WO1996032662A2

WO1996032662A2 - Apparatus and method for scanning a laser beam

Info

Publication number: WO1996032662A2
Application number: PCT/GB1996/000893
Authority: WO
Inventors: Geoffrey Philip Naylor
Original assignee: Imperial Chemical Industries Plc
Priority date: 1995-04-11
Filing date: 1996-04-11
Publication date: 1996-10-17
Also published as: GB9507485D0; WO1996032662A3

Abstract

The invention provides an apparatus and a method for scanning a laser beam (2), such as from a multi-mode laser diode (1), which is particularly useful in dye thermal transfer printing such as printing 35mm slides and credit or security cards. Light from a multi-mode laser diode (1) is collimated by optics (3) and deflected and focused by optical means (4) mounted on a carriage (5) which reciprocates along the path of the collimated beam to scan the beam in a line parallel to the direction of movement of the carriage (5). A cam (13; 22), crank (26) or drive belt (33) may drive the carriage (5). Alternatively, the optical means (4) may be mounted directly to a belt drive (42).

Description

Apparatus and Method for Scanning a Laser Beam

The present invention relates to apparatus and a method for scanning a laser beam, and particularly, but not exclusively, to a laser beam scanning system for use in dye transfer printing, including diffusion, sublimation and melt transfer. In dye diffusion thermal transfer printing, a dye donor element and a dye receiving element, such as a dye sheet and a receiver sheet, are held in intimate contact with one another. Selected regions of the dye sheet are heated by a modulated scanning laser beam. This causes dye from the selected regions to diffuse into the receiver sheet to form a corresponding image therein.

Typically, scanning is achieved by reflecting the laser beam from a galvanometer mirror, i.e. a planar mirror mounted on a wire for rotation, or from a rotating multifaceted mirror. The laser beam is scanned across the dye sheet as the mirror rotates.

In such a system, the focus of the laser beam is scanned in an arc.

Often a single mode laser diode is used, as it may be focused to a diffraction-limited spot, and enables a lens of long focal length to be used, whilst retaining a small spot size. This allows the distance from the scanning mirror to the dye sheet to be large, and produces a scanning arc of low curvature and large depth of field, thereby enabling the beam to remain substantially focused at a desired constant depth within the dye sheet (where laser light absorbing material is located) even though the scanning path is slightly curved. Single mode laser diodes which achieve the necessary high powers for high speed printing are, however, expensive.

Multi ode laser diodes provide a less expensive high power source, but emit light from a stripe-shaped output port of long length. Therefore, in order to focus the beam to a small scanning spot size for, for example, high resolution printing, the optics need to be of short focal length. This causes complications with the above scanning systems, as the working distance between parts is smaller, the curvature of the scanning arc larger and the depth of field shorter. Accordingly, in order to ensure that the beam retains its focus at a desired constant depth within the dye sheet throughout the scan, the dye and the receiver sheets need to be arranged to lie in an arcuate plane corresponding to the arc traced out by the beam focus. Alternatively compensating optics, such as an fθ lens, have to be used to correct the beam focus so that it is scanned in a flat plane. Such systems are somewhat complex and costly.

The present invention aims to provide an inexpensive apparatus and method for scanning a laser beam, which is able to utilize a poorer quality/less expensive laser source than a single mode laser diode, such as a multimode laser diode.

Viewed from a first aspect, the invention provides laser scanning apparatus comprising a laser source emitting light from a stripe-shaped port, means for producing a coUimated laser beam from the light from the port, and means repeatably movable along the path of the coUimated beam from a first position to a second position for deflecting and focusing the coUimated beam to scan in a line parallel to the direction of movement of the deflecting and focusing means.

Viewed from a second aspect, the present invention provides laser scanning apparatus comprising a laser source emitting light from a stripe-shaped port, means repeatably movable in a straight line between a first position and a second position for deflecting and focusing a coUimated laser beam from the laser source which is directed along the straight line such that the beam focus is scanned in a flat plane parallel to the direction of motion of the deflecting and focusing means.

The present invention enables the focal length of the deflecting and focusing means to be relatively short, as nothing, such as a rotating mirror, need be between this means and the object to be scanned. Therefore, the invention is able to use a poorer quality beam than that used in the simple galvanometer mirror systems of the prior art, whilst retaining a small spot size, for example a beam from a ultimode laser diode. By using a coUimated beam which is deflected and focused by means moving along the beam, the beam focus is scanned in a straight line in a flat plane. This enables an element to be scanned to be simply arranged to lie along this flat scan line, without the need for complex mounting of the element in an arc or for compensating optics.

The invention thus provides an inexpensive and simple scanning apparatus which may be advantageously used in, for example, high speed high resolution dye thermal transfer printing.

In a preferred embodiment of the invention, the deflecting and focusing means reciprocates back and forth, preferably scanning the beam in both directions. Thus, viewed from a further aspect, the present invention provides laser scanning apparatus comprising a laser source emitting light from a stripe-shaped port, means for producing a coUimated laser beam from the light from the port, and means reciprocable back and forth along the path of the coUimated beam for deflecting and focusing the coUimated beam to scan in a line parallel to the axis of reciprocation.

Also, viewed from a still further aspect, the present invention provides laser scanning apparatus comprising a laser source emitting light from a stripe- shaped port, means reciprocable back and forth in a straight line for deflecting and focusing a coUimated laser beam from the laser source which is directed along the axis of reciprocation such that the beam focus is scanned in a flat plane parallel to the axis of reciprocation. Preferably, the deflecting and focusing means deflects the coUimated beam through substantially 90°, so that the focused beam falls on the scan line normal thereto. The beam focus then lies fully in the plane of the scan. The deflecting and focusing means may include a mirror, prism, beam splitter, diffraction grating or any other suitable means for deflecting the beam, and may also include an objective focusing lens.

The deflecting and focusing means may be mounted upon any suitable carrier, such as a slide or a table, which may for example be constrained to move in a straight line by any suitable means, such as along runners or guide rails.

The deflecting and focusing means may be driven by any suitable means. In a preferred embodiment, a cam means is used, which may drive a carrier on which the deflecting and focusing means are mounted via a cam follower.

The cam means are preferably shaped so as to provide motion at a constant velocity, and may comprise a rotating heart-shaped cam. Scanning at a constant velocity is advantageous in, for example, dye transfer print systems, in which the amount of dye transferred from any one pixel region of a dye sheet depends upon the amount of energy supplied to that pixel region, and in which a pixel region across which the laser beam is scanned slowly will generally receive more energy than a pixel region across which the laser beam is scanned more quickly. In such systems, a constant scan speed ensures that under the same modulation (for example to produce a set print tone) the beam will transfer the same amount of dye at each point along the scan line.

To ensure that the exact profile of the cam is followed, the carrier may be positively urged against the cam by, for example, being sprung-loaded in compression and/or tension to one or more fixed points on, for example, a base plate of the scanning apparatus on which the carrier may run and the cam may be mounted. In an alternative embodiment, the cam follower may be constrained by a box cam.

In one embodiment, a cam track is utilised. For example, a cylindrical cam may be used with a track on its surface. Such a cam may be configured as a rotating drum having a curved channel running about its surface, with the cam follower extending into the channel perpendicular to the drum's rotational axis. Advantages of a cylindrical cam are that it is quite compact and simple to construct.

The cam track may be configured so that the follower moves in one direction when the cam rotates clockwise, and in the other direction when the cam rotates anticlockwise, in which case the motor turning the cam must be stopped and reversed to provide reciprocal scanning. Preferably, however, the cam track is configured so that the cam follower reciprocates at least once back and forth per revolution of the cam, as this allows the motor driving the cam to run continually without stopping or reversing, thus producing a quicker and more accurate scan.

Instead of a cam system, the deflecting and focusing means may be driven by a crank system, for example, a crank wheel connected to a carrier via a connecting rod. Such a system is able to move a relatively high mass at high reciprocating speeds.

A point to note with the crank system is that the motion may be of a harmonic nature, i.e. may be slow to begin with, speed up towards the centre of the scan, and then slow down towards the end of the scan. This may cause problems in, for example, dye transfer printing, because of the above-mentioned problem of providing a uniform amount of heat (under identical modulation conditions) to each pixel area of the dye sheet along the whole of the scan line. Accordingly, it is preferred that means are provided to adjust the power or modulation of the laser beam to compensate for the change in speed of the reciprocating means and to ensure that the scanned beam is able to supply a uniform amount of energy along the whole of the scan line. This would be in addition to any other modulation required to produce, for example, a desired print tone. This compensation may also be used in any other system, such as a cam system in which the cam shape provides movement at non-constant speed.

A further alternative means of driving the deflecting and focusing means is to use a drive belt. In one embodiment, the deflecting and focusing means may be mounted on a carrier, such as a linear slide, and the belt may drive the carrier back and forth along the slide. The belt may be connected to the carrier in any suitable manner. The belt need not be continuous, and may be mounted between a pair of take-up rollers, with first one roller being driven to take-up the belt, and then the other, to provide reciprocating motion. Preferably, however, a continuous belt mounted between a pair of rollers is used. In this embodiment, a pin connected to the belt may be mounted in a slot of the carrier in order to pull the carrier along the slide, with the slot extending generally perpendicularly to the direction of motion and with the pin initially at one end of the slot. The pin and slot arrangement allows the belt to run continuously about the rollers, whilst the carrier reciprocates back and forth along the slide. When the pin reaches one of the rollers, it continues to run about the roller with the belt. At this time, the carrier remains stationary, and the pin runs along the length of the slot in the carrier to the slot's opposite end as it passes around the roller. When the pin has passed around the roller and continues again towards the other roller, it drives the carrier along the slide from the other end of the slot.

The belt provides a compact and simple drive means, which may provide linear scanning. A continuous belt allows the motor to turn continuously, and is able to provide a smooth turn round at the end of each scan line.

Preferably, means, such as optical detecting means, are provided near the start of the scan line for sensing when the slide is in position at the start of a scan, and scanning or printing is triggered when this occurs, perhaps after a preset delay time. This removes the need to know the absolute position of the driving motor. Scanning is preferably carried out whilst the motor is under constant load, and the start of the scan is preferably set at a position when it is known that the motor load will be constant, such as after the pin has travelled a short distance past a roller in the above embodiment.

In an alternative belt embodiment, the deflecting and focusing means may be mounted on the belt itself, in which case means are preferably provided to ensure that the deflecting and focusing means are constrained to move accurately along the correct path at a constant distance from the scan line. The above embodiments are mainly for use in reciprocating systems, in which a single deflecting and focusing means is continuously reciprocated back and forth along the scan line. In an alternative embodiment, however, a plurality of deflecting and focusing means are used, such that when one deflecting and focusing means reaches the end of a scan line, another has moved into position at the start of the scan line to take over scanning.

Such a system may advantageously be provided using a driving belt. This embodiment has the advantage that the motor driving the belt may continually rotate in the same direction with a near constant load applied to it. Also, as there is no delay time whilst the deflecting and focusing means changes direction, any delay time between scan lines can be kept small. Further, when printing, lines are always printed to in the same direction. This allows better registration to be achieved, and allows image data to be supplied in the same direction, as is usual with prior print systems. The system is compact and simple and allows for linear scanning.

Where the deflecting and focusing means are mounted on the belt, means may be provided to ensure that the means moves accurately in a straight line over the scan area. This may be achieved by providing bearing surfaces above and/or below the drive belt along which bearings connected with the deflecting and focusing means may run. For example, the deflecting and focusing means may be mounted on an axle attached to the belt and having bearings on either end. The bearings and bearing surfaces may be of V section for greater positional accuracy. A sensor may be used to sense the passing of each axle and to start scanning or printing as each axle is sensed. Means may be provided to determine which axle is passing the sensor, so that the sensor may vary the delay time before printing to take account of any differences between the axle structures, thereby ensuring pixel alignment from line to line.

The beam may be modulated by any suitable means mounted either on or upstream of the carrier, or by modulating the laser source itself. The element to be scanned may be mounted in any suitable manner. For example, in dye transfer printing, a dye sheet may be mounted above a receiver sheet about a platen roller. In a preferred system, the element to be scanned is mounted on a flat support bed. This further eases material handling, and compliments the flat scanning movement of the deflecting and focusing means. The flat bed is particularly advantageous in the printing of 35mm slides and credit or security cards. which may be somewhat rigid and need to lie flat.

It is further preferred that the support bed and the scanning apparatus be relatively movable in a direction normal to the scan line, in order to provide 2D scanning - for example, to print to the whole of a receiver sheet. The support bed may move in the normal direction to provide the relative motion, or the whole beam scanning apparatus, for example the optical means, the carrier and the cam, crank or belt means, may be supported on a base which is movable normal to the scan direction.

The support bed is preferably transparent to the laser light, and may, for example, be made of glass, at least over the scan area. This allows the element to be scanned to be mounted on the opposite side of the support bed to the scanning apparatus, and, in one advantageous arrangement, the beam scanning means is mounted beneath a flat support bed on which an element to be scanned can be easily placed and held. A further advantage, in printing slides (or other transparent receiving medium) , of using a support bed which is also transparent is that the slide can be mounted adjacent the support bed, and the laser beam may pass through both bed and slide to be absorbed at the surface of the dye sheet contacting the slide. This is more efficient than passing the beam through the dye sheet from the other side and heating its whole depth.

Overall, the present invention provides apparatus in which the material handling is simplified and in which no focusing correction is required. The apparatus is able to minimise the use of optics, may use component parts of low cost, and of particular advantage is able to use multimode laser diodes in high speed high resolution printing. The invention is especially suitable for use in dye transfer printing and in the production of 35 mm slides and other high resolution printing situations. It is also useful where printing needs to be carried out on a flat bed, such as in the printing of credit and security cards and 35 mm slides.

The invention extends to a method of scanning using any of the above-mentioned apparatus, and especially to a method of dye thermal transfer printing using such apparatus.

Although emphasis has been given to the use of a poor quality multimode laser diode and to dye thermal transfer printing, the above scanning apparatus may advantageously be used in any light scanning system not limited to lasers or printing.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 shows schematically a print system incorporating scanning apparatus according to the present invention;

Fig. 2 shows in plan view cam scanning apparatus according to a first embodiment of the invention,- Fig. 3 shows in elevation cam scanning apparatus according to a second embodiment of the invention,-

Fig. 4 shows cam scanning apparatus according to a third embodiment of the invention,-

Figs. 5a and 5b show crank scanning apparatus in plan and elevation respectively;

Fig. 6 shows a belt driven system,- Fig. 7 shows an alternative belt driven system; and

Fig. 8 shows the mounting of optical means of Fig. 7 with respect to the drive belt.

Referring to Figure 1, a multimode laser diode 1 produces a beam 2 which is coUimated by a suitable lens system 3. The coUimated beam 2 is deflected and focused by optical means 4 mounted upon a reciprocating carriage 5, so that the deflected beam 2' is focused to a desired depth within a dye sheet 6 mounted above a receiver sheet 7 about a platen roller 8.

Reciprocal movement of the carriage 5 back and forth in the direction of the arrows 9, along the path of the coUimated beam 2, causes the focused beam 2' to scan across the dye sheet 6.

As the beam 2' scans across the dye sheet 6, it is modulated by modulation of the laser diode 1, so that selected pixel regions in the dye sheet 6 along the scan line are heated to a desired degree. Dye transfers from these heated regions into the receiver sheet 7, and, by rotating the platen roller 8 via an electric motor 10, a desired print image may be built up in the receiver sheet 1 , line-by-line.

The distance between the optical means 4 and the dye sheet 6 may be kept short, and this allows the optical means 4 to have a short focal length to thereby allow the beam from the multimode laser diode 1 to be focused to a small spot size.

As the distance from the optical means 4 to the dye sheet 6 remains constant, the focusing elements in the optical means 4 may be of a constant focus, with the beam 2 ' still remaining focused at the desired depth within the dye sheet 6 throughout the scan, without the need for corrective optics.

Thus, high resolution printing may be achieved using inexpensive and simple componentry. Referring to Figure 2, the details of one embodiment of a scanning system usable in Fig. 1 are shown. The optical means 4 comprises a 45° mirror 11 and a focusing lens 12. These are mounted upon a carriage 5 which is constrained to move in a straight line by suitable guide means (not shown) and is acted on by a heart-shaped rotating cam 13 via a cam follower 14 mounted on one end of the carriage 5. To ensure that the carriage 5 accurately follows the profile of the rotating cam 13, it is urged towards the cam 13 by a spring 15 mounted in compression between the carriage 5 and a fixing plate 16 extending up from a base 17 upon which the carriage 5 and cam 13 are mounted. Cam 13 is connected to the shaft 18 of a constant speed motor (not shown) mounted therebelow also upon base 17. The shape of the cam 13 ensures that the carriage 5 reciprocates back and forth at a constant speed.

In use, a coUimated laser beam, incident from the right of Figure 2 , is reflected through 90° by the 45° mirror 11 and is focused by lens 12 to a spot on a scan line (e.g. at a desired depth within a dye sheet where a laser light absorber is located) lying parallel to the path of the incident coUimated beam. One complete rotation of cam 13 causes the beam to scan twice across the scan line, once in each direction.

Figure 3 shows a side view of a further cam scanning system, similar to that of Fig. 2, but with carriage 5 held against the cam 13 by a tensioned spring 19, as opposed to the compressed spring 15. In this example, the laser beam is incident from the left.

As can be seen, carriage 5 is slidably mounted upon a support table 20 fixed to the base 17, and the cam 13 is driven by a constant speed motor 21. Fig. 4 shows a further cam scanning system, in which a cylindrical cam 22 is used. Carriage 5 is mounted upon a slide 23, and has a cam follower 24 connected to it which extends into a track 25 formed on the surface of the cylindrical cam 22. As the cylindrical cam 22 is rotated by a constant speed motor 21, the edges of the track 25 urge the cam follower 24 into left and right movement.

The track 25 is configured so that the cam follower 24 will reciprocate back and forth once on one complete rotation of the cylindrical cam 22, thus causing the beam to scan twice across the scan line, once in each direction. The track 25 is also configured so that this movement is linear, i.e. at a constant velocity, during the printing phase. It would of course be possible to configure the track so that carriage 5 moves back and forth more than once per rotation, or so that carriage 5 only moves in one direction per cam rotation. In this latter case, the motor 21 would need to reverse the drive direction at the end of each scan line.

Figs. 5a and 5b show a crank driven scanning system. The carriage 5 is driven along a slide 23 by a crank wheel or disc 26 via a crank arm 27.

In a specific example of this embodiment put into practice, a standard ICI dye sheet 28 and transparent receiver sheet 29 were mounted on a 2 mm thick glass support bed 30. A 500 mm x 1 mm multimode laser beam 2 of 0.5W emitted by a Sony SDL-2352-H1 diode 1 was coUimated to form a 3 mm x 4 mm beam 2. This beam was directed at the mirror 11 along the axis of the slide 23, via an intermediate mirror 44, and the reflected beam 2 ' was focused just inside the dye sheet 28 by an asymmetric biconvex lens 12 of focal length 10 mm. The light energy was converted to heat by an infra-red absorber within the dye sheet. The mirror 11 and lens 12 were reciprocated back and forth along the slide 23 a distance of 46 mm by the crank arm 27 attached to the disk revolving at 2100 rpm. The laser was modulated to switch on during the central 35 mm of the 46 mm traversed by the lens. The slide and crank were mounted on a linear table 32 that was able to reciprocate and move at 90 to the slide 23 in the direction of the arrows 31, a distance of 25 mm to produce a 2D scan.

Mirror 44 was also movable with the slide and crank to ensure that the laser beam 2 remained aligned with mirror 11.

When the laser beam 2 remained continuously on during the central 35 mm of the slide's travel, a solid block of print was produced. The optical density of this block in transmission was 1.41 at the edge of the print and 0.81 at the centre along the slide scan direction measured using a Sakura PDA65 densitometer. This difference in dye density was due to the harmonic motion imparted to the carriage 5 by the crank, i.e. the carriage 5 moves more quickly nearer the centre of the scan, and more slowly at the edges, so that the edges of the dye sheet are heated for longer and thus transmit more dye. This is correctable to produce a uniform transfer of dye by modulating the laser beam power so that it is less at the start and end of the scan. For example, the beam's maximum power may be modulated in a harmonic fashion in correspondence with the carriage's position. This is in addition to any other modulation required to produce, for example, a set print tone by varying the amount of dye transferred, in, for example, continuous tone printing.

Fig. 6 shows a drive system using a belt 33. The 45 mirror 11 and focusing lens 12 are again mounted upon a carriage 5 which reciprocates back and forth along a slide 23. In this embodiment, however, the carriage 5 is driven by the belt 33 via a pin 34. Pin 34 is mounted on the belt, and extends into a slot 35 running across the width of the carriage 5 perpendicular to the carriage's direction of motion. Belt 33 is a continuous belt which extends about rollers 36 and 37. One of these rollers is driven clockwise by a motor (not shown) , so that pin 34 engages a side of the slot and pulls the carriage 5 along the slide 23 towards the right roller 37. At the end of a run to the right, the pin 34 passes around the roller 37. As it does this, it stops pulling the carriage 5, and instead runs along the length of the slot 35 to the other end of the slot. The pin 34 then moves with the belt in the other direction back to the left roller 36, pulling the carriage 5 with it from the bottom of the slot 35. Sensors 38 and 39, such as optical sensors, determine when the carriage 5 is in the correct position to start printing, and the laser beam 2 is activated accordingly. In order to produce a linear scan, i.e. at constant speed, the beam 2 is not activated until the carriage 5 is in a position in which the motor driving the rollers will be on constant load.

Figs. 7 and 8 show a slightly different arrangement to the systems of Figs. 1-6. Instead of using a single optical means, e.g. mirror 11 and lens 12, which reciprocates back and forth along the scan line, this embodiment uses a plurality of optical means, which merely scan in one direction. In the embodiment shown, three optical means 4a-4c are used. When one of the optical means 4a has completed a scan line, the next optical means 4b is automatically brought into position at the start of the scan line to do the next scan. Each optical means 4a-4c is mounted on one end of an axle 40 having bearings 41 at each end, which run along the edges of V-shaped bearing surfaces 42 to keep the optical means 4a-4c in alignment and at constant focal distance from, for example, the dye sheet of a printing system. The axle 40 is connected to a drive belt 33 by a fixing 43, so that the belt 33, driven by rollers 36 and 37, drives the optical means 4a-4c around the bearing surfaces 42. A sensor 43, such as an optical sensor, is mounted adjacent one of the rollers, and as it detects an axle 40, printing is initiated by activating the laser beam 2. As the position of each optical means in relation to its axle may be slightly different, the sensor or a further sensor may also determine which particular optical means is passing. This then allows a different compensating delay to the start of printing to be used for each axle, to thus ensure pixel alignment from line to line.

Various modifications of the above embodiments are of course possible, and although the systems have been described with reference to multimode laser diodes and also to dye thermal transfer printing, where they provide particular and important advantages, they may also be used advantageously to scan any light beam for any use.

Claims

1. Laser scanning apparatus comprising a laser source emitting light from a stripe-shaped port, means for producing a coUimated laser beam from the light from the port, and means repeatably movable along the path of the coUimated beam from a first position to a second position for deflecting and focusing the coUimated beam to scan in a line parallel to the direction of movement of the deflecting and focusing means.

2. Laser scanning apparatus according to claim 1, wherein said deflecting and focusing means reciprocates back and forth along the path of the beam.

3. Laser scanning apparatus according to claim 1 or 2, wherein the deflecting and focusing means is driven by cam means.

4. Laser scanning apparatus according to claim 3, wherein the cam means includes a cam track.

5. Laser scanning apparatus according to claim 4, wherein the cam means comprises a cylindrical cam having a cam track on its surface.

6. Laser scanning apparatus according to claim 4 or 5, wherein the cam track is configured so that a cam follower which follows the track moves in one direction when the cam rotates clockwise, and in an opposite direction when the cam rotates anticlockwise.

7. Laser scanning apparatus according to claim 4 or 5, wherein the cam track is configured so that a cam follower which follows the track reciprocates at least once back and forth per revolution of the cam.

8. Laser scanning apparatus according to claim 1 or 2, wherein the deflecting and focusing means is driven by crank means.

9. Laser scanning apparatus according to claim 1 or 2, wherein the deflecting and focusing means is driven by a drive belt.

10. Laser scanning apparatus according to claim 9, wherein the drive belt is mounted between a pair of take-up rollers.

11. Laser scanning apparatus according to claim 9, wherein the drive belt comprises a continuous belt mounted between a pair of rollers.

12. Laser scanning apparatus according to claim 11, wherein a pin connected to the drive belt is mounted in a slot of a carrier on which the deflecting and focusing means are mounted in order to pull the carrier along a guide means, with the slot extending generally perpendicularly to the direction of motion of the carrier.

13. Laser scanning apparatus according to claim 9, 10 or 11, wherein the deflecting and focusing means is mounted on the drive belt.

14. Laser scanning apparatus according to claim 13, wherein bearing surfaces are provided above and/or below the drive belt along which bearings connected with the deflecting and focusing means run.

15. Laser scanning apparatus according to claim 14, wherein the deflecting and focusing means is mounted on an axle which is attached to the drive belt and has bearings at either end.

16. Laser scanning apparatus according to any preceding claim, including a plurality of deflecting and focusing means, the plurality of deflecting and focusing means being arranged such that when one deflecting and focusing means reaches the second position corresponding to the end of the scan line, another is moved into the first position corresponding to the start of the scan line.

17. Laser scanning apparatus according to any preceding claim, wherein the laser source comprises a multimode laser diode.

18. A method of scanning a laser beam emitted by a stripe-shaped laser source, wherein the beam is coUimated and then deflected and focused by optical means which are moved along the path of the beam to scan the beam in a line parallel to the direction of movement of the optical means.

19. A method of laser dye thermal transfer printing in which transfer of dye from a donor to a receiver is effected by a scanning laser beam from a multi-mode laser diode, an output beam from the laser diode being coUimated and then deflected and focused by optical means which move along the path of the output beam to scan the beam across the donor and receiver.

20. Laser dye thermal transfer printing apparatus including a laser source emitting light from a stripe- shaped port, means repeatably movable in a line between a first position and a second position for deflecting and focusing a coUimated laser beam from the laser source, such that the beam focus is scanned in a line in a flat plane parallel to the direction of motion of the deflecting and focusing means.

21. Laser scanning apparatus comprising a multi-mode laser diode source, means for producing a coUimated laser beam from the output of the source, and means repeatably movable along the path of the beam from a first position to a second position for deflecting and focusing the beam to scan the beam in a line parallel to the line of movement.

22. Laser dye thermal printing apparatus including a multi-mode laser diode source, and means repeatably movable in a straight line from a first to a second position for deflecting and focusing a coUimated laser beam from the laser source, such that the beam focus is scanned in a line in a flat plane parallel to the line of movement.