WO1999060673A2

WO1999060673A2 - Doped laser

Info

Publication number: WO1999060673A2
Application number: PCT/US1999/010513
Authority: WO
Inventors: Yusong Yin
Original assignee: Photonics Industries International Inc
Current assignee: Photonics Industries International Inc
Priority date: 1998-05-15
Filing date: 1999-05-12
Publication date: 1999-11-25
Anticipated expiration: 2000-11-15
Also published as: WO1999060673A3

Abstract

An end pumped laser having crystal or glass lasing material is provided. At least one pumping laser (LD) in optical communication with an end of the lasing material is used to pump the laser. The lasing material is composed of a laser host material doped with a laser active ion. The laser material has a first zone (Z11) having a preselected level of laser active ions. The lasing material has a second zone (Z12) located between the first zone and pumping laser. The second zone has a lower level of laser active ions than said first zone.

Description

DOPED LASER

Field of the Invention

The field of the invention relates to end pumped lasers.

Background of the Invention

In an end pumped laser, the radiation from a single laser, a laser diode or a laser array is focussed on the end of a laser rod. Prior art end pumped lasers have been developed using doped crystals such as NdrYAG crystals which can be end pumped from both ends. However, thermal distortion and crystal fracture have been problems which result in limiting the pumping power from the pumping lasers.

Summary of the Invention

According to the invention, an end pumped laser is provided. The device includes at least one pumping laser or laser array in optical communication with one end of a lasing material. Desirably a second pumping laser or second laser array in optical communication with the other end of the lasing material is also provided so the laser can be pumped from both ends. The lasing material is composed of a host material doped with a laser active ion. Preferably the host material is a crystal or glass. The lasing material is preferably formed into a rod desirably a rectangular or cylindrical rod. The lasing material has a preselected lower doping level at the end or ends adjacent to the pumping laser. The doping level increased as the distance from the pump lasers is increased. Preferably, the lasing material has at least two zones having different levels of doped laser active ion in the two zones. The first zone has a preselected level of doped laser active ions. The second zone located between the first zone and first pumping laser has a lower doped level of laser active ions than the first zone. Desirably the level of doping in the second zone is from 5% to 70% of the level of doping in the first zone. When the laser is pumped from both ends, the lasing material preferably includes a third zone located between the first zone and the second pumping laser. The third zone has a lower level of doped laser active ions than the first zone. Desirably the level of doping in the third zone is from 5% to 70% of the level of doping in the first zone.

Optionally, the lasing material has a plurality of zones of doped laser active ions. The doping level within the lasing material increases from zone to zone as the distance of the zone from the pumping laser increases. Desirably, the lasing material is a unitary crystal rod formed by diffusion bonding two or more separate crystals of different doping levels to form a laser crystal according to the invention eg. a cylindrical or rectangular rod, having two or more zones.

In another aspect of the invention, the lasing material is composed of two or more separate crystals of preselected doping levels. The crystals are mounted in close proximity to one another on a base and aligned on the laser's optic axis so the EMR propagating from one crystal is directed across the adjacent crystal. As a result, a multi-zone lasing material will be formed with two or more zones and desirable 3 to 5 zones or more having preselected doping levels in each zone. The doping levels increase as the distance of crystal from a pumping laser increases .

According to the invention, a lasing material desirably a laser rod having multiple doped zones of laser active ions is pumped by a pumping laser preferable pumping lasers located adjacent to the both ends of the laser rod. The largest amount of energy, supplied by the pumping lasers, contacts the zones of the laser crystal adjacent to the pumping lasers. These zones have the lowest percentage of laser active ions. As a result more of the energy from the pumping laser will pass to the interior zone of the laser where additional laser active ions will be excited than in lasers with uniform high doping levels. The ends of the laser rod therefore will not be heated to the same degree as if the high level of the doping of the first zone was extended to the zone adjacent to the ends of the rod adjacent to pumping lasers. As a result, the lasing material is subject to reduced thermal stress and will be less likely to crack when subjected to high power pumping lasers. Desirably there will be a more uniform absorption rate of energy across the crystal.

It is an object of the invention to provide an end pumped laser which can be pumped at a higher level without damage to the lasing material.

It is an object of the invention to provide an end pumped YAG, YLF or YV04 crystal laser which can withstand a pumping laser input of 20 watts or higher simultaneously from both ends without crystal cracking.

It is an object of the invention to provide an end pumped laser which exhibits reduced thermal distortion.

It is a further object of the invention to provide a end pumped laser with a more uniform thermal load along the lasing material .

Other and further objects will become apparent from the specification, drawings and claims.

The preferred embodiment of the present invention is illustrated in the drawings and examples. However, it should be expressly, understood that the present invention should not be limited solely to the illustrative embodiment.

Description of the Drawings

Fig. 1 is a diagrammatic view of an end pumped laser according to the invention.

Fig. 2 is a diagrammatic view of an alternative embodiment of the laser according to the invention.

Fig. 3 is a diagrammatic view of a laser rod according to the invention.

Fig. 4 is a diagrammatic view of an alternative embodiment of a laser rod according to the invention having a heat exchanger .

Fig. 5 is graph showing the absorption rate of the crystal according to the invention.

Fig. 6 is partial perspective view of a water cooled laser housing according to the invention.

Detailed Description of the Invention

According to the invention an end pumped laser having an improved resistance to laser crystal fracture at high power output and more uniform thermal load along the lasing material is provided. The end pumped laser is pumped from at least one end and preferably from both ends. A pumping laser desirably a diode or diode array, or optionally other pump source preferably a NdrYLF or NdrYAG pump laser is provided on at least one and preferably on each end of the end pumped laser. The pumped laser includes a lasing material having at least two zones and preferably three zones or more. Desirably a laser crystal, optionally a crystal rod is used as the lasing material. Optionally a glass laser rod can be used. Each zone has a preselected amount of doping in the lasing material. The pumped laser has at least two zones when one end only is pumped and at least three zone when both ends are pumped. Preferably in the single end pumped laser embodiment, the lasing material will have two zones of differing doping levels. Preferably the first zone has a high doping level of lasing ions in the host material as is typical for the type of host material. Optionally lower doping levels are used. Desirably the crystal host materials is YLF, YAG or YVO, . Desirably the doping ions are Nd, Er or Ho. Optionally according to the invention other lasing material can be employed for example Ti: Sapphire, Cr : LiSAF wherein the doping ions are Ti and Cr . Desirably the doping level for zone 1 for NdrYLF crystals is about .8% to about 1.8% (Atomic %) . A second zone having a lower doping level is located between the first zone and the pumping laser. The doping level in the second zone is lower than the that of the first zone. The second zone desirably has a doping level of 5% to 70% of the first zone and preferably from 30% to 60% of that of the first zone.

According to the invention when the pumped laser is pumped from both ends, a third zone is provided between the first zone and the second pumping laser. The third zone has a doping level of from 5% to 70% and preferable from 30% to 60% of the doping level in the first zone.

Optionally, as best seen in Fig. 3 a plurality of zones in the lasing material can be provided. The zone of the lasing material nearest a pumping laser has the lowest doping level. The zone of the lasing material furthest from a pumping laser has the highest doping level. In a five zone embodiment, the central zone, zone 1 has the highest doping level. Zones 4 and zone 5 will have a lower doping level 5% to 70% preferably 30% to 60% of that of zone 1 and are located on either side of zone 1. Zones 2 and zone 3 which are located nearest to where the energy from the pumping lasers enter the lasing material will have the lowest doping level, 5% to 70% preferably 30% to 60% of the level of zone 4 and zone 5. For example, according to the invention a Nd: YLF crystal has a central zone 1 with a Nd doping of 1.5% (Atomic %) . A second zone Z2 located adjacent to the first pumping laser, having Nd doping level of .375% and a third zone adjacent to the second pumping laser having a doping level of .375% are provided. A fourth zone Z4 with has a doping level of .75% and is located between the second zone and first zone. A optional fifth zone Z5 having a Nd doping level of .75% is located between the third zone and the first zone. As a result the doping level increases from a low point at the ends of the crystal adjacent to the pumping lasers to a high point at the interior of the crystal .

Alternatively a crystal that has a multiplicity of zones of ascending doping levels from the end of the crystal adjacent a pumping laser is used. When the laser is pumped from both ends, the doping level is at a minimum at either end and gradually increases to a maximum near the center of the rod.

Desirably, a unitary crystal is formed by diffusion bonding two or more separate crystal of different doping levels to form a laser crystal according to the invention eg. a rod either rectangular or cylindrical having two or more zones.

In another aspect of the invention, the lasing material is composed of two or more separate crystals of preselected doping levels. The crystals are mounted in close proximity to one another on a base in the laser's optical cavity. The crystals are aligned on the laser's optic axis so that the EMR propagating from one crystal is directed across the adjacent crystal. As a result, a multi-zone lasing material will be formed with two or more zones and desirably 3 to 5 zones or more having preselected doping levels in each zone.

As best seen in Fig. 1 a pumped laser according to the invention having a lasing material desirably crystal or glass, preferable crystal rod LR is provided. The lasing material desirably has an increasing level of doping as the distance from an end pumped laser increases. Desirably for a laser pumped from both ends, multiple doped zones are provided in lasing rod LR. Desirably as shown in Fig. 1, three zones, Zl, Z2 and Z3 are provided. Optionally, five or more zones can be provided. Referring to Fig. 1, Zl is centrally located in the interior of the lasing material. Z2 and Z3 are located on the left and right ends of the lasing material. Preferably the lasing material LR is a crystal rod selected from a number of laser crystal host materials, for example, YLF, YAG and YV0₄. The crystal can be doped with a number of laser active ions such as Nd (Neodymium) , Er (Erbium) and Ho (Holmium) , preferably Nd. Optionally glass laser rods doped with laser active ions such as Nd, Er, Ho, Yb (Ytterbium) , and Tm (Thulium) are provided. Optionally, according to the invention other lasing materials can be employed for example Ti: Sapphire, Cr:LiSAF crystals wherein the doping ions are Ti (Titanium) and Cr (Chromium) . Preferably NdrYAG, NdrYLF or NdrYV04 crystals are used.

A pumping laser is provided to supply power to the lasing material as shown in Fig. 2. Desirably as best seen in Fig. 1 pumping lasers are provided at either end of the lasing material LR preferably laser diodes LD1 and LD2. Desirably where the lasing material LR is an NdrYLF, NdrYAG and NdrYV0₄ crystal rod, the laser diodes have a power output of greater than 16 watts each and preferably 20 watts or higher and desirably 20 to 60 watts. Most preferably the power output of LD1 and LD2 is 20 to 30 watts. Focussing optics, preferably lens LI and lens L2 are provided between pumping laser LD1 and LD2 and lasing material LR to focus the beam propagating from pumping laser LD1 and LD2 on lasing material LR. In the embodiment of Fig. 1, a laser cavity is formed around LR by mirrors desirably four mirrors Ml, M2 , M3 and M4. Mirror Ml is located between LI and LR along the path of the pumping beam from LDl. Mirror Ml is coated to highly transmit the wavelength of the beam propagating from LDl and highly reflect the beam propagating from LR. When the pumping beam propagating from LDl and LD2 has a wavelength of about 806 nm and LR is a NdrYLF laser rod, LR will lases at about 1053nm or 1047nm depending on designer choice. Mirror Ml is coated to highly transmit at a wavelength of about 806 nm (± 15nm) and highly reflect at a wavelength of 1053 nm (± 15nm) . Mirror M2 is coated to transmit the wavelength of the beam propagating from LD2 and reflect the beam propagating from LR. M2 is similar to Ml and is coated to highly transmit at about 806 nm and highly reflective at about 1053 nm. Mirror M3 which is highly reflect at 1053 nm is located in optical communication with Mirror M2 along the optic axis of the pumped laser. An optional Q-Switch QS and optional polarizer PL are provided between M3 and M2 along the optic axis. Mirror M4 is an output coupler which is partially transmissive and partially reflective at 1053 nm desirably from about 5% to 30% preferably about 12% transmissive and about 70% to 95% preferably about 88% reflective. Laser rod LR preferably a NdrYLF laser rod desirably includes three zones Zl, Z2 and Z3 having predetermined doping levels. Central Zone Zl has the highest doping level. Lower doping levels are provided on the ends of laser rod LR wherein the pump beams incident on laser rod LR. For example for a NdrYLF rod a doping level .8 to 1.5 atomic percent Nd preferably about 1.1 is desired. Zones 2 and 3 have a lower doping level of 5% to 70% of the doping level of the zone 1 and preferably 30% to 60% of the doping level of Zone 1 for example for a NdrYLF rod approximately .5% Nd doping for a 1.1 doping level in zone 1.

In operation a pumping laser beam propagates from laser diodes LDl and LD2 respectively. The pumping beam propagating from LDl having a wavelength of about 806 nm, is directed through focussing optics LI and is transmitted through Mirror Ml to incident on lasing material LR at zone Z2. Similarly the beam propagating from LD2 is focussed by focussing optics L2 through mirror M2 which transmits beams having a wavelength of about 806. The focussed beam incidents on lasing material LR at zone Z3. Zones Z2 and Z3 are first excited and absorb a portion of the energy of the pumping beams prior to their incedenting on Zone Zl. LR then lases at a wavelength of about 1053nm. The beam propagating from LR is reflected by M2 to M3 where it is reflected back to M2. The beam is reflected for a second pass through the lasing material LR to be amplified and then reflected by Mirror Ml to mirror M4. Mirror 4 is output coupler which partially transmits the beam outside the cavity and reflects the untransmitted beam back to Ml for amplification through another pass through the lasing material LR. An optional Q- switch QS and polarizer PL can be provided in the cavity adjacent desirably a mirror M3.

Where LR is a NdrYAG, NdrYLF or NdrYV04, pumping laser LDl and LD2 , desirably have a power output of greater than 16 watts and most preferably 20 watts or higher and desirably 20 to 60 watts. For example where LDl and LD2 supply of 30 watts at each end of the rod for a total input of 60 watts. The resulting output of the pumped laser from the laser cavity at M4 has a power of 15 to 25 watts at TMoo mode.

The intensity of the beams propagating from LDl and LD2 is highest when the beams first contact the lasing rod LR. Zone 2 and zone 3 absorb some of the energy prior to the pumping laser beam reaching zone 1 which has a higher level of doping. As a result, the thermal stress in zone 2 and 3 is lower than would be encountered if the zones 2 and 3 were doped to the same degree as zone 1. Fig. 5 shows that for a pumped laser according to the invention a more uniform energy absorption is achieved across the length of the laser rod than where the laser rod has a uniform doping level of the prior art.

Fig. 2 shows another embodiment of the invention. Fig. 2 shows an end pumped laser pumped from just one end. Pump laser LP is desirably an NdrYAG or Nd:YLF pumping laser desirably Nd:YLF. In this embodiment the pumping laser beam has a wavelength of about 527 nm. The beam propagating from LP is directed across focussing optics, lens L3 through Mirror M5 across lasing material LR1 which is desirably a Ti: Sapphire laser rod having two zones Zll and Z12. Zone Zll has a higher doping level than zone Z12. Preferably the Ti doping in the Ti: Sapphire laser LR1 in zone Z12 is 30% to 60% percent of the doping level in Zll. Desirably the doping level in Zll is approximately 0.1% (by atomic weight) and the doping level of Z12 is for example approximately .04%. The optical cavity is defined by mirrors M5 and M6. Laser rod LR1 is located between mirror M5 and M6. Mirror M6 is an output coupler which is approximately 15% transmissive at 800 nm and 85% reflective at 800 nm. Mirror M5 is highly reflective at about 800 nm and highly transmissive at about 527 nm which is the wavelength of the Nd:YLF second harmonic pumping laser shown herein.

Fig. 4 shows another embodiment of a material according to the invention which includes a heat exchanger to cool the laser rod. Referring to Fig. 4, a laser rod LR2 is provided, having a first zone Zl of a high doping level, for example an Nd:YLF crystal having a 1.1% atomic percent doping. Zones Z2 and Z3 are provided having a lower doping, from 5% to 70% of Zl and preferably 30% to 60% of the doping level of Zl . The laser rod is formed by diffusion bonding three laser crystals having preselected doping levels and two undoped crystals to form a unitary crystal rod having undoped zone Z0 at either end. The rod LR2 includes a high doped zone Zl in the middle and two low doped zones Z2 and Z3 between the high doped zone Zl and undoped zones Z0. The two undoped ends Z0 provide a convenient mounting platform for the heat exchanger, desirably a direct contact liquid cooling, HE.

Fig. 5 is a graphically representation of the absorption rate for a crystal of the prior art and a crystal according the invention plotted against the distance along the crystal. It can be seen that the absorption rate of the three zone crystal according to the invention is more uniform across the length of the crystal. As a result a more uniform thermal load can be expected along the lasing material and improved resistance of the lasing material to laser rod fracture is expected.

In another aspect of the invention a water cooled crystal housing is provided. A lasing material is formed by mounting two or more separate crystals in close proximity to one another. As shown in Fig. 6 three crystals of varying doping levels are mounted in a water cooled copper mounting base. Crystals CR1 , CR2 and CR3 are provided. The crystals can be provided by any suitable crystal material as described above for example an Nd:YAG or NdrYLF crystals. The crystals are positioned on a mounting base preferably a copper mounting base. Desirably releasable thermal adhesive is applied to the base in the position in which the crystals are to be placed to releasable secure the crystal in their desired location. Preferably the crystals are mounted closely adjoining one another with a spacing of preferably less than a millimeter. The crystals CR1 has the highest doping level with CR2 and CR3 having a doping level from 5% to 70% of the doping level CR1 preferably 30% to 60%. The releasable thermal adhesive serves several purposes. It secures the crystal in their desired position. It prevents the crystals from dislodging in the copper container and thus being damaged. It allows the crystal to be realigned if necessary. It provides a thermal conductivity between the copper base and the crystals. Water cooling channels are provided in the copper base to dissipate heat from the crystals.

As shown in Fig. 6 a water cooled crystal housing is provided. The crystal housing includes a top cover 10 a left base side 12 and a right base side 14. A three piece lasing crystal is provided having a central crystal CR1 which has the highest doping level and left crystal CR3 and right crystal CR2 which are in alignment with central CR1. The doping level in CR2 and CR3 is from 5% to 70% of the doping level of CR1. Water cooling channels are provided through the housing. Water inlet 18 is provided for the entry of the water through channels in the housing. Water outlet 20 are provided for the water to exit after having cooled the crystal. The left base side and right base side are held together by mounting screws not shown which are inserted through mounting holes 22 and 24. The crystal is laid on the assembly left and right base sides which have been pre-coated with a releasable adhesive at the points where the crystal is contacted by the base so that the crystal is held in the appropriate position. Mounting holes 26 are provided in the top cover for alignment with mounting holes 28 in the left and right said base so that when assembled the crystal housing can be secured together by mounting screws not shown. The entire assembly is mounted to a base plate (not shown) by mounting screws through mounting holes 30 and 32.

The foregoing is considered as illustrative only to the principles of the invention. Further, since numerous changes and modifications will occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described above, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

1. An end pumped laser comprising r a laser rod having a right end and a left end opposed to said right end; a pumping laser in optical communication with an end of said laser rod; said laser rod comprising a laser ion host material doped with a laser active ion; said laser rod having a first zone; said first zone having a presected level of doped laser active ions; a second zone located between said first zone and said pumping laser; said second zone having a lower level of laser active ions than said first zone.

2. The end pumped laser according to claim 1 wherein the laser ion host material is a crystal or glass.

3. The end pumped laser according to claim 2 wherein the laser ion host material is a YLF crystal, a YAG crystal or a YV0₄ crystal.

4. The end pumped laser according to claim 3 wherein the laser ion host material is a YLF crystal.

5. The end pumped laser according to claim 1 wherein the laser is a Ti Sapphire crystal.

6. The end pumped laser according to claim 1 wherein the laser rod is a Cr:LiSAF crystal.

7. The end pumped laser according to claim 1 wherein said laser rod includes an undoped zone at an end of said laser rod.

8. The end pumped laser according to claim 3 wherein said pumping laser provides above about 20 watts to the end of said laser rod.

9. The end pumped laser according to claim 3 wherein said pumping laser provides above about 30 watts to the end of said laser rod.

10. The end pumped laser according to claim 7 further comprising a heat exchanger in thermal communication with said crystal laser rod to cool said end pumped laser.

11. The end pumped laser according to claim 10 wherein said crystal undoped zone of said laser rod supports said heat exchanger .

12. The end pumped laser according to claim 11 wherein said heat exchanger is a water cooled heat exchanger.

13. An end pumped laser comprising r a laser rod having a right end and a left end opposed to said right end; a first pumping laser in optical communication with the left end of said laser rod; a second pumping laser in optical communication with the right end of said laser rod; said laser rod comprising a laser ion host material doped with a laser active ion; said laser rod having a first zone; said first zone having a presected level of doped laser active ions; a second zone located between said first zone and said first pumping laser; said second zone having a lower level of laser doped active ions than said first zone; a third zone located between said first zone and said second pumping laser; said third zone having a lower level of doped laser active ions than said first zone.

14. The end pumped laser according to claim 13 wherein the laser ion host material is a YAG crystal a YLF crystal or a YV04 crystal .

15. The end pumped laser according to claim 14 wherein the ion host material is a YLF crystal.

16. The end pumped laser according to claim 14 wherein ion host material is a YAG crystal.

17. An end pumped laser according to claim 13 wherein the laser is a Ti r Sapphire crystal.

18. An end pumped laser according to claim 13 wherein the laser rod is a CrrLiSAF crystal.

19. The end pumped laser according to claim 13 wherein said laser rod includes an undoped zone at the ends of said laser rod.

20. The end pumped laser according to claim 13 wherein said first pumping laser provides above about 20 watts to said left end and said second pumping laser provides above about 20 watts to said right end.

21. The end pumped laser according to claim 14 wherein said first pumping laser provides above about 30 watts to said left end of said crystal rod and said second pumping laser provides above about 30 watts to said right end of said crystal rod.

22. The end pumped laser according to claim 19 further comprising a heat exchanger in thermal communication with said laser rod to cool said end pumped laser.

23. The end pumped laser according to claim 22 wherein said undoped zone of said laser rod supports said heat exchanger.

24. The end pumped laser according to claim 23 wherein said heat exchanger is a water cooled heat exchanger.

25. The end pumped laser according to claim 13 wherein the laser active ions are Nd, Er or Ho ions.

26. The end pumped laser according to claim 14 wherein the laser active ions are Nd, Er or Ho ions.

27. The end pumped laser according to claim 26 wherein the laser active ions are Nd.

28. The end pumped laser according to claim 13 wherein the laser ion host material is glass.

29. The end pumped laser according to claim 28 wherein the laser active ions are Nd, Er, Ho, Yb or Tm.

30. The end pumped laser according to claim 28 wherein the laser active ions are Nd.

31. The end pumped laser according to claim 30 wherein the laser active ions are Er.

32. The end pumped laser according to claim 13 wherein the laser ion host material is a crystal.

34. An end pumped laser according to claim 13 further comprising a fourth zone located between second zone and said first pumping laser; said fourth zone having a lower level of doped laser active ions than said second zone; a fifth zone located between third zone and said second pumping laser, said fifth zone having a lower level of doped laser active ions than said third zone;

35. An end pumped laser according to claim 13 wherein the level of doping of the second and third zone is from 5% to 70% of the level of doping of said first zone.

36. The end pumped laser according to claim 35 wherein the level of doping of the second and third zone is from 30% to 60% of the level of doping of said first zone.

37. An end pumped laser comprisingr a lasing material having a right end and a left end opposed to said right end and a central portion; a first pumping laser in optical communication with the left end of said lasing material; a second pumping laser in optical communication with the right end of said lasing material; said lasing material comprising a laser ion host material doped with a preselect level of laser active ions; the doped level of laser active ions decreasing from a maximum presected amount in said central portion of said laser material to 5% to 70% of the doped level of said central portion at said left and right ends of said lasing material;

38. The end pumped laser according to claim 37 wherein the doped level of said left and right ends of said lasing material is 30% to 60% of the doped level of said central portion of said lasing material;

39. An end pumped laser comprising; a lasing material having a right end and a left end opposed to said right end; a first pumping laser in optical communication with the left end of said lasing material; said lasing material comprising a laser ion host material doped with a laser active ion; said lasing material including at least a first and second zone having different levels of doped laser active ions; said first zone having a presected level of doped laser active ions; and a second zone located between said first zone and said pumping laser; said second zone having a lower level of laser active ions than said first zone.

40. An end pumped laser according to claim 39 further comprising a base for receiving said lasing material; a first laser crystal having a preselected level of doping ions mounted to said base to form said first zone; a second laser crystal having a lower level of laser active ions than said first laser crystal mounted to said base to form said second zone; said second laser crystal mounted adjacent to said first laser crystal; said first laser crystal in optical communications with second laser crystal.

41. An end pumped laser according to claim 40 further comprising a second pumping laser in optical communication with the right end of the lasing material; a third laser crystal mounted to said base, adjacent to said first laser crystal and located between said first laser crystal and said second pumping laser; said third laser crystal having a lower level of doped laser active ions than said first crystal .

42. An end pumped laser according to claim 41 further comprising a fourth laser crystal mounted to the said base adjacent to said second laser crystal and located between said first pumping laser and said second laser crystal; a fifth laser crystal mounted to said laser adjacent to said third laser crystal and located between said second pumping laser and said third laser crystal; said fourth laser crystal having a lower level of doped laser active ions than said second laser crystal; said fifth laser crystal have a lower level of doped laser active ions than said third laser crystal.