CN109510059B - A Q-switched laser with long pulse output - Google Patents

Abstract

A Q-switched laser that outputs long pulses, comprising: a quartz glass rod (4), an output mirror (5), a mirror (1), a Q switch (2) and a gain medium (3) arranged in sequence along the optical axis; The glass rod (4) is provided with an incident window (401) and an exit window (404); one end of the quartz glass rod (4) is provided with a first reflective surface (402) whose curvature is R; Two reflection surfaces (403); the incident window (401) is arranged on the second reflection surface (403), and the exit window (404) is arranged on the first reflection surface (402) or the second reflection surface (403); the output mirror ( 5) It is arranged on the optical axis of the light beam emitted through the exit window (404). The Q-switched laser provided by the present invention is provided with a quartz glass rod 4. On the one hand, the quartz glass rod can increase the actual optical path of the optical path in the Q-switched laser. Output stable long pulse Q-switched laser.

Description

A Q-switched laser with long pulse output

technical field

The invention relates to the technical field of Q-switched lasers, in particular to a long-pulse Q-switched laser output.

Background technique

The pulse width of Q-switched lasers is generally between 10 ns and 500 ns, and the pulse peak power of long-pulse Q-switched lasers with a pulse width of 0.5 to 10 μs is not high, but the average power is much greater than that of ordinary pulsed lasers. It has great development potential and application prospects in scientific research and other applications. The pulse width of the Q-switched laser output laser is proportional to the cavity length of the laser, so the method of increasing the cavity length is usually used to obtain long-pulse Q-switched laser output. At present, in order to output long-pulse Q-switched lasers, the prior art is realized by directly pulling the cavity technology or using a multi-pass long cavity technology composed of a pair of concave mirrors separated by a certain distance. However, these solutions themselves have the following defects:

1) Using direct cavity pulling technology: directly extend the cavity length of the laser resonator without inserting any other optical components to introduce losses. Although this technology is relatively simple, directly pulling the cavity will cause the cavity length of the entire laser resonator to be too long and the volume will become larger, which is not conducive to miniaturization and practicality, and the production cost is high.

2) Multi-pass long cavity technology is adopted: the multi-pass long cavity is composed of a pair of concave mirrors separated by a certain distance, each concave mirror has an optical slot, and the beam is injected into the multi-pass long cavity from the slot of one of the concave mirrors ; Then it reflects multiple times on two concave mirrors, transmits back and forth, and shoots out from the slot of another concave mirror. Although the multi-pass long-cavity technology can meet the purpose of increasing the actual optical path of the optical path to obtain long-pulse Q laser output and reducing the volume of the laser. However, this technology requires two concave mirrors to be installed in the resonant cavity, and the adjustment accuracy and maintenance accuracy of the two concave mirrors are very high. If the positions of the two concave mirrors change, the laser may not be output. In addition, the stability of the laser is further reduced due to the influence of airflow between the two concave mirrors.

Contents of the invention

The purpose of the present invention is to provide a Q-switched laser that outputs long pulses. By setting a quartz glass rod in the optical path of the Q-switched laser, the light beam can be injected into the reflective surfaces at both ends of the quartz glass rod from the incident window of the quartz glass rod. Reflected multiple times, the light beam conforming to νθ=μπ is output from the exit window of the quartz glass rod. The Q-switched laser provided by the present invention is provided with a quartz glass rod 4. On the one hand, the actual optical path of the optical path in the Q-switched laser can be increased; It is exactly the same as before, that is, the unit conversion of the q parameter is realized, so that a stable long-pulse Q laser output can be obtained.

In order to solve the above problems, the first aspect of the present invention provides a long-pulse Q-switched laser, comprising: a quartz glass rod, an output mirror, a reflective mirror, a Q switch and a gain medium arranged in sequence along the optical axis; the quartz glass rod is provided with An incident window and an exit window; one end of the quartz glass rod is provided with a first reflective surface whose curvature is R; the other end is provided with a second reflective surface whose curvature is R; the incident window is arranged on the second reflective surface, and the exit window is arranged at A reflective surface or a second reflective surface; the output mirror is arranged on the optical axis of the light beam emitted through the exit window.

Further, the light beam entering the quartz glass rod from the incident window is reflected from the first reflective surface to the second reflective surface to form a reflection cycle; or, the light beam entering the quartz glass rod from the incident window is reflected from the second reflective surface to the first reflective surface and reflected back to the second reflective surface to form a reflection cycle; in two adjacent reflection cycles, two reflections from the first reflection surface to the second reflection surface or two reflections from the second reflection surface to the second reflection surface The included angle of the light on the first reflective surface is θ, and θ=2cos ^-1 (1-d/R), and satisfies νθ=μπ; where, d is the length of the quartz glass rod, ν is the number of round trips, and ν and μ are all positive integers.

Further, the mirror is coated with a high reflection film.

Further, the Q switch is one of an electro-optic Q-switch, an acousto-optic Q-switch, a dye Q-switch or a color center crystal Q-switch.

Further, the gain medium is Nd:YAG, Yb:YAG, ceramics, carbon dioxide CO ₂ , helium-neon gas, copper vapor, gallium arsenide GaAs, cadmium sulfide CdS, indium phosphide InP, rhodamine 6G or rhodamine One of B.

Further, the pumping mode of the Q-switched laser is end pumping or side pumping.

Further, the first reflective surface and the second reflective surface are coated with a high reflective film.

Further, the output mirror is coated with a film with a certain transmittance for the output wavelength.

Further, an etalon, a wave plate, a volume Bragg grating, a birefringent filter, a nonlinear frequency conversion crystal, and a polarizer are arranged between any of the mirror, the Q switch, the gain medium, the quartz glass rod, and the output mirror. any one or more of.

Further, two places of the quartz glass rod are respectively provided with high-transmission films, and the positions where the high-transmission films are provided are the incident window and the exit window.

Further, the incident window and the exit window are planar structures.

The technical solution of the present invention has the following beneficial technical effects:

(1) By setting a quartz glass rod in the optical path of the Q-switched laser, the light beam can be incident from the incident window of the quartz glass rod and reflected on the reflective surfaces at both ends of the quartz glass rod for multiple reflections. The glass rod exits the window output. Through the above-mentioned quartz glass rod, on the one hand, the light travels back and forth for ν times, which can increase the actual optical path length of the optical path; on the other hand, when the θ angle meets the closing condition, the q parameter and It is exactly the same before the injection, that is, the unit conversion of the q parameter is realized, so that the quartz glass rod itself has a zero effect length in the optical path, so that a stable long-pulse Q laser output can be obtained.

(2) Since the quartz glass rod has the characteristics of low loss and extremely small thermal expansion coefficient, the present invention obtains a long pulse output compared with the multi-pass long cavity technology by replacing the quartz glass rod with a multi-pass long cavity composed of a pair of concave mirrors For lasers, the requirements for adjusting the position accuracy and maintaining accuracy of the two concave mirrors are reduced, and a solid quartz glass rod can be set without considering the influence of airflow, which further improves the stability of the laser.

Description of drawings

Fig. 1 is a schematic structural diagram of a long-pulse Q-switched laser according to a first embodiment of the present invention;

Fig. 2 is a schematic diagram of the transmission of the light beam in the quartz glass rod in the Q-switched laser according to the first embodiment of the present invention;

3 is a schematic structural diagram of a Q-switched laser according to a second embodiment of the present invention;

4 is a schematic diagram of spot distribution on the first reflective surface or the second reflective surface of the quartz glass rod in the Q-switched laser shown in FIG. 3;

5 is a schematic structural diagram of a Q-switched laser according to a third embodiment of the present invention;

FIG. 6 is a schematic diagram of spot distribution on the first reflective surface or the second reflective surface of the quartz glass rod in the Q-switched laser shown in FIG. 5 .

Reference signs:

1: mirror; 2: Q switch; 3: gain medium; 4: quartz glass rod; 401: incident window; 402: first reflective surface; 403: second reflective surface; 404: exit window; 5: output mirror; 6: Pump source.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are exemplary only, and are not intended to limit the scope of the present invention. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concept of the present invention.

Fig. 1 is a schematic structural diagram of a long-pulse Q-switched laser according to the first embodiment of the present invention.

As shown in FIG. 1 , the laser includes: a quartz glass rod 4 , an output mirror 5 , and a reflection mirror 1 , a Q switch 2 and a gain medium 3 arranged in sequence along the optical axis.

Wherein, the quartz glass rod 4 is provided with an incident window 401 and an exit window 404; one end of the quartz glass rod 4 is provided with a first reflective surface 402 with a curvature of R; the other end is provided with a second reflective surface 403 with a curvature of R; the incident window 401 is set on the second reflective surface 403 , and the exit window 404 is set on the first reflective surface 402 or the second reflective surface 403 ; the output mirror 5 is set on the optical axis of the light beam emitted through the exit window 404 .

Specifically, FIG. 2 is a schematic diagram of beam transmission in a quartz glass rod in the Q-switched laser shown in FIG. 1 .

As shown in Figures 1 and 2, the oscillation path of light in the Q-switched laser includes: the light emitted by the stimulated radiation of the gain medium 3 enters the quartz glass rod 4 through the incident window 401 along the optical axis, and is reflected by the first reflective surface 402 to The second reflective surface 403, constantly reflecting between the first reflective surface 402 and the second reflective surface 403, emits from the exit window 404, exits to the surface of the output mirror 5, and is reflected by the surface of the output mirror 5, and the original path is from the exit window 404 It is injected into the quartz glass rod 4, passes through the first reflective surface 402 and the second reflective surface 403 multiple round-trip transmissions, is emitted from the incident window 401, passes through the gain medium 3, the Q switch 2 and is reflected to the gain medium 3 by the reflector 1, and passes through the gain medium 3. After the gain medium 3, it enters the quartz glass rod 4, so that it oscillates back and forth continuously. When the number of photons in the resonator reaches the output threshold, that is, when the energy contained in the number of photons in the resonator is higher than the loss of the light beam in the resonator, the light is output from the output mirror 5, and the light output from the output mirror 5 is is the output laser of the long-pulse Q-switched laser, and the output laser is a long-pulse Q-switched laser.

It should be noted that since the first reflective surface 402 is provided with a preset curvature R, in the longitudinal direction, the light beam passing through the first reflective surface 402 will be reflected to the second reflective surface 403 at an angle α. Since the second reflective surface 403 is also provided with the same curvature R as that of the first reflective surface. Therefore, the second reflective surface 403 reflects the light beam incident on its surface to the first reflective surface at an angle of α, the light beam is continuously reflected on the two reflective surfaces, and finally output through the exit window 404 . Therefore, every time the light is reflected by the reflective surface, there is a rotation angle of ɑ, and the angle between two adjacent reflected light rays on the same reflective surface is θ, and θ=2ɑ. The rotation angle θ will be described in detail below.

In the embodiment shown in Fig. 1 and Fig. 2, the light beam entering the quartz glass rod 4 from the incident window 401, initially, the light beam entering the quartz glass rod 4 from the incident window 401 is reflected by the first reflecting surface 402 to The second reflective surface 403 forms a reflection cycle; or, after the light beam is reflected to the first reflective surface for the second time, the light beam is reflected from the first reflective surface 402 to the second reflective surface 403 and reflected back to the first reflective surface 402 to form a cycle. A reflection cycle; or, a light beam entering the quartz glass rod 4 from the incident window 401 is reflected from the second reflection surface 403 to the first reflection surface 402 and reflected back to the second reflection surface 403 to form a reflection cycle.

In two adjacent reflection cycles, the included angles of the two rays reflected from the first reflective surface 402 to the second reflective surface 403 and the included angles of the two rays reflected from the second reflective surface to the first reflective surface 403 are the same, both Be rotation angle θ, θ is less than or equal to 180 ° (when ν=μ=1, θ=180 °), and θ=2cos ^-1 (1-d/R), wherein, d is the length of quartz glass rod 4 , R is the radius of curvature of the first reflective surface and the second reflective surface. When the light beam satisfies νθ=μπ, a closed optical path will be formed, where ν is the number of round trips, that is, the number of cycles, and both ν and μ are positive integers.

According to the above formula νθ=μπ, from the ABCD matrix transmission theory, the matrix T of the light beam forming a closed optical path in the quartz glass rod after ν round-trip propagation can be calculated as:

It can be known from the above matrix that the matrix is an identity matrix, that is to say, after ν round trips, the quartz glass rod provides the unit transformation of the q parameter to the light beam, that is, the light is transmitted from the exit window (404) through ν round trips. The q parameter when ejecting is exactly the same as before injecting from the incident window (401), it can be seen that the quartz glass rod 4 has a zero effect length in the optical path, that is, the quartz glass rod 4 is added in the laser, except for increasing the actual light of the optical path. The process does not change the properties of the beam spot size and divergence angle.

Therefore, the Q-switched laser provided by the present invention adopts a quartz glass rod instead of a multi-pass long cavity composed of a pair of concave mirrors, which reduces the need for adjusting two concave mirrors compared to the multi-pass long cavity technology to obtain a long pulse output laser. The position accuracy of the mirror and the requirements for maintaining accuracy, and a solid quartz glass rod can be set without considering the influence of the airflow, which further improves the stability of the laser.

In a preferred embodiment, the mirror 1 is coated with a high-reflection film, which refers to a film with high reflectivity for the wavelength of the oscillating laser.

In one embodiment, the Q switch 2 is one of electro-optic Q-switches, acousto-optic Q-switches, dye Q-switches or color center crystal Q-switches.

In one embodiment, the gain medium 3 is Nd:YAG, Yb:YAG, ceramic, carbon dioxide CO ₂ , helium-neon gas, copper vapor, gallium arsenide GaAs, cadmium sulfide CdS, indium phosphide InP, rhodamine 6G Or one of Rhodamine B.

It should be noted that when the gain medium is in a gaseous state, the gaseous gain medium is accommodated in a gas storage tank, which can be pumped electrically; when the gain medium is in a liquid state (such as Rhodamine 6G or Rhodamine B, etc. dye gain medium), put the liquid gain medium into the dye box.

In one embodiment, the pumping mode of the Q-switched laser is end-pumped or side-pumped.

In one embodiment, the first reflective surface 402 and the second reflective surface 403 are coated with a high reflective film, and the high reflective film refers to a film with high reflectivity for the wavelength of the oscillating laser. For example, if the wavelength of the oscillating laser is 1064nm, then the high-reflection film reflects the laser with a wavelength of 1064nm, and the general reflectivity can reach more than 99.9%.

In one embodiment, the output mirror 5 is coated with a film with a certain transmittance for the output wavelength.

It should be noted that a film with a certain transmittance refers to how much energy can be transmitted or reflected for laser light of this wavelength. For example, a film with a certain transmittance has a transmittance of 40% for a wavelength of 1064nm, which means that when 1064nm light passes through the film coated with a certain transmittance, 40% of the energy can pass through and 60% is reflected. For example, if the laser energy is 100W and the wavelength is 1064nm through a film with a transmittance of 40%, the laser energy with a wavelength of 1064nm will pass through 40W and the energy will reflect 60W; for example, if it is coated with a 99.9% reflective film, the wavelength is 99.9% of the energy of 1064nm light is reflected, and only 0.1% is transmitted.

In one embodiment, an etalon, wave plate, volume Bragg grating, birefringence filter, Any one or more of nonlinear frequency conversion crystals and polarizers.

Specifically, due to the characteristics of optics, an optical element may be disposed between any of the reflector 1 , the Q switch 2 , the gain medium 3 , the quartz glass rod 4 and the output mirror 5 . For example, an etalon is inserted along the optical path between the reflector 1 and the Q switch 2, and the etalon can be used to narrow the line width and select the wavelength.

In one embodiment, two places of the quartz glass rod 4 are respectively provided with a high-transmission film, and the positions where the high-transmission film is provided are the incident window 401 and the exit window 404 . Among them, the high-transmittance film is a film with high transmittance to an oscillating light beam. For example, if the wavelength of the oscillating laser is 1064nm, then the high-transparency film can transmit the laser with a wavelength of 1064nm, and the general transmittance can reach more than 99.9%.

The above-mentioned technical scheme of the present application has the following beneficial effects:

(1) By setting a quartz glass rod in the optical path of the Q-switched laser, the light beam can be incident from the incident window of the quartz glass rod and reflected on the reflective surfaces at both ends of the quartz glass rod for multiple reflections. The glass rod exits the window output. Through the above-mentioned quartz glass rod, on the one hand, the light travels back and forth for ν times, which can increase the actual optical path length of the optical path; on the other hand, when the θ angle meets the closing condition, the q parameter and It is exactly the same before the injection, that is, the unit conversion of the q parameter is realized, so that the quartz glass rod itself has a zero effect length in the optical path, so that a stable long-pulse Q laser output can be obtained.

(2) Since the quartz glass rod has the characteristics of low loss and extremely small thermal expansion coefficient, the present invention obtains a long pulse output compared with the multi-pass long cavity technology by replacing the quartz glass rod with a multi-pass long cavity composed of a pair of concave mirrors For lasers, the requirements for adjusting the position accuracy and maintaining accuracy of the two concave mirrors are reduced, and a solid quartz glass rod can be set without considering the influence of airflow, which further improves the stability of the laser.

Fig. 3 is a schematic structural diagram of a long-pulse Q-switched laser according to the second embodiment of the present invention; Fig. 4 is a schematic diagram of spot distribution on the first reflective surface or the second reflective surface of the quartz glass rod in the Q-switched laser shown in Fig. 3 .

As shown in FIG. 3 , the pumping source 6 used in the second embodiment of the present invention is a side pump. Wherein, the reflective mirror 1 is a flat mirror, and is coated with a high reflective film for a wavelength of 1064nm.

Q switch 2 is an acousto-optic Q switch.

The gain medium is Nd:YAG. The incident window 401 and the exit window 404 of the quartz glass rod 4 are coated with a high-transmission film for a wavelength of 1064 nm, and the first reflective surface 402 and the second reflective surface window 403 are coated with a high-reflection film for a wavelength of 1064 nm.

The pumping method is side pumping, and the pumping source 6 may be optical pumping.

The output mirror 5 is a flat mirror coated with a certain transmittance for a wavelength of 1064nm.

The oscillating path of light in the above-mentioned laser is: the light of the stimulated radiation of the gain medium 3 enters the quartz glass rod 4 through the incident window 401 along the optical axis direction, and is reflected to the second reflective surface 403 through the first reflective surface 402. The continuous reflection between the reflective surface 402 and the second reflective surface 403 emits from the exit window 404, exits to the surface of the output mirror 5, is reflected by the surface of the output mirror 5, and injects into the quartz glass rod 4 from the exit window 404 in the original path, and passes through The first reflective surface 402 and the second reflective surface 403 transmit multiple times back and forth from the incident window 401, pass through the gain medium 3, the Q switch 2 and reflect to the gain medium 3 through the mirror 1, and then enter the quartz glass after passing through the gain medium 3 Constantly vibrate back and forth like this in the rod 4. When the number of photons in the cavity reaches the output threshold, the long-pulse Q-switched laser is output from the output mirror 5 coated with a certain transmittance.

It should be noted that, in the long-pulse Q-switched laser provided in the second embodiment of the present application, the light stimulated to radiate from the gain medium 3 is incident on the quartz glass rod 4 at a certain angle, and when νθ=μπ is satisfied, the beam will emerge from Window 404 output.

There is an α every time the light beam is reflected by the first reflective surface or the second reflective surface. If the angle of the incident light beam relative to the optical axis is changed, the distribution locus of the reflected light spots on the first reflective surface or the second reflective surface forms an ellipse or a circle.

As shown in Figure 4, when the number of round trips of the beam is ν=4, μ=2, θ=90°, the light spot distribution diagram on the first reflective surface or the second reflective surface of the quartz glass rod. The light spots in solid lines are the light spots on the first reflective surface 402 , and the light spots in dashed lines are the light spots on the second reflective surface 403 viewed from the first reflective surface 402 .

The light beam enters the quartz glass rod 4 from P ₀ , P ₀ → P ₁ ′ → P ₁ → P ₂ ′ → P ₂ → P ₃ ′ → P ₃ → P ₄ ′, and exits from P ₄ ′; it is reflected by the output mirror 5 After that, it is injected from P ₄ ′, P ₄ ′→P ₃ →P ₃ ′→P ₂ →P ₂ ′→P ₁ →P ₁ ′→P ₀ , and is emitted from P ₀ to the gain medium 3, passing through the gain medium Finally, after being reflected by the mirror 1, it is injected into the quartz glass rod 4 through the gain medium 3 again, and continuously oscillates in this way. When the number of photons in the cavity reaches the output threshold, the long-pulse Q-switched laser is emitted from the Output mirror 5 output.

The above-mentioned technical scheme of the present application has the following beneficial effects:

(1) By setting a quartz glass rod in the optical path of the Q-switched laser, the light beam can be incident from the incident window of the quartz glass rod and reflected on the reflective surfaces at both ends of the quartz glass rod for multiple reflections. The glass rod exits the window output. Through the above-mentioned quartz glass rod, on the one hand, the light can increase the actual optical path of the optical path through ν times of round-trip transmission; The q parameter of the laser is exactly the same as that before the injection, that is, the unit conversion of the q parameter is realized, so that the quartz glass rod itself has a zero effect length in the optical path, so that a stable long-pulse Q laser output can be obtained.

(2) Since the quartz glass rod has the characteristics of low loss and extremely small thermal expansion coefficient, the present invention obtains a long pulse output compared with the multi-pass long cavity technology by replacing the quartz glass rod with a multi-pass long cavity composed of a pair of concave mirrors For lasers, the requirements for adjusting the position accuracy and maintaining accuracy of the two concave mirrors are reduced, and a solid quartz glass rod can be set without considering the influence of airflow, which further improves the stability of the laser.

5 is a schematic structural diagram of a long-pulse Q-switched laser according to a third embodiment of the present invention; FIG. 6 is a schematic diagram of spot distribution on the reflective surface of the quartz glass rod in the Q-switched laser shown in FIG. 5 .

As shown in FIG. 5 , the laser includes: a quartz glass rod 4 , an output mirror 5 , and a mirror 1 , a Q switch 2 and a gain medium 3 arranged in sequence along the optical axis.

Wherein, the first reflective surface 402 is provided with an incident window 401 for the beam to enter and an exit window 404 for the beam to exit; or, the second reflective surface 403 is also provided with an incident window 401 for the beam to enter and an exit window 404 for the beam to exit. Window 404; or, the first reflective surface 402 is provided with the incident window 401 for the light beam to enter, and the second reflective surface 403 is provided with the exit window 404 for the light beam to exit; perhaps, the first reflective surface 402 is provided with the exit window 401 for the light beam to exit Window 404, the second reflective surface 403 is provided with an incident window 401 for incident light beams.

The output mirror 5 is arranged on the optical axis of the light beam emitted through the exit window 404 .

Wherein, the reflective mirror 1 is a plane mirror coated with a film with high reflectivity at 820nm.

The Q switch 2 is an electro-optical Q switch.

The gain medium in gain medium 3 is Ti:sapphire titanium sapphire crystal.

The incident window 401 and the exit window 404 of the quartz glass rod 4 are coated with a high-transmission film for a wavelength of 820nm, and the first reflective surface 402 and the second reflective surface 403 are coated with a high-reflection film for a wavelength of 820nm.

The output mirror 5 is a plane mirror coated with a film with a certain transmittance for a wavelength of 820nm.

The pumping source 6 is pumped by a flash lamp.

The oscillation process of the light beam in the Q-switched laser provided by the third embodiment of the present invention is as follows: the light of the stimulated radiation of the gain medium 3 enters the quartz glass rod 4 through the incident window 401 along the optical axis, and is reflected by the first reflecting surface 402 to the second Two reflective surfaces 403, continuously reflect between the first reflective surface 402 and the second reflective surface 403, emit from the exit window 404, exit to the surface of the output mirror 5, reflect on the surface of the output mirror 5, and shoot from the exit window 404 in the same way Into the quartz glass rod 4, through the first reflective surface 402 and the second reflective surface 403 multiple times of back and forth transmission from the incident window 401, through the gain medium 3, Q switch 2 and reflect to the gain medium 3 through the mirror 1, after the gain After the medium 3, it enters the quartz glass rod 4 and oscillates continuously like this. When the number of photons in the cavity reaches the output threshold, the long-pulse Q-switched laser is output from the output mirror 5 coated with a certain transmittance.

It should be noted that, since the first reflective surface 402 is provided with a preset curvature R, in the longitudinal direction, the light beam passing through the first reflective surface 402 will be reflected to the second reflective surface 403 at an angle α. Since the second reflective surface 403 is also provided with the same curvature R as that of the first reflective surface. Therefore, the second reflective surface 403 reflects the light beam incident on its surface to the first reflective surface at an angle of α, the light beam is continuously reflected on the two reflective surfaces, and finally output through the exit window 404 . Every time the light is reflected by a reflective surface, there is a rotation angle of ɑ. The angle between two adjacent reflections on a single reflective surface is θ, and θ=2ɑ. The rotation angle θ will be described in detail below.

The light beam entering the quartz glass rod 4 from the incident window 401 is reflected to the second reflecting surface 403 through the first reflective surface 402 to form a reflection cycle; or, the light beam entering the quartz glass rod 4 from the incident window 401, from the second Reflection from the reflective surface 403 to the first reflective surface 402 and back to the second reflective surface 403 constitutes a reflection cycle.

In two adjacent reflection cycles, the included angles of the two rays reflected from the first reflective surface 402 to the second reflective surface 403 and the included angles of the two rays reflected from the second reflective surface to the first reflective surface 403 are the same, both is the rotation angle θ, and θ=2cos ⁻¹ (1−d/R), wherein, d is the length of the quartz glass rod 4, and R is the radius of curvature of the first reflective surface and the second reflective surface. When the light beam satisfies νθ=μπ, a closed optical path will be formed, where ν is the number of round trips, and ν and μ are both positive integers.

According to the above formula νθ=μπ, from the ABCD matrix transmission theory, it can be calculated that the matrix of the light beam forming a closed optical path after ν round-trip propagation in the quartz glass rod is:

From the above matrix, it can be known that the matrix is a unit matrix, that is to say, after ν round trips, the quartz glass rod provides the unit transformation of the q parameter to the light beam, that is, when the light is emitted from the exit window after multiple round trips. The q parameter is exactly the same as before the incident from the incident window, so that the quartz glass rod has zero effective length in the optical path of the resonant cavity of the Q-switched laser.

Therefore, the Q-switched laser provided by the present invention adopts a quartz glass rod instead of a multi-pass long cavity composed of a pair of concave mirrors, which reduces the need for adjusting two concave mirrors compared to the multi-pass long cavity technology to obtain a long pulse output laser. Mirror position accuracy and requirements for maintaining accuracy. Moreover, a solid quartz glass rod can be set without considering the influence of airflow, which further improves the stability of the laser.

FIG. 6 is a schematic diagram of spot distribution on the reflective surface of the quartz glass rod in the Q-switched laser shown in FIG. 5 .

In the example shown in Fig. 6 (a), when making ν=9, μ=2, θ=40 °, the point pattern of the light spot distribution on the first reflective surface or the second reflective surface of the quartz glass rod, the solid point is The light spot formed on the first reflective surface 402, the hollow point is the light spot formed on the second reflective surface, compared with the parameter ν=4, μ=2, θ=90° of the beam in the laser shown in Figure 4, μ At the same time, changing the number of round trips ν can change the number of spots on the reflection window, that is, change the actual optical path of the optical path, and it is inversely proportional to the rotation angle θ.

In the example shown in Fig. 6 (b), when making ν=9, μ=4, θ=80°, the point pattern of the light spot distribution on the curved surface at both ends of the quartz glass rod is the same as that in Fig. 6 (a) ν=9, Compared with μ=2 and θ=40°, when the number of round-trips ν is the same, changing μ can change the angle θ of the light spot formed by two adjacent cycles on the reflection window, and it is proportional to it.

Optionally, determine the size and curvature of the quartz glass rod by:

First of all, according to the needs, determine the number of times v and μ of the beam retracement of the quartz glass rod (no practical significance, just as an integer multiple of π) and calculate the rotation angle θ according to the closed optical path formula νθ=μπ, according to θ=2cos ^-1 (1 -d/R) Calculate the relationship between the curvature R of the quartz glass rod and the length d, the length of the quartz glass rod can be determined first, so as to obtain the curvature of the quartz glass rod.

To sum up, the actual optical path of the optical path can be changed by adjusting the number of round trips ν of the light between the first reflective surface and the second reflective surface, so as to obtain a stable Q-switched long-pulse laser output.

The above-mentioned technical scheme of the present application has the following beneficial effects:

(1) By setting a quartz glass rod in the optical path of the Q-switched laser, the light beam can be incident from the incident window of the quartz glass rod and reflected on the reflective surfaces at both ends of the quartz glass rod for multiple reflections. The glass rod exits the window output. Through the above-mentioned quartz glass rod, on the one hand, the light travels back and forth for ν times, which can increase the actual optical path length of the optical path; on the other hand, when the θ angle meets the closing condition, the q parameter and It is exactly the same before the injection, that is, the unit conversion of the q parameter is realized, so that the quartz glass rod itself has a zero effect length in the optical path, so that a stable long-pulse Q laser output can be obtained.

(2) Since the quartz glass rod has the characteristics of low loss and extremely small thermal expansion coefficient, the present invention obtains a long pulse output compared with the multi-pass long cavity technology by replacing the quartz glass rod with a multi-pass long cavity composed of a pair of concave mirrors For lasers, the requirements for adjusting the position accuracy and maintaining accuracy of the two concave mirrors are reduced, and a solid quartz glass rod can be set without considering the influence of airflow, which further improves the stability of the laser.

It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and not to limit the present invention. Therefore, any modification, equivalent replacement, improvement, etc. made without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention. Furthermore, it is intended that the appended claims of the present invention embrace all changes and modifications that come within the scope and metesques of the appended claims, or equivalents of such scope and metes and bounds.

Claims (9)

1. A Q-switched laser outputting long pulses, comprising: the device comprises a quartz glass rod (4), an output mirror (5), a reflector (1), a Q switch (2) and a gain medium (3), wherein the reflector, the Q switch and the gain medium are sequentially arranged along an optical axis;

the quartz glass rod (4) is provided with an incident window (401) and an exit window (404);

one end of the quartz glass rod (4) is provided with a first reflecting surface (402) with the curvature of R; a second reflecting surface (403) with the other end provided with a curvature R;

the entrance window (401) is arranged on the second reflecting surface (403), and the exit window (404) is arranged on the first reflecting surface (402) or the second reflecting surface (403);

the output mirror (5) is arranged on the optical axis of the light beam emitted through the exit window (404);

the light beam entering the quartz glass rod (4) from the incidence window (401) is reflected to the second reflecting surface (403) through the first reflecting surface (402) to form a reflection cycle period; or,

the light beam entering the quartz glass rod (4) from the incidence window (401) is reflected from the second reflecting surface (403) to the first reflecting surface (402) and back to the second reflecting surface (403) to form a reflection cycle period;

in two adjacent reflection cycle periods, the included angle of two light rays reflected from the first reflection surface (402) to the second reflection surface (403) is theta, and the included angle of two light rays reflected from the second reflection surface (403) to the first reflection surface (402) is theta; wherein θ is 2cos^-1(1-d/R), and satisfies ν θ ═ μ pi;

wherein d is the length of the quartz glass rod (4), ν is the round-trip frequency, and ν and μ are positive integers.

2. The Q-switched laser according to claim 1, wherein the mirror (1) is coated with a high reflective film.

3. The Q-switched laser according to claim 1, wherein the Q-switch (2) is one of an electro-optic Q-switch, an acousto-optic Q-switch, a dye Q-switch or a color-centered crystal Q-switch.

4. The Q-switched laser according to claim 1, wherein the gain medium (3) is Nd-doped YAG-garnet Nd: YAG, Yb: YAG-doped Yb-doped YAG-garnet, ceramic, carbon dioxide CO₂Helium-neon, copper vapor, gallium arsenide GaAs, cadmium sulfide CdS, indium phosphide InP, rhodamine 6G, or rhodamine B.

5. The Q-switched laser of claim 1, wherein the laser is pumped by end-pumping or side-pumping.

6. The Q-switched laser according to claim 1, wherein the first reflecting surface (402) and the second reflecting surface (403) are plated with high reflective films; the output mirror (5) is coated with a film having a transmittance for the output wavelength.

7. The Q-switched laser according to claim 1, wherein any one or more of an etalon, a wave plate, a volume Bragg grating, a birefringent filter, a nonlinear frequency conversion crystal and a polarizing plate is arranged between any two of the reflector (1), the Q-switch (2), the gain medium (3), the quartz glass rod (4) and the output mirror (5).

8. The Q-switched laser according to claim 1, wherein the quartz glass rod (4) is provided at two places with high-transmission films respectively at the entrance window (401) and the exit window (404).

9. The Q-switched laser according to claim 8, wherein the entrance window (401) and the exit window (404) are planar structures.