GB2497106A - Laser System and path length of radiation - Google Patents

Laser System and path length of radiation Download PDF

Info

Publication number
GB2497106A
GB2497106A GB201120666A GB201120666A GB2497106A GB 2497106 A GB2497106 A GB 2497106A GB 201120666 A GB201120666 A GB 201120666A GB 201120666 A GB201120666 A GB 201120666A GB 2497106 A GB2497106 A GB 2497106A
Authority
GB
United Kingdom
Prior art keywords
text
gain material
radiation
laser system
laser
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB201120666A
Other versions
GB201120666D0 (en
Inventor
Stephen Lee
William Alexander
Trevor Cook
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales Holdings UK PLC
Original Assignee
Thales Holdings UK PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thales Holdings UK PLC filed Critical Thales Holdings UK PLC
Priority to GB201120666A priority Critical patent/GB2497106A/en
Publication of GB201120666D0 publication Critical patent/GB201120666D0/en
Priority to PCT/GB2012/052942 priority patent/WO2013079940A1/en
Publication of GB2497106A publication Critical patent/GB2497106A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/061—Crystal lasers or glass lasers with elliptical or circular cross-section and elongated shape, e.g. rod
    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0606—Crystal lasers or glass lasers with polygonal cross-section, e.g. slab, prism
    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0612—Non-homogeneous structure
    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0617—Crystal lasers or glass lasers having a varying composition or cross-section in a specific direction
    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/0619—Coatings, e.g. AR, HR, passivation layer
    • H01S3/0625—Coatings on surfaces other than the end-faces
    • 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
    • H01S3/08072—Thermal lensing or thermally induced birefringence; Compensation 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
    • H01S3/05—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
    • H01S3/08095—Zig-zag travelling beam through the active medium
    • 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
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094049—Guiding of the pump light
    • H01S3/094057—Guiding of the pump light by tapered duct or homogenized light pipe, e.g. for concentrating pump light
    • 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
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
    • 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
    • H01S3/164—Solid materials characterised by a crystal matrix garnet
    • H01S3/1643—YAG
    • 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
    • H01S3/1653—YLiF4(YLF, LYF)
    • 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
    • H01S3/1691—Solid materials characterised by additives / sensitisers / promoters as further dopants
    • H01S3/1698—Solid materials characterised by additives / sensitisers / promoters as further dopants rare earth
    • 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
    • H01S3/20—Liquids
    • 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
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094084—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light with pump light recycling, i.e. with reinjection of the unused pump light, e.g. by reflectors or circulators

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Lasers (AREA)

Abstract

A laser system 5, comprises a radiation source 20 for example a diode stack and laser gain material 10 of Nd:YAG, Nd:YVO4, Nd:YLF, Nd:GSGG or ErGlass, wherein the radiation source is configured to pump or provide radiation to the laser gain material at one or more ends of the gain material and/or along a long axis of the gain material; and wherein the gain material comprises at least one reflective surface (a reflective coating). The system may be configured such that the path length through which the radiation travels through the gain material is the same length longer than the absorption lens of radiation produced by the radiation source 20 at an operational temperature of the laser system 5 associated with the lowest absorption by the gain material 10 of the radiation produced by the radiation source 20.

Description

I
Laser System The present invention relates to a laser system, and particularly but not exclusively to a laser system that comprises a pumping system whose output varies with temperature and/or S comprises a gain medium whose absorption varies with the wavetength of radiation.
Background
Many làsing or gain materials have favourable properties such as high gain and good robustness, but absorption of pump radiation by the gain material can vary markedly with wavelength. Examples of such materials include Nd:YAG, which has a primary absorption band at SOBnm that has a full width half maximum of approximately ±2nm. Other examples of such materials include ND:YV04, ND:YLF, Nd:GSGG and Er:Glass. The variation of absorption with wavelength is not so much of an issue in systems that use a broadband light source. However, such systems are generally less efficient, since the light source produces radiation over a wide spectrum and therefore a significant proportion of the radiation produced by the light source lies out with the absorption band of the lasing material and therefore does not result in pumping of the gain material.
Narrow band light sources such as laser diodes can be advantageously used to increase the efficiency of a laser by producing energy at a wavelength that can be matched to the absorption band of the gain medium of the laser, thereby resulting in good absorption efficiency. However, many such narrow band light sources, particularly diode based light sources, suffer from wavelength drift, wherein the wavelength of radiation produced by the light source varies with temperature. For example, in some laser diode systems, the wavelength can vary at a rate of between approximately O.25nm/°C and 0.35nm/°C depending on the material in question. In applications such as automotive, rail and military, that require use of the laser over a wide range of ambient temperatures, this drift in wavelength can result in significant variations of the absorption of the pump radiation by the gain materiaL For example, in a laser system required to operate in a temperature range of -50°C to +70°C, a temperature dependent wavelength drift of 0.2Snm/°C would result in a drift of the wavelength of the light produced by the laser diode of 33.6nm across the operational temperature range. A popular laser gain material is Nd:YAG, whose absorption spectrum is shown in Figure 1. It is clear from this that the absorption properties of Nd:YAG vary considerably with wavelength such that a 33.6nm drift in the wavelength produced by a laser diode operating as a pump source would result in significant variations of absorption length of the radiation by the gain material, as shown in Figure 2. It will be appreciated that this would lead to corresponding variations in laser efficiency with ambient temperature.
s Some solutions to this problem already exist. For example, temperature controlled diodes may be used. However, such solutions generally result in reduced efficiency, for example due to the energy used to control the temperature, which is a disadvantage in systems where power is limited, such as battery powered systems, or where a reduction in power consumption of the apparatus would be beneficial. Furthermore, the additional systems required for temperature control adds complexity and cost to the laser.
It is at least one object of at least one embodiment of the present invention to provide an improved laser pumping system and associated laser, for example, a system having an improved efficiency and being operable over a wide temperature range. is
Statements of Invention
According to a first aspect of the present invention is a laser system, the laser system comprising a radiation source and laser gain material, wherein the radiation source is configured to pump or provide radiation to the laser gain material at one or more ends of the gain material and/or along a long axis of the gain material.
Advantageously, the gain material may comprise at least one reflective surface, which may be a surface extending in the same direction as a long axis of the gain material and/or a barrel surface of the gain material.
The at least one reflective surface may configured to reflect light travelling within the gain material. For example, the reflective surface may comprise or be provided with a reflective coating. The gain material may be provided with or placed within a reflective sleeve. The laser system may be configured such that radiation is internally reflected from the reflective surface of the gain material, for example, by appropriate selection of the index of refraction of the gain material and/or by configuring the pump source such that the radiation produced is incident on the outer surface of the gain material at an angle that results in total internal reflection.
The gain material may be elongated. The gain material may comprise or be comprised in a rod but may comprise or be comprised in a slab or block, or another configuration, such as a liquid gain material held within an elongate container. The laser system may be configured such that radiation from the radiation source generally propagates along the long/elongated direction of the gain material.
S The laser system may be configured such that the path length through which the radiation travels through the gain material is the same length or longer than an absorption length of radiation produced by the radiation source at an operational temperature of the system associated with the lowest absorption by the gain material of the radiation produced by the radiation source. The absorption length of the radiation may be an absorption length that produces a required absorption level of the radiation1 e.g. a 75%, 90% or 100% absorption.
The laser gain material may comprise a cylindrical rod. The rod of laser gain material may comprise or consist of at least one side and two opposed ends, wherein at least one of the opposed ends may be pumped or receive radiation from the pumping system. The opposed ends may comprise flat faces of the gain material, such as circular faces. The at least one side of the gain material may comprise a surface of the gain material that extends in a direction along or parallel to the long axis of the gain material. The at least one side of the gain material may comprise the barrel surface of the gain material. The at least one side of the gain material may comprise the reflective surface.
The radiation source may comprise a light source, which may comprise one or more diode based light sources such as laser diodes. The radiation may comprise light and the gain material may be optically pumped.
The gain material may be provided in an optical cavity that comprises at least an end mirror and an output coupler, which may be in any suitable configuration known in the art.
The light source may comprise a divergent light source. The light source may be a narrowband light source, for example, having a bandwidth of less than lOnm, preferably less than Snm and optionally of 2nm or less, The gain material may be core doped, for example in the form of a core doped rod. The highest level of doping may extend along the long axis of the gain material. The doping at the centre or long axis of the gain material may be higher than at the outside or periphery of the gain material in a radial direction (e.g. at the side or barrel surface of the gain material).
The doping profile of the gain material may comprise a radial doping profile, for example, the doping may vary (and preferably decrease) from the centre of the gain material to the sides of the gain material in a radial direction.
At least one and preferably both ends of the gain material may be undoped or have reduced S doping relative to at least part of the rest of the gain material. The gain material may be provided with undoped end caps.
By end pumping an elongate gain material such that the gain material is pumped or provided with radiation from the pumping system along the long axis of the gain material, a longer potential absorption path is provided for the pump radiation. Advantageously, if the path length of radiation passing along the gain material in the pumping direction is equal to or greater than a maximum absorption path length associated with radiation produced by the radiation source within the operational temperature range, then as the wavelength of the radiation produced by the radiation source varies with temperature over the operational temperature range of the laser and the absorption path length varies accordingly, then the absorption efficiency of the gain material remains relatively constant, as a longer length/higher volume of gain material will be used for absorption as the wavelength of the radiation varies to a wavelength that is absorbed less by the gain material and a shorter length/lower volume of gain material will be used for absorption as the wavelength of the radiation varies to a wavelength that is absorbed more by the gain material, By making the outer side, e.g. the barrel surface, of the laser reflective, radiation within the gain material that is incident on the reflective surface may be reflected back into the gain material, thus increasing the path length that radiation may travel within the gain material.
This also allows the pump energy to be confined within the laser mode volume, thus increasing the efficiency of the system, particularly for highly divergent light sources.
Use of a highly divergent light source in the above system may result in a longer path length and may result in a very uniform radial energy distribution within the gain material. This may lead to a more consistent absorption efficiency of the gain material when subject to variations in the wavelength of the pump radiation due to temperature. Furthermore, this may result in a parabolic temperature within the gain material and a well defined and well behaved thermal lens, which is relatively easy to compensate for.
The above system may result in pumping of a very high proportion of the gain material, which may lead to the propagation of unwanted modes. By reducing the cross section of the gain material, the unwanted modes can be inhibited or eliminated and the beam quality
S
improved. However, manufacturing a physically thinner rod or slab of gain material can lead to manufacturing and/or handling difficulties. Therefore, varying the doping profile of the gain material in order to promote favoured propagation modes, for example by providing a higher level of doping towards the centre of the rod than the doping level at or toward the outside1 may provide improved beam quality without the manufacturing, handling or robustness issues associated with a very thin or narrow rod.
Providing at least one end section with an end cap of undoped material or material having a reduced doping level, preferably adjacent to or towards the radiation source, bulging of the rod at one end may be reduced.
According to a second aspect of the invention is an apparatus comprising a laser system of the first aspect.
The apparatus may be or comprise at least one of a laser designator, a rangefinder, a scanner, an analytical device, an optical storage reader, a sensor or the like, According to a third aspect of the invention is a method of producing or designing a laser system, wherein the laser system comprises a radiation source and laser gain material and the radiation source is configured to pump or provide radiation to the laser gain material at one or more ends of the gain material and/or along a long axis of the gain material, the method comprising sizing the laser gain material such that the path length through which the radiation travels along the length or long axis of the gain material is the same length or longer than an absorption length of radiation produced by the radiation source at an operational temperature of the system associated with the lowest absorption of the radiation produced by the radiation source by the gain material.
According to a fourth aspect of the present invention is a method of operating a laser system, the laser system comprising a radiation source and laser gain material, the method comprising pumping or providing radiation to the laser gain material at one or more ends of the gain material and/or along a long axis of the gain material.
Advantageously, the gain material may comprise a reflective surface, for example, on at least one surface of the gain material extending in a longitudinal direction of the gain material.
The method may comprise use of a laser system of the first aspect or an apparatus of the second aspect.
It will be appreciated that features analogous to those described in relation to any of the S above aspects may be applicable to any of the other aspects, Method features corresponding to use of any features described above in relation to apparatus and/or apparatus features configured to implement any features described above in relation to a method are also contemplated as falling within the scope of the present invention.
Brief Description of the Drawings
The invention will be described herein with respect to the following drawings: Figure 1 shows an absorption spectrum of Nd:YAG; Figure 2 shows the variation of absorption length in Nd:YAG with wavelength for radiation sources having varying bandwidths; Figure 3 is a schematic of a laser apparatus in a first condition; and Figure 4 is a schematic of the laser apparatus in a second condition.
Detailed Description of the Drawings
Figures 3 and 4 show schematics of at least part of a laser system 5 according to embodiments of the present invention and in particular show the volume of a gain medium of the laser system 5 that is pumped by a pumping system 15 at a wavelength of radiation that is highly absorbed by the gain medium 10 and at a wavelength of radiation that is absorbed less by the gain medium respectively.
The laser system 5 comprises a radiation source 20, in this case in the form of a laser diode stack, coupled via a concentrator element 25 for concentrating the diffuse radiation produced by the laser diode stack 20 to an end 30 of an elongate rod of gain medium 10. In this way, radiation emitted by the laser diode stack 20 is concentrated in the pump concentrator element 25 and provided to the pumped end 30 of the rod of gain medium 10 such that it propagates generally in the elongate or long direction of the gain medium 10.
In certain narrow bandwidth radiation sources, particularly diode based radiation sources S such the laser diodes 20, the wavelength of the radiation produced thereby varies with the temperature of the radiation source. At the same time, in many popular materials used as gain media such Nd:YAG, Nd:YVO4, Nd:YLF, Nd:GSGG and Er:Glass, the absorption coefficient varies with wavelength of the radiation, for example as shown in Figure 1 for Nd:YAG. Using the variation in absorption coefficient with temperature, a skilled person could determine the corresponding variation in absorption path length for radiation at any given wavelength and therefore at any given temperature of the radiation source 20. For example, Figure 2 shows the variation in absorption length of Nd:YAG with wavelength for radiation sources of varying bandwidths and for 90% absorption.
Therefore, given an operational temperature range that a laser 5 is to be designed for1 a designer can determine the minimum absorption coefficient for the gain medium 10 within the band of wavelengths associated with the operational temperature range of the radiation source 20. From this, the designer could readily determine the maximum path length that the radiation will require to travel through the gain medium 10 in order to achieve a required absorption, such as over 75%, over 90% or even (theoretically) 100% absorption and configure the system accordingly, for example by selecting an appropriate elongate length of the rod of gain medium 10.
In this way, for example, if the temperature of the radiation source 20 results in production of radiation having a wavelength that results in the radiation being strongly adsorbed by the gain medium 10, then a pumped volume 35a of the gain medium 10 is relatively small, as shown in Figure 3. In contrast, if the temperature of the radiation source 20 is such that the radiation produced has a wavelength that results in the radiation being weakly absorbed by the gain medium 10, then the pumped volume 35b of the gain medium 10 is increased, as shown in Figure 4. In either event, since the rod of gain medium 10 is sized such that the path length of radiation produced by the radiation source 20 within an operational temperature range having a wavelength that is least strongly absorbed by the gain medium is shorter or the same as the path length the radiation travels through the gain medium 10, then at least a required amount of pump radiation is absorbed by the gain medium 10. In this way, there is little or no variation in output of the laser 5 with temperature.
Advantageously, this compensation mechanism is essentially passive and requires no heaters or sophisticated controllers or radiation sources. In other words, the system is an
S
entirely free running, non-temperature controlled system using a non-controlled narrowband radiation source.
Advantageously, the path length of the radiation can be increased without having to significantly increase the length of the rod of gain medium 10. In embodiments, a barrel surface or radial surface or elongate surface 40 of the gain medium 10 is reflective, wherein the reflective surface 40 is arranged to reflect radiation within the gain medium 10 back to the gain medium 10. Such a reflective surface 40 may be provided, for example, using a reflective coating provided on the barrel surface of the gain medium 10, or configuring the gain medium 10 such that total internal reflection occurs on the outer / barrel surface or by placing the gain medium 10 within a sleeve having a reflective inner surface.
Advantageously, if the radiation source 20 is a highly divergent radiation source, such as a diode based radiation source and most preferably comprising a laser diode, then the radiation advantageously propagates at a large angle to the long axis 45 of the gain medium 10. Since the gain medium 10 is provided with the reflective surface 40, any divergent pump radiation provided into the end 30 of the rod of gain medium 10 can be confined within the rod via reflections from the reflective surface 40 as it propagates down the length of the rod of gain medium 10. It will be appreciated that the maximum divergence angle of the light will be limited if total internal reflection from the surface 40 of the gain medium 10 is used.
However, this need not be the case with less angular sensitive reflective surfaces 40 such as reflective coatings or reflective sleeves.
Use of the combination of the reflective surface 40 of the gain medium 10 and a divergent (i.e. non coherent) light source 20 leads to a uniform energy distribution radially within the pumped region of the gain medium 10. This advantageously leads to a parabolic temperature distribution within the gain medium 10 and a well behaved spherical thermal lens. This allows appropriate compensation for the thermal lens to be more easily used. It will be appreciated that this is an improvement over end pumping the gain medium 10 with a high beam quality Gaussian beam, where a non-spherical lens can often be produced.
The apparatus and pumping mechanism described above tends to lead to substantially the entire cross section of the gain medium 10 being pumped. This may lead to the promotion of unwanted modes of propagation and thereby a reduction in beam quality. In this case, the beam quality can be improved by reducing the diameter or cross section of the rod of gain medium 10. However, it will be appreciated that there is a limit on how small the rod of gain medium 10 may be made before handling, manufacturing and robustness of the gain medium 10 is adversely affected.
According to an embodiment of the invention, the effect of a thinner rod can be produced by varying the doping of the gain medium 10 in a radial direction, i.e. the gain medium 10 is more heavily or optimally doped at the centre of the rod of gain medium 10 than at the periphery of the gain medium 10 in a radial direction, i.e. the rod of gain medium 10 is core doped. Alternatively, the doping of the gain medium 10 can be provided in a radial doping profile that is maximised along the rotation symmetry axis 45 of the rod of gain medium 10 and reduces in the radial direction towards the periphery of the gain medium 10 such that it is ata minimum at the radial surface 40 of the gain medium 10.
It will be appreciated that the above laser system 5 and method may result in variations in the distribution of pump energy within the gain medium 10 as the temperature changes.
However, this may be minimised by increasing the bandwidth of the radiation source 20.
Another result of end pumping the gain medium 10 is that more heat may be provided to the end 30 of the gain medium 10 closest to the radiation source 20 (e.g. the end of the gain medium that receives the radiation from the radiation source). One option for addressing this issue is to provide reduced doping or undoped caps or portions of the gain medium 10 adjacent or towards the radiation source. In this way, less heat is absorbed closest to the radiation source 20 and the problem of bulging of the end faces 30 due to thermal expansion can be minimised.
It will be appreciated that although an advantageous example of the invention is described above, variations to the above example are contemplated.
For example, it will appreciated that the present invention is operable with a wide variety of suitable gain medium 10 materials, laser 5 configurations and resonant cavity configurations known in the art, with varying degrees of efficacy, and is not limited to any particular configuration.
For instance, although the gain medium 10 described above is advantageously provided in the form of a rod, it will be appreciated by a skilled person that the gain medium 10 may be provided in other configurations such as an elongate slab, block or the like. Indeed, the gain medium 10 may comprise a liquid gain medium provided in a container.
In addition, whilst the radiation source 20 is advantageously described as comprising a laser diode, it will be appreciated that other suitable radiation sources, such as art LED, may be used. Furthermore, it will be appreciated that the lasers 5 of the present invention may comprise additional components to those described above such as one or more output S couplers, end mirrors, q-switches, telescopes, lenses, reflectors or other optical elements known in the art.
Therefore, it will be appreciated that the above specific description is provided by way of example only and that the scope of the invention is defined by the claims.

Claims (1)

  1. <claim-text>Claims 1. A laser system (5), the laser system (5) comprising a radiation source (20) and laser S gain material (20), wherein the radiation source (20) is configured to pump or provide radiation to the laser gain material (10) at one or more ends (30) of the gain material (20) and/or along a long axis (45) of the gain material (10); and wherein the gain material (10) comprises at least one reflective surface (40).</claim-text> <claim-text>2. The laser system (5) according to claim 1, wherein the gain material (10) is elongated.</claim-text> <claim-text>3. The laser system (5) according to claim 2, wherein the reflective surface (40) extends in the same direction as a long axis (45) of the gain material (10).</claim-text> <claim-text>4. The laser system (5) according to any preceding claim, wherein the laser system (5) is configured such that the path length through which the radiation travels through the gain material (10) is the same length or longer than an absorption length of radiation produced by the radiation source (20) at an operational temperature of the laser system (5) associated with the lowest absorption by the gain material (10) of the radiation produced by the radiation source (20).</claim-text> <claim-text>5. The laser system (5) according to any preceding claim, wherein the at least one reflective surface (40) is internally reflective so as to reflect light travelling within the gain material (10).</claim-text> <claim-text>6. The laser system (5) according to any preceding claim, wherein the reflective surface (40) comprises or is provided with a reflective coating.</claim-text> <claim-text>7, The laser system (5) according to any preceding claim, wherein the gain material (10) is provided with or placed within a reflective sleeve.</claim-text> <claim-text>8. The laser system (5) according to any preceding claim, wherein the radiation source (20) comprises one or more laser diodes.</claim-text> <claim-text>9. The laser system (5) according to any preceding claim, wherein the gain material (10) is core doped, such that the highest level of doping extends along the long axis (45) of the gain material (10).S</claim-text> <claim-text>10. The laser system (5) according to claim 9, wherein the gain material (10) comprises a radial doping profile.</claim-text> <claim-text>11. The laser system (5) according to any preceding claim, wherein at least one end of the gain material (10) is undoped or has reduced doping relative to at least part of the rest of the gain material (10).</claim-text> <claim-text>12. The laser system (5) according to any preceding claim, wherein the gain material (10) is provided with at least one undoped end cap.</claim-text> <claim-text>13. An apparatus comprising a laser system (5) according to any preceding claim.</claim-text> <claim-text>14. A method of producing or designing a laser system (5), wherein the laser system (5) comprises a radiation source (20) and laser gain material (10) and the radiation source (20) is configured to pump or provide radiation to the laser gain material (10) atone or more ends (30) of the gain material (10) and/or along a long axis (45) of the gain material (10), the method comprising sizing the laser gain material (10) such that the path length through which the radiation travels along the length or long axis of the gain material (10) is the same length or longer than an absorption length of radiation produced by the radiation source (20) at an operational temperature of the laser system (5) associated with the lowest absorption of the radiation produced by the radiation source (20) by the gain material (10).</claim-text> <claim-text>15. A method of operating a laser system (5), the laser system (5) comprising a radiation source (20) and laser gain material (10), the method comprising pumping or providing radiation to the laser gain material (10) at one or more ends of the gain material (10) and/or along a long axis (45) of the gain material (10).</claim-text> <claim-text>16. The method according to claim 15, wherein the method comprises use of a laser system (5) of any of claims ito 12 and/or an apparatus according to claim 13.</claim-text> <claim-text>17. A laser system (5) as shown herein in the drawings and/or as described herein in relation to the drawings.</claim-text>
GB201120666A 2011-11-30 2011-11-30 Laser System and path length of radiation Withdrawn GB2497106A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB201120666A GB2497106A (en) 2011-11-30 2011-11-30 Laser System and path length of radiation
PCT/GB2012/052942 WO2013079940A1 (en) 2011-11-30 2012-11-29 Pump absorption equalisation

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB201120666A GB2497106A (en) 2011-11-30 2011-11-30 Laser System and path length of radiation

Publications (2)

Publication Number Publication Date
GB201120666D0 GB201120666D0 (en) 2012-01-11
GB2497106A true GB2497106A (en) 2013-06-05

Family

ID=45508992

Family Applications (1)

Application Number Title Priority Date Filing Date
GB201120666A Withdrawn GB2497106A (en) 2011-11-30 2011-11-30 Laser System and path length of radiation

Country Status (2)

Country Link
GB (1) GB2497106A (en)
WO (1) WO2013079940A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017205851A1 (en) * 2016-05-26 2017-11-30 Compound Photonics Ltd Solid-state laser systems
US20190245320A1 (en) * 2016-05-26 2019-08-08 Compound Photonics Limited Solid-state laser system

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3679995A (en) * 1970-03-11 1972-07-25 Ibm Optically pumped liquid lasers
GB1373336A (en) * 1972-06-26 1974-11-13 Western Electric Co Laser assemblies
US3982201A (en) * 1975-01-24 1976-09-21 The Perkin-Elmer Corporation CW solid state laser
EP0973236A2 (en) * 1998-07-07 2000-01-19 TRW Inc. End pumped zig-zag slab laser gain medium
US20020191664A1 (en) * 2001-06-14 2002-12-19 Trussell C. Ward Diode array end pumped slab laser
EP1717914A1 (en) * 2005-04-28 2006-11-02 Compagnie Industrielle des Lasers Cilas Active element for laser source and laser source comprising such active element
WO2007051138A2 (en) * 2005-10-28 2007-05-03 Laserscope High power, end pumped laser with off-peak pumping

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110134945A1 (en) * 2005-03-01 2011-06-09 Elbit Systems Electro-Optics Elop Ltd. Lengthening the path of a pump beam in a monolothic solid state laser apparatus
FR2917543B1 (en) * 2007-06-12 2009-10-16 Cie Ind Des Lasers Cilas Sa ACTIVE ELEMENT FOR LASER SOURCE AND LASER SOURCE COMPRISING SUCH AN ACTIVE ELEMENT.
US20110104491A1 (en) * 2009-10-30 2011-05-05 The Government Of The United States Of America As Represented By The Secretary Of The Navy Functionally Doped Polycrystalline Ceramic Laser Materials

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3679995A (en) * 1970-03-11 1972-07-25 Ibm Optically pumped liquid lasers
GB1373336A (en) * 1972-06-26 1974-11-13 Western Electric Co Laser assemblies
US3982201A (en) * 1975-01-24 1976-09-21 The Perkin-Elmer Corporation CW solid state laser
EP0973236A2 (en) * 1998-07-07 2000-01-19 TRW Inc. End pumped zig-zag slab laser gain medium
US20020191664A1 (en) * 2001-06-14 2002-12-19 Trussell C. Ward Diode array end pumped slab laser
EP1717914A1 (en) * 2005-04-28 2006-11-02 Compagnie Industrielle des Lasers Cilas Active element for laser source and laser source comprising such active element
WO2007051138A2 (en) * 2005-10-28 2007-05-03 Laserscope High power, end pumped laser with off-peak pumping

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017205851A1 (en) * 2016-05-26 2017-11-30 Compound Photonics Ltd Solid-state laser systems
US20190245320A1 (en) * 2016-05-26 2019-08-08 Compound Photonics Limited Solid-state laser system

Also Published As

Publication number Publication date
GB201120666D0 (en) 2012-01-11
WO2013079940A1 (en) 2013-06-06

Similar Documents

Publication Publication Date Title
US8705918B2 (en) Multi-sectional fiber laser system with mode selection
CN205790934U (en) A kind of semiconductor laser
GB2497106A (en) Laser System and path length of radiation
CN203645130U (en) High-power glass-doped laser device
CN103151700B (en) A kind of angular momentum tunable full-solid-state laser that there is multi-wavelength and export
CN113594842A (en) Device and method for generating ultrashort pulse of erbium-doped laser
US8189644B2 (en) High-efficiency Ho:YAG laser
CN101179175A (en) Laser diode pumped solid state laser with high peak power
Ju et al. Single-longitudinal-mode lasing of Tm, Ho: GdVO 4 using a filter of Fabry-Perot etalon and volume Bragg grating
EP2260550B1 (en) Method and apparatus for generation and amplification of light in a semi-guiding high aspect ratio core fiber
CN101442177B (en) Method for implementing low pump power density and continuous light pump laser
CN109149351B (en) Q-switched laser
CN201230128Y (en) High peak value power laser diode pump solid state laser device
CN112886374A (en) Fiber laser for inhibiting stimulated Raman scattering effect and manufacturing method thereof
RU2269848C1 (en) Solid-state laser with a zigzag ray path
Li et al. High power single-mode large-mode-area photonic crystal fiber laser with improved Fabry-Perot cavity
WO2020003140A1 (en) Thermo-optic intracavity beam shaping and mode control with doped optical materials
US9548585B1 (en) Multi-point laser ignition device
Wu et al. Thermal analysis and experimental study of end-pumped continuous-wave thulium-doped laser
CN104393475A (en) All-solid-state laser
CN103390853A (en) Hectowatt-grade 1.9 mu m solid laser
CN203326351U (en) 100W-level 1064nm end-pumped all-solid-state laser
CN113809627B (en) Laser amplifier
Aubourg et al. Wavelength selection, spatial filtering and polarization control of an Er: YAG laser cavity by resonant-grating mirror
Yang et al. A narrow linewidth continuous wave Ho: SSO laser with Fabry–Perot etalons

Legal Events

Date Code Title Description
REG Reference to a national code

Ref country code: HK

Ref legal event code: DE

Ref document number: 1186307

Country of ref document: HK

WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)
REG Reference to a national code

Ref country code: HK

Ref legal event code: WD

Ref document number: 1186307

Country of ref document: HK