CN112448257A - Q-switched holmium laser - Google Patents

Q-switched holmium laser Download PDF

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Publication number
CN112448257A
CN112448257A CN201910821710.3A CN201910821710A CN112448257A CN 112448257 A CN112448257 A CN 112448257A CN 201910821710 A CN201910821710 A CN 201910821710A CN 112448257 A CN112448257 A CN 112448257A
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laser
cavity
resonant cavity
gain medium
filter
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黄海洲
林文雄
李锦辉
邓晶
葛燕
翁文
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Fujian Institute of Research on the Structure of Matter of CAS
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Fujian Institute of Research on the Structure of Matter of CAS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/113—Q-switching using intracavity saturable absorbers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/161—Solid materials characterised by an active (lasing) ion rare earth holmium

Abstract

The application discloses a Q-switched holmium laser, which comprises a composite resonant cavity, a Tm/Ho composite gain medium, a Q-switched element and a pumping source; the composite resonant cavity comprises a laser resonant cavity and a filtering resonant cavity; the filtering resonant cavity and the Q-switching element are sequentially positioned in the laser resonant cavity along the light path direction; the Tm/Ho composite gain medium is positioned in the filter resonant cavity; the pumping source is positioned outside the laser resonant cavity; wherein, the filter resonant cavity is used for separating Tm laser and Ho laser. The laser comprises a composite resonant cavity, the composite resonant cavity realizes the separation of Tm laser and Ho laser, and the Tm laser is confined in a filtering resonant cavity, so that a Q-switching element only influences the Ho laser, and the Tm laser can effectively excite the Ho laser to form stable Q-switching pulse output.

Description

Q-switched holmium laser
Technical Field
The application relates to a Q-switched holmium laser and belongs to the technical field of solid laser.
Background
In the existing all-solid-state holmium (Ho) laser implementation mode, compared with a Tm laser pumping Ho laser with large volume, a 1.9 mu m semiconductor laser LD pumping Ho laser with high price and a Tm laser resonant cavity pumping Ho laser with a complex structure, the Tm/Ho bonding laser is a Ho laser implementation mode which is compact in structure, can be miniaturized, is economical and convenient, and can directly utilize a conventional LD (with the wavelength of 750 nm-810 nm) to efficiently realize room-temperature Ho laser output. However, the Tm-doped portion and the Ho-doped portion in the bonding gain medium affect each other, the Tm-doped portion provides both Tm laser for pumping the Ho-doped portion and acts as a saturated absorber of the Ho laser, and the Ho-doped portion also acts as a saturated absorber of the Tm laser while consuming the energy of the Tm laser in the cavity, and affects the temporal stability of Tm pump light in the cavity.
The above situation causes that the Tm/Ho bonding laser generates disordered pulse signals in a free running state, and cannot generate stable Q-switched pulse output in a traditional active Q-switching mode (namely, an acousto-optic or electro-optic modulation device is inserted into a resonant cavity of the Tm/Ho bonding laser). On the other hand, the conventional passive Q-switching mode in which a saturable absorber is directly inserted into a resonant cavity is also difficult to realize laser output on a Tm/Ho bonding laser, because the introduction of the saturable absorber increases the resonant cavity loss, which causes loss on Ho lasers, especially on Tm lasers in an intracavity pump Ho-doped portion, and thus laser oscillation output cannot be formed. That is, since the Tm laser and the Ho laser are simultaneously provided in the cavity, the Tm laser is weakened by the Q-switching element, and the Ho laser cannot be sufficiently excited by the Tm laser, and thus an effective Ho laser output cannot be formed. Therefore, there is a need to develop an efficient mechanism that can achieve a stable Q-switched pulse output from a Tm/Ho bonding laser.
Disclosure of Invention
According to one aspect of the application, a Q-switched holmium laser is provided, the laser comprises a composite resonant cavity, the composite resonant cavity realizes the separation of Tm laser and Ho laser, and the Tm laser is confined in a filtering resonant cavity, so that a Q-switched element only influences the Ho laser, and the Tm laser can effectively excite the Ho laser to form stable Q-switched pulse output.
A Q-switched holmium laser comprises a composite resonant cavity, a Tm/Ho composite gain medium, a Q-switched element and a pumping source;
the composite resonant cavity comprises a laser resonant cavity and a filtering resonant cavity;
the filtering resonant cavity and the Q-switching element are sequentially positioned in the laser resonant cavity along the direction of a light path;
the Tm/Ho composite gain medium is positioned in the filter resonant cavity;
the pumping source is positioned outside the laser resonant cavity;
wherein, the filter resonant cavity is used for separating Tm laser and Ho laser.
Optionally, a front cavity surface of the filtering resonant cavity and a rear cavity surface of the filtering resonant cavity are both plated with Tm laser high-reflection films, and the Tm laser oscillates in the filtering resonant cavity; the front cavity surface of the laser resonant cavity and the rear cavity surface of the laser resonant cavity are respectively plated with a Ho laser high-reflection film and a Ho laser partial reflection film, and the Ho laser oscillates in the laser resonant cavity.
Optionally, both the front cavity surface of the filter resonator and the rear cavity surface of the filter resonator are plated with a first reflective film having a reflectivity of greater than 95% to Tm laser, and the Tm laser oscillates in the filter resonator; the front cavity surface of the laser resonant cavity is plated with a second reflecting film with the reflectivity of Ho laser being more than 99%; the rear cavity surface of the laser resonant cavity is plated with a partial reflection film with the reflectivity of 2-50% for Ho laser, and the Ho laser oscillates in the laser resonant cavity.
Optionally, the front cavity surface of the filtering resonant cavity is a front cavity mirror, and the rear cavity surface of the filtering resonant cavity is a filter device; the front cavity surface of the laser resonant cavity is a front cavity mirror; the rear cavity surface of the laser resonant cavity is a rear cavity mirror; the front cavity mirror, the Tm/Ho composite gain medium, the filter, the Q-switching element and the rear cavity mirror are sequentially arranged along the light path direction.
Optionally, a front cavity surface of the filtering resonant cavity is a front end surface of the Tm/Ho composite gain medium, and a rear cavity surface of the filtering resonant cavity is a rear end surface of the Tm/Ho composite gain medium; the front cavity surface of the laser resonant cavity is the front end surface of the Tm/Ho composite gain medium; the rear cavity surface of the laser resonant cavity is a rear cavity mirror; the Tm/Ho composite gain medium, the Q-switching element and the rear cavity mirror are sequentially arranged along the direction of an optical path.
Optionally, the Q-switched element is interposed between the filter resonator and the rear mirror; or the Q-switching element is a film coated on the front end face of the rear cavity mirror.
Optionally, the Q-switched element includes any one of an electro-optic Q-switched switch, an acousto-optic Q-switched switch, a transition metal doped group-two-six compound crystal, a transition metal disulfide crystal, a transition metal diselenide crystal, a semiconductor saturable absorber, a graphene two-dimensional material, a carbon nanotube two-dimensional material, a topological insulator, and a saturable absorber material that realizes Q-switched pulse output at a 2 μm band.
Optionally, the Tm/Ho composite gain medium includes a Tm doped portion and a Ho doped portion sequentially arranged along the optical path direction.
Optionally, the Tm-doped portion is selected from the group consisting of Tm: YAG crystals, Tm: LuAG crystals, Tm: YLF crystals, Tm: LuLiF crystals, Tm: YAP crystals, Tm: YAB crystals, Tm: KGW crystals, Tm: GdVO crystals4Crystal Tm: YVO4Crystal, Tm: YAG transparent ceramic, Tm: Al2O3Any one of transparent ceramics;
the Ho-doped part is selected from Ho: YAG crystal, Ho: LuAG crystal, Ho: YLF crystal, Ho: LuLiF crystal, Ho: YAP crystal, Ho: KGW crystal, Ho: YAB crystal, Ho: GdVO4Crystal, Ho: YVO4Crystal, Ho YAG transparent ceramic, Ho Al2O3Any one of transparent ceramics.
Optionally, in the Tm-doped part, the doping concentration of Tm ions is 2-7 at%; in the Ho-doped part, the doping concentration of Ho ions is 0.2-2 at%.
Optionally, a medium without rare earth ions is compounded between the front end face of the Tm-doped part and the rear end face of the Ho-doped part; alternatively, the first and second electrodes may be,
and compounding a rare earth ion-free doping medium between the rear end face of the Tm-doped part and the front end face of the Ho-doped part.
Optionally, a side surface of the Tm/Ho composite gain medium parallel to the optical path direction is plated with a silicon dioxide film.
Optionally, the Q-switched holmium laser further comprises a heat dissipation member, and the heat dissipation member is arranged on the side surface of the Tm/Ho composite gain medium, which is parallel to the optical path direction.
Optionally, the heat dissipation member is a copper block, a microchannel for cooling fluid to flow through is arranged inside the copper block, and a liquid inlet and a liquid outlet of the microchannel are connected with an external water cooling system.
Optionally, a metal foil is disposed between the heat sink and a side surface of the Tm/Ho composite gain medium.
The beneficial effects that this application can produce include:
1) according to the Q-switched holmium laser, the Tm laser and the Ho laser in the resonant cavity are separated through the composite resonant cavity structure, and the bottleneck problem that a Tm/Ho bonded laser cannot realize Q-switched pulse output in a conventional Q-switched mode due to the fact that the Tm-doped part and the Ho-doped part have saturation absorption effects at the same time in a 2-micrometer laser wave band is solved. A Q-switching element in the Q-switching holmium laser only acts on Ho laser and does not affect Tm laser (because Tm laser is confined in a filter resonant cavity), so that the Q-switching holmium laser can realize stable Q-switching pulse output under the action of an active Q-switching component or a saturable absorber, and has the comprehensive advantages of compact structure, miniaturization, conventional LD pumping, normal-temperature refrigeration and the like.
Drawings
Fig. 1 is a schematic structural diagram of a Q-switched holmium laser according to a first embodiment of the present application;
fig. 2 is a schematic structural diagram of a Q-switched holmium laser according to a second embodiment of the present application;
fig. 3 is a schematic structural diagram of a Q-switched holmium laser according to a third embodiment of the present application;
FIG. 4 shows the pulse output characteristics of a Q-switched holmium laser without the filter element of FIG. 1;
fig. 5 shows the pulse output effect of the Q-switched holmium laser according to the first embodiment of the present application.
List of parts and reference numerals:
100 a pump source; 200 of a front cavity mirror;
300Tm/Ho composite gain media; 400 a filter device;
500Q-switching elements; 501 ultrasonic ring energy device and ultrasonic driver;
502 acousto-optic Q-switched crystals; 600 rear cavity mirror;
Detailed Description
The present application will be described in detail with reference to examples, but the present application is not limited to these examples.
A Q-switched holmium laser comprises a composite resonant cavity, a Tm/Ho composite gain medium, a Q-switched element and a pumping source;
the composite resonant cavity comprises a laser resonant cavity and a filtering resonant cavity;
the filtering resonant cavity and the Q-switching element are sequentially positioned in the laser resonant cavity along the light path direction;
the Tm/Ho composite gain medium is positioned in the filter resonant cavity;
the pumping source is positioned outside the laser resonant cavity; wherein, the filter resonant cavity is used for separating Tm laser and Ho laser.
Aiming at the problem that a Q-switching component is inserted into a laser resonant cavity in the prior art and cannot realize Q-switching laser output from a Tm/Ho bonding laser, the invention provides a laser capable of realizing stable Q-switching pulse output from the Ho laser. And adding another resonant cavity with a filtering effect into a laser resonant cavity based on a Tm/Ho bonding gain medium formed by bonding a Tm-doped gain medium and a Ho-doped gain medium to form a composite resonant cavity structure for effectively separating Tm laser and Ho laser, thereby realizing stable Q-switched pulse output from the Tm/Ho bonding laser under the action of a saturable absorber or an active pulse modulation device.
Optionally, a front cavity surface of the filtering resonant cavity and a rear cavity surface of the filtering resonant cavity are both plated with Tm laser high-reflection films, and the Tm laser oscillates in the filtering resonant cavity; the front cavity surface of the laser resonant cavity and the rear cavity surface of the laser resonant cavity are respectively plated with a Ho laser high-reflection film and a partial reflection film, and the Ho laser oscillates in the laser resonant cavity.
Specifically, a front cavity surface of the filtering resonant cavity and a rear cavity surface of the filtering resonant cavity are both plated with a first reflective film with reflectivity of greater than 95% for Tm laser, and the Tm laser oscillates in the filtering resonant cavity; the front cavity surface of the laser resonant cavity is plated with a second reflecting film with the reflectivity of more than 99% for Ho laser, the rear cavity surface of the laser resonant cavity is plated with a partial reflecting film with the transmissivity of 2% -50% for Ho laser, and the Ho laser oscillates in the laser resonant cavity.
In the present application, the Tm laser high-reflection film and the first reflection film denote the same film; the Ho laser high reflection film and the second reflection film represent the same film.
Specifically, the filtering resonant cavity and the laser resonant cavity realize the effect of separating Tm laser and Ho laser by respectively setting specific functional films. Specifically, the first reflection film with the reflectivity of greater than 95% for Tm laser is arranged on the filtering resonant cavity, so that the Tm laser is confined in the filtering resonant cavity, and the Tm/Ho composite gain medium is also positioned in the filtering resonant cavity, so that the Tm laser can effectively excite the Ho laser. The laser resonant cavity is provided with a second reflecting film with the reflectivity of more than 99% to Ho laser on the front cavity mirror, and a partial reflecting film with the reflectivity of 2% -50% to Ho laser on the rear cavity mirror, so that the excited Ho laser can oscillate in the laser resonant cavity. The Q-switching element is positioned in the laser resonant cavity and outside the filtering resonant cavity, so that the Q-switching element cannot act on Tm laser and only can control the emission of Ho laser to form stable Q-switching pulse output.
Optionally, the front cavity surface of the filtering resonant cavity is a front cavity mirror, and the rear cavity surface of the filtering resonant cavity is a filter device; the front cavity surface of the laser resonant cavity is a front cavity mirror; the rear cavity surface of the laser resonant cavity is a rear cavity mirror; the front cavity mirror, the Tm/Ho composite gain medium, the filter, the Q-switching element and the rear cavity mirror are sequentially arranged along the light path direction.
Specifically, the filtering resonant cavity in the composite resonant cavity is composed of a front cavity mirror and a filter device, namely, the front cavity mirror serves as a front cavity surface of the filtering resonant cavity, the filter device serves as a rear cavity surface of the filtering resonant cavity, and the Tm laser oscillates between the front cavity mirror and the filter device. The laser resonant cavity is composed of a front cavity mirror and a rear cavity mirror, namely the front cavity mirror serves as a front cavity surface of the laser resonant cavity, the rear cavity mirror serves as a rear cavity surface of the laser resonant cavity, and Ho laser oscillates between the front cavity mirror and the rear cavity mirror.
In the composite resonant cavity, a front cavity mirror, a Tm/Ho composite gain medium, a filter, a Q-switching element and a rear cavity mirror are sequentially arranged along the direction of a light path; the rear end face of the front cavity mirror is plated with a first reflecting film and a second reflecting film, the filter is a transparent insulator, the front end face of the transparent insulator is plated with the first reflecting film, and the front end face of the rear cavity mirror is plated with a partial reflecting film of Ho laser; a filtering resonant cavity is formed between the front cavity mirror and the filtering device; a laser resonant cavity is formed between the front cavity mirror and the rear cavity mirror.
The composite resonant cavity can be realized by coating corresponding functional films on the front cavity mirror, the filter and the rear cavity mirror. The rear end face of the front cavity mirror and the front end face of the filter device are both plated with a first reflection film, so that a filtering resonant cavity for Tm laser oscillation is formed between the front cavity mirror and the filter device. The rear end face of the front cavity mirror is plated with a second reflecting film, and the front end face of the rear cavity mirror is plated with a partial reflecting film of the Ho laser, so that a laser resonant cavity for Ho laser oscillation is formed between the front cavity mirror and the rear cavity mirror.
The filter is a transparent insulator capable of high transmittance (transmittance > 90%), and may be fused silica glass, YAG crystal, optically transparent ceramic, plastic, or the like, for example. The front end face of the transparent insulator is plated with a high-reflection 1.9-2.02 μm Tm laser and a high-transmission 2.05-2.2 μmHo laser film layer (i.e. a first reflection film).
In the present application, the first reflective film and the second reflective film may be in the form of a single film, that is, the film is highly reflective to both Tm laser light and Ho laser light, and the film may be plated on the rear end surface of the front cavity mirror or on the front end surface of the Tm-doped portion of the composite gain medium.
Optionally, a front cavity surface of the filtering resonant cavity is a front end surface of the Tm/Ho composite gain medium, and a rear cavity surface of the filtering resonant cavity is a rear end surface of the Tm/Ho composite gain medium; the front cavity surface of the laser resonant cavity is the front end surface of the Tm/Ho composite gain medium; the rear cavity surface of the laser resonant cavity is a rear cavity mirror; the Tm/Ho composite gain medium, the Q-switching element and the rear cavity mirror are sequentially arranged along the direction of an optical path.
Specifically, a filter resonant cavity in the composite resonant cavity is formed by a front end surface and a rear end surface of a Tm/Ho composite gain medium, that is, the front end surface of the composite gain medium serves as a front cavity surface of the filter resonant cavity, the rear end surface of the composite gain medium serves as a rear cavity surface of the filter resonant cavity, and Tm laser forms oscillation in the Tm/Ho composite gain medium. The laser resonant cavity is composed of a front end surface and a rear cavity mirror of the Tm/Ho composite gain medium, namely the front end surface of the Tm/Ho composite gain medium serves as the front cavity surface of the laser resonant cavity, the rear cavity mirror serves as the rear cavity surface of the laser resonant cavity, and Ho laser oscillates between the front end surface and the rear cavity mirror of the Tm/Ho composite gain medium.
The Tm/Ho composite gain medium, the Q-switching element and the rear cavity mirror are sequentially arranged along the direction of an optical path; a first reflection film and a second reflection film are plated on the front end face of the Tm/Ho composite gain medium; a first reflecting film is plated on the rear end face of the Tm/Ho composite gain medium; a Ho laser partial reflection film is plated on the front end surface of the rear cavity mirror; a filtering resonant cavity is formed between the front end surface of the Tm/Ho composite gain medium and the rear end surface of the Tm/Ho composite gain medium; and a laser resonant cavity is formed between the front end surface of the Tm/Ho composite gain medium and the rear cavity mirror.
The composite resonant cavity can also be realized by plating a functional film on the rear cavity mirror and the Tm/Ho composite gain medium. The front end face and the rear end face of the Tm/Ho composite gain medium are both plated with first reflection films, so that a filter resonant cavity for confining Tm laser is formed between the front end face and the rear end face of the Tm/Ho composite gain medium, namely the Tm laser is confined in the Tm/Ho composite gain medium to oscillate. And a second reflecting film is plated on the front end surface of the Tm/Ho composite gain medium, a Ho laser partial reflecting film is plated on the front end surface of the rear cavity mirror, and a Ho oscillating laser resonant cavity is formed between the front end surface of the Tm/Ho composite gain medium and the rear cavity mirror. The filter resonant cavity and the laser resonant cavity are realized by utilizing the Tm/Ho composite gain medium, the structure of the Q-switched holmium laser is greatly simplified by the design, and the miniaturization of the conventional LD pumping Q-switched holmium laser are facilitated.
The Tm laser with high reflection of 1.9-2.02 mu m and the laser film with high reflection of 2.05-2.2 mu mHo are plated on the front end face of the Tm doped part, and the Tm laser with high reflection of 1.9-2.02 mu m and the laser film with high transmission of 2.05-2.2 mu mHo are plated on the rear end face of the Ho doped part, so that the end face of the composite gain medium has the function of separating the Tm laser and the Ho laser in the resonant cavity, and the structure of the composite resonant cavity is further simplified.
Optionally, the Q-switched element is interposed between the filter resonator and the rear mirror; or the Q-switching element is coated on the front end surface of the rear cavity mirror.
Optionally, the Q-switched element includes any one of an electro-optic Q-switched switch, an acousto-optic Q-switched switch, a transition metal doped group-two-six compound crystal, a transition metal disulfide crystal, a transition metal diselenide crystal, a semiconductor saturable absorber, a graphene two-dimensional material, a carbon nanotube two-dimensional material, a topological insulator, and a saturable absorber material that realizes Q-switched pulse output at a 2 μm band.
The Q-switch element is a Q-switch element capable of modulating 2 μm laser pulse, such as acousto-optic Q-switch based on fused quartz crystal and ultrasonic transducer, electro-optic Q-switch based on electro-optic crystal KTP or RTP and high-voltage signal generator, di-six-group compound ZnS, ZnSe or CdSe doped with transition metal ions Cr, Fe or Co, two-dimensional material graphene, two-dimensional material carbon nanotube and topological insulator (Bi)2Te3Or Bi2Se3) Transition metal disulfides (WS)2、MoS2) Or diselenide (WSe)2、MoSe2) Semiconductor saturable absorber InGaAs or GaAs, and other saturable absorber materials capable of realizing Q-switched pulse output in 2 μm waveband such as gold nanorods, PbS quantum dots or black scales.
In some possible embodiment modes, an electro-optical Q-switch, an acousto-optical Q-switch, a transition metal doped group-two-six compound crystal, a transition metal disulfide crystal, a transition metal diselenide crystal, and a semiconductor saturable absorber can be inserted between the filter resonator and the rear cavity mirror, and a graphene two-dimensional material, a carbon nanotube two-dimensional material, a topological insulator, and a saturable absorption material for realizing Q-switched pulse output in a 2 μm band can be coated on the front end face of the rear cavity mirror.
Optionally, the Tm/Ho composite gain medium includes a Tm doped portion and a Ho doped portion arranged in order along the optical path direction.
Tm-doped and Ho-doped gain media refer to the same laser gain medium, such as crystal, ceramic, glass, or plastic. I.e., Tm-doped and Ho-doped gain media refer to the same medium.
Alternatively, the Tm-doped portion is selected from the group consisting of Tm: YAG crystals, Tm: LuAG crystals, Tm: YLF crystals, Tm: LuLiF crystals, Tm: YAP crystals, Tm: YAB crystals, Tm: KGW crystals, Tm: GdVO crystals4Crystal Tm: YVO4Crystal, Tm: YAG transparent ceramic, Tm: Al2O3Any one of transparent ceramics;
the Ho-doped part is selected from Ho: YAG crystal, Ho: LuAG crystal, Ho: YLF crystal, Ho: LuLiF crystal, Ho: YAP crystal, Ho: KGW crystal, Ho: YAB crystal, Ho: GdVO4Crystal, Ho: YVO4Crystal, Ho YAG transparent ceramic, Ho Al2O3Any one of transparent ceramics.
Optionally, in the Tm doped part, the doping concentration of Tm ions is 2-7 at%; in the Ho-doped part, the doping concentration of Ho ions is 0.2-2 at%.
The Tm/Ho composite gain medium mainly comprises a Tm-doped part and a Ho-doped part. The Tm-doped part and the Ho-doped part in the composite gain medium can be integrated into the composite gain medium with the Tm-doped part and the Ho-doped part through the methods of the prior art, such as diffusion bonding, ion implantation, optical gluing, ceramic slurry sintering and the like. The Tm doped portion and the Ho doped portion of the composite gain media may be doped with varying concentrations using well-established glass, crystal, or transparent ceramic growth techniques. The Tm-doped part can be any gain medium capable of generating thulium laser output, and the crystal can be Tm: YAG, Tm: LuAG, Tm: YLF, Tm: LuLiF, Tm: YAP, Tm: YAB, Tm: KGW，Tm:GdVO4And Tm: YVO4Etc., transparent ceramics, such as Tm: YAG and Tm: Al2O3The Tm ion doping concentration is 2-7 at%. The Ho-doped part can be any gain medium capable of generating holmium laser output, and the crystals are Ho: YAG, Ho: LuAG, Ho: YLF, Ho: LuLiF, Ho: YAP, Ho: KGW, Ho: YAB, Ho: GdVO4And Ho: YVO4Etc., transparent ceramics such as Ho: YAG and Ho: Al2O3And the doping concentration of the Ho ions is between 0.2at percent and 1.5at percent.
The Tm/Ho composite gain medium may be in the form of a slab, a column, or a rod, and the specific shape of the Tm/Ho composite gain medium is not limited in the embodiment of the present invention.
When the Tm/Ho composite gain medium is in a lath shape, the length-width ratio of one outer surface is larger than 2, so that the temperature gradient in the gain medium and the refractive index gradient and thermal stress caused by the temperature gradient can be remarkably relieved, the beam quality and the bearable pumping power of the laser are improved, and the pulse Ho laser output with high average power and high beam quality is realized. .
Optionally, compounding a rare earth ion-free doped medium on the front end face of the Tm-doped part and the rear end face of the Ho-doped part; alternatively, the first and second electrodes may be,
and a medium without rare earth ions is compounded between the rear end face of the Tm-doped part and the front end face of the Ho-doped part.
Specifically, by using a gain medium compounding technology, a non-rare earth ion doped medium can be compounded between the front end surface of the Tm doped gain medium and the rear end surface of the Ho doped gain medium, or between the rear end surface of the Tm doped gain medium and the front end surface of the Ho doped gain medium, so as to relieve the thermal effect of the Q-switched laser or improve the Q-switched performance, such as pulse stability or average output power.
Optionally, a side surface of the Tm/Ho composite gain medium parallel to the optical path direction is plated with a silicon dioxide film.
In one example, a pair of planes parallel to each other and having the largest area in the side surfaces of the Tm/Ho composite gain medium are plated with silicon dioxide films to realize total reflection of the pump light, Tm laser and Ho laser inside the slab, so that the pump light, Tm laser and Ho laser are confined inside the slab at the same time.
Optionally, the Q-switched holmium laser further comprises a heat dissipation member, and the heat dissipation member is arranged on the side surface of the Tm/Ho composite gain medium, which is parallel to the optical path direction.
Specifically, the four side surfaces of the composite gain medium are heat radiating surfaces that are in contact with the heat radiating member. Through setting up the radiating piece, reduced the damage of thermal stress to the laser instrument, effect such as improvement laser instrument performance.
Optionally, the heat sink is a copper block, a microchannel for cooling fluid to flow through is arranged inside the copper block, and a liquid inlet and a liquid outlet of the microchannel are connected with an external water cooling system.
Specifically, a microchannel capable of circulating cooling liquid is designed in the cooling copper block, and the microchannel is connected with a circulating water cooling system through a water nozzle on the copper block to form a water cooling loop of the Tm/Ho composite gain medium. And controlling the temperature of the cooling water to be a specific value in the range of 5-30 ℃ according to requirements. The cooling copper block is clamped on the side surface of the composite gain medium.
Optionally, a metal foil is arranged between the heat sink and the side surface of the Tm/Ho composite gain medium.
Specifically, in the present application, the Tm/Ho composite gain medium is clamped by a cooling copper block to thermally manage the laser, and for the thermal resistance between the Tm/Ho composite gain medium and the cooling copper block, a metal foil with good thermal conductivity, such as indium or gold, is used to wrap the gain medium.
The wavelength of the pumping source is 760-820 nm, and the specific output wavelength depends on the absorption characteristic of the Tm-doped part and the material of the gain medium. For example, for YAG and LuAG crystals, the output wavelength of the pump source may be 785 nm; for Tm, YLF and Tm, LuLiF crystals, the output wavelength of the pumping source can be 792 nm; for YAP crystals, the output wavelength of the pump source may be 795 nm; and the wavelength band far away from the Tm doped part, such as 781nm or 808nm, can be used for side lobe pumping and the like.
The pumping wavelength used for the YAG crystal is 785nm, and the output wavelength and the line width of a pumping source can be locked on the optimal pumping peak position of the Tm: YAG, so that the optical-optical conversion efficiency of the holmium laser is obviously improved.
The pumping source is an optical fiber coupling semiconductor Laser (LD) or an LD stacked array integrated by an LD chip. When the fiber coupled semiconductor laser is used as a pumping source, the pumping light is shaped into a pumping focusing light spot matched with the cavity film radius of Tm laser in the composite resonant cavity through a pumping shaping system consisting of convex lenses, and then the Q Ho laser is efficiently pumped.
The length-width ratio of the incident light spot of the pump light is larger than or equal to the length-width ratio of the light-transmitting end face of the composite gain medium, and the pump light generated by the pump source is shaped by an optical system consisting of a cylindrical mirror, an aspherical mirror or a diffraction optical element.
Example 1
Fig. 1 is a schematic structural diagram of a Q-switched holmium laser provided in this embodiment, and this embodiment is described below with reference to fig. 1.
As shown in fig. 1, the Q-switched holmium laser sequentially comprises a pumping source 100, a front cavity mirror 200, a Tm/Ho composite gain medium 300, a filter 400, a Q-switched element 500 and a rear cavity mirror 600 along the optical path direction. The Tm/Ho composite gain medium 300 includes a Tm-doped portion 301 and a Ho-doped portion 302, and is wrapped with indium foil and fixed in a cooled copper block (not shown in the figure) having a micro flow channel built therein. The Q-switching element 500 is interposed between the filter device 400 and the rear cavity mirror 600.
The rear end face of the front cavity mirror 200 is coated with a first reflective film having a reflectivity of greater than 99.7% to Tm laser a, and the front end face of the transparent insulator of the filter device 400 is also coated with a first reflective film having a reflectivity of greater than 95% to Tm laser a. The front cavity mirror 200 and the filter device 400 form a filter cavity for the Tm laser a to oscillate back and forth.
The rear end face of the front cavity mirror 200 is coated with a second reflection film with the reflectivity of more than 99.7% of Ho laser b, the front end face of the rear cavity mirror 600 is also coated with a partial reflection film with the reflectivity of 2-50% of Ho laser b, and a laser resonant cavity for the Ho laser b to oscillate back and forth is formed between the front cavity mirror 200 and the rear cavity mirror 600.
The working process of the laser is described as follows:
the pumping light is emitted by the pumping source 100, and is incident to the Tm-doped portion 301 of the composite gain medium 300 through the front cavity mirror 200 to form the population inversion of Tm ions, and Tm laser a confined in the filter resonator is generated under the action of the front cavity mirror 200 and the filter device 400. The Tm laser a uniformly pumps the Ho doped portion 302 in the process of passing back and forth through the Tm/Ho composite gain medium 300, the population of Ho ions is inverted, the population inversion of Ho ions is rapidly released under the action of the Q-switching element 500, and the Ho laser rapidly oscillates between the front cavity mirror 200 and the rear cavity mirror 600, so that the output of the pulse Ho laser b is realized.
That is, in this embodiment, Tm laser a confined between the front cavity mirror 200 and the filter 400 is generated under the pumping of the Tm/Ho composite gain medium 300 by the pump source 100 to the Tm doped portion 301, and the Ho doped portion 302 is pumped to form the ion number inversion of the Ho doped portion 302. The stable Q-switched Ho laser output is realized under the action of the Q-switched element 500 located between the filter device 400 and the rear cavity mirror 600. In the present example, the Q-switching element 500 employed is a transition metal ion doped crystalline form of a group III-VI compound (Cr)2+：ZnSe)。
In the experimental demonstration process, the filter device 400 is removed, and the Q-switched QHo laser cannot normally emit light because the Tm laser and the Ho laser in the laser resonant cavity are both saturable absorbed by the Q-switched element 500, so that the pumping threshold of the Tm/Ho bonding laser is greatly increased, and the laser cannot emit light.
With the filter device 400 inserted and the Q-switching element 500 removed, the Tm/Ho bonded laser cannot produce a stable Q-switched pulse output. As shown in fig. 4, the amplitude, frequency, and fluctuation of the pulse are varied drastically, and the amplitude of the pulse is weak.
After the filter device 400 and the Q-switching element 500 are simultaneously inserted into the laser resonant cavity, stable Q-switching pulse output is generated, as shown in FIG. 5, compared with FIG. 4, under the same average output power (50-150 mW), the amplitude of the pulse signal is obviously enhanced, and the pulse sequence becomes regular.
Example 2
Fig. 2 is a schematic structural diagram of a Q-switched holmium laser provided in this embodiment, and this embodiment is described below with reference to fig. 2.
In specific implementation, as shown in fig. 2, the functional film layer (i.e., the first reflective film) of the filter device 400 in embodiment 1 is plated on the rear end surface of the composite gain medium 300, and the functional film layers (the first reflective film and the second reflective film) of the front cavity mirror 200 in embodiment 1 are plated on the front end surface of the composite gain medium 300, so that the composite gain medium 300 becomes a resonant cavity (i.e., a filter resonant cavity) for trapping Tm laser a, the composite gain medium 300 also becomes one end of the laser resonant cavity, the second reflective film is plated on the front end surface of the rear cavity mirror 600, and the rear cavity mirror 600 becomes the other end of the laser resonant cavity. The design greatly simplifies the structure of the Tm/Ho bonding Q-switched laser and is beneficial to the miniaturization and the microminiaturization of the conventional LD pumping Q-switched Ho laser. In this example, the Q-switching element 500 is an acousto-optic Q-switching crystal 502 (fused silica crystal) with an ultrasonic ring energy and ultrasonic driver 501.
Example 3
Fig. 3 is a schematic structural diagram of a Q-switched holmium laser provided in this embodiment, and this embodiment is described below with reference to fig. 3.
The Q-switching element 500 may be a saturable absorber or saturable absorber material based on one-dimensional or two-dimensional materials, such as MoSe2On the front end face of the rear cavity mirror 600, the front and rear end faces of the composite gain medium 300 are respectively used as the front cavity mirror and the filter in embodiment 1, and Tm laser a is confined inside the composite gain medium 300 to uniformly pump the Ho-doped portion (similar to the composite gain medium in embodiment 2), thereby realizing pulse Ho laser output. The structure of fig. 3 is advantageous to further simplify the structure and size of the laser based on the structure of fig. 2, and the pulsed Ho laser output is realized under the conventional LD pumping.
Although the present application has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application.

Claims (10)

1. A Q-switched holmium laser is characterized by comprising a composite resonant cavity, a Tm/Ho composite gain medium, a Q-switched element and a pumping source;
the composite resonant cavity comprises a laser resonant cavity and a filtering resonant cavity;
the filtering resonant cavity and the Q-switching element are sequentially positioned in the laser resonant cavity along the direction of a light path;
the Tm/Ho composite gain medium is positioned in the filter resonant cavity;
the pumping source is positioned outside the laser resonant cavity;
wherein, the filter resonant cavity is used for separating Tm laser and Ho laser.
2. The Q-switched holmium laser as claimed in claim 1, wherein the front cavity surface of the filter cavity and the rear cavity surface of the filter cavity are both coated with Tm laser high-reflection films, and the Tm laser oscillates in the filter cavity;
the front cavity surface of the laser resonant cavity and the rear cavity surface of the laser resonant cavity are respectively plated with a Ho laser high-reflection film and a Ho laser partial reflection film, and the Ho laser oscillates in the laser resonant cavity.
3. The Q-switched holmium laser of claim 2, wherein the front cavity surface of the filter resonator is a front cavity mirror and the back cavity surface of the filter resonator is a filter device;
the front cavity surface of the laser resonant cavity is a front cavity mirror; the rear cavity surface of the laser resonant cavity is a rear cavity mirror;
the front cavity mirror, the Tm/Ho composite gain medium, the filter, the Q-switching element and the rear cavity mirror are sequentially arranged along the light path direction.
4. The Q-switched holmium laser of claim 2, wherein the front cavity surface of the filter cavity is the front end surface of the Tm/Ho composite gain medium, and the back cavity surface of the filter cavity is the back end surface of the Tm/Ho composite gain medium;
the front cavity surface of the laser resonant cavity is the front end surface of the Tm/Ho composite gain medium; the rear cavity surface of the laser resonant cavity is a rear cavity mirror;
the Tm/Ho composite gain medium, the Q-switching element and the rear cavity mirror are sequentially arranged along the direction of an optical path.
5. The Q-switched holmium laser of claim 1, wherein the Q-switching element is interposed between the filtering resonator and a back mirror; alternatively, the first and second electrodes may be,
the Q-switching element is a film coated on the front end face of the rear cavity mirror.
6. The Q-switched holmium laser of claim 1, wherein the Tm/Ho composite gain medium includes a Tm-doped portion and a Ho-doped portion arranged in this order along the optical path direction.
7. The Q-switched holmium laser device according to claim 6, characterized in that in the Tm-doped part, the doping concentration of Tm ions is 2-7 at%; in the Ho-doped part, the doping concentration of Ho ions is 0.2-2 at%.
8. The Q-switched holmium laser of claim 6, characterized in that a rare earth ion-free doped medium is compounded between the front facet of the Tm-doped part and the back facet of the Ho-doped part; alternatively, the first and second electrodes may be,
and compounding a rare earth ion-free doping medium between the rear end face of the Tm-doped part and the front end face of the Ho-doped part.
9. The Q-switched holmium laser of claim 1, further comprising a heat dissipation member disposed at a side of the Tm/Ho composite gain medium parallel to the optical path direction.
10. The Q-switched holmium laser device according to claim 9, wherein the heat sink is a copper block, a microchannel for cooling fluid to flow through is arranged in the copper block, and a liquid inlet and a liquid outlet of the microchannel are connected with an external water cooling system;
preferably, a metal foil is arranged between the heat dissipation element and the side face of the Tm/Ho composite gain medium.
CN201910821710.3A 2019-09-02 2019-09-02 Q-switched holmium laser Pending CN112448257A (en)

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