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CN-122026212-A - Active Q-switched nanosecond pulse laser based on crystal waveguide with extremely thin cladding structure

CN122026212ACN 122026212 ACN122026212 ACN 122026212ACN-122026212-A

Abstract

The invention discloses an active Q-switched nanosecond pulse laser based on an ultrathin cladding structure crystal waveguide, which comprises a crystal waveguide, a pumping source, a pumping collimation focusing system and a Q-switched system, wherein the crystal waveguide and the Q-switched system jointly form a laser resonant cavity, the crystal waveguide adopts an ultrathin cladding structure with refractive index matching and mode competition optimization design, still supports fundamental mode oscillation under the condition of a larger core diameter, and forms high saturation gain in the Q-switched working process. The high-efficiency constraint of the crystal waveguide to the pump light realizes high inversion particle number density and high single-pass gain under the condition of medium-cavity long strip, namely larger film volume, and the electro-optic Q-switching technology is matched, so that the energy in the cavity is intensively released in a short time, and the pulse laser output with subnanosecond pulse width and several millijoules of energy is obtained, and the beam quality is close to the diffraction limit. The invention realizes high-stability narrow pulse width Q-switched laser output on the premise of not depending on a microchip short cavity structure.

Inventors

  • LEI HENG
  • LIU SIQI
  • HAN XUE
  • ZHU ZHANDA
  • LI QIANG

Assignees

  • 北京工业大学

Dates

Publication Date
20260512
Application Date
20260224

Claims (10)

  1. 1. An active Q-switched nanosecond pulse laser based on an extremely thin cladding structure crystal waveguide is characterized by comprising a crystal waveguide (1), a pumping source (2), a pumping collimation focusing system (3) and a Q-switched system (4); The crystal waveguide (1) is of a double-cladding circular structure and comprises a core layer, an inner cladding layer and an outer cladding layer, wherein the core layer is a rare earth ion doped laser gain crystal, the inner cladding layer is of an extremely thin cladding layer structure design, the thickness of the inner cladding layer is compressed to a minimum interval on the premise of meeting the total reflection penetration depth requirement, and the crystal waveguide still keeps stable fundamental mode oscillation under a high saturation gain working state; The pump light emitted by the pump source (2) is coupled into the core layer of the crystal waveguide after passing through the pump collimation focusing system (3) to provide laser gain for the crystal waveguide (1); The crystal waveguide (1) and the Q-switching system (4) jointly form a laser resonant cavity, and the resonant cavity loss is modulated to enable the energy in the cavity to be built and rapidly released in a short time, so that pulse laser with subnanosecond pulse width and several millijoules of energy is output under the condition that the cavity length is 70 mm-80 mm.
  2. 2. The nanosecond pulse laser of claim 1, wherein the inner cladding has a thickness of 80-150 μιη.
  3. 3. The nanosecond pulse laser according to claim 1, wherein the refractive index between the core layer and the inner cladding layer is controlled by doping inactive ions, so that the refractive index difference deltan between the core layer and the inner cladding layer is in the order of 10 -6 , thereby suppressing the higher-order transverse mode under the condition of large core diameter and only supporting the fundamental mode oscillation.
  4. 4. The nanosecond pulse laser of claim 1, wherein the laser beam quality factor M 2 of the laser output in the Q-switched operating state is less than 1.1.
  5. 5. Nanosecond pulse laser according to claim 1, characterized in that the crystal waveguide (1) has a diameter of 0.7 mm-0.9 mm, a length of 5 mm-15 mm and a cross-sectional dimension of the core layer of 0.3 mm-0.6 mm.
  6. 6. Nanosecond pulse laser according to claim 1, characterized in that the pump source (2) is a fiber-coupled semiconductor laser diode module.
  7. 7. Nanosecond pulse laser according to claim 1, characterized in that the pump collimation focusing system (3) comprises a first collimation mirror (6), a protection mirror (7) and a first focusing mirror (8) arranged in sequence along the direction of the optical path.
  8. 8. The nanosecond pulse laser according to claim 1, wherein the Q-switched system (4) comprises a front cavity mirror (9), a polarization control element (10), a phase delay element (11), an electro-optic Q-switched crystal (12) and a rear cavity mirror (13) which are sequentially arranged along the optical path direction, the crystal waveguide (1) is positioned between the front cavity mirror (9) and the polarization control element (10), and nanosecond pulse laser output is achieved by modulating the resonant cavity loss at a high speed.
  9. 9. The nanosecond pulse laser of claim 8, wherein the electro-optically Q-switched crystal is an RTP crystal.
  10. 10. The nanosecond pulse laser according to claim 1, further comprising a frequency doubling system (5) arranged at the laser output end and used for performing frequency conversion on the nanosecond pulse laser so as to obtain pulse laser outputs with different wavelengths, wherein the frequency doubling system (5) comprises a second collimating mirror (14), a second focusing mirror (15), a half-wave plate (16), a nonlinear frequency doubling crystal (17) and a dichroic mirror (18) which are sequentially arranged along the optical path direction.

Description

Active Q-switched nanosecond pulse laser based on crystal waveguide with extremely thin cladding structure Technical Field The invention relates to the technical field of solid lasers, in particular to an active Q-switched nanosecond pulse laser based on an extremely thin cladding structure crystal waveguide, which is based on an extremely thin cladding structure crystal waveguide gain medium and utilizes high saturation gain to realize pulse laser output with subnanosecond pulse width, energy of a plurality of millijoules and beam quality approaching a diffraction limit. Background The nanosecond pulse solid laser has important application value in the fields of precision machining, laser ranging, nonlinear optics, scientific research and the like. Nanosecond pulse lasers are typically implemented by Q-switched techniques, however, prior art techniques have great difficulty in achieving a narrow pulse width, high energy, and high beam quality balance under medium cavity conditions. The fiber laser has good heat radiation performance, can obtain higher average power output, but is limited by the fiber core size, is easy to generate nonlinear effects such as self-phase modulation, stimulated Raman scattering and the like under the condition of high peak power, and is difficult to realize high-energy nanosecond pulse output. Bulk solid state lasers typically employ free space resonator structures, although energy-bearing, but to achieve sub-nanosecond pulse widths, they typically require a microchip structure with a cavity length compressed to within 20mm (see ：WANG Y, GONG M, ZHANG H J E L. 2 ns pulse width high repetition rate short cavity acousto-optically Q-switched Nd: YVO4 laser [J]. 2007, 43(7): 394-6）,, which limits the element integration space, limits the gain medium mode volume, and has severe thermal effects under high pumping conditions, resulting in poor beam quality, planar waveguide or slab lasers improve thermal management issues to some extent, but they typically limit the lasing modes in only a single direction, making it difficult to obtain highly symmetric near-diffraction-limited fundamental mode beams. The prior art (such as publication number CN101276983A, CN201726032U, etc.) generally follows the linear physical rule of "short cavity length corresponds to short pulse width", and the narrow pulse width is realized by compressing the physical length of the resonant cavity to the limit (typically less than 60mm, even within 20mm by using an optical cement process). However, the extremely short cavity length severely limits the integration space of the functional element and the thermal stability at high power densities is poor. The prior art (such as CN205452777U, CN104201554A, CN1328831C, etc.) mostly adopts conventional bulk crystal, ceramic rod or bonded crystal as gain medium, at high pumping power density, serious thermal lens effect and thermally induced birefringence are inevitably generated inside the crystal, resulting in difficulty in maintaining beam quality near diffraction limit at high energy output, and difficulty in further compressing pulse width by increasing pumping density. The prior art (e.g., CN201124237Y, CN121035754A, CN104466547 a) adjusts or narrows the pulse width by changing the cavity length through a mechanical displacement mechanism, introducing multiple fiber switches, or adding complex feedback clipping/saturable absorbing elements outside the cavity. The schemes obviously increase the mechanical complexity and optical loss of the system, reduce the long-term stability of the laser in vibration and temperature changing environments, and are difficult to simultaneously meet the double indexes of 'subnanosecond narrow pulse width' and 'millijoule high energy'. Therefore, developing a laser with high energy carrying capacity, narrow pulse width and excellent beam quality is a technical problem to be solved in the art. The crystalline waveguide structure combines the mode confinement characteristics of the fiber structure with the higher energy carrying capacity and damage threshold of bulk solid crystalline materials, which is potentially advantageous in solving the above-mentioned problems. The double-clad circular crystal waveguide structure （LI S, HUANG Y, NIE X, et al. High-efficiency and high-brightness circular-clad, large-size, rectangular core crystalline waveguide Yb:YAG laser [J]. Optics Letters, 2025, 50(5): 1665-8.） disclosed by the subject group is only a conventional thickness clad, continuous oscillation and high average power output are taken as design targets, and the clad thickness and the thermal management scheme are suitable for a steady-state gain extraction process, but are not considered and are not suitable for realizing nanosecond pulse width at high pump power density. Disclosure of Invention Aiming at the defects in the prior art, the invention provides an active Q-switched nanosecond pulse laser based on an extremely thin claddin