CN104483758A - Method for inhibiting turbulence flashing and speckling of light spot of laser far field - Google Patents

Abstract

The invention relates to a method for inhibiting turbulence flashing and speckling of a light spot of a laser far field. The method comprises the following steps: splitting incident laser light into four beams of energy adjustable co-polarization laser light, ensuring that an optical path difference between every two beams to be greater than coherence length of each beam to avoid mutual coherence in a light splitting process of the four beams of light, adjusting a vibration direction of each beam of light with a 1/2 wave plate, and superimposing the four beams of light at a target. According to the method, with the adoption of an energy adjustable and polarization adjustable light splitting and emission technology scheme, the purpose of inhibiting the turbulence flashing and the speckling of an illumination light field is achieved by employing a 1/2 wave plate polarization beam splitter prism combination and damaging outgoing beam time coherence and laser light spatial coherence, the polarization diversity of the illumination light field is improved by employing the 1/2 wave plate, and the nonuniformity of the light field due to the speckling is further inhibited.

Description

A kind of for suppressing the method for the flicker of laser far field hot spot turbulent flow and speckle

Technical field

The present invention relates to laser far field applied technical field, being specifically related to a kind of for suppressing the method for the flicker of laser far field hot spot turbulent flow and speckle.

Background technology

In laser far field application, the homogeneity of far field energy is extremely important, such as: in the application of laser lighting Active Imaging, if laser illuminator can Uniform Illumination target area, for the picture contrast of whole imaging system, resolution and clear to there being great lifting; In laser communication application, if uniform and stable to target laser energy, error rate of system can be reduced greatly, thus increase system efficiency; In laser radar application, initiatively launch spot energy uniformity is to the detection and identify of dark target, Small object all important in inhibitings.

Because laser is in propagation in atmosphere process, due to atmosphere temperature field random variation, the refractive index random fluctuation on transmission path, causes the random deviation of transmission ray and interferes, and the final energy random fluctuation arriving target light field, is subject to the impact of turbulent flow flicker; Subsequently with the effect of target rough surface, because rough surface height random rises and falls, cause light that random deviation occurs again and be concerned with, being subject to the impact of speckle phenomena, final far-field spot energy uneven distribution.

Turbulent flow flicker and speckle phenomena are on the impact of far-field spot energy uniformity, usually ADAPTIVE OPTICS SYSTEMS is utilized to carry out suppressing and accurate correction in laser far field application again, but its cost is very expensive, be not suitable for low-cost system to use, and for the less demanding application of far-field spot wavefront, also do not need accurate correction.

Summary of the invention

The present invention is in order to solve laser after turbulent atmosphere transmission and rough surface reflection, the problem that far-field spot energy is uneven, propose a kind of for suppressing the method for the flicker of laser far field hot spot turbulent flow and speckle: utilize optical path difference between light beam to destroy transmission laser spatial coherence, different polarization states between light beam is utilized to increase far-field spot polarization diversity, thus arriving the effect suppressing turbulent flow flicker and speckle phenomena, concrete grammar realizes by building the adjustable beam splitting system of energy adjustable offset polarization state.

Energy adjustable offset polarization state adjustable light splitting emission coefficient comprises laser instrument, eliminating coherence multiple beam beam splitting system, polarization state regulating system.

Technical scheme of the present invention is as follows:

For suppressing a method for the flicker of laser far field hot spot turbulent flow and speckle, comprise the following steps:

4 bundles being divided into energy adjustable incident laser are with polarization state laser, and in 4 bundle light spectroscopic processes, the optical path difference ensureing each other is greater than self coherent length, makes it irrelevant mutually;

1/2 wave plate is utilized to regulate the direction of vibration of every Shu Guang;

Restraint light at target place 4 mutually to superpose.

In technique scheme, 4 bundles being divided into energy adjustable incident laser comprise with the concrete steps of polarization state laser:

Laser emitting light, through No. 1 1/2 wave plate transmission, adjusts No. 1 1/2 wave plate and makes out its optical axis and x angular separation θ _{1 λ}, after No. 1 1/2 wave plate, linearly polarized light direction of vibration and x angular separation are θ ₁, wherein θ _{1 λ}and θ ₁meet:

$\begin{array}{c}{\mathrm{\θ}}_1=\arccos \left(\frac{E_{1x}}{E}\right)\\ {\mathrm{\θ}}_{1\mathrm{\λ}}=\frac{\mathrm{\θ}+{\mathrm{\θ}}_1}{2}\end{array}---\left(1\right)$

Shoot laser optical axis direction of vibration to turn clockwise 2 × θ along wave plate optical axis _{1 δ}, θ _{1 δ}=(θ-θ ₁)/2, now linearly polarized light x oriented energy is E _1x, vertical y oriented energy is E _1y=Esin (θ ₁); Laser beam is through the light splitting of polarization spectro crystal, and reflected light is x direction oscillating component, and energy is E _1x; Transmitted light is y direction oscillating component, and energy is E ₂=E _1y;

Transmitted light beam through No. 2 1/2 wave plates, wave plate optical axis and x angular separation θ _{2 λ}, after No. 2 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are θ ₂, wherein θ _{2 λ}and θ ₂meet:

(2)

Outgoing beam direction of vibration turns clockwise 2 × θ _{2 δ}, θ _{2 δ}=(90 ° of-θ ₂)/2, now linearly polarized light x oriented energy is E _2x, vertical y oriented energy is:

E _2y＝E _1ysin(θ ₂)＝E sin(θ ₁)sin(θ ₂)

Laser beam is through the light splitting of polarization spectro crystal, and reflected light is x direction oscillating component, and energy is E _2x; Transmitted light is y direction oscillating component, and energy is E ₃=E _2y;

Transmitted light beam through No. 3 1/2 wave plates, wave plate optical axis and x angular separation θ _{3 λ}, after No. 3 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are θ ₃, wherein θ _{3 λ}and θ ₃meet:

Outgoing beam direction of vibration turns clockwise 2 × θ _{3 δ}, θ _{3 δ}=(90 ° of-θ ₃)/2, now linearly polarized light x oriented energy is E _3x, vertical y oriented energy is:

E _3y＝E _2ysin(θ ₃)＝E sin(θ ₁)sin(θ ₂)sin(θ ₃)

Laser beam is through the light splitting of polarization spectro crystal, and reflected light is x direction oscillating component, and energy is E _3x; Transmitted light is y direction oscillating component, and energy is E _3y;

Transmitted light beam is through No. 4 1/2 wave plates, and wave plate optical axis and 45 °, x angular separation, after No. 4 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are 0 °, and outgoing beam direction of vibration turns clockwise 2 × 45 °, and now linearly polarized light x oriented energy is E _4x=E _3y, vertical y oriented energy is 0;

2nd, 3 and 4 bundle emergent lights are through 5,6 and No. 7 1/2 wave plate transmission, and direction of vibration rotates again, and 5,6 and No. 7 1/2 wave plate optical axises and x angular separation are respectively θ _{5 δ}=(0 ° of-α)/2, θ _{6 δ}=(0 ° of-β)/2 and θ _{7 δ}=(0 ° of-γ)/2, emergent light direction of vibration and x angular separation are respectively α, β and γ;

Finally be met 4 bundle laser beam of requirement.

Beneficial effect of the present invention:

Energy adjustable offset polarization state adjustable light splitting lift-off technology scheme of the present invention, adopt 1/2 wave plate polarization splitting prism combination, laser spatial coherence is destroyed by destroying outgoing beam temporal coherence, achieve the order ground suppressing the turbulent flow flicker of illumination light field and speckle phenomena, adopt 1/2 wave plate to increase illumination light field polarization diversity, further suppress the light field unevenness that speckle causes.

Accompanying drawing explanation

Fig. 1 is energy adjustable offset polarization state adjustable multi-light bundle emission coefficient structural representation of the present invention;

Fig. 2 is 1/2 wave plate optical axis direction and incident emergent light polarization direction of vibration angled relationships schematic diagram;

Fig. 3 is energy and polarization state change schematic diagram (be 54.7 ° with linearly polarized light direction of vibration and x-axis angle, incident light energy is 3mJ is example) after polarization spectro crystal of the present invention light splitting;

Fig. 4 is plane of departure hot spot distribution schematic diagram of the present invention;

Fig. 5 is a kind of embodiment example schematic diagram (incident laser energy 4mJ of the present invention, linear polarization direction of vibration and x-axis angle 73 °, need to produce homenergic 4 and restraint emergent light, polarization direction of vibration and x-axis angle are 0 °, 45 °, 90 ° and 135 ° separately for they).

Embodiment

Invention thought of the present invention is: by destroying laser facula spatial coherence, increasing light field polarization diversity, suppress laser through the flicker of turbulent flow that propagation in atmosphere faces and laser facula and the speckle phenomena produced during rough surface effect, thus increase laser far field light spot energy homogeneity.

Principle of work of the present invention: the present invention proposes a set of energy adjustable offset polarization state adjustable light splitting lift-off technology scheme that can suppress laser far field light spot energy unevenness, can increase the homogeneity of light spot energy in far-field laser application.4 bundles that the technical program utilizes polarization spectro principle to be divided into energy adjustable incident laser are with polarization state laser, and in 4 bundle light spectroscopic processes, the optical path difference ensureing each other is greater than self coherent length, makes it irrelevant mutually; Afterwards, 1/2 wave plate is utilized to regulate the direction of vibration of every Shu Guang; Finally, restraint light at target place 4 mutually to superpose.Final spatial coherence declines and the diversified far-field spot of polarization state, thus suppresses turbulent flow flicker and speckle phenomena.

Below in conjunction with accompanying drawing, the present invention will be described.

Suppose that energy of lasers is E, linearly polarized light (direction of vibration and x-axis angle are θ), in order to suppress far-field spot inhomogeneity in energy, need to obtain 4 bundle shoot laser bundles, its energy is respectively E _1x, E _2x, E _3xand E _4x, linearly polarized light direction of vibration and x angular separation are respectively 0 °, α, β and γ.Its embodiment is as follows:

In Fig. 1, laser emitting light (suppose linearly polarized laser direction of vibration and horizontal x angular separation θ, energy is E) transmits through No. 1 1/2 wave plate (being assumed to be negative crystal), adjusts No. 1 1/2 wave plate and makes out its optical axis and x angular separation θ _{1 λ}, after No. 1 1/2 wave plate, linearly polarized light direction of vibration and x angular separation are θ ₁, wherein θ _{1 λ}and θ ₁meet:

$\begin{array}{c}{\mathrm{\θ}}_1=\arccos \left(\frac{E_{1x}}{E}\right)\\ {\mathrm{\θ}}_{1\mathrm{\λ}}=\frac{\mathrm{\θ}+{\mathrm{\θ}}_1}{2}\end{array}---\left(1\right)$

Shoot laser optical axis direction of vibration to turn clockwise 2 × θ along wave plate optical axis _{1 δ}, θ _{1 δ}=(θ-θ ₁)/2, now linearly polarized light x oriented energy is E _1x, vertical y oriented energy is E _1y=Esin (θ ₁).Laser beam is through polarization spectro crystal (PBS) light splitting, and reflected light is x direction oscillating component, and energy is E _1x; Transmitted light is y direction oscillating component, and energy is E ₂=E _1y.Transmitted light beam through No. 2 1/2 wave plates, wave plate optical axis and x angular separation θ _{2 λ}, after No. 2 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are θ ₂, wherein θ _{2 λ}and θ ₂meet:

Outgoing beam direction of vibration turns clockwise 2 × θ _{2 δ}, θ _{2 δ}=(90 ° of-θ ₂)/2, now linearly polarized light x oriented energy is E _2x, vertical y oriented energy is:

E _2y＝E _1ysin(θ ₂)＝E sin(θ ₁)sin(θ ₂)

Laser beam is through polarization spectro crystal (PBS) light splitting, and reflected light is x direction oscillating component, and energy is E _2x; Transmitted light is y direction oscillating component, and energy is E ₃=E _2y.Transmitted light beam through No. 3 1/2 wave plates, wave plate optical axis and x angular separation θ _{3 λ}, after No. 3 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are θ ₃, wherein θ _{3 λ}and θ ₃meet:

Outgoing beam direction of vibration turns clockwise 2 × θ _{3 δ}, θ _{3 δ}=(90 ° of-θ ₃)/2, now linearly polarized light x oriented energy is E _3x, vertical y oriented energy is:

E _3y＝E _2ysin(θ ₃)＝E sin(θ ₁)sin(θ ₂)sin(θ ₃)

Laser beam is through polarization spectro crystal (PBS) light splitting, and reflected light is x direction oscillating component, and energy is E _3x; Transmitted light is y direction oscillating component, and energy is E _3y.Transmitted light beam is through No. 4 1/2 wave plates, and wave plate optical axis and 45 °, x angular separation, after No. 4 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are 0 °, and outgoing beam direction of vibration turns clockwise 2 × 45 °, and now linearly polarized light x oriented energy is E _4x=E _3y, vertical y oriented energy is 0.2nd, 3 and 4 bundle emergent lights are through 5,6 and No. 7 1/2 wave plate transmission, and direction of vibration rotates again, and 5,6 and No. 7 1/2 wave plate optical axises and x angular separation are respectively θ _{5 δ}=(0 ° of-α)/2, θ _{6 δ}=(0 ° of-β)/2 and θ _{7 δ}=(0 ° of-γ)/2, emergent light direction of vibration and x angular separation are respectively α, β and γ.Finally be met 4 bundle laser beam of requirement.

To Figure 2 shows that in Fig. 1 the angled relationships in 7 piece of 1/2 wave plate optical axis, incident light direction of vibration, emergent light direction of vibration and x direction.

Fig. 3 is laser emergent light direction of vibration and all directions energy after No. 2 1/2 wave plate transmission, then transmit after light splitting through PSB, reflection emergent light and projection outgoing optical vibration direction and energy diagram (be 54.7 ° with linearly polarized light direction of vibration and x-axis angle, incident light energy is 3mJ is example).

Fig. 4 is the distribution of final emergent light hot spot, W ₀for spot radius.

Illustrate invention has been example in Figure 5, with incident laser energy 4mJ, linear polarization direction of vibration and x-axis angle 73 °, need to produce homenergic 4 and restraint emergent light, polarization direction of vibration and x-axis angle are 0 °, 45 °, 90 ° and 135 ° separately for they.

In Fig. 5, laser emitting light (supposes linearly polarized laser direction of vibration and 73 °, horizontal x angular separation, energy is 4mJ) through No. 1 1/2 wave plate (being assumed to be negative crystal) transmission, adjust No. 1 1/2 wave plate and make out its optical axis and 66.5 °, x angular separation, shoot laser optical axis direction of vibration turns clockwise 2 × 6.5 ° along wave plate optical axis, and now linearly polarized light x oriented energy is the vertical y oriented energy of 1mJ is 3mJ.Laser beam is through polarization spectro crystal (PBS) light splitting, and reflected light is x direction oscillating component, and energy is 1mJ; Transmitted light is y direction oscillating component, and energy is 3mJ.Transmitted light beam is through No. 2 1/2 wave plates, and wave plate optical axis and 72.35 °, x angular separation, outgoing beam direction of vibration turns clockwise 2 × 17.65 °, and now linearly polarized light x oriented energy is the vertical y oriented energy of 1mJ is 2mJ.Same x direction vibration light reflection outgoing after PBS, the outgoing of y direction vibration Transmission light, transmit by that analogy, wherein, No. 3 1/2 wave plate optical axis directions and 67.5 °, x angular separation, No. 4 1/2 wave plate optical axis directions and 45 °, x angular separation, reflection outgoing luminous energy is 1mJ, and direction of vibration is x direction.2nd, 3 and 4 bundle emergent lights are through 5,6 and No. 7 1/2 wave plate transmission, direction of vibration rotates again, 5,6 and No. 7 1/2 wave plate optical axises and x angular separation are respectively 22.5 °, 45 ° and 67.5 °, and emergent light direction of vibration and x angular separation are respectively 45 °, 90 ° and 135 °.

Need in implementation process to ensure light beam 1,2, between 3 and 4, optical path difference is greater than laser instrument coherent length.

Obviously, above-described embodiment is only for clearly example being described, and the restriction not to embodiment.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here exhaustive without the need to also giving all embodiments.And thus the apparent change of extending out or variation be still among the protection domain of the invention.

Claims (5)

1., for suppressing a method for the flicker of laser far field hot spot turbulent flow and speckle, it is characterized in that, comprise the following steps:

4 bundles being divided into energy adjustable incident laser are with polarization state laser, and in 4 bundle light spectroscopic processes, the optical path difference ensureing each other is greater than self coherent length, makes it irrelevant mutually;

1/2 wave plate is utilized to regulate the direction of vibration of every Shu Guang;

Restraint light at target place 4 mutually to superpose.

2. according to claim 1ly it is characterized in that for suppressing laser far field hot spot turbulent flow to be glimmered and the method for speckle, 4 bundles being divided into energy adjustable incident laser comprise with the concrete steps of polarization state laser:

Laser emitting light, through No. 1 1/2 wave plate transmission, adjusts No. 1 1/2 wave plate and makes out its optical axis and x angular separation θ _{1 λ}, after No. 1 1/2 wave plate, linearly polarized light direction of vibration and x angular separation are θ ₁, wherein θ _{1 λ}and θ ₁meet:

$\begin{array}{c}{\mathrm{\θ}}_1=\arccos \left(\frac{E_{1x}}{E}\right)\\ {\mathrm{\θ}}_{1\mathrm{\λ}}=\frac{\mathrm{\θ}+{\mathrm{\θ}}_1}{2}\end{array}---\left(1\right)$

Shoot laser optical axis direction of vibration to turn clockwise 2 × θ along wave plate optical axis _{1 δ}, θ _{1 δ}=(θ-θ ₁)/2, now linearly polarized light x oriented energy is E _1x, vertical y oriented energy is E _1y=Esin (θ ₁); Laser beam is through the light splitting of polarization spectro crystal, and reflected light is x direction oscillating component, and energy is E _1x; Transmitted light is y direction oscillating component, and energy is E ₂=E _1y.

3. according to claim 2ly it is characterized in that for suppressing laser far field hot spot turbulent flow to be glimmered and the method for speckle, 4 bundles being divided into energy adjustable incident laser also continue to comprise with the concrete steps of polarization state laser:

Transmitted light beam through No. 2 1/2 wave plates, wave plate optical axis and x angular separation θ _{2 λ}, after No. 2 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are θ ₂, wherein θ _{2 λ}and θ ₂meet:

Outgoing beam direction of vibration turns clockwise 2 × θ _{2 δ}, θ _{2 δ}=(90 ° of-θ ₂)/2, now linearly polarized light x oriented energy is E _2x, vertical y oriented energy is:

E _2y＝E _1ysin(θ ₂)＝Esin(θ ₁)sin(θ ₂)

Laser beam is through the light splitting of polarization spectro crystal, and reflected light is x direction oscillating component, and energy is E _2x; Transmitted light is y direction oscillating component, and energy is E ₃=E _2y.

4. according to claim 3ly it is characterized in that for suppressing laser far field hot spot turbulent flow to be glimmered and the method for speckle, 4 bundles being divided into energy adjustable incident laser also continue to comprise with the concrete steps of polarization state laser:

Transmitted light beam through No. 3 1/2 wave plates, wave plate optical axis and x angular separation θ _{3 λ}, after No. 3 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are θ ₃, wherein θ _{3 λ}and θ ₃meet:

Outgoing beam direction of vibration turns clockwise 2 × θ _{3 δ}, θ _{3 δ}=(90 ° of-θ ₃)/2, now linearly polarized light x oriented energy is E _3x, vertical y oriented energy is:

E _3y＝E _2ysin(θ ₃)＝Esin(θ ₁)sin(θ ₂)sin(θ ₃)

Laser beam is through the light splitting of polarization spectro crystal, and reflected light is x direction oscillating component, and energy is E _3x; Transmitted light is y direction oscillating component, and energy is E _3y.

5. according to claim 4ly it is characterized in that for suppressing laser far field hot spot turbulent flow to be glimmered and the method for speckle, 4 bundles being divided into energy adjustable incident laser also continue to comprise with the concrete steps of polarization state laser:

Transmitted light beam is through No. 4 1/2 wave plates, and wave plate optical axis and 45 °, x angular separation, after No. 4 1/2 wave plates, linearly polarized light direction of vibration and x angular separation are 0 °, and outgoing beam direction of vibration turns clockwise 2 × 45 °, and now linearly polarized light x oriented energy is E _4x=E _3y, vertical y oriented energy is 0;

2nd, 3 and 4 bundle emergent lights are through 5,6 and No. 7 1/2 wave plate transmission, and direction of vibration rotates again, and 5,6 and No. 7 1/2 wave plate optical axises and x angular separation are respectively θ _{5 δ}=(0 ° of-α)/2, θ _{6 δ}=(0 ° of-β)/2 and θ _{7 δ}=(0 ° of-γ)/2, emergent light direction of vibration and x angular separation are respectively α, β and γ;

Finally be met 4 bundle laser beam of requirement.