CN101950915A - Resonant cavity capable of obtaining hollow laser beams - Google Patents

Abstract

The invention relates to a resonant cavity capable of obtaining hollow laser beams, which can directly output hollow conical laser beams, belonging to the field of laser technology. The current technology for obtaining the hollow laser beams uses an optical device outside the resonant cavity for reshaping the laser beams emitted by the resonant cavity to obtain the hollow laser beams, and the scheme not only has a complex structure, but also has large energy loss. The resonant cavity capable of obtaining the hollow laser beams of the invention comprises a reflector, a laser gain medium and an output coupling mirror, wherein the material of the output coupling mirror is biaxial crystal, and one optical axis of the biaxial crystal is parallel to the axial line of the resonant cavity.

Description

Can obtain the resonant cavity of hollow laser beam

Technical field

The present invention relates to a kind of resonant cavity that can obtain hollow laser beam, can directly export open circles taper laser beam, belong to laser technology field.

Background technology

Along with the development of laser technology, hollow laser beam not only is used widely at aspects such as biology, laser processing and atom coolings, and can be applied to fields such as scanning imagery, remote sensing guidance, range finding.The existing technology that obtains hollow laser beam all is by an outer laser beam reshaping that Optical devices send resonant cavity of resonant cavity, obtain to form hollow laser beam, this class scheme is complex structure not only, and energy loss is also very big, also causes the degree of coherence of laser beam to reduce in addition.

In the optical crystal material field, biaxial crystal has conical surface refraction effect.

Summary of the invention

In order to realize directly exporting the purpose of hollow laser beam by resonant cavity, we have invented a kind of resonant cavity that can obtain hollow laser beam, can directly export open circles taper laser beam, have apparatus structure simultaneously and simply, do not have extra energy loss, keep the original degree of coherence of laser beam simultaneously.

The present invention's the resonant cavity that can obtain hollow laser beam is made up of speculum, gain medium and output coupling mirror, it is characterized in that, the output coupling mirror material is a biaxial crystal, and an optical axis of biaxial crystal is parallel with resonator axis.

Because biaxial crystal has conical surface refraction effect, the resonant cavity output coupling mirror that adopts this crystal to make, resonant cavity can directly be exported open circles taper laser beam, and with respect to prior art, its structure is very simple, just the material selected for use of the output coupling mirror of resonant cavity unlike the prior art, not adding Optical devices in addition, therefore just do not have extra energy loss yet, is not to obtain hollow laser beam by laser beam reshaping, therefore, the degree of coherence of laser beam does not reduce.

The harmonic light of incident biaxial crystal propagate put to

Parallel with resonator axis, see shown in Figure 1, by crystal optics as can be known:

$\stackrel{\→}{k}\⊥\stackrel{\→}{D},$

Then:

$\stackrel{\→}{D}\·\stackrel{\→}{k}=0,$

k _xD _x+k _yD _y+k _zD _z＝0，

∵D _x＝ε _xE _x，D _y＝ε _yE _y，D _z＝ε _zE _z，

And because of described optical axis on the xoz plane,

Also on the xoz plane, that is:

k _y＝0，

So:

k _xD _x+k _zD _z＝0，

ε _xk _xE _x+ε _zk _zE _z＝0，

Make vector $\stackrel{\→}{m}={\mathrm{\ϵ}}_x{k}_x\stackrel{\→}{a}+{\mathrm{\ϵ}}_z{k}_z\stackrel{\→}{c},$

Wherein:

Be respectively x, z direction unit vector.

As seen,

Vector with

Vector is vertical, promptly

So,

Must

Vertical plane on.

If plane π is vertical

Intersection point is the Q point, plane Λ vertical vector

AB is the intersection of plane π and plane Λ, because On the Λ plane, Must on the intersection AB of plane π and plane Λ, do with the intersection point P of plane π

Meet at the R point with plane π, because of

Coplane, so, on the π plane, R, Q, P on same straight line, in Δ RPO, So:

Therefore,

Anyway change, always satisfy formula (1), be unable to do without the Λ plane simultaneously, Change, be equivalent to the P point and move on intersection AB, the mobile R point that is equivalent to of P point moves, and satisfies formula (1), and because of the track of P point on intersection AB is straight line, the track of R is circle, so, all

Constitute taper seat.Therefore, when harmonic light is propagated, electric displacement vector no matter

Get any direction, unique phase velocity is all arranged, still, because electric field strength

With electric displacement vector

Not not in the same way, unlimited a plurality of radiation direction will occur, these light surround a taper seat.Its effect shows as, harmonic light propagate put to

During with the biaxial crystal optical axis coincidence parallel with resonator axis, the Energy distribution of output is on the hollow conical surface, and therefore, the laser beam of resonant cavity output is the open circles taper, and hot spot therefore also just in the form of a ring; Conical surface wall is thin, the power density height of laser beam.

Description of drawings

Fig. 1 is that biaxial crystal produces hollow cone shaped light beam schematic diagram.Fig. 2 is the structural representation of the present invention's the resonant cavity that can obtain hollow laser beam, and this figure double as is a Figure of abstract.

Embodiment

The present invention's the resonant cavity that can obtain hollow laser beam is made up of speculum 1, gain medium 2 and output coupling mirror 3, sees shown in Figure 2ly, and output coupling mirror 3 materials are biaxial crystal, and an optical axis of biaxial crystal is parallel with resonator axis.Pumping source 4 is a 808nm 30W diode laser matrix.Pump light 4 is coupled in the gain medium 2 in the resonant cavity by coupled apparatus.Coupled apparatus is made up of coupled fiber 5, coupled lens 6.Coupled fiber 5 core diameters are 400 μ m, numerical aperture NA=0.22.Coupled lens 6 is made up of a pair of planoconvex spotlight, and convex surface is relative, and the convex surface radius is 50mm, each planoconvex spotlight two sides plating 808nm anti-reflection film, transmitance T＞95%.Speculum 1 is the plano-concave mirror, and one side is a concave surface in the chamber, two sides plating 808nm anti-reflection film and 1064nm highly reflecting films, anti-reflection film transmitance T＞95%, highly reflecting films reflectivity R＞98%.Gain medium 2 is Nd:YAG crystal bars, and neodymium ion doped concentration N=1% is of a size of

Output coupling mirror 3 adopts KTP (KTP) crystal to make, and an optical axis of this biaxial crystal is parallel with resonator axis, and ktp crystal is of a size of 4mm * 4mm * 2mm, and ktp crystal skin covering of the surface system is 10% to the transmitance of 1064nm wavelength.

When diode laser matrix was injected into power in the Nd:YAG crystal bar and surpasses the laser generation threshold value, the 1064nm harmonic light in the optical axis transmission of optical direction along ktp crystal, just can obtain open circles taper laser beam by outgoing mirror outside the chamber.

According to crystal optics, the cone angle of open circles taper laser beam is determined by formula (2):

$\tan \mathrm{\α}=\frac{1}{n_y^2}[(n_y^2-n_x^2)(n_z^2-n_y^2){]}^{1/2}---\left(2\right)$

In the formula: n _x, n _y, n _zBe three major axes orientation refractive indexes of ktp crystal, and, n _x=1.7416, n _y=1.7496, n _z=1.8323, get α=1.7 ° by formula.

Claims (2)

1. the resonant cavity that can obtain hollow laser beam is made up of speculum, gain medium and output coupling mirror, it is characterized in that, the output coupling mirror material is a biaxial crystal, and an optical axis of biaxial crystal is parallel with resonator axis.

2. the resonant cavity that can obtain hollow laser beam according to claim 1, it is characterized in that, output coupling mirror (3) adopts KTP (KTP) crystal to make, an optical axis of this biaxial crystal is parallel with resonator axis, ktp crystal is of a size of 4mm * 4mm * 2mm, and ktp crystal skin covering of the surface system is 10% to the transmitance of 1064nm wavelength.

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