GB2215078A

GB2215078A - Apparatus for producing holograms

Info

Publication number: GB2215078A
Application number: GB8803022A
Authority: GB
Inventors: R Arthur Maitland
Original assignee: English Electric Valve Co Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1988-02-10
Filing date: 1988-02-10
Publication date: 1989-09-13
Anticipated expiration: 2008-02-10
Also published as: GB8803022D0; GB2215078B

Abstract

A hologram of a transparent object 3 is recorded on a moving film 4 using a high-powered, pulsed laser 1. The film 4 may move at up to 2 metres per second and still enable good resolution to be achieved as the copper vapour laser 1 may be operated for short pulses of approximately 30 nanoseconds. Instead of separate object and reference beams (2, 5), they may travel parallel to each other to achieve equal path length. <IMAGE>

Description

APPARATUS FOR PRODUCING HOLOGRAMS This invention relates to apparatus for producing holograms and more particularly, but not exclusively, to apparatus which is suitable for manufacturing a large number of identical holograms.

Hitherto, holographic replication has tended to be a relatively slow process. A hologram of an object is recorded by illuminating the object with the so-called "object beam" of radiation and producing interference between the diffracted/reflected radiation from the object and radiation of a so-called "reference beam" which has not been incident on the object and which is coherent with the object beam radiation. The resulting interference pattern is recorded on a photographic emulsion to produce a hologram. As high resolution is necessary to enable an interference pattern to be recorded sufficiently well to obtain a good hologram, the film is kept stationary with respect to the object and reference beams. To achieve this, it is common practice to use apparatus which is vibration-free.

The present invention seeks to provide apparatus for producing holograms which is particularly suitable for holographic replication at high rates.

According to the invention, there is provided apparatus for producing holograms comprising means arranged to illuminate film with radiation to produce a hologram, the film being arranged to move during exposure with respect to the incident radiation which is substantially fixed in direction. The inventor has realised that, contrary to previous practices, it is possible to obtain acceptably good holograms even when the film onto which interference patterns are recorded is moved during the exposure period. This avoids the need for vibration-free equipment and furthermore, enables greater numbers of high quality holograms to be produced in a given time. Advantageously, therefore, a plurality of holograms are arranged to be produced in succession at different parts of the film.Thus, as the film is transported through the region to which the radiation is directed, one hologram is formed and then, as its motion continues, another hologram is formed adjacent to the first. This is obviously particularly advantageous where the holograms are identical, although a series of holograms of a moving object might be recorded, for example. By using a high power pulsed radiation source, such as a copper vapour laser which operates at 510.6 nm or 578.2 nm wavelength, the exposure time may be kept short such that movement of the film during the exposure period is not appreciable when compared with the line spacing of the hologram. A copper vapour laser is able to deliver a radiation energy at the film of about 1 mJcm 2 and this is sufficiently high to enable an exposure time of only 30 ns to give a good image.It is preferred that the film moves at a constant speed above 0.1 metres per second.It is believed that acceptable results can be obtained for film moving at relatively high speeds of 2 ms or more.

It should be noted that the term "film" in this specification is intended to include all types of media which may be used to record an interference pattern.

Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings in which: Figure 1 schematically illustrates an apparatus in accordance with the invention; and Figure 2 is a schematic diagram of another apparatus in accordance with the invention.

With reference to Figure 1, apparatus for producing holograms include a copper vapour laser 1 which is arranged to illuminate a transparent object 2 of which a hologram is to be made. The diffracted radiation from the object 2 forms the object beam 3 which is arranged to be incident on a film 4. The reference beam 5 from the laser 1 is also directed onto the film 4. The path length of the object beam 3 is made the same as that of the reference beam 5 by including folding mirrors. The film 4 is 70 mm roll film of Agfa type 8E56HD and is arranged to move at 2 metres per second in the direction shown by the arrow. By illuminating it with the coherent radiation from the laser 1 and producing an interference pattern between the diffracted and undiffracted beams 3 and 5 on the film 4, a hologram is produced.

In this apparatus1 the size of the hologram on the film 4 is 2 cms x 2 cms. Good resolution is achieved if the hologram has 2,500 lines per mm, that is, if the line spacing is 400 nm. The copper vapour laser is pulsed and has a power output of about 5 mJ per pulse, the duration of each laser pulse being approximately 30 ns. Thus about 1 mJ cm 2 of the radiation is incident on the film 4.

For a film transport speed of 2 metres per second, the distance travelled by the film 4 during the 30 ns pulse is 60 nm. This is a movement of only 0.15 of one line spacing movement per exposure. Thus, even at these high speeds, very little degradation of the holographic quality occurs. It is possible to achieve this because of the high power levels available from the copper vapour laser in a very short pulse.

After exposure of one part of the film 4 during the laser pulse, the film 4 is permitted to move through a sufficient distance to prevent overlap and the next laser pulse is transmitted to produce the next hologram.

With reference to Figure 2, in another embodiment of the invention, the reference beam 6 is arranged to travel in a parallel direction to the object beam 7 to achieve equal path length.

Claims

1. Apparatus for producing holograms comprising: means arranged to illuminate a moving film with radiation to produce a hologram, the film being arranged to move during exposure with respect to the incident radiation which is substantially fixed in direction.

2. Apparatus as claimed in claim 1 wherein a plurality of holograms are arranged to be produced in succession at different parts of the film.

3. Apparatus as claimed in claim 2 wherein the holograms are identical.

4. Apparatus as claimed in any preceding claim wherein the film moves at a substantially constant speed above 0.1 metre per second.

5. Apparatus as claimed in any preceding claim wherein the resolution of a hologram produced by the apparatus is substantially 2,500 lines per mm.

6. Apparatus as claimed in any preceding claim wherein the radiation energy at the film is approximately 1 mJ per square cm.

7. Apparatus as claimed in any preceding claim wherein the radiation is derived from a pulsed laser having a pulse length of approximately 30 ns.

8. Apparatus as claimed in any preceding claim wherein the radiation is derived from a copper vapour laser.

9. Apparatus substantially as illustrated in and described with reference to Figure 1 or 2 of the accompanying drawings.