CN113572010A - Laser, lidar comprising same and method for generating laser light - Google Patents

Laser, lidar comprising same and method for generating laser light Download PDF

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CN113572010A
CN113572010A CN202010354107.1A CN202010354107A CN113572010A CN 113572010 A CN113572010 A CN 113572010A CN 202010354107 A CN202010354107 A CN 202010354107A CN 113572010 A CN113572010 A CN 113572010A
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laser
gain
unit
light
pumping
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CN113572010B (en
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付萌
李大汕
向少卿
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Hesai Technology Co Ltd
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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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/0915—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light
    • H01S3/0933—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light of a semiconductor, e.g. light emitting diode
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/484—Transmitters
    • 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
    • H01S3/1106—Mode locking
    • H01S3/1112—Passive mode locking
    • H01S3/1115—Passive mode locking 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
    • H01S3/163—Solid materials characterised by a crystal matrix
    • H01S3/1645—Solid materials characterised by a crystal matrix halide
    • H01S3/1648—Solid materials characterised by a crystal matrix halide with the formula XYZF6 (Colquiriite structure), wherein X is Li, Na, K or Rb, Y is Mg, Ca, Sr, Cd or Ba and Z is Al, Sc or Ga

Abstract

The invention relates to a diode-pumped solid laser using a blue laser diode as a pumping light source, which takes Cr-doped fluor-aluminum-calcium-lithium as a gain medium and can obtain 850nm laser output suitable for a laser radar. Due to the advantages of the blue laser diode in the aspects of beam quality and power, the structure of a pumping system can be simplified, and the overall structure of the solid laser can be further simplified; due to the advantages of the blue laser diode in the aspects of temperature range and temperature drift, the solid laser is slightly influenced by the temperature drift movement of the wavelength of the pumping light, has high reliability and is suitable for vehicle-scale application. The micro-chip structure for fixing the heat-conducting transparent material is beneficial to reducing the influence of the pumping heat effect and obtaining higher laser output under higher pumping power.

Description

Laser, lidar comprising same and method for generating laser light
Technical Field
The present invention relates generally to the field of optoelectronics, and more particularly to a laser, a lidar including the laser, and a method of generating laser light.
Background
Diode Pumped Solid State Laser (DPSSL), a new type of laser, has developed rapidly in recent years. Compared with the traditional lamp-pumped solid-state laser, the DPSSL replaces a flash lamp with a laser diode with a specific wavelength, and achieves higher light-light conversion efficiency, longer working time and small size. At present, many types of diode-pumped solid-state lasers are commercialized and widely used for laser ranging, industrial processing and the like.
Passive Q-switching is one way in which a solid-state laser generates pulsed laser light. The Q-value of the cavity is defined as the ratio of the total energy stored to the energy lost per unit time in the cavity. The Q value in the cavity is adjusted by changing the loss in the cavity, and a laser pulse is formed when the Q switch is opened. The passive Q-switching is realized by arranging a saturable absorber in a resonant cavity, changing the transmittance of light by utilizing the modulation of light intensity on the absorption coefficient of the saturable absorber and generating laser oscillation to output Q-switching laser pulses when the saturable absorber is saturated. This technique is advantageous for obtaining a pulsed laser with a narrow pulse width.
The existing diode-pumped solid-state laser mostly adopts a red laser diode as a pumping light source, but because the power of a single red laser diode is low, a plurality of laser diodes are generally needed to be combined for pumping, and a pumping system is complex; and the central wavelength of the red laser diode drifts with the temperature, the working temperature of the red laser diode is generally limited to 0 ℃ to 50 ℃, and the application scene is also limited (for example, the laser radar is applied to the field of automatic driving, and the temperature range of the vehicle gauge is-40 ℃ to 120 ℃).
The statements in the background section are merely prior art as they are known to the inventors and do not, of course, represent prior art in the field.
Disclosure of Invention
In view of at least one of the deficiencies of the prior art, the present invention provides a laser comprising:
a pumping unit including a blue laser diode configured to generate blue pumping light;
the gain unit is positioned on the downstream of the optical path of the pumping unit and receives the blue light pumping light, and the gain unit comprises Cr-doped calcium aluminum garnet serving as a gain medium;
the laser resonant cavity comprises a first resonant part and a second resonant part, wherein the first resonant part is positioned between the pumping unit and the gain unit, the gain unit is positioned in the laser resonant cavity, and laser generated in the laser resonant cavity is emitted from the second resonant part; and
a quality factor adjustment unit configured to adjust a quality factor of the laser resonator.
According to an aspect of the present invention, the quality factor adjusting unit is located between the gain medium and the second resonance section.
According to an aspect of the present invention, the first resonance section includes a first dielectric film configured to allow the blue pump light to pass through and be incident into the gain cell and to reflect a beam from the gain cell toward the pump cell back to the gain cell, and the second resonance section includes a second dielectric film configured to reflect a beam from the gain cell back to the gain cell to finally form laser oscillation of a specific wavelength in the laser cavity from which laser light generated in the laser cavity exits.
According to an aspect of the present invention, the first dielectric film is located on an end surface of the gain unit close to the pumping unit, and the second dielectric film is located on an end surface of the quality factor adjusting unit far from the pumping unit.
According to an aspect of the present invention, the second resonance portion further includes a concave mirror having a concave surface facing the first resonance portion, the second dielectric film is disposed on the concave surface, and the laser light generated in the laser resonator cavity is emitted from the second dielectric film and the concave mirror.
According to an aspect of the present invention, the laser further includes a thermally conductive transparent material between the first resonance section and the gain cell, the thermally conductive transparent material being attached to a side of the gain cell facing the first resonance section.
According to one aspect of the invention, the Cr-doped fluoroaluminium calcium lithiumate comprises one or more of Cr: LiCFA, Cr: LiSAF and Cr: LiSGaF.
According to an aspect of the present invention, the laser further includes a metal housing, and the pumping unit, the gain unit, the first resonance portion, the second resonance portion, and the quality factor adjusting unit are packaged in the metal housing, and the metal housing includes a transparent light exit window for laser light to exit.
According to one aspect of the invention, the gain medium is a microchip type gain medium; the quality factor adjusting unit comprises a saturable absorber, the saturable absorber is a microchip type saturable absorber, and the gain unit and the quality factor adjusting unit are mutually attached.
According to an aspect of the present invention, the laser further includes a pump optical element disposed between the pump unit and the first resonance portion, and adapted to receive the blue pump light and condense it into the gain unit.
The present invention also provides a laser radar comprising:
a transmitting device comprising a laser as described above;
the receiving device is configured to receive an echo generated after the laser emitted by the laser is reflected on a target object; and
a signal processing device configured to obtain a distance and/or reflectivity of the target object from the echo.
The present invention also provides a method of generating laser light, comprising:
generating pump light by a pump unit, wherein the pump unit comprises a blue laser diode and is configured to generate blue pump light;
receiving the blue light pump light through a gain unit, and forming laser oscillation with a specific wavelength through a laser resonant cavity in which the gain unit is positioned, wherein the gain unit comprises Cr-doped fluoralcalikite as a gain medium, the blue light pump light is received by the gain unit after being transmitted from a first resonant part of the laser resonant cavity, and the quality factor of the laser resonant cavity can be adjusted through a quality factor adjusting unit; and
and emitting laser through a second resonance part of the laser resonance cavity.
According to another aspect of the present invention, the method further includes reducing a pumping thermal effect by a thermally conductive transparent material between the first resonance part and the gain cell, the thermally conductive transparent material being attached to a side of the gain cell facing the first resonance part.
The preferred embodiment of the invention provides a diode-pumped solid-state laser using a blue laser diode as a pumping light source, and the Cr-doped fluoroaluminated hectorite is used as a gain medium, so that 850nm laser output suitable for a laser radar can be obtained. Due to the advantages of the blue laser diode in the aspects of beam quality and power, the structure of a pumping system can be simplified, and the overall structure of the solid laser can be further simplified; due to the advantages of the blue laser diode in the aspects of temperature range and temperature drift, the solid laser is slightly influenced by the temperature drift movement of the wavelength of the pumping light, has high reliability and is suitable for vehicle-scale application. The micro-chip structure for fixing the heat-conducting transparent material is beneficial to reducing the influence of the pumping heat effect and obtaining higher laser output under higher pumping power.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 shows the emission wavelengths of various laser crystals;
FIG. 2 shows an emission spectrum and an absorption spectrum of Cr: LiSAF;
fig. 3 shows an emission spectrum and an absorption spectrum of Cr: LiSGaF;
FIG. 4 shows an emission spectrum and an absorption spectrum of Cr: LiCFA;
FIG. 5 schematically illustrates a laser structure according to a preferred embodiment of the present invention;
FIG. 6 schematically illustrates a laser structure according to a preferred embodiment of the present invention;
FIG. 7 schematically illustrates a laser structure according to a preferred embodiment of the present invention;
FIG. 8 schematically illustrates a laser structure according to a preferred embodiment of the present invention;
fig. 9 schematically shows a package structure of a laser according to a preferred embodiment of the present invention;
fig. 10 schematically shows a package structure of a laser according to a preferred embodiment of the present invention;
fig. 11 schematically shows a package structure of a laser according to a preferred embodiment of the present invention;
fig. 12 schematically shows a package structure of a laser according to a preferred embodiment of the present invention;
fig. 13 shows a flow chart of a method of generating laser light according to a preferred embodiment of the present invention.
Detailed Description
In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection, either mechanically, electrically, or in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.
The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.
The embodiments of the present invention will be described in conjunction with the accompanying drawings, and it should be understood that the embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.
As shown in FIGS. 1 and 2, the emission wavelength of Cr-doped LiFeAlFeLi (Cr: LiCaF, Cr: LiSGaF, Cr: LiSAF) covers the wavelength range of 720nm to 1100nm, and the peak value is near 850nm, so that the Cr-doped LiFeAlFeLi is suitable for being used as a light source of a vehicle-mounted laser radar. As shown in fig. 2, the LiSAF absorption spectrum of crystal Cr has a wider absorption band at the red wavelength (about 630 nm) and a larger absorption cross section (higher peak in the figure), and similarly, as shown in fig. 3, the LiSGaF absorption spectrum of crystal Cr (pi and sigma represent different polarization states of the pump light), and as shown in fig. 4, the LiCAF absorption spectrum of crystal Cr (pi and sigma) also has a larger absorption cross section (higher peak in the figure), so that solid-state lasers using this type of laser crystal as the gain medium usually use a red (about 630 nm) laser diode as the pump to generate near-infrared laser.
The inventors of the present application have found that there are several drawbacks to the solution of using a red diode as a pump and Cr-doped fluoralcalicite as a gain medium to generate infrared laser light. The red laser diode is adopted as a pumping light source, and because the power of a single red laser diode is low, a plurality of laser diodes are generally required to be subjected to beam combination pumping, and a pumping system is complex; the central wavelength of the red laser diode drifts with the temperature, the working temperature is generally limited to 0 ℃ to 50 ℃, the application scene is also limited, for example, the laser radar is applied to the field of automatic driving, and the temperature range of the vehicle gauge is-40 ℃ to 120 ℃.
As shown in FIGS. 2, 3 and 4, the Cr-doped fluoroaluminatite laser crystal also has a wide absorption band near 450nm and a relatively large absorption cross-section (relatively high peak in the figure, absorption cross-section is close to half of 630 nm). The present invention therefore provides a solid state laser with a blue laser diode (wavelength around 450nm) as a pump light source, which overcomes the above problems at least to some extent, as described in detail below with reference to fig. 5.
As shown in fig. 5, the laser 10 includes a pumping unit 11, a gain unit 12, a laser resonator 13, and a quality factor adjusting unit 14. The pump unit 11 comprises a blue laser diode configured to generate blue pump light, for example, at a wavelength of around 450 nm. The gain unit 12 is located downstream of the optical path of the pumping unit 11 and receives the blue pumping light, the gain unit 12 includes Cr-doped fluor-aluminum-calcium-lithium as a gain medium, the laser resonator 13 includes a first resonance part 15 and a second resonance part 16, wherein the first resonance part 15 is located between the pumping unit 11 and the gain unit 12, the gain unit 12 is located in the laser resonator 13, and the laser generated in the laser resonator 13 is emitted from the second resonance part 16. The quality factor adjusting unit 14 is configured to adjust the quality factor of the laser resonator 13. The Q-factor adjustment unit 14 comprises a saturable absorber as a Q-switch for passive Q-switching for generating laser pulses. The saturable absorber material includes: at least one of YAG, carbon nanotube and graphene. Preferably, the material of the saturable absorber is at least one of carbon nanotubes or graphene. The carbon nano tube or the graphene has good heat conductivity, and can effectively improve the heat conduction and heat dissipation effects of components in the laser resonant cavity.
In the laser 10 shown in fig. 5, the gain medium within the gain cell 12 is used to achieve population inversion to create optical amplification. Since the pump unit 11 is configured to generate blue pump light, a laser crystal having a large absorption cross section and a wide absorption band around the blue wavelength, such as one or more of Cr: LiCFA, Cr: LiSAF, and Cr: LiSGaF, is selected as the gain medium accordingly. The central wavelength of the emission spectrum of the gain medium is about 850nm, the coverage range is 750nm to 950nm, and the gain medium is suitable for laser radars. Therefore, the combination of a blue laser diode pump and Cr-doped fluor-aluminum-calcium-lithium as a gain medium can obtain 850nm laser output suitable for laser radar.
As shown in fig. 5, the laser resonator 13 includes a first resonance section 15 and a second resonance section 16, and according to a preferred embodiment of the present invention, the first resonance section 15 includes a first dielectric film configured to allow blue pump light to pass through and be incident into the gain cell 12, and to reflect a beam from the gain cell 12 toward the pump cell 11 back to the gain cell 12. The second resonance section 16 includes a second dielectric film configured to reflect the light beam projected thereon from the gain unit 12 back to the gain unit 12 to finally form laser oscillation of a specific wavelength in the laser cavity 13, and the laser light generated in the laser cavity 13 is emitted from the second dielectric film. The second resonance part 16 is typically significantly more reflective than transmissive, e.g. 5-10%. Therefore, the blue pump light of the pump unit 11 is incident into the gain unit 12, and the laser resonator 13 generates the excitation radiation, and the excitation radiation is reflected back and forth in the laser resonator formed by the first resonance portion 15 and the second resonance portion 16 to perform optical amplification, and finally forms laser oscillation of a specific wavelength, and is emitted from the second resonance portion 16.
According to a preferred embodiment of the invention, the quality factor adjustment unit 14 is located between the gain medium 12 and the second resonance part 16. The Q-factor adjustment unit 14 acts as a Q-switch for the laser 10 to control the Q-value of the laser cavity.
The Q value is called quality factor and is an index for evaluating the quality of an optical resonant cavity in a laser. The Q-value is defined as the ratio of the stored energy to the energy lost per unit time in the cavity, in the laser cavity:
Figure RE-GDA0002685008020000081
wherein W is the total energy stored in the laser resonant cavity; dW/dt is the loss rate of photon energy in the laser resonant cavity, namely the energy lost in unit time; v is0The center frequency of the generated laser light.
The Q-switching technique is realized byThe Q value of the laser resonant cavity is adjusted, and the laser energy generated by the laser is compressed into a pulse with extremely narrow width for emission, so that the peak power of the generated laser is improved by several orders of magnitude, and the laser with narrow pulse width and high peak value is obtained. In particular, the peak power of the laser can reach megawatt level (10) by the Q-switching technology6W) or more, pulse width compression to nanosecond (10)-9s) of the pulse.
In general, the adjustment of the Q value of the laser resonant cavity is realized by changing the loss in the cavity. Specifically, when the pumping starts, the loss of the laser resonant cavity is large, that is, the Q value of the laser resonant cavity is reduced, so that the gain medium accumulates the population of the inversion; after pumping for a certain time, the loss of the laser resonant cavity is suddenly reduced, namely the Q value of the laser resonant cavity is increased, so that the accumulated inversion population completes stimulated radiation in a short time to form optical pulses with narrow pulse width and high peak power. In the Q-switching technology, the laser resonant cavity is in a high-loss and low-Q-value state in most of the pumping process, so that the resonant cavity has a high threshold value and cannot start oscillation, and the population number in the gain medium, which is positioned at an upper energy level and realizes inversion, is continuously accumulated; when the number of the accumulated particles for realizing the inversion reaches a certain value, the loss of the resonant cavity suddenly drops, the Q value suddenly rises, and the threshold value of the laser oscillation is rapidly reduced; then laser oscillation begins to be established in the laser resonant cavity; because the number of particles accumulated during the loss reduction and Q value increase is large, the stimulated radiation is enhanced very quickly at the moment, and the energy stored in the gain medium is released in a short time, so that high-peak narrow-pulse-width laser is formed.
The quality factor adjusting unit 14 includes a saturable absorber, which is a nonlinear absorption medium whose absorption coefficient is not constant. Under the action of stronger laser, the absorption coefficient of the saturable absorber is reduced until saturation along with the increase of light intensity, and the saturable absorber has the characteristic of transparency to light. When the light intensity projected to the saturable absorber is comparable to the saturated absorption light intensity, the absorption coefficient is gradually reduced, and the transmittance is gradually increased; when the light intensity projected on the saturable absorber reaches a certain value, the absorption of the saturable absorber on the light intensity reaches a saturation (absorption minimum) value, the absorption coefficient of the saturable absorber decreases suddenly, the transmittance increases sharply, and the saturable absorber is suddenly bleached to become transparent.
After a blue-light semiconductor laser diode generates pump laser beams, the pump laser beams enter a laser gain medium to generate population inversion, a saturable absorber is placed in a resonant cavity, at the beginning, autofluorescence in the cavity is weak, the absorption coefficient of the saturable absorber is large, the transmittance of light is low, and the cavity is in a low Q value (high loss) state, so that laser oscillation cannot be formed. The reversed particle number Is accumulated along with the continuous action of the optical pump, the fluorescence in the cavity gradually becomes stronger, when the light intensity Is comparable to Is (the saturation absorption light intensity of the saturable absorber), the absorption coefficient of the saturable absorber becomes smaller, the transmittance gradually increases, when reaching a certain value, the absorption reaches saturation (the absorption minimum value), the absorption Is suddenly bleached and becomes transparent, and the Q value in the cavity Is suddenly increased, so that the laser oscillation output Q-switched laser pulse Is generated.
According to a preferred embodiment of the present invention, the first resonance part 15 comprises a first dielectric film on the end surface of the gain unit 12 close to the pump unit 11, i.e. the incident surface of the laser gain medium is plated with a dielectric film with high transmissivity to blue pump light and high reflectivity to laser wavelength; the second resonance part 16 includes a second dielectric film on the end surface of the quality factor adjustment unit 14 away from the pumping unit 11, i.e., the exit surface of the saturable absorber is coated with a dielectric film that is partially reflective to the laser wavelength, and the reflectivity of the second dielectric film is significantly higher than the transmittance to form a resonant cavity. The gain medium is, for example, a microchip-type gain medium, the saturable absorber is, for example, a microchip-type saturable absorber, the gain unit 12 and the quality factor adjusting unit 14 are attached to each other, for example, optical cement is used for connection, so that the cavity length of the resonant cavity can be effectively shortened, the structure of the resonant cavity is simplified, and laser pulses with narrow pulse width and high energy can be obtained more favorably.
In the embodiment of fig. 5, the pumping unit 11 includes a semiconductor laser diode, which has the advantages of low power consumption and small volume. In addition, the blue laser diode is adopted as a pumping light source, and compared with a red laser diode, the blue laser diode has the following advantages:
1) the area of a luminous area is small, and the quality of light beams is good;
2) the single laser power is higher;
3) can work under a wider temperature range (can be used for the temperature range of the vehicle gauge);
4) the Cr-doped calcium aluminum fluoride lithionite has a wider absorption band near the blue light wavelength (450nm), the absorption cross section is close to half of 630nm, and the absorption cross section is small, so that heat dissipation is facilitated;
5) the wavelength drift coefficient of the 450nm blue laser diode is less than 0.07 nm/DEG C along with the temperature, and the temperature drift coefficient of the red light is generally 0.2 nm/DEG C. Therefore, the solid laser is less affected by the temperature drift shift of the wavelength of the pump light.
As shown in fig. 5, according to a preferred embodiment of the present invention, the laser 10 further includes a pump optical element 17 disposed between the pump unit 11 and the first resonance part 15, the pump optical element 17 including a lens or a lens group or a coupling mirror for receiving and coupling the blue pump light into the gain unit 12.
As shown in fig. 6, according to a preferred embodiment of the present invention, the laser 20 includes a pumping unit 11, a gain unit 12, a laser resonator 13, a quality factor adjusting unit 14, and a thermally conductive transparent material 18. The pump unit 11 includes a blue laser diode configured to generate blue pump light. The gain unit 12 is located in the optical path downstream of the pumping unit 11 and receives the blue pumping light, and the gain unit 12 includes Cr-doped fluoroaluminate hectorite as a gain medium. The laser cavity 13 includes a first resonance portion 15 and a second resonance portion 16, wherein the first resonance portion 15 is located between the pumping unit 11 and the gain unit 12, the gain unit 12 is located in the laser cavity 13, and laser light generated in the laser cavity 13 exits from the second resonance portion 16. The quality factor adjusting unit 14 is configured to adjust the quality factor of the laser resonator 13. The thermally conductive transparent material 18 is located between the first resonance portion 15 and the gain cell 12, and is attached to the side of the gain cell 12 facing the first resonance portion 15. When the pumping light is converted into laser, the residual energy is converted into thermal power to affect the laser resonant cavity, and the front end of the gain medium is the place where the heat is most concentrated. A transparent material sheet with high thermal conductivity is fixed for heat dissipation, so that the heat distribution can be effectively improved, the influence of a thermal lens effect on a laser resonant cavity is reduced, and a laser crystal can bear higher pumping power and is beneficial to obtaining high-power laser output. The heat-conducting transparent material 18 can be made of sapphire sheets or YAG, and the heat conductivity of the sapphire can reach 25.12W/m/k (@100 ℃).
As shown in fig. 7, a laser 30 according to a preferred embodiment of the present invention, wherein second resonance part 16 further includes concave mirror 19. Due to the effect of the gain medium thermal lens effect (the first resonance part 15 can be equivalently a concave surface), and due to the fact that the flat concave cavity is an unstable cavity, in order to improve the light emitting capability of the laser, the concave surface of the concave mirror 19 faces the first resonance part 15, the second dielectric film is arranged on the concave surface of the concave mirror 19, and laser generated in the laser resonant cavity 13 is emitted from the second dielectric film and the concave mirror 19.
As shown in fig. 8, a laser 40 according to a preferred embodiment of the present invention includes a pumping unit 11, a gain unit 12, a laser resonator 13, a quality factor adjusting unit 14, a thermally conductive transparent material 18, and a concave mirror 19. The working process and functions of each part are as described above, and are not described herein again.
The laser radar has variable working environment, the performance of the laser radar is easily influenced by natural conditions such as atmospheric circulation, air temperature, rain, snow, fog and the like, and the laser radar meets the requirements on the reliability of a laser. Higher reliability and stability can be achieved if it can be packaged as a whole. Fig. 9 to 12 are corresponding package structures of the preferred embodiments in fig. 5 to 8. In the preferred embodiment of fig. 9 to 12, the pumping unit 11, the gain unit 12, the first resonance part 15, the second resonance part 16, the quality factor adjusting unit 14, and the like are packaged in a metal housing 20 by using the metal housing 20, so as to realize the solid laser integrated package, and the metal housing 20 includes a transparent light exit window 21 for emitting laser light.
The present invention also provides a laser radar comprising: a transmitting device comprising a laser as described in any of the above preferred embodiments; the receiving device is configured to receive an echo of the laser emitted by the laser after the laser is reflected on a target object; and the signal processing device is configured to obtain the distance and/or the reflectivity of the target object according to the radar echo.
As shown in fig. 13, the present invention also provides a method 120 of generating laser light:
in step S121, blue pump light is generated by the pump unit. The pumping unit includes a blue laser diode configured to generate blue pump light.
In step S122, the blue light pump light is received by the gain unit, and laser oscillation with a specific wavelength is formed by the laser resonator in which the gain unit is located, where the gain unit includes Cr-doped fluoralcalipatite as a gain medium, the blue light pump light is received by the gain unit after being transmitted from the first resonance portion of the laser resonator, and the quality factor of the laser resonator is adjustable by the quality factor adjusting unit.
In step S123, laser light is emitted through the second resonance portion of the laser resonator.
The method 120 of lasing, as shown in fig. 13, further includes reducing the pumping thermal effect by a thermally conductive transparent material. The heat conduction transparent material is located between the first resonance part and the gain unit, and the heat conduction transparent material is attached to one side, facing the first resonance part, of the gain unit.
The preferred embodiment of the invention provides a diode-pumped solid-state laser using a blue laser diode as a pumping light source, and the output of 850nm laser suitable for a laser radar can be obtained by using Cr-doped fluoroaluminated hectorite as a gain medium. The blue laser diode has small area of a light emitting area, good beam quality and high power of a single laser, so that the structure of a pumping system can be simplified, and the overall structure of the solid laser can be further simplified; because the blue laser diode has small wavelength drift coefficient along with the temperature and can work under a wider temperature range, the solid laser is slightly influenced by the temperature drift of the wavelength of the pumping light, has high reliability and is suitable for vehicle-scale application. The micro-chip structure for fixing the heat-conducting transparent material is beneficial to reducing the influence of the pumping heat effect and obtaining higher laser output under higher pumping power.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (13)

1. A laser, comprising:
a pumping unit including a blue laser diode configured to generate blue pumping light;
the gain unit is positioned on the downstream of the optical path of the pumping unit and receives the blue light pumping light, and the gain unit comprises Cr-doped calcium aluminum garnet serving as a gain medium;
the laser resonant cavity comprises a first resonant part and a second resonant part, wherein the first resonant part is positioned between the pumping unit and the gain unit, the gain unit is positioned in the laser resonant cavity, and laser generated in the laser resonant cavity is emitted from the second resonant part; and
a quality factor adjustment unit configured to adjust a quality factor of the laser resonator.
2. The laser of claim 1, wherein the quality factor adjustment unit is located between the gain medium and the second resonance section.
3. The laser according to claim 1 or 2, wherein the first resonance section includes a first dielectric film configured to allow the blue pump light to pass through and be incident into the gain cell and to reflect a beam from the gain cell toward the pump cell back to the gain cell, and the second resonance section includes a second dielectric film configured to reflect a beam from the gain cell back to the gain cell to finally form laser oscillation of a specific wavelength in the laser cavity from which the laser light generated in the laser cavity exits.
4. The laser of claim 3, wherein the first dielectric film is located on an end face of the gain cell close to the pumping cell, and the second dielectric film is located on an end face of the quality factor adjusting cell far from the pumping cell.
5. The laser according to claim 3, wherein the second resonance portion further comprises a concave mirror having a concave surface facing the first resonance portion, the second dielectric film is provided on the concave surface, and the laser light generated in the laser resonator cavity exits from the second dielectric film and the concave mirror.
6. The laser of claim 1 or 2, wherein the laser further comprises a thermally conductive transparent material between the first resonance section and the gain cell, the thermally conductive transparent material being attached to a side of the gain cell facing the first resonance section.
7. The laser of claim 1 or 2, wherein the Cr doped LiFeCaLiF comprises one or more of Cr: LiCFA, Cr: LiSAF, and Cr: LiSGaF.
8. The laser of claim 1 or 2, further comprising a metal housing, the pumping unit, the gain unit, the first and second resonating sections, and the quality factor adjusting unit being enclosed within the metal housing, the metal housing comprising a transparent light exit window for laser light exit.
9. The laser of claim 1 or 2, wherein the gain medium is a microchip-type gain medium; the quality factor adjusting unit comprises a saturable absorber, the saturable absorber is a microchip type saturable absorber, and the gain unit and the quality factor adjusting unit are mutually attached.
10. The laser of claim 1 or 2, further comprising a pump optical element disposed between the pump unit and the first resonator portion, the pump optical element being operable to receive the blue pump light and condense it into the gain cell.
11. A lidar comprising:
a transmitting device comprising a laser as claimed in any one of claims 1 to 10;
the receiving device is configured to receive an echo generated after the laser emitted by the laser is reflected on a target object; and
a signal processing device configured to obtain a distance and/or reflectivity of the target object from the echo.
12. A method of generating laser light, comprising:
generating pump light by a pump unit, wherein the pump unit comprises a blue laser diode and is configured to generate blue pump light;
receiving the blue light pump light through a gain unit, and forming laser oscillation with a specific wavelength through a laser resonant cavity in which the gain unit is positioned, wherein the gain unit comprises Cr-doped fluoralcalikite as a gain medium, the blue light pump light is received by the gain unit after being transmitted from a first resonant part of the laser resonant cavity, and the quality factor of the laser resonant cavity can be adjusted through a quality factor adjusting unit; and
and emitting laser through a second resonance part of the laser resonance cavity.
13. The method of claim 12, further comprising reducing pumping heat effects by a thermally conductive transparent material between the first resonant section and the gain cell, the thermally conductive transparent material conforming to a side of the gain cell facing the first resonant section.
CN202010354107.1A 2020-04-29 2020-04-29 Laser, lidar comprising same and method for generating laser light Active CN113572010B (en)

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CN102244349A (en) * 2011-05-26 2011-11-16 天津大学 Neodymium-doped yttrium vanadate crystal all-solid-state laser with double-wavelength end pump
CN106921110A (en) * 2017-03-30 2017-07-04 华中科技大学 The intracavity pump continuous wave optical parametric oscillator of diode-end-pumped
CN109950784A (en) * 2019-04-10 2019-06-28 上海禾赛光电科技有限公司 Laser and laser radar

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080247425A1 (en) * 2007-04-03 2008-10-09 David Welford Q-switched microlaser apparatus and method for use
CN102044836A (en) * 2010-10-28 2011-05-04 福州高意通讯有限公司 Microchip laser capable of tuning output pulse width
CN102244349A (en) * 2011-05-26 2011-11-16 天津大学 Neodymium-doped yttrium vanadate crystal all-solid-state laser with double-wavelength end pump
CN106921110A (en) * 2017-03-30 2017-07-04 华中科技大学 The intracavity pump continuous wave optical parametric oscillator of diode-end-pumped
CN109950784A (en) * 2019-04-10 2019-06-28 上海禾赛光电科技有限公司 Laser and laser radar

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