Space-time coherence adjustable light source based on external cavity feedback and degenerate cavity

Abstract

The utility model relates to the technical field of laser devices, and provides a space-time coherence adjustable light source based on external cavity feedback and a degenerate cavity, the space-time coherence adjustable light source comprises a degenerate cavity laser and an external feedback assembly which are coaxially arranged, and the degenerate cavity laser comprises a first reflector, a first lens, a variable aperture diaphragm, a second lens and an output coupling mirror which are sequentially arranged. According to the invention, the adjustable space-time low-coherence light source can be realized in a specific application scene, and the laser use effect is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser devices, in particular to a time-space coherence adjustable light source based on external cavity feedback and degenerate cavity. BACKGROUND

[0002] Traditional laser is a light source with high time-space coherence, which enables laser to produce focusing, interference and other precise optical phenomena, but high time-space coherence brings negative effects to some applications. For example, in space laser communication, the light beam with high coherence is greatly affected by atmospheric disturbance, resulting in uneven light intensity distribution and high error rate at the receiving end; in optical imaging field, the high coherence causes serious speckle in the imaging pattern, reducing the imaging quality; in laser nuclear fusion, the high coherence of strong laser enhances the nonlinear local interaction between laser and plasma, seriously restricting the coupling performance of the beam target; in laser heat treatment, the interference caused by high coherence leads to rough processing surface.

[0003] Therefore, in view of the application fields of space laser communication, optical imaging, laser heat treatment and the like, it is urgent to develop a low coherence light source to improve the above situations.

[0004] CONTENT

[0005] The purpose of the present application is to provide a time-space coherence adjustable light source based on external cavity feedback and degenerate cavity to reduce the coherence of the light source and improve the use effect of laser in specific application scenarios.

[0006] The embodiment of the present application is implemented by the following technical scheme: a time-space coherence adjustable light source based on external cavity feedback and degenerate cavity, comprising a degenerate cavity laser and an external feedback assembly arranged coaxially, wherein the degenerate cavity laser comprises a first mirror, a first lens, a variable aperture diaphragm, a second lens and an output coupling mirror arranged in sequence.

[0007] Further, the variable aperture diaphragm comprises a cover ring, an arc-shaped piece and a mounting ring stacked in sequence, one end of the arc-shaped piece is provided with a rotating shaft for rotating connection with the end face of the cover ring; a plurality of adjusting sliding grooves are formed around the mounting ring, the other end of the arc-shaped piece is clamped into the adjusting sliding groove and slidably matched therewith; a light transmission hole is formed in the middle part of the plurality of arc-shaped pieces.

[0008] Further, an adjusting handle is arranged on the outer edge surface of the mounting ring.

[0009] Further, the external feedback assembly comprises a non-polarized cubic beam splitter, an adjustable neutral density attenuator and a second mirror, and the non-polarized cubic beam splitter is arranged on the side close to the output coupling mirror.

[0010] Further, the degenerate cavity laser further comprises a pump source and a gain medium, the pump source and the gain medium are arranged between the first mirror and the first lens, and the pump source is arranged above the gain medium.

[0011] Further, the first lens and the second lens are a plano-convex lens or a biconvex lens.

[0012] Further, the focal length of the first lens and the second lens is 20 cm or 30 cm.

[0013] The technical scheme of the embodiment of the application has at least the following advantages and beneficial effects: the application starts from the regulation of spatial spectrum and time spectrum, adjusts the spatial coherence by using a variable aperture diaphragm through a degenerate cavity structure, and adjusts the time coherence by using an adjustable neutral density filter through an external cavity feedback structure, and the two structures together build an adjustable time-space low-coherence light source, which helps the laser to be applied to different fields and achieve better effects. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical scheme of the embodiment of the application, the following will briefly introduce the drawings needed to be used in the embodiment, and it should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation to the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of the drawings.

[0015] Figure 1 The structure schematic diagram of the time-space coherence adjustable light source based on external cavity feedback and degenerate cavity provided by the embodiment of the application is shown in the figure.

[0016] Figure 2 The structure schematic diagram of the variable aperture diaphragm in the application is shown in the figure.

[0017] Figure 3 The exploded view of the variable aperture diaphragm in the application is shown in the figure.

[0018] Figure legend: 1-degenerate cavity laser, 11-first mirror, 12-gain medium, 13-pump source, 14-first lens, 15-variable aperture diaphragm, 151-cover ring, 152-arc-shaped piece, 1521-rotation shaft, 1522-transparent hole, 153-mounting ring, 1531-adjusting slot, 1532-adjusting handle, 16-second lens, 17-output coupling mirror, 2-external feedback assembly, 21-unpolarized cube beam splitter, 22-adjustable neutral density filter, 23-second mirror. DETAILED DESCRIPTION

[0019] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0021] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0022] Embodiments

[0023] The following will be further described with reference to specific embodiments, referring to Figures 1-3 As shown in the figure, the embodiment is a time-space coherence adjustable light source based on external cavity feedback and degenerate cavity, which comprises a degenerate cavity laser 1 and an external feedback component 2 arranged coaxially. The degenerate cavity laser 1 comprises a first mirror 11, a first lens 14, a variable pinhole diaphragm 15, a second lens 16 and an output coupling mirror 17 arranged in sequence. The degenerate cavity laser 1 further comprises a pump source 13 and a gain medium 12. The pump source 13 and the gain medium 12 are arranged between the first mirror 11 and the first lens 14, and the pump source 13 is arranged above the gain medium 12. Specifically, the first mirror 11 is installed at the front focal plane of the first lens 14, and the first mirror 11 and the output coupling mirror 17 form a laser resonant cavity. The gain medium 12 provides a population inversion energy level structure, and electrons are stimulated to jump between energy levels under the stimulation of external photons to produce laser. The pump source 13 serves as an excitation source to pump particles from a low energy level to a high energy level to achieve population inversion. The first lens 14 and the second lens 16 form a self-imaging structure, so that the resonant cavity is a self-imaging cavity, all transverse modes are intrinsic modes of the cavity, have the same Q factor, and can output spatially partially coherent light. The variable pinhole diaphragm 15 has a loss of high-order transverse modes greater than that of low-order transverse modes in the spectral plane, is used for transverse selection of transverse modes, adjusts the number of transverse modes, controls the spatial coherence dynamics of the degenerate cavity laser 1, adopts a degenerate cavity structure, and uses the variable pinhole diaphragm 15 to realize adjustment of spatial coherence, thereby reducing coherence.

[0024] Spatial coherence describes the phase relationship between each point on the wave surface perpendicular to the direction of light beam propagation, and refers to the coherence of different spatial points in the light field at the same time, which can be described by the coherence width d, i.e. where λ is the laser wavelength and θ is the beam plane divergence angle. The better the beam directionality, the better the spatial coherence. For laser, all photons belonging to the same transverse mode are spatially coherent, and photons not belonging to the same transverse mode are incoherent. Therefore, the spatial coherence of laser is determined by its transverse mode structure, and single-transverse-mode laser is fully coherent, and the coherence of multi-transverse-mode beam is poor. At the same time, the directionality of single-transverse-mode beam is the best, and the higher the transverse mode order, the worse the directionality. It can be seen that the spatial coherence of the beam is closely related to its directionality (described by the beam divergence angle). The resonant frequency v qmn of the eigenmode of the resonant cavity is

[0025]

[0026] The subscript q represents the longitudinal mode number of the eigenmode, the subscripts m and n represent the two transverse mode numbers of the eigenmode, c is the speed of light in vacuum, and L is the optical length of the resonant cavity. In the degenerate cavity, since g1g2=1, at this time This indicates that there are countless transverse modes simultaneously and independently vibrating under the same longitudinal mode. The aperture size of the pinhole diaphragm 15 can be adjusted to adjust the number of transverse modes, and the larger the aperture, the more the number of transverse modes, the worse the directionality of the beam, and the lower the spatial coherence, so the spatial coherence of the beam can be controlled by changing the aperture of the pinhole.

[0027] In addition, the gain medium 12 can be Nd:YAG, Nd:YLF, Nd:YVO4, etc. Nd 3+ doped gain medium 12 with a concentration of 0.8at%-1.2at% and a thickness of 1-3mm, in a cylindrical or square structure;

[0028] The gain medium 12 and the pump source 13 as a whole can be installed between the first lens 14 and the variable pinhole diaphragm 15, between the variable pinhole diaphragm 15 and the second lens 16, and between the second lens 16 and the output coupling mirror 17.

[0029] Referring to Figure 2 and Figure 3 The variable pinhole diaphragm 15 in the embodiment includes a cover ring 151, an arc-shaped piece 152 and a mounting ring 153 stacked in sequence, one end of the arc-shaped piece 152 is provided with a rotating shaft 1521 used to be rotatably connected with the end face of the cover ring 151; a plurality of adjusting sliding grooves 1531 are formed around the mounting ring 153, and the other end of the arc-shaped piece 152 is clamped into the adjusting sliding groove 1531 and slidably matched therewith; and a light-transmitting hole 1522 is formed in the middle part of the plurality of arc-shaped pieces 152.

[0030] In order to facilitate the aperture adjustment operation, the outer edge surface of the mounting ring 153 is provided with an adjustment handle 1532. By rotating the adjustment handle 1532 by a certain angle in the circumferential direction, the size of the middle light transmission hole 1522 is changed to meet the use requirement.

[0031] As shown in Figure 1 The external feedback component 2 in the embodiment includes a non-polarized cube beam splitter 21, an adjustable neutral density attenuation sheet 22 and a second mirror 23. The non-polarized cube beam splitter 21 is arranged on the side close to the output coupling mirror 17. Specifically, in order to realize the regulation and control of the time coherence, the non-polarized cube beam splitter 21 divides the light beam into two beams, one of which is used for outputting the time-space coherence adjustable light beam, and the other of which is used for external feedback. The adjustable neutral density attenuation sheet 22 is used for adjusting the feedback intensity and regulating and controlling the time coherence dynamics of the degenerate cavity laser 1. The second mirror 23 is used for reflecting the light beam back into the resonant cavity. Since the time coherence refers to the coherence between the light wave fields at the same space and different times. The coherence time describes the maximum time interval at which the light wave fields can maintain coherence at a certain point in the direction of light propagation, which represents the coherence of the wave train emitted by the light source within a limited time duration. Since narrow linewidth means frequency stability of the light wave, the increase of the light source linewidth will prolong the coherence time, thereby increasing the ability of the light wave field to maintain coherence. The external feedback component 2 generates an external cavity mode in the cavity through the delay self-feedback, which can be used to expand the spectral linewidth of the laser. Under the steady-state condition, the characteristic equation of the external cavity mode is:

[0032] ω s -ω0-κsin(ω s τ)=0

[0033] wherein ω s is the steady-state angular frequency of the laser output, ω0is the isolated frequency of the degenerate cavity laser, which corresponds to the eigenfrequency of the laser output without external cavity feedback, κ is the feedback intensity, which can be adjusted by the adjustable neutral density attenuation sheet 22 and the external cavity length, is the delay of the laser in the external cavity, L is the cavity length, c and c is the speed of light. With the increase of the feedback intensity, the number of the steady-state angular frequency of the laser increases, the range expands, the bandwidth Δν of the spectrum increases, the coherence time decreases, so the time coherence decreases with the increase of the feedback intensity.

[0034] The positions of the non-polarized cube beam splitter 21 and the adjustable neutral density attenuation sheet 22 can be exchanged. The distance between the output coupling mirror 17, the non-polarized cube beam splitter 21, the adjustable neutral density attenuation sheet 22 and the second mirror 23 can be changed between 1-10 cm.

[0035] It is worth mentioning that the first lens 14 and the second lens 16 are flat convex lenses or double convex lenses; and the focal length of the first lens 14 and the second lens 16 is 20 cm or 30 cm, and the diameter is 25.4 cm or 50.8 cm, and a high transmittance film layer for 1064 nm wavelength needs to be plated.

[0036] As shown in Figure 4 The near-field distribution and the mode number N of the light field generated by the pinhole aperture d in the embodiment increase with the increase of the pinhole aperture, the high-order mode number supported by the cavity increases, and the output spot area increases.

[0037] As shown in Figure 5 The speckle image and the speckle contrast C in the embodiment increase with the increase of the pinhole aperture d, the number of independent modes increases, the spatial coherence decreases, and the speckle contrast decreases.

[0038] The above is only the preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A spatiotemporally coherent tunable light source based on external cavity feedback and a degenerate cavity, characterized in that: The system includes a coaxially arranged degenerate cavity laser (1) and an external feedback assembly (2). The degenerate cavity laser (1) includes a first reflector (11), a first lens (14), a variable pinhole aperture (15), a second lens (16), and an output coupling mirror (17) arranged in sequence.

2. The spatiotemporally coherent tunable light source based on external cavity feedback and degenerate cavity according to claim 1, characterized in that: The variable aperture stop (15) includes a cover ring (151), an arc-shaped piece (152) and a mounting ring (153) stacked in sequence. One end of the arc-shaped piece (152) is equipped with a rotating shaft (1521) for rotatably connecting with the end face of the cover ring (151). The mounting ring (153) is provided with a plurality of adjusting grooves (1531) around it, and the other end of the arc-shaped piece (152) is inserted into the adjusting grooves (1531) and slides in cooperation with them; A light-transmitting hole (1522) is formed in the middle of several of the aforementioned arc-shaped pieces (152).

3. The spatiotemporally coherent tunable light source based on external cavity feedback and degenerate cavity according to claim 2, characterized in that: The outer edge of the mounting ring (153) is provided with an adjustment handle (1532).

4. The spatiotemporally coherent tunable light source based on external cavity feedback and degenerate cavity according to claim 1, characterized in that: The external feedback component (2) includes a non-polarized cubic beam splitter (21), an adjustable neutral density attenuator (22), and a second reflector (23). The non-polarized cubic beam splitter (21) is located close to the output coupling mirror (17).

5. The spatiotemporally coherent tunable light source based on external cavity feedback and degenerate cavity according to claim 1, characterized in that: The degenerate cavity laser (1) further includes a pump source (13) and a gain medium (12). The pump source (13) and the gain medium (12) are disposed between the first reflector (11) and the first lens (14), and the pump source (13) is disposed above the gain medium (12).

6. The spatiotemporally coherent tunable light source based on external cavity feedback and degenerate cavity according to claim 1, characterized in that: The first lens (14) and the second lens (16) are plano-convex lenses or biconvex lenses.

7. The spatiotemporally coherent tunable light source based on external cavity feedback and degenerate cavity according to claim 6, characterized in that: The focal lengths of the first lens (14) and the second lens (16) are 20cm or 30cm.

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