CN1369728A - Long-distance axial line focusing optical system with adjustable focal line length - Google Patents

Abstract

A long-distance axial line focusing optical system with an adjustable focal line length mainly comprises a plano-concave spherical lens and a plano-convex conical lens. The two lenses are made of materials with the same refractive index. The central axes of the two lenses are on the same straight line. The plane of the plane convex conical lens is arranged in parallel front and back opposite to the concave surface of the plane concave spherical lens. The radius of the plano-convex conical lens is larger than that of the plano-concave spherical lens. The distance between the two lenses is adjustable. The circular parallel incident laser beam with the central optical axis coaxial with the central axis of the lens system is vertically incident on one surface of the plane of the plano-concave spherical lens, emitted from the concave surface and then diverged, and the diverged laser beam enters the plano-convex conical lens and then converges on the central axis. By adjusting the distance between the two lenses, the length of the focal line can be varied. Compared with the prior art, the adjustable laser has the advantages of simple structure, convenient adjustment, easy realization of continuous adjustment of the length of the focal line, and suitability for ultrashort laser pulses, short pulses and long-pulse high-power lasers.

Description

The length-adjustable long-distance axial focusing optical system of focal line

Technical field:

The present invention is the continuously adjustable long-distance axial focusing optical system of focal line length, is applicable to excite length apart from high-power laser beam used in the straight line plasma in air, or is applicable to the occasion that laser beam need be carried out axial focusing.

Background technology:

Excite in the experiment of elongated linear plasma in the air at the research high power laser light, laser sequential focusing vertically need be distributed, to form an elongated straight focal line, generally require tens microns of radial width, axial length is more than several meters, and length is adjustable continuously, so that change the energy density on the focal line.

Focus in the experiment at general laser rays, be utilize cylindrical lens (referring to technology [1] king Zhijiang River chief editor formerly, the optical technology handbook, China Machine Press, in November, 1987 Beijing first published, the 1172nd page.) or utilize the continuously adjustable uniform line Focused Optical system of focal line length (referring to technology [2] number of patent application 93112629.0 formerly) of invention such as Qiu Yue, their shortcoming is that focal line is short, be a centimetre magnitude only, be difficult to realize the line focus length of several meters and even tens meters.

Utilize the bootstrap effect of ultrashort superpower femtosecond laser in the low-density plasma (referring to technology [3] A.Braun et al formerly, Optics Letters, 20 (1), 1995,73), can realize that pulse femtosecond laser radial width in air is 80 microns, axial length reaches 20 meters stable propagation.Its shortcoming is the situation that is not suitable for air middle-high density plasma, because the further propagation that the generation of high-density plasma will absorb follow-up laser and hinder laser is a shielding effect.In addition, the laser pulse wide than long pulse also is difficult to realize the bootstrap propagation of long distance.

Summary of the invention:

Purpose of the present invention provides a kind of continuously adjustable long-distance axial focusing optical system of focal line length of utilizing in order to overcome the defective of above-mentioned technology formerly, makes high power pulsed laser can excite elongated straight wire high-density plasma in air.

The present invention utilizes the combination of plano-concave spherical lens peace dome axicon lens, utilize the plano-concave spherical lens to disperse incident beam, utilize the plano-convex Conical Lenses as the axial focusing lens again, the distance between the adjusting plano-concave spherical lens peace dome axicon lens changes the length of focal line.

Fig. 1 is the continuously adjustable long-distance axial focusing optical system of a focal line length of the present invention synoptic diagram.Optical system of the present invention comprises that mainly plano-concave spherical lens 1 peaceful dome axicon lens 2, two lens are to be made of the material with identical refractive index n.The radius of plano-concave spherical lens 1 is E, and sphere curvature radius is R, and edge thickness is m.The radius of plano-convex Conical Lenses 2 is D, and the circular cone drift angle is β, and edge thickness is a.The central axis of two lens is on same straight line O ' F, and the plane of plano-convex Conical Lenses 2 faces toward the concave surface of plano-concave spherical lens 1, the parallel placement in front and back, and the conical tip O of plano-convex Conical Lenses 2 is positioned on central axis O ' F.Distance between the plano-concave spherical lens 1 peaceful dome axicon lens 2 can be adjusted to variable L.

For radius is the parallel incident laser light beam of circle (like this generally speaking) of d, the central optical axis O ' O of laser beam " disperses after by the concave surface outgoing with the coaxial one side that is normally incident in plano-concave spherical lens 1 plane of the central axis O ' F of lens combination.By the angle of divergence maximum of concave surface ejaculation outer beam, therefore main trace outer beam gets final product.Outer beam is with the angle of divergence alpha outgoing and enter plano-convex Conical Lenses 2.Plano-convex Conical Lenses 2 converges on central axis O ' F focal point F farthest with outer beam with low-angle η, and η is outside converging ray and axis angle, η＜α, and often be η＜＜α.All the other inboard light will be focused at OF section on the central axis continuously, and focal line length is k.Change the distance L between the plano-concave spherical lens 1 peaceful dome axicon lens 2, such as reducing L, so, focal point F will move to the summit of plano-convex Conical Lenses 2 O direction farthest, and focal line length shortens.On the contrary, increase L, focal line length will prolong.Certainly, the radius D of plano-convex Conical Lenses 2 and circular cone apex angle ss must satisfy certain condition and could realize axial focusing.The radius D of plano-convex Conical Lenses 2 is D＞E greater than the radius E of plano-concave spherical lens 1.

For radius is the parallel incident laser light beam of circle of d, is n through refractive index, and radius-of-curvature is that the angle of divergence alpha (angle of outside outgoing beam and central optical axis) after plano-concave spherical lens 1 outgoing of R can get (only considering outer beam) by simple optical computing $\mathrm{\α}=\arcsin \frac{\mathrm{nd}}{R}-\arcsin \frac{d}{R}.-------\left(1\right)$

Outside divergent beams are with identical incident angle α incident plano-convex Conical Lenses 2, and with angle θ outgoing, θ is the angle of outside emergent ray and circular conical surface normal.Be not difficult to try to achieve (refractive index of air is taken as 1) according to the refraction law of light ray propagation: $\sin \mathrm{\&theta;}=\left(\sqrt{n^2-\mathrm{<figure-callout\; id="2"\; label="si\; n"\; filenames="A0211098600071.png"\; state="\{\{state\}\}">si</figure-callout>}{n}^{}{}^2\mathrm{\&alpha;}}\right)\sin \mathrm{\&gamma;}-\cos \mathrm{\&gamma;}\sin \mathrm{\&alpha;},---\left(2\right)$ In the formula, γ is the circular conical surface bus of plano-convex Conical Lenses 2 and the angle on lens plane.Obvious, θ must just can assemble to axis direction by the outside emergent ray of plano-convex Conical Lenses 2, promptly greater than γ $\frac{\sin \mathrm{\&theta;}}{\sin \mathrm{\&gamma;}}=\left(\sqrt{n^2-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A0211098600071.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&alpha;}}\right)-\mathrm{ctg\&gamma;}\sin \mathrm{\&alpha;}>1,---\left(3\right)$ $\mathrm{\&gamma;}>\mathrm{arctg}\frac{\sin \mathrm{\&alpha;}}{\left(\sqrt{n^2-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A0211098600071.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&alpha;}}\right)-1}---\left(4\right)$ Correspondingly, the circular cone apex angle ss of plano-convex Conical Lenses 2 should satisfy:

Long distance is focused on, and convergent angle η is in a small amount.Therefore the length k of focal line OF is approximate can get: $k\&ap;\frac{h}{\mathrm{\&eta;}}=\frac{h}{\mathrm{\&theta;}-\mathrm{\&gamma;}},---\left(6\right)$

H is outer side beam through the eye point of plano-convex Conical Lenses 2 distance to central axis OF.

Can clearly be seen that from formula (6) focal line length k changes with h.Distance L between the adjusting plano-concave spherical lens 1 peaceful dome axicon lens 2 can change the size of h.That is, regulate L, just continuously regulating shaft to the length of focal line.The longest focal line k _MaxFor $k_{\max }\&ap;\frac{D}{\mathrm{\&theta;}-\mathrm{\&gamma;}}---\left(7\right)$ The shortest focal line k _MinFor $k_{\min }\&ap;\frac{d}{\mathrm{\&theta;}-\mathrm{\&gamma;}}.-----\left(8\right)$

The present invention compares with technology formerly, and is simple in structure, easy to adjust, realizes easily.Do not exist laser to shield the propagation that phenomenon hinders follow-up laser, thereby laser utilization factor height, short pulse and ultrashort pulse high power laser light be applicable to.The plasma continous-stable that produces, length is adjustable continuously.Be not only applicable to ultra-short pulse laser, be applicable to high power laser lights such as short pulse or long pulse yet.Can regulate focal line length easily according to incident laser energy like this, to obtain optimum capacity density.

Description of drawings:

Fig. 1 is the continuously adjustable long-distance axial focusing optical system of a focal line length of the present invention synoptic diagram.1 is the plano-concave spherical lens, and R is a sphere curvature radius, and E is the radius of plano-concave spherical lens 1, and m is an edge thickness.2 is the plano-convex Conical Lenses, and D is the radius of plano-convex Conical Lenses 2, and β is the circular cone drift angle, and a is an edge thickness.Two coaxial parallel placements of lens, O is the conical tip of plano-convex Conical Lenses 2.L is the distance between the plane of the thickest peaceful dome axicon lens 2 of point of the concave surface of plano-concave spherical lens 1.

D is the radius of the parallel incident laser light beam of circle, α is that outer beam is by the angle of divergence of plano-concave spherical lens 1 relative central optical axis and the incident angle that enters plano-convex Conical Lenses 2, θ is the emergence angle after outer beam passes through plano-convex Conical Lenses 2, γ is the circular conical surface bus of plano-convex Conical Lenses 2 and the angle between the plane, η is the convergent angle of outer beam to central axis OF, F is the focus of outer beam on central axis OF, h is an outer beam in the distance of the eye point on the plano-convex Conical Lenses 2 to the central axis OF, and k is the length of focal line OF.

Embodiment:

To have the lens material that homogeneous refractive index distributes, constitute two lens 1,2 such as optical glass and be example.The refractive index n of its optical glass=1.5, incident beam radius d is 25mm, and the radius E of plano-concave spherical lens 1 gets 26mm, and radius of curvature R is 50mm, and so, incident beam is after 1 outgoing of plano-concave spherical lens, and according to formula (1), the angle of divergence alpha of outer beam is

The radius D of plano-convex Conical Lenses 2 gets 100mm, and according to above-mentioned formula (4), the angle γ on circular conical surface bus and lens plane must satisfy:

Get γ and equal 34.5 °.Correspondingly, the circular conical surface apex angle ss of plano-convex Conical Lenses 2 is 111 °.

According to above-mentioned formula (2), outer side beam has by plano-convex Conical Lenses 2 back shooting angle θ $\sin \mathrm{\&theta;}=\left(\sqrt{n^2-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A0211098600071.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&alpha;}}\right)\sin \mathrm{\&gamma;}-\cos \mathrm{\&gamma;}\sin \mathrm{\&alpha;}$ Be that θ is 34.57 °.

According to above-mentioned formula (7), (8), the longest focal line k _MaxFor The shortest focal line k _MinFor The maximal regulated distance is about between the plano-concave spherical lens 1 peaceful dome axicon lens 2

Claims (1)

1. length-adjustable long-distance axial focusing optical system of focal line, comprise plano-concave spherical lens (1), it is characterized in that having the plano-convex Conical Lenses (2) of identical refractive index n material formation with plano-concave spherical lens (1), the plane of plano-convex Conical Lenses (2) facing to the concave surface of plano-concave spherical lens (1) the central axis of two lens coexist straight line (O ' F) go up before and after parallel storing, the conical tip (O) of plano-convex Conical Lenses (2) is at central axis (on the O ' F), distance (L) between plano-convex Conical Lenses (2) and the plano-concave spherical lens (1) is adjustable, the radius of circle (D) of plano-convex Conical Lenses (2) is greater than the radius of circle (E) of plano-concave spherical lens (1), and the circular cone apex angle ss of plano-convex Conical Lenses (2) is

In the following formula, n is plano-convex Conical Lenses (a 2) refractive index, and to be laser beam disperse the angle of back outside divergent beams and laser beam central optical axis by the one side incident on plano-concave spherical lens (1) plane by the concave surface outgoing to α, $\mathrm{\&alpha;}=\arcsin \frac{\mathrm{nd}}{R}-\arcsin \frac{d}{R}$ Wherein, n is the refractive index of plano-concave spherical lens (1), and d is the radius of incident circle parallel laser light beam, and R is the radius-of-curvature of plano-concave spherical lens (1).

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