Description:FIELD OF THE INVENTION:

The invention relates to a technical field of airborne or aerospace system application comprising zoom optical system. In particular, the invention relates to a zoom optical system for laser beam rider guidance technique for missile application. More particularly, the invention relates to a zoom optical system to maintain the constant laser beam diameter with respect to missile position throughout the flight by moving the single lens element only.

BACKGROUND OF THE INVENTION:

The laser beam rider guidance (LBRG) system maintains the missile in the line of sight in the desired direction. Such systems are used for short range anti-tank missiles and low altitude air defence missiles. The laser beam guidance system consists of a transmitter and receiver with the receiver being located on the rear section of the missile.

In laser beam rider guidance (LBRG) system, a spatially modulated laser beam is projected towards target and the missile follows the projected beam towards the target. For generation of guidance command, it requires to maintain the constant laser beam diameter with respect to missile position throughout the flight. The projected beam forms the guidance field/information for missile guidance. The laser transmitter system of the guidance scheme consists of solid-state laser, beam expander, laser beam modulation system and zoom projection optics.

The operation of the laser beam rider guidance (LBRG) system involves acquisition of target by the operator and projection of laser beam towards aimed target before the missile is fired. The projected laser beam forms the guidance field or information field for the missile to extract its correct instantaneous position with respect to line of sight during the missile flight. The task is accomplished by spatially modulating the beam at the transmitter; the modulation is detected and decoded at the missile receiver. The decoded modulation provides data, indicative of missile position relative to the beam axis, to missile on-board electronics. This enables generation of appropriate commands for correction of trajectory by the missile to hit the target. The instantaneous guidance field diameter is required to be maintained approximately constant for the missile throughout the flight. To achieve this, the laser beam projection is required to be controlled using zoom optical system.

The function of the laser beam guidance system is to maintain the missile in the line of sight in a desired direction. Such systems are used for short range missiles (Anti-tank missiles) and surface-to-air missiles (primarily short-range air defence missiles). Examples of such laser beam projection system for beam rider guidance application can be found in the existing prior arts as described below.

US Patent No. US5259568A discloses an optical system which is utilized to provide guidance information in the form of a modulated beam for a beamrider missile during its rocket powered flight phase. The system comprises first and second zoom type optical subsystems arranged to function cooperatively in object space, utilizing coincident lines of sight, with these optical subsystems serving to provide guidance information to the missile when the exhaust plume from its rocket engine is relatively difficult to penetrate. The first optical subsystem is utilized in a closed loop servo system for positioning a mirror gimballed about two axes, such that it continuously tracks the missile. The second optical subsystem, along the optical axis of which the modulated beam is directed, comprises a negative optical group and a positive optical group combined into a defocusable beam expander. These groups are initially defocused, and during flight of the missile, the negative group is movable in a linear manner away from the positive group, toward the focused position, so as to maintain by utilization of the gimballed mirror, a constant beam diameter at the missile.
Chinese Publication No. CN113866967A discloses a zoom optical system comprises four optical lenes and two plane mirrors to achieve high-magnification continuous zoom of a cooling infrared optical system. The system is provided to constrain the diameter of the large objective lens and achieve 100% cold screen efficiency by using secondary imaging technology. The zooming optical system provided by the prior art is sequentially arranged from an object side to an image side in the optical axis direction determined on the medium-wave infrared ray path radiated by a scene target: the system comprises a positive focal power meniscus lens as a front fixed group, a negative focal power biconcave lens as a zoom group, a positive focal power biconvex lens as a compensation group, a non-focal power plane reflecting mirror, a non-focal power plane reflecting mirror, a positive focal power meniscus lens as a middle dimension group, a middle wave refrigeration detector window and a middle wave refrigeration detector focal plane. The lens material of the system is silicon single crystal.

US Patent No. US3398918A discloses an optical system for guiding a projectile. There is provided an optical beam-rider guidance system for guiding a missile from a launching base to a target, wherein said launching base comprises: sighting means having an optical axis for sighting said target; laser means generating a plurality of fan-shaped light beams crossing each other, means for deflecting said beams laterally of said axis and means for modulating said beams. An optical anamorphotic device consists of a fixed cylindrical lens and a mobile cylindrical lens. These two lenses cooperate in substantially increasing the divergence of the beam in the plane of curvature of the lenses, without altering it in the plane normal thereto.

The non-patent literature that is, research paper titled as “The Study of Laser Beam Riding Guided System based on 980 nm Diode Laser”; Zhou Qu, Haifeng Xu, Xin Sui, Kun Yang; October 2015, describes the zoom projection system which changes the divergence angle of the laser beam and which guide the missile to the optic axis. During the process of flying towards the target, the angle of the laser beam becomes smaller along the flight of the missile, and diameter of the laser beam is kept constant.

In the zoom system of one of the existing prior arts, there are four lenses 1, 2, 3 and 4 considering as shown in figure 1. The lenses 1, 3, 4 are moving relative to lens 2. The change in the lateral magnification of the system is due to the variation of relative location of lens 1, 3, 4, 2. In the above mentioned existing prior arts for similar application, it is described that moving of more than one lens is required to get desired beam diameter by changing the position of the lenses. In the earlier system, more lenses were used for focusing. The track length of projection optics is large.

The laser beam guidance system consists of transmitter and receiver, the receiver is being located on the rear section of the missile. In operation, an operator locates the target and projects the projected beam of laser from transmitter to the target. The beam of electromagnetic radiation may be viewed as volume of radiation forming a guidance to the target which is followed by the missile, will cause it to strike the target. To assure missile to hit the target, it is necessary to launch the missile into the electromagnetic radiation of the beam, to follow the beam axis during the flight.

The partially modulated laser beam consists of uniquely defined resolution elements with unique assignment of frequency and time period. The missile corrects its trajectory to be online of sight by correctly decoding the signatures. As already described above, in earlier patents of projection optics, it is showed that moving Group II and Group III lenses get desired beam diameter by changing the divergence of the lenses wherein more lenses are used, and it is focusing optics and the track length of this projection optics is large.

Therefore, there is a need to design a novel optical system comprising four lenses utilized to give guidance information to the beam rider missile during its flight mode by moving single lens element only. Thus, the zoom projection system which is compact, lightweight, simple in construction, economical to manufacture, highly reliable and accurate is required to be designed.

The present invention relates to a zoom optical system for laser beam rider guidance technique for missile application. The designed system consists of four lenses made up of fused silica and with single lens movement for the desired zoom, it is achieved to maintain the constant laser diameter with respect to missile speed. The shape of the beam is not disturbed during zoom operations. The track length of zoom projection optics is very less when compared to the zoom projection optics of the prior arts. In laser beam rider guidance system, a spatially modulated laser beam is projected towards target and the missile flies on the projected beam towards the target. For generation of guidance command, it requires to maintain the constant laser beam diameter with respect to missile position throughout the flight. The zoom projection optics of the present invention makes the guidance field diameter of 4 m for a range of 500 m to 5000 m for every interval of 500 m during the missile flight.

OBJECT(S) OF THE INVENTION:

A primary object of the present invention is to provide a zoom optical system for laser beam rider guidance technique for missile application.

Another object of the present invention is to design a zoom optical system utilized to give guidance information to the beam rider missile during its flight mode.

Another object of the present invention is to design a zoom optical system comprising four lenses made up of an amorphous (non-crystalline) material.

Another object of the present invention is to design a zoom optical system comprising four lenses made up of fused silica to withstand higher temperature because solid-state laser is used in the laser beam rider guidance is of higher power.

Another object of the present invention is to design a zoom optical system to maintain a constant laser guidance field of diameter of 4 m on the missile, as it moves towards the selected target.

Another object of the present invention is to design a zoom optical system to make the guidance field diameter of 4 m for a range of 500 m to 5000 m for every interval of 500 m during the missile flight.

Another object of the present invention is to design a zoom optical system wherein the track length of zoom projection optics is very less.

Another object of the present invention is to design a zoom optical system wherein the track length of zoom projection optics is 120 mm.

Another object of the present invention is to design a zoom optical system comprising only one stepper motor for zooming operation to make the system compact.

Another object of the present invention is to design a zoom optical system which is compact, lightweight, simple in construction, economical to manufacture, highly reliable and accurate.

SUMMARY OF THE INVENTION:

Accordingly, the present invention provides a zoom optical system for laser beam rider guidance technique for missile application. In particular, the present invention relates to a zoom optical system to provide a constant laser guidance field of diameter of 4 m on the missile with single moving lens, as it moves towards the selected target. More particularly, the present invention relates to a zoom optical system wherein zoom projection optics make the guidance field diameter of 4 m for a range of 500 m to 5000 m for every interval of 500 m during the missile flight.

The present invention represents a novel optical system utilized to give guidance information to the beam rider missile during its flight mode. The spatially modulated beam is projected by zoom projection optics such that the beam diameter is 4 m over an operating range from 500 m to 5000 m for the missile in flight. The total track length of zoom projection optics is very less, preferably 120 mm. The zoom optical system comprises only one stepper motor for zooming operation. The designed zoom projection system of the present invention is simple in construction, economical to manufacture, compact, lightweight, highly reliable and accurate.

In one aspect of the present invention, the invention provides a zoom optical system for laser beam rider guidance technique for missile application providing guidance information to the missile in the form of modulated beam during the missile in the flight mode comprises four lenses (1, 2, 3, 4) made up of an amorphous (non-crystalline) material;
wherein a spatially modulated beam is projected by the zoom optical system to maintain the constant laser beam diameter over an operating range for the missile in flight and is enabled by synchronizing the missile velocity with optical element position control; and
wherein by moving a single lens element, the laser beam diameter of electromagnetic radiation with respect to missile position is maintained constant throughout the flight.

The four lenses (1, 2, 3, 4) of the zoom optical system are made up of fused silica material.

The laser beam diameter of electromagnetic radiation is maintained constant with the dimension of 4 m for every interval of 500 m upto 5000 m by only changing the position of lens (4) relative to lens (3) without change in position of the remaining lenses.

The total track length of zoom optical system is 120 mm.

The zoom optical system comprises a stepper motor for zooming operation.

In another aspect of the present invention, the invention provides a laser beam rider guidance (LBRG) system to maintain the missile in the line of sight in the desired direction, the laser beam rider guidance (LBRG) system comprises a transmitter assembly and a receiver being located on the rear section of the missile;
wherein the transmitter assembly of the laser beam rider guidance (LBRG) system comprises a solid-state laser, a beam expander, a laser beam modulation system and a zoom optical system;
wherein the zoom optical system comprises four lenses (1, 2, 3, 4) made up of an amorphous (non-crystalline) material;
wherein a spatially modulated beam is projected by the zoom optical system to maintain the constant laser beam diameter over an operating range for the missile in flight and is enabled by synchronizing the missile velocity with optical element position control; and
wherein by moving a single lens element, the laser beam diameter of electromagnetic radiation with respect to missile position is maintained constant throughout the flight.

The solid-state laser is Nd-Yag laser operating at 1.06 micron wavelength.

The laser beam rider guidance (LBRG) system comprises the beam expander for collimating and expanding the beam of diameter of 6 mm and a chopper to give guidance to the missile and projection optics to increase the beam diameter of 4 m for every interval of 500 m up to 5000 m.

The four lenses (1, 2, 3, 4) of the zoom optical system are made up of fused silica material.

The laser beam diameter of electromagnetic radiation is maintained constant with the dimension of 4 m for every interval of 500 m upto 5000 m by only changing the position of lens (4) relative to lens (3) of the zoom optical system without change in position of the remaining lenses.

The above description merely is an outline of the technical solution of the present disclosure. The summary is descriptive and exemplary only and is not intended to be in any way restricting. In order to know the technical means of the present disclosure more clearly so that implementation may be carried out according to contents of the specification, and in order to make the above and other objectives, characteristics and advantages of the present disclosure clear and easy to understand, specific embodiments of the present invention will be described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS:

The drawings described herein are intended to provide a further understanding of the invention and are intended to be a part of the invention. However, the drawings as shown are representative for illustration and are non-limiting the scope of the invention. In the drawings:

Figure 1 shows the layout diagram of zoom projection optics.

Figure 2 shows the cam curve displaying the zoom positions at different positions of flying missile from transmitter to keep diameter of the output beam constant.

Figure 3a shows the layout diagram of the zoom projection optics for operational distance of 500 m.

Figure 3b shows the layout diagram of the zoom projection optics for operational distance of 2000 m.

Figure 3c shows the layout diagram of the zoom projection optics for operational distance of 3000 m.

Figure 3d shows the layout diagram of the zoom projection optics for operational distance of 4000 m.

Figure 3e shows the layout diagram of the zoom projection optics for operational distance of 5000 m.

Figure 4a shows the output beam diameter (irradiance) at 500 m from the zoom projection optics.

Figure 4b shows the output beam diameter (irradiance) at 2000 m from the zoom projection optics.

Figure 4c shows the output beam diameter (irradiance) at 3000 m from the zoom projection optics.

Figure 4d shows the output beam diameter (irradiance) at 4000 m from the zoom projection optics.

Figure 4e shows the output beam diameter (irradiance) at 5000 m from the zoom projection optics.

DETAILED DESCRIPTION OF THE INVENTION:

The present invention relates to a zoom optical system for laser beam rider guidance technique for missile application.

The laser beam rider guidance (LBRG) system maintains the missile in the line of sight in the desired direction. Such systems are used for short range anti-tank missiles and low altitude air defence missiles. The laser beam guidance system consists of a transmitter and receiver with the receiver being located on the rear section of the missile.

In laser beam rider guidance (LBRG) system, a spatially modulated laser beam is projected towards target and the missile follows the projected beam towards the target. For generation of guidance command, it requires to maintain the constant laser beam diameter with respect to missile position throughout the flight. The projected beam forms the guidance field/information for missile guidance. The laser transmitter system of the guidance scheme consists of solid-state laser, beam expander, laser beam modulation system and zoom projection optics.

The operation of the laser beam rider guidance (LBRG) system involves acquisition of target by the operator and projection of laser beam towards aimed target before the missile is fired. The projected laser beam forms the guidance field or information field for the missile to extract its correct instantaneous position with respect to line of sight during the missile flight. The task is accomplished by spatially modulating the beam at the transmitter; the modulation is detected and decoded at the missile receiver. The decoded modulation provides data, indicative of missile position relative to the beam axis, to missile on-board electronics. This enables generation of appropriate commands for correction of trajectory by the missile to hit the target. The instantaneous guidance field diameter is required to be maintained approximately constant for the missile throughout the flight. To achieve this, the laser beam projection is required to be controlled using zoom optical system.

In the zoom system of the existing prior arts, there are four lenses 1, 2, 3 and 4 considering as shown in figure 1. The lenses 1, 3, 4 are moving relative to lens 2. The change in the lateral magnification of the system is due to the variation of relative location of lens 1, 3, 4, 2. In the above-mentioned prior arts for the similar application, it is described that moving of more than one lens is required to get desired beam diameter by changing the position of the lenses. In the earlier system, more lenses were used for focusing. The track length of projection optics is large.

Accordingly, the present invention provides a novel optical system utilized to give guidance information to the beam rider missile during its flight mode. The spatially modulated beam is projected by zoom projection optics such that the beam diameter is 4 m over an operating range from 500 m to 5000 m for the missile in flight. This is enabled by synchronizing the missile velocity with optical element position control i.e. programmed CAM.

During complete flight duration the missile is required to be in the guidance field. Moreover, the intensity of the laser guidance field should be sufficient enough to be detected by the laser receiver placed in the rear section of the missile. The zoom projection optics controls the projected laser beam as a result, along with retention of the dimensions of the guidance field, the energy density is sufficiently maintained.

The main object of the present invention is to provide a constant laser guidance field of diameter of 4 m on the missile, as it moves towards the selected target.

In one aspect of the present invention, the invention provides a zoom optical system for laser beam rider guidance technique for missile application. Figure 1 shows the layout diagram of zoom projection optics.

The projection optics is the important part of laser projection system. The present invention describes compact projection optics with single moving lens. The designed system consists of four lenses (1, 2, 3, 4) made up of an amorphous (non-crystalline) material such as fused silica material. With single lens movement for the desired zoom, it is achieved to maintain the constant laser diameter with respect to missile speed. The shape of the beam is not disturbed during zoom operations.

Figure 1 shows the layout diagram of zoom projection optics comprising four lenses (1, 2, 3, 4). The distance between the respective lenses of zoom projection optics is given below in table below:

Table 1: The Distance between the lenses
Zoom Projection Optics
Sr. No. Distance between Lenses Value (mm) Tolerance Value (mm)
1 Lens 1 and lens 2 29.53 ± 0.025
2 Lens 2 and Lens 3 30 ± 0.025
3 Lens 3 and Lens 4 Zoom Position

The lenses (1, 2, 3, 4) are made up of fused silica material. In a preferred embodiment, the design of zoom projection system is done by using only fused silica material. Fused silica is selected for the design of zoom projection system to withstand higher temperature and lower thermal expansion coefficient because solid-state laser is used in the laser beam rider guidance is of higher power.

The track length of zoom projection optics is very less as compared to the existing zoom projection optics reported till date. In a preferred embodiment, the total track length of projection optics is 120 mm.

The beam diameter of 4 m is achieved for interval of 500 m up to 5000 m by moving single lens element only. By only changing the position of lens (4) relative to lens (3) of the zoom projection system can change diameter of electromagnetic beam of diameter 4 m for every interval of 500 m up to 5000 m. The projection zoom system of the present invention is very compact. It needs only one stepper motor for generating zooming operation and it generates output beam diameter of 4 m during flight of the missile for a range of 500 m to 5000 m for interval of 500 m.

Figure 2 shows the cam curve displaying the zoom positions at different positions of flying missile from transmitter to keep diameter of the output beam constant. During the operation of zoom projection optics, only lens (4) is moved relative to lens (3) as per the designed cam curve shown in Figure 2 without change in position of the remaining lenses. Only a single CAM curve and hence a single DC motor is sufficient for the complete operation which makes the system extremely compact and lightweight.

Thus, the above-mentioned description can be summarized as, a zoom optical system for laser beam rider guidance technique for missile application providing guidance information to the missile in the form of modulated beam during the missile in the flight mode comprises four lenses (1, 2, 3, 4) made up of an amorphous (non-crystalline) material;
wherein a spatially modulated beam is projected by the zoom optical system to maintain the constant laser beam diameter over an operating range for the missile in flight and is enabled by synchronizing the missile velocity with optical element position control; and
wherein by moving a single lens element, the laser beam diameter of electromagnetic radiation with respect to missile position is maintained constant throughout the flight.

Optical layouts of zoom projection optics for different operational distances of 500 m, 2000 m, 3000 m, 4000 m and 5000 m for constant uniform diameter of 4 m are shown in Figures 3a-3e, respectively.

Figures 4a-4d shows the irradiance diagrams for different operating distances of 500 m, 2000 m, 3000 m, 4000 m and 5000m, respectively. The irradiance diagrams for different operating distances of 500 m, 2000 m, 3000 m, 4000 m and 5000 m respectively, shows that the guidance field diameter is 4 m and the Gaussian nature of the field distribution is intact.

In another aspect of the present invention, the invention provides a laser beam rider guidance (LBRG) system comprising transmitter and receiver with the receiver being located on the rear section of the missile. In laser beam rider guidance (LBRG) system, a spatially modulated laser beam is projected towards target and the missile follows the projected beam towards the target. For generation of guidance command, it requires to maintain the constant laser beam diameter with respect to missile position throughout the flight. The projected beam forms the guidance field/information for missile guidance. The laser transmitter system of the guidance scheme consists of solid-state laser, beam expander, laser beam modulation system and zoom projection optics.

In particular, the laser beam rider guidance (LBRG) system consists of a ground-based station of launcher and missile. The ground-based system includes an optical sighting assembly and laser beam transmitter assembly. The optical assembly provides guidance information to the missile in the form of modulated beam during the missile in the flight mode. The laser beam guidance system consists of solid-state laser, preferably Nd-Yag laser operating at 1.06 micron wavelength, beam expander for collimating and expanding the beam of diameter of 6 mm, a chopper to give guidance to the missile and projection optics to increase the beam diameter of 4 m for every interval of 500 m upto 5000 m.

The operation of the laser beam rider guidance (LBRG) system involves acquisition of target by the operator and projection of laser beam towards aimed target before the missile is fired. The projected laser beam forms the guidance field or information field for the missile to extract its correct instantaneous position with respect to line of sight during the missile flight. The task is accomplished by spatially modulating the beam at the transmitter; the modulation is detected and decoded at the missile receiver. The decoded modulation provides data, indicative of missile position relative to the beam axis, to missile on-board electronics. This enables generation of appropriate commands for correction of trajectory by the missile to hit the target. The instantaneous guidance field diameter is required to be maintained approximately constant for the missile throughout the flight. To achieve this, the laser beam projection is required to be controlled using zoom optical system as described above.

Thus, the above-mentioned description can be summarized as, a laser beam rider guidance (LBRG) system to maintain the missile in the line of sight in the desired direction, the laser beam rider guidance (LBRG) system comprises a transmitter assembly and a receiver being located on the rear section of the missile;
wherein the transmitter assembly of the laser beam rider guidance (LBRG) system comprises a solid-state laser, a beam expander, a laser beam modulation system and a zoom optical system;
wherein the zoom optical system comprises four lenses (1, 2, 3, 4) made up of an amorphous (non-crystalline) material;
wherein a spatially modulated beam is projected by the zoom optical system to maintain the constant laser beam diameter over an operating range for the missile in flight and is enabled by synchronizing the missile velocity with optical element position control; and
wherein by moving a single lens element, the laser beam diameter of electromagnetic radiation with respect to missile position is maintained constant throughout the flight.

Thus, the present invention provides a zoom optical system for laser beam rider guidance technique for missile application. The present invention relates to compact projection optics with single moving lens. The designed system consists of four lenses (1, 2, 3, 4) made up of fused silica material and with single lens movement for the desired zoom, it is achieved to maintain the constant laser diameter with respect to missile speed. The shape of the beam is not disturbed during zoom operations. In laser beam rider guidance system, a spatially modulated laser beam is projected towards target and the missile flies on the projected beam towards the target. For generation of guidance command, it requires to maintain the constant laser beam diameter with respect to missile position throughout the flight. The zoom projection optics of the present invention make the guidance field diameter of 4 m for a range of 500 m to 5,000 for every interval of 500 m during the missile flight.

APPLICATION AND/OR ADVANTAGES:

A zoom optical system for laser beam rider guidance technique for missile application of the present invention provides the following advantages:
- By only changing the position of lens (4) relative to lens (3) of the zoom projection system can change diameter of electromagnetic beam of diameter 4 m for every interval of 500 m up to 5000 m.
- The projection zoom system is very compact as it needs only one stepper motor for generating zooming operation.
- The zoom optical system requires only a single CAM curve and hence a single DC motor is sufficient for the complete operation which makes the system extremely compact and lightweight.
- The track length of zoom projection optics is very less as compared with the existing prior arts.
- The designed zoom projection system is simple in construction, economical to manufacture, highly reliable and accurate.
, Claims:
1. A zoom optical system for laser beam rider guidance technique for missile application providing guidance information to the missile in the form of modulated beam during the missile in the flight mode comprises four lenses (1, 2, 3, 4) made up of an amorphous material;
wherein a spatially modulated beam is projected by the zoom optical system to maintain the constant laser beam diameter over an operating range for the missile in flight and is enabled by synchronizing the missile velocity with optical element position control; and
wherein by moving a single lens element, the laser beam diameter of electromagnetic radiation with respect to missile position is maintained constant throughout the flight.

2. The zoom optical system as claimed in claim 1, wherein the four lenses (1, 2, 3, 4) are made up of fused silica material.

3. The zoom optical system as claimed in claim 1, wherein the laser beam diameter of electromagnetic radiation is maintained constant with the dimension of 4 m for every interval of 500 m upto 5000 m by only changing the position of lens (4) relative to lens (3) without change in position of the remaining lenses.

4. The zoom optical system as claimed in claim 1, wherein the total track length of zoom optical system is 120 mm.

5. The zoom optical system as claimed in claim 1, wherein the system comprises a stepper motor for zooming operation.

6. A laser beam rider guidance (LBRG) system to maintain the missile in the line of sight in the desired direction, the laser beam rider guidance (LBRG) system comprises a transmitter assembly and a receiver being located on the rear section of the missile;
wherein the transmitter assembly of the laser beam rider guidance (LBRG) system comprises a solid-state laser, a beam expander, a laser beam modulation system and a zoom optical system as claimed in claim 1;
wherein the zoom optical system as claimed in claim 1 comprises four lenses (1, 2, 3, 4) made up of an amorphous material;
wherein a spatially modulated beam is projected by the zoom optical system to maintain the constant laser beam diameter over an operating range for the missile in flight and is enabled by synchronizing the missile velocity with optical element position control; and wherein by moving a single lens element, the laser beam diameter of electromagnetic radiation with respect to missile position is maintained constant throughout the flight.

7. The laser beam rider guidance (LBRG) system as claimed in claim 6, wherein the solid-state laser is Nd-Yag laser operating at 1.06 micron wavelength.

8. The laser beam rider guidance (LBRG) system as claimed in claim 6, wherein the system comprises the beam expander for collimating and expanding the beam of diameter of 6 mm and a chopper to give guidance to the missile and projection optics to increase the beam diameter of 4 m for every interval of 500 m up to 5000 m.

9. The laser beam rider guidance (LBRG) system as claimed in claim 6, wherein the four lenses (1, 2, 3, 4) of the zoom optical system are made up of fused silica material.

10. The laser beam rider guidance (LBRG) system as claimed in claim 6, wherein the laser beam diameter of electromagnetic radiation is maintained constant with the dimension of 4 m for every interval of 500 m upto 5000 m by only changing the position of lens (4) relative to lens (3) of the zoom optical system without change in position of the remaining lenses.