) to make sure the stability of the imaging system
For we use the laser wavelength is 632 .. eight nm of H J-Ⅱ type helium-neon laser, the publicity course of, we must be sure that the motion of the imaging system shall not exceed the interference fringe spacing of 1/4, our laboratory using GSZ - Ⅱ sort optical experimental platform, holographic optics bench are all firmly with magnetic suction plate on the table. Every optical aspect holding steady, cement will probably be illuminated objects on the stage or clamped on the shelf, leaving the publicity timer holographic items placed. As air circulation by the light path.
Acoustic interference and ambient temperature changes will trigger modifications in air density, subsequently, able to shoot away before holographic table, maintain quiet, nonetheless greater than 2 m in re-start the exposure timer, and exposure period can't converse, stroll and make a sound ensure environmental stability, publicity and then sit around and wait 20 s or more, in an effort to remove the dry plate, with black wrapped in paper.
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(2) To organize and regulate the optical path of the particular practices
(1) placed within the optical path: optical path shown in Determine 1 to place the elements considerably akin to the respective position, adjusting the varied parts and the desk so that the beams are parallel and coincident with the center of the element, (the start of a beam expander not add mirror).
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(2) Measurement of optical path: Measurement object beam and the reference optical path from the start beamsplitter along the forward course of the beam quantity hologram dry plate to date, in accordance with press row aplanatic optical path as well, no larger than the optical path distinction 1 cm.
(3) the angle choice: Primarily based on the above analysis, this was chosen in the mild of the angle between the reference gentle and the thing 20 .. 30 .. take appropriate.
(4) modify the sunshine depth ratio: From the above we can see that to achieve good outcomes, the reference gentle to be enhanced, to avoid non-linear area to cut back the speckle effect. But while doing issues with a bouquet of bright gentle illumination onto the object substance absorbed by the body and then reflected to the dry plate light was a lot weaker than the reference beam, and for our power is barely 5mW lasers, the reference mild and object mild The light depth ratio is simply too large, it is going to cause poor distinction, because the clear. So it should make issues gentle enhancement. Experimental research have shown that many times: if the topic is male porcelain
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Aberdeen, ought to hologram dry plate close proximity (3 ~ 5 cm), if the cash with taking pictures distance holographic plate number (as much as 10 cm). Into the beam expander, modify the placement of the object in order that the item of the strongest a part of the diffusely reflected mild falls evenly holographic plate, the reference light ought to have uniform illumination and canopy all the hologram dry plate, two gentle intensity ratio of three .. 1 ~ 5 .. 1 is more appropriate. (Three) and reproducibility observed hologram recording
(1) on film camera: Flip off any mild, in dark circumstances, learn to evaluate the whole hologram dry plate membrane surface methodology, which uses two fingers concurrently touching both sides of the hologram dry plate, representing one aspect of the membrane surface astringent, easy one side of the glass surface. Take away the black and white, the hologram dry plate emulsion aspect facing the topic fastened on dry plate rack.
(2) Set the publicity time: the length of time and lightweight publicity related to an influence, for bigger power supply, the exposure time may be shorter, if the light supply power is small, the publicity time could also be longer. Basic literature requires an publicity time of 3 to four
m in, the truth is, difficult to ensure a long exposure time throughout capturing absolutely quiet environment, for us to make use of the ability of 5mW H J-Ⅱ sort helium-neon laser and photographic movie plant in Tianjin Ⅰ type hologram dry plate is publicity time choice in about 30 s on it, but it surely also will depend on the degree reflective topic, for extremely reflective objects, the exposure time could be shortened,
On the contrary, be lengthened.
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(2) Setting Developing time: Select the publicity time needs to be the event, the creating resolution focus and temperature conditions to be considered. Within the case of normal exposure, a developer D-19, its temperature at 20 .. 0 .. 5 .., the developing time is usually ten seconds could be, but at increased temperatures and the new feature of syrup , it may be a number of seconds to dry plate will probably be darkened, the creating time should be because the case may be, (but no more than 3m in). Dry plate needs to be placed on growing resolution and gently stir the liquid, just a few seconds after the dry plate against dark
Inexperienced observed, when you may see the blackish rinse, rinse into the fixer 2 ~ 4m in, the fusing process must also be damaged agitation fixer, washed into the water after 5 ~ 15 m in, and then drying . Notice: Configuring good drugs must be placed in brown glass bottles stored in the dark, the student might be one form of operation to keep away from another syrup into syrup. Case of creating or overexposed, might be positioned in bleach answer thinning therapy, thinning treatment could be carried out underneath white light, kept out of commentary, thinning degree in moderation, not an excessive amount of, otherwise the hologram disappears.
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(3) the replica observation: the processed hologram on the optical path of the commentary in Figure 2 hologram reproducing a hologram may also be irradiated with mild in order to increase its brightness. Through these research, the guidance of lecturers, students to do that experiment from the past success rate increased to twenty%
About 90%, laser holography experiments engineering college students has turn into one of the vital fascinating experiments to enhance the engineering college students on university property affordable interest in experimental class
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