RU2411598C2 - Method and device for moving laser beam neck - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of moving exit neck while keeping its size constant involves using a two-component laser optical system. The laser optical system has a first movable component at a distance d₁ from the entrance neck, a second movable component at a distance d₂ from the first component and the exit neck. The exit neck lies at a distance d₃ from the second component. Parametres of the laser optical system are linked by the relationships: magnification of the first component

defocusing of components

focal distance of the second component

. Longitudinal distances d₁, d₂ and d₃ are varied according to the following laws:

;

Movement of the exit neck with change in the length of the laser optical system is realised according to the following law:

where: α is longitudinal magnification of the laser optical system;

is focal distance of the first component; Z_k is a confocal parametre, Z_p is the distance from the focus of the first component to the entrance neck; P₀=P(z_pt,Δ_t)=const is the full, characteristic relationship between longitudinal magnification and the current structural parametres.

EFFECT: possibility of moving a constant-size neck in a wide range with small displacement of components of the laser optical system.

2 cl, 2 dwg

Description

The invention relates to optics, and more specifically to the design of laser optical systems, and can be used in the development of high-quality optical systems for moving the waist (spot) of the laser beam, including waist of constant size.

The widespread adoption of laser technologies in various industries has necessitated application developments related, in particular, to high-precision movement of the laser beam spot relative to the target object. Methods and devices for solving this problem are used in industry, for example, when cutting and welding sheet metal and in digital devices, for example, when recording and reproducing data on optical discs. In this case, the simplest devices provide for mechanical movement of the laser radiation source relative to the target or vice versa (see, for example, US patent No. 6462301 [1]). Due to its size and linearity of movement, this design has very limited use. Other known solutions employ optical microswitches that mechanically act on a mirror directing a laser beam to an object (see US Pat. Nos. 6,360,035 [2] and 6,463,201 [3]). This technology is designed for relatively low laser beam energies and a limited range of spot movement.

Closest to the claimed invention is a device based on the principle of "flying optics" (English "flying optics") and described in the published European application (see Mizuno S., Yamada N., Gotoh Y. Flying optical head and optical information recording and reproducing apparatus. // European Patent Specification EP 0409468 (B1), published - 1995-09-13) [4]. This device relates to optical heads for recording and reading information from optical disks. The device diagram is presented in figure 1.

Moving the waist of the laser beam is implemented in this device as follows. The lens 7 collimates the radiation of the laser 6, and the lens 14 focuses the radiation on the information surface 5 of the optical disk 1. The movement of the laser beam on the information surface of the disk is carried out by changing the distance between the lenses 7 and 14, between which the laser beam is collimated. This method of moving the constriction is based on changing the longitudinal distance between the lenses 7 and 14 and translating this movement in the transverse (relative to the axis of the laser beam) using a mirror 13 mounted in front of the lens 14 of the forming optical system.

Essentially, the above construction is based on the fact that the intermediate hauling after the first lens 7 is removed a large distance from both lenses 7 and 14. Moreover, the movement of the block 4, consisting of a mirror 13 and a second lens 14, changes the distance from this very slightly hauling to the second lens 14. Due to the smallness of this change, the output hauling after the second lens 14 is formed at almost the same distance from it and has the same size.

где f′ - фокусное расстояние оптической системы; z_k - параметр конфокальности входного лазерного пучка; Z_p - расстояние от переднего фокуса оптической системы до входной перетяжки.In fact, from a published study by Pakhomov II, Tsibulya AB Computtional Methods for Laser Optical Systems Design // Journal of Soviet Laser Research. - V.9. - No. 3. - 1998. - New York. - p.321-429 [5], it is known that the longitudinal increase in α of the optical system when working with laser beams is determined by the expression

where f ′ is the focal length of the optical system; z _k is the confocal parameter of the input laser beam; Z _p is the distance from the front focus of the optical system to the input constriction.

, где

- фокусное расстояние второго компонента; Z_k1 - параметр конфокальности лазерного пучка между компонентами; Z_p2 - расстояние от переднего фокуса второго компонента до промежуточной перетяжки, которое зависит от расстояния между фокусами компонентов системы Δ (дефокусировки компонентов).The approach to moving the laser beam waist described in the prototype violates the aforementioned relationship existing in laser optical systems between its structural parameters, longitudinal magnification, and the position of the output waist. As a result of this, the constancy of both the size and the position of the output constriction relative to the lens 14 is inevitably violated. The device uses a special case of the interaction of the first and second components of the laser system when the first component is designed as a collimator. It is this circumstance that leads to a very weak dependence of the size and position of the outlet constriction on the position of the second component, which allows the authors of the device [4] to neglect it. However, in reality it is necessary to take into account that the intermediate constriction of the laser beam after the first component is located at a sufficiently large distance from the first component and, accordingly, from the second component. When the distance between the components changes, the distance from the intermediate waist to the second component changes, which inevitably leads to a change in the position and size of the waist at the output of the two-component system. This follows from the dependence below for a longitudinal increase in the second component:

where

- focal length of the second component; Z _k1 is the confocal parameter of the laser beam between the components; Z _p2 is the distance from the front focus of the second component to the intermediate constriction, which depends on the distance between the foci of the components of the system Δ (defocusing of the components).

It is clear that the use of this method is possible only in schemes with the first collimation lens. To move the output banner by a given distance, it is necessary to move the lenses of the forming system to the same distance, which is extremely inconvenient and irrational. In addition, during its implementation it is impossible to achieve significant movements of the output constriction while maintaining its size constancy.

The tasks to which the claimed invention is directed are to develop for laser optical systems (VOCs) a method for moving a constant-size waist over a wide range with a small movement of components and a compact device that provides such movement.

The technical result in terms of the method is achieved through the use of an improved hauling of the waist, which consists in using a two-component laser optical system with moving components and changing the longitudinal distances d ₁ (distance from the entrance waist of the laser beam to the first component, i.e. to its front main plane) ₂ and d (spacing between components), and characterized in that the parameters used by the two-laser optical system for each position of the input constriction Z _p knit relationships:

;- increase in the first component

;

;- defocusing components

;

, а продольные расстояния в системе изменяют строго согласованно по следующим законам:- focal length of the second component

, and the longitudinal distances in the system are changed strictly in accordance with the following laws:

- distance d ₁ from the input constriction of the laser beam to the first component

- distance d ₂ between components

- distance d ₃ from the second component to the output constriction

and provide the movement of the output banner of the required size with a change in the length of the VOCs according to the law:

.

.

The main distinguishing features of the proposed approach are the use of the analytical relationship between the parameters of the laser beam and the two-component optical system that converts it, obtained by the authors based on the theory of designing laser optical systems [5]. The revealed patterns allow us to develop high-quality optical systems for moving the waist of a laser beam, including a constant size, in a short time.

перетяжек, а с другой стороны обеспечивается сочетанием ее конструктивных параметров и конфокальным параметром Z_k лазерного пучка:The inventive method works as follows. The required longitudinal increase in a two-component laser optical system (VOC) is determined by the known sizes (radii) of the input h _p and the output

constrictions, and on the other hand is provided by a combination of its design parameters and the confocal parameter Z _{k of the} laser beam:

,

,

и

- фокусные расстояния соответственно первого и второго компонентов; P(Z_p,Δ) - полином, характеризующий зависимость продольного увеличения от текущих конструктивных параметров: Z_p (расстояние от фокуса первого компонента до входной перетяжки) и Δ (дефокусировка компонентов, т.е. расстояние между фокусами компонентов ЛОС) и конфокального параметра Z_k лазерного пучка:Where

and

- focal lengths of the first and second components, respectively; P (Z _p , Δ) is a polynomial characterizing the dependence of the longitudinal increase on the current design parameters: Z _p (distance from the focus of the first component to the input constriction) and Δ (defocusing of the components, i.e. the distance between the foci of the VOC components) and the confocal parameter Z _k laser beam:

Moreover, on the plane of the design parameters (Z _p , Δ), their relationship, ensuring the maintenance of any final value of the polynomial P (z _p , Δ) = P ₀ , corresponds to second-order curves whose existence region is infinite in the parameter Z _p and bounded in the parameter Δ .

In order for the laser optical system to move the constriction of constant size, i.e. worked with a = const, it is necessary to fulfill the condition: P (z _pt , Δ _t ) = const = P ₀ .

For any current hauling position Z _p, the VOC parameters should be determined by the following relationships:

;- increase in the first component

;

;- defocusing components

;

;- focal length of the second component

;

;- distance d ₁ from the input constriction of the laser beam to the first component

;

- distance d ₂ between components

;

;

- distance d ₃ from the second component to the output constriction

It should be noted that when changing the position Z _{p of the} input banner, the VOC length (i.e., the position of the output banner relative to the input) L will change according to the following law:

.For the feasibility of this method, it is necessary that for any Z _{p the} discriminant of the equation P (Z _p , Δ) = P ₀ would be non-negative. If P ₀ > 1 is selected, this condition is always automatically satisfied. And when choosing P ₀ <1, the range of variation of Z _p must be chosen so as to satisfy the condition

.

при P₀≥1 и

при P₀<1.In addition, the physical feasibility of the method must be ensured when the distances d ₂ (distance between components) and d ₃ (distance from the second component to the output constriction of the laser beam) are positive. From the boundedness of the parameter Δ for any value of P ₀ it follows that the parameters f ', P ₀ can always be performed so that the physical realizability of the method is performed. In this case, it is desirable to choose the range of variation of Z _p so that the length L of the VOC increases monotonically. In this case, the minimum value of Z _{p min} depends on the choice of parameter P ₀ as follows:

at P ₀ ≥1 and

for P ₀ <1.

Thus, when developing a real VOC design for moving a constant-size waist, the longitudinal increase α and the confocal parameter Z _{k of the} laser beam are known, and the VOC parameters P ₀ , f ₁ must be chosen. Then it becomes known the value of the minimum defocusing Z _{p min} and the minimum length L _min VOC. The maximum defocus value Z _{p max} is determined by the required value L _max . Since for any value of P _{0 the} region of possible parameter variation is not limited, such a choice can always be made. Moreover, over the entire range of variations of Z _p for changing L, the discriminants of the quadratic equation P (z _pt , Δ _t ) = P ₀ (i.e., all the radical expressions) will be positive.

To characterize the increase (gain) in the movement of the output constriction with respect to the displacement Z _{p of the} input constriction in such laser systems, the average multiplication factor of the displacement Z _p is usually introduced:

где L_max и L_min - соответственно максимальная и минимальная длины системы; Z_{p max} и Z_{p min} - соответственно максимальное и минимальное расстояния от переднего фокуса первого компонента до входной перетяжки.

where L _max and L _min - respectively, the maximum and minimum lengths of the system; Z _{p max} and Z _{p min} - respectively, the maximum and minimum distances from the front focus of the first component to the input constriction.

ΔL = L _max -L _min - the range of the length of the laser optical system;

ΔZ _p = Z _{p max} -Z _{p min} - the range of movement of the first component.

To implement the proposed method, it is proposed to use a device containing a laser emitting a laser beam with an initial (input) constriction, a first movable VOC component located at a distance d ₁ from the input constriction of the laser beam, a second movable VOC component located at a distance d ₂ from the first component , and an output constriction located at a distance of d ₃ from the second component, characterized in that the design parameters of the device are related by the ratios:

;- increase in the first component

;

;- defocusing components

;

,- focal length of the second component

,

and moving the output banner of the required size with a change in the length of the VOCs according to the law:

carried out by changing the longitudinal distances in strict accordance with the laws:

;- distance d ₁ from the input constriction of the laser beam to the first component

;

- distance d ₂ between components

Further, the claimed method and device are illustrated with the use of graphic materials.

Figure 1 illustrates a diagram of a device that implements the prototype method, where:

1 - optical disk

2 - fixed block,

3 - collimated laser beam,

4 - movable block,

5 - information surface,

6 - laser

7 - collimating lens,

8 - polarizing beam splitter,

9 - quarter-wave plate,

10 is a cylindrical lens,

11 - photodetector,

12 - actuator,

13 - a deaf mirror

14 - focusing lens

15 is a linear electric motor,

16 - a directing rail.

Figure 2 shows the operation of the inventive two-component laser optical system for moving the constriction of constant size, where:

Z _p is the distance from the front focus F _{1 of the} optical system to the input constriction;

f ₁ is the focal length of the first component;

f ₂ is the focal length of the second component;

h _p - size (radius) of the input constriction,

- размер (радиус) выходной перетяжки,

- size (radius) of the output constriction,

d ₁ is the distance from the input constriction of the laser beam to the first component;

d ₂ is the distance between the components;

d ₃ - the distance from the second component to the output constriction;

L is the distance between the input and output constrictions (system length);

Δ is the distance between the foci of the system components.

A preferred embodiment of the invention is as follows. When developing a VOC for moving the constriction of high-power gas (molecular) lasers with a large value of the confocal parameter Z _{k, the} best results in terms of the average increase in the displacement G are observed when choosing the parameter P ₀ in the region P ₀ ≈0.5.

When using this method, it is possible to move the constriction of a strictly constant size over large distances (meters or more) due to the relatively small (tens of millimeters) movements of the VOC components. The claimed method and device can be successfully applied, in particular, in technological installations for laser precision cutting of sheet materials of large sizes.

Claims (2)

1. The method of moving the output waist of the laser beam while maintaining its size constant, which consists in using a two-component laser optical system (VOC) with moving components and changing the longitudinal distances d ₁ and d ₂ , characterized in that the parameters of the two-component laser optical system for each position Z _p input constriction are related by the relations:
increase in the first component

component defocusing

;
focal length of the second component

,
and the longitudinal distances d ₁ and d ₂ in the system change strictly agreed according to the following laws:
distance d ₁ from the input constriction of the laser beam to the first component

,
distance d2 between components

distance d ₃ from the second component to the output constriction

and provide the movement of the output banner of the required size with a change in the length of the VOCs according to the law:

,
where α is the longitudinal magnification of a two-component laser optical system;

- focal length of the first component; Z _k is the confocal parameter, Z _p is the distance from the focus of the first component to the input constriction; P ₀ = P (z _pt , Δ _t ) const is a polynomial characterizing the dependence of the longitudinal increase on the current design parameters. 2. A device for moving the output beam of the laser beam while maintaining its size, containing a laser emitting a laser beam with the original banner, the first movable VOC component at a distance d ₁ from the input constriction of the laser beam, the second movable VOC component at a distance d ₂ from the first component and an output constriction located at a distance of d ₃ from the second component, characterized in that the design parameters of the VOC are connected by the relations:
increase in the first component

component defocusing

;
focal length of the second component

, and moving the output banner of the required size with a change in the length of the VOCs according to the law:

;
carried out due to changes in VOC longitudinal distances in strict accordance with the laws:
distance d ₁ from the input constriction of the laser beam to the first component

;
distance d2 between components

,
where α is the longitudinal magnification of a two-component laser optical system;

- focal length of the first component; Z _k is the confocal parameter, Z _p is the distance from the focus of the first component to the input constriction; P ₀ = P (z _pt , Δ _t ) = const is a polynomial characterizing the dependence of the longitudinal increase on the current design parameters.

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