TW405285B - High power diode end-pumped solid state laser and its manufacture method - Google Patents

Abstract

A high power diode end-pumped solid state laser is disclosed, which primarily utilizes the laser composed of the neodymium-doped vanadium-based crystals. There is a higher fracture-limited pump power for the neodymium-doped vanadium-based crystals, which could fulfill the operation of high power laser light. The composite device of this end-pumped solid state laser has a resonance chamber including a resonance chamber mirror and an output coupling mirror, a laser crystal, a laser diode used as the pumped light source for providing a pumped light beam to the laser crystal, and an optical coupling mirror set for collecting the pumped light beam to the laser crystal, and selecting the proper resonance chamber length to avoid the instability caused by the thermal lens effect of the crystal. This invention also provides the method of manufacturing the same.

Description

_405285__ V. Description of the invention α) Field of the invention The present invention relates to a high power diode end-pumped sol id-state laser device, mainly a kind of vanadium using a low thorium ion concentration. Lasers composed of neodymiura-doped vanadium-based crystals. Low 'ion concentrations of osmic acid crystals have higher fracture-limited pump power, resulting in higher power output. BACKGROUND OF THE INVENTION In the past few years, some doped neodymium-doped vanadium-based crystals have been regarded as important materials for diode-excited solid-state lasers. The vanadate crystals include yttrium vanadate (YV04), vanadate l (0 (1 y04), and fluorinated vanadate fluoride (5) " 5 (¥ 04) 3 [(^ 8- ¥ six?)). Compared with traditional yttrium aluminum garnet crystal (YAG), vanadate crystals have higher gain cross-section, lower critical excitation power (threshold), and wider absorption band (absorption). bandwidth) and other advantages, and because this type of crystal is an anisotropic crystal, it can produce linearly polarized output. This feature can avoid the birefringence effect that occurs at high power. Although vanadate crystal materials are in a diode-excited solid state Laser design has many advantages over traditional YAG crystals, but the thermal conductivity of these materials

D: \ Patent \ pdl602. Ptd Page 4 A0 & M5 5. Explanation of the invention (2) The coefficient is much lower than that of the YAG crystal, so when the laser diode end face is used for excitation, the heat generated in the excitation area is not easily transmitted to the outside world. . Theoretical and experimental results show that the maximum output power of the end-excitation solid-state laser is limited by the thermal fracture of the laser crystal due to heat. Therefore, the maximum excitation power that end-face excited solid-state lasers can withstand can be referred to as "fracture-limited excitation power." Tsunekane et al. In IEEE J. Select. Topics Quantum Electron, vol. 3, 9 (1997) reported the experimental results of yttrium vanadate (γ V 〇4) doped with 1.1% erbium ion concentration, showing 1. The maximum excitation power of 1% Nd: YV04 is 13.5 watts. On the other hand, Tidwell et al. In IEEE J. Quantum Electron., Vol. 28, 9 97 (19 2 2) estimated that the Nd: Y AG's burst-limited excitation power is about 50 ~ 70 watts. The low thermal conductivity is one of the reasons that the “fracture limiting excitation power” of vanadate crystals is much lower than that of YAG. However, the thermal conductivity is the basic physical property of the crystal base material and cannot be changed. In addition to the thermal conductivity, the rupture-limiting excitation power of the end-excitation solid-state laser is closely related to the absorption coefficient of the crystal to the excitation light source (absorption co oe f f c i e n t). Although crystals with high absorption coefficients tend to have higher TEMoo output slope efficiency at low power operation, they are often used as short monolithic cavities to produce green and vertical mode operation, such as Sasaki et al. In Opt Lett. Vol. 16, 1665 (1991) reported 'but high absorption coefficients will cause large temperature gradients inside the crystal, resulting in a large amount of thermal stress on the excited end face of the crystal. It is generally believed that the thermal cracking of the crystal caused by thermal stress is the main technical bottleneck in the design of high-power end-face excited solid-state lasers. In other words, high absorption

D: \ Patent \ pdl602. Ptd Page 5 _ 4Π5285 _____ 5. Description of the invention (3) The number of laser materials will be limited during high-power operation. In low-power excitation ’, it ’s generally for the South ’s output efficiency,

Nd: YV04 has an ion concentration of between 0.5 and 3.0%, usually 1.0%. The absorption coefficient of 1.0% Nd: YV04 at a wavelength of 808-nm is five times that of the same concentration YAG crystal. The experimental results show that Nd. · YV04 with a concentration of 1.0% under single-ended excitation has a rupture-limited excitation power of about 15 watts, and the corresponding maximum output power of TEMoo is about 7 watts. The output of Nd: YV04 with a single-ended excitation concentration of 1.0% is used as a standard for high-power lasers. The 7-watt TEMoo power output can be used as a benchmark for high-power lasers. Therefore, any diode end-excitation solid-state laser can have a TEMoo output power of more than 7 watts, and an output slope efficiency of more than 40%, which can be referred to as a high-efficiency, high-power end-face excitation of a diode. Solid-state laser. In recent years, some researchers have used diffusion bonded crystals to increase the "fracture-limiting excitation power" and obtain higher output power. For example, Tsunekane et al. In IEEE J. Select. Topics Quantum Electron, vol. 3, g (1997) reported the characteristics of diffusion bonded N d: YV 〇 * crystals' they will have a concentration of 1.% nd: γ vh and YV O4, which is not doped with a titanium ion concentration, is joined by a diffusion bonding method. The results show that 'diffusion dry-type Nd: YV04 with a concentration of 1.1% can withstand a maximum excitation power of about 20 watts', resulting in a laser output of 1.0 um of about 9 watts. However, in order to maintain the linear polar output, the diffusion bonded Nd · YVO4 crystal must accurately align the optical axes of the two crystals. The process is complicated and difficult, and the cost is not the best method. In addition to diffused point-contact crystals,

--- 405 Tear-5. Description of the invention (4) Hair is often used to obtain a method greater than 10 watts, such as the result published by Nighan et al. In OSA Tech · Dig. Series, Washington DC, 17 (1995) . However, the design of multi-facet excitation requires the addition of additional components. In order to obtain the best output, precision alignment is usually required, which is limited in industrial applications. It can be seen that how to reduce the cost and the complexity of manufacturing alignment to obtain two-power, high-efficiency lasers' is an important requirement for the current design of diode-side excited solid-state lasers. How to use a single-end-excitation method of a strong-absorptive material such as an acid crystal to obtain a laser output of more than 10 watts has become an important development topic, and the main obstacle of this design is thermal cracking caused by excitation. Brief description of the invention In view of the difficulties of the current technology, the object of the present invention is to design a diode end-excitation solid-state laser assembled with erbium-doped vanadate crystals. Can produce high efficiency, high power, and linearly polarized laser output. A further object of the present invention is to design a diode-end-excited solid-state laser assembled with a vanadic acid-doped crystal. It can be effectively operated in 9K mode, producing high efficiency, high power, and linearly polarized pulsed laser wheels. These objects of the present invention are accomplished by a high-efficiency, high-power diode end-excitation solid-state laser system. The laser system includes a resonant cavity lens and a resonant cavity composed of an output coupling mirror. And there is an astringent sharp acid

D: \ Patent \ pdl602. Ptd 4 Ο 5-2 B 5 5. Description of the invention (5) The crystal is placed in the resonance cavity. The reason for using vanadate-doped crystals is that they have the advantages of higher gain cross section, lower critical excitation power, wider absorption band, etc., and can produce linearly polarized output. The laser crystal used in one of the important bodies of the present invention is Nd. · YV04. In order to increase the rupture-limited excitation power, a higher output power is obtained, whose ion concentration is not higher than 0.5%. The conventional ionic concentration of N d: Y V 04 is between 0.5 and 3.0%, usually 1.0%. Although the present invention uses a non-conventional ion concentration, it has a high-efficiency, high-power laser output. As an example, using “Nd: YV04 with an ion concentration of 0.30%” as the laser crystal, its “fracture-limiting excitation power” can exceed 27 watts, and at an excitation power of 27 watts, more than 16 watts can be obtained Mode output, which has about 13 watts or more of TEMoo output. Brief description of the drawings In order to illustrate other objects and advantages of the present invention, the following preferred embodiments will be described below in conjunction with the description of the drawings, where: Figure 1: Nd: Y V04 shows the "fracture limiting excitation power" Experimental results of the correlation with the inverse of its absorption coefficient. Figure 2: An illustration of a high-power diode end-excitation solid-state laser, in which a vanadic acid crystal with a low 'ion concentration is used to obtain an output of more than 10 watts. 100… Laser diode array 102… Receiving-condensing lens group 101… Optical fiber or fiber bundle 103… Laser crystal 104… Resonant cavity mirror 105… Output coupling mirror

D: \ Patent \ pdl602. Ptd Page 8 5'Invention description (6) 1 0 6… Q switch invention description and patent description The present invention is a high-power, high-efficiency diode end-excitation solid-state laser. The laser resonant cavity is composed of a resonant cavity mirror, an output coupling mirror, and a slave acid crystal with a low radon ion concentration. The laser of the present invention has the following characteristics: the output power when the single-ended end face is excited can be greater than watts, the output The efficiency is greater than 50% in the multi-modal state 'more than 40% in the TEMoo' low vanadic acid crystals having a low titanium ion concentration 'for example Nd: YV〇4' is between 0.4 and 0.49%, mainly between 0.2 ~ 〇 · 4%. T dwe 1 1 et al. 1 EEE J. Quantum Electron., Vol. 28, 997 (1992), and Cousins in IEEE J. Quantum

Electron., Vol. 28, 1057 (1992) has reported the establishment of a design mode to analyze the power output limit of a diode-excited Nd: Y AG laser under thermal cracking limits. However, the effect of absorption coefficient on the "fracture-limited excitation power" has not been considered in these research literatures. "Experimental and theoretical analysis shows that" fracture-limited excitation power "is inversely proportional to the absorption coefficient. The absorption coefficient is proportional to the concentration of ions doped into the crystal. Therefore, lowering the ion concentration of anoic acid crystals can improve the "breaking limit excitation power". The vanadic acid crystal has a large absorption cross section, so for the vanadic acid crystal, there is a large range that can reduce the concentration of doping, and it has a higher absorption coefficient and output efficiency than Nd: YAG. Plane stress approximation based on general edge cooling

_405285_ V. Description of the invention (7) (plane stress approximation), we can derive a general analytical formula. The error of this approximation has been proven to be within 10%. The plane stress approximation method is used to consider the general end face excitation. The relationship between the "breaking limit excitation power" Pabs, lim and the crystal absorption coefficient α 1 can be expressed as

Pabs, lim = 4 7Γ R / (α ξ) (1) where fTM is the fractional thermal loading, and R = (Kc amax) / (aTE) (2 is the so-called “thermal shock parameter” From the equation (2), it can be known that the "thermal shock parameter" is related to the mechanical and thermal properties of the crystal material, where ση3χ is the maximum stress when thermal cracking occurs, and Ke is the thermal conductivity, E is Young's modulus, and ατ is the coefficient of thermal expansion (coefficient oftherma 1 expansi ο η). From the formula (1), we can see that the larger the "thermal shock parameter" is, the higher the "fracture limit excitation" can be. "Power". However, for a specific crystal, the "thermal shock parameter" is a basic property of the crystal and cannot be changed. On the other hand, the "fracture-limiting excitation power" is inversely proportional to the absorption coefficient. The absorption coefficient is proportional to the incorporation The ion concentration of the crystal. Therefore, lowering the ion concentration of the acetic acid crystals can increase the "fracture-limited excitation power." Generally speaking, laser The relationship between the long absorption coefficient, α stone, and the ion concentration can be expressed as a = CNd, where C is a proportional constant, which is proportional to the absorptiori cross section, and Ion concentration in atomic%.

Mam V. Description of the invention (8) For WNd: YV〇4, its C value is about 20 ~ 25 cm-1. The C value of Nd: YAG is about f 5 Cm 1 °. In comparison, any laser crystal that meets C 220 cm is called a strong absorption material. Vanadic acid crystal materials are generally highly absorbing materials. To reduce the absorption coefficient of strongly absorbing materials, the concentration of doped ions must be reduced. Figure 1 shows the correlation between the "fracture-limited excitation power" Pabs Hm and the reciprocal of the absorption coefficient α-1 obtained from experiments of exciting the Nd: YV〇4 crystal by the laser diode end face. As the result of the above theoretical analysis, there is an inverse trend between the "fracture-limiting excitation power" and the absorption coefficient. In a general laser diode end-face excitation type solid-state laser system, the input excitation power must be greater than about 20 watts to produce a laser output of more than 10 watts. It can be seen from Fig. 1 that for Nd: 04V04 crystal, the absorption coefficient of the crystal must be less than 10 cm-1 to withstand the excitation power of more than 20 watts. In other words, the ion concentration of the Nd ·· YV04 crystal cannot exceed 0.5 at.%, So the commonly used 1.0 at.% Nd: YV04 crystal cannot obtain a laser output of 10 watts. The vanadic acid crystals of low hafnium ion concentration used in the present invention, such as Nd: YV04, have an ion concentration between 0.4 and 0.4%, mainly between 0.2 and 0.4%. FIG. 2 is an embodiment of the present invention. Referring to FIG. 2, the composition of the high-power diode-excited solid-state laser includes: a laser diode array 100, which is coupled and output through the optical fiber 101, and the excitation-condensing lens group 102 converges the excitation beam to the low chirp ion Concentration of vanadate crystals 103. Suitable laser crystals 103 include, but are not limited to, Nd: YV04 and Nd: GV04. The absorption coefficient of laser crystals is between 2 and 10 cnf1, mainly about 5 cnf1. A preferred crystal 103 is a low erbium ion

D: \ Patent \ pdl602. Ptd Page 11 405285 V. Description of the invention (9) The concentration of Nd: YV04, the ion concentration is between 0.049% and 0.2-0.4%. The two worm surfaces of the laser crystal are plated with anti-reflection films of fundamental frequency light. The laser crystal is covered with an indium junction 'and mounted on a copper base, and the temperature can be operated between 15 and 35 ° C. The laser system of the present invention has little effect on this temperature range. The mirror 104 of the resonant cavity is a concave mirror, and an anti-reflection film is provided on the light incident surface for the excitation wavelength key radiated by the laser diode 100. On the second side, a high-reflection film with a fundamental frequency light wavelength and an anti-reflection film with a laser diode excitation wavelength are forged. The preferred radius of curvature of the mirror 104 is lm. The length between the cavity mirror 104 and the output coupling mirror 105 is adjustable to avoid instability caused by the thermal lens effect of the crystal. The output coupling mirror 105 is plated with a transparent part of the high-frequency light as the output. In order to obtain a stable single-mode laser, a suitable cavity length ranges from about 2 to 10 cm, and in the embodiment is about 5 cm. The resonant cavity also contains a Q switch 106. For example, a 30-watt fiber-optic surface-coupled laser diode is used to excite a Nd: YV04 laser crystal with a concentration of 0.3 at.%. Both ends of Nd: YV04 are plated with anti-reflection films of 1064nm. The excitation beam was focused on the Nd: Y V04 with 0.5x and 84% optical coupling lens group. The laser crystal is covered with indium foil and mounted on a copper base. The temperature remains around 20 ° C. Output coupling mirror 妁 Reflectivity is 90%. Experimental results show that a 30-watt excitation power has a 16-watt laser output, and this output power is approximately 2.3 times the maximum output power of a 1.0 at.% Nd: YV04 crystal. The literature shows that the laser output of 16 watts is currently the highest record for a single-ended excited N d: Y V 04 crystal. Those who are familiar with this skill can use the artisan thinking to modify it, but

D: \ Patent \ pdl602. Ptd page 12 V. Description of the invention (10) It is better to protect the applicant than the scope of patent application attached Ιϋϋ D: \ Patent \ pdl602. Ptd page 13

Claims (1)

405285 6. Scope of patent application 1. A method for manufacturing a high-power diode-excited solid-state laser includes the following steps: providing a laser resonant cavity having a resonant cavity mirror and an output coupling mirror; and using a low ion concentration Doping neodymium-doped vanadium-based crystals to form a laser crystal; using a laser diode as an excitation light source to provide an excitation beam to the laser crystal; and a body. 2 · As described in the first patent application scope, the power rate diode-excited solid-state mine is the end face laser of the laser system. 3 Please state the lightning described in the first patent scope of the patent scope. ≫ where the length of the resonant cavity is 4 ^ The state of lightning field described in item 1 of the patent scope ^ wherein the laser crystal and the resonant optical coupling lens group are used to focus the excitation beam on the laser crystal Power Diode Excitation Solid Rate Diode Zhao Excitation Solid Distance 0.5-2.0 mm The laser crystal described in item 1 of the patent scope is described in item Nd: YV > The state patent scope is about 0.1 to 0.4 9 ° / 〇. 7 · The ion concentration in the state lightning described in item 6 of the patent application range is about 0 ·: 8 · The ion concentration in the state lightning described in item 7 of the patent scope is 0.3%. Power diode excitation solid , The power rate of the diode excited solid 0.4%. 'Power Diode Excitation D: \ Patent \ pdl602. Ptd Page 14 405285 VI. Scope of patent application 9. A high-power diode-excited solid-state laser includes: a laser resonant cavity with a resonant cavity mirror and an output coupling mirror; A laser crystal composed of neodymium-doped vanadium-based crystals with a low ion concentration is placed in the laser resonance cavity; a laser diode is used as an excitation light source to provide an excitation beam to the laser Laser crystal Zhao and an optical coupling lens group converge the excitation beam to the laser crystal. 10. The high-power diode-excited solid-state laser as described in item 9 of the scope of patent application, wherein the laser is an end-excitation type. 1 1 · The high-power diode-excited solid-state laser according to item 9 of the scope of the patent application, wherein the length of the resonant cavity is adjustable. 12. The high-power diode-excited solid-state laser according to item 9 of the scope of the patent application, wherein the length of the resonant cavity is 2 to 10 cm. 13. The high-power diode-excited solid-state laser according to item 12 of the scope of the patent application, wherein the length of the resonant cavity mirror is about 5 cm. 1 4 · The high-power diode-excited solid-state laser as described in item 9 of the scope of the patent application, wherein the distance between the laser crystal and the resonant cavity mirror is 0.5-2.0 mm ° .1 5 · As the scope of the patent application 49% »High-power diode-excited solid-state laser according to item 9, wherein the laser crystal is Nd: YV0 1 6 2 17 · As described in item 16 of the patent application scope, the power diode suffers from its m-body excitation D: \ Patent \ pdl602. Ptd Page 15 of 4 of 285 6. Patent application range solid-state laser, in which the titanium ion concentration is about 0.2% to 0.18 · As described in item 17 of the patent application range 3%。 High-power solid-state laser, in which the ion concentration is 0.3%. 1 9 · The high-power solid-state laser according to item 9 in the scope of the patent application, wherein the curvature radius of the resonant cavity mirror is lm 2 0 · The high-power solid-state laser according to item 9 in the scope of the patent application, where The diode excitation light source is a diode bar ° 2 1 · The high-power solid-state laser according to item 9 of the patent application scope, wherein the diode excitation light source is a group of diode bars. 2 2 · The high-power solid-state laser according to item 9 of the scope of the patent application, wherein the diode excitation light source is a fiber-coupled fiber. 2 3 · The high-power solid-state laser as described in item 9 of the scope of the patent application, wherein the diode excitation light source is a fiber bundle. 24. The high-power solid-state laser as described in item 9 of the scope of patent application, with an output power of more than 7 watts. .2 5 · The high-power solid-state laser as described in item 9 of the scope of patent application, with an output power of more than 10 watts. 2 6 · The high-power μ ·, i ^ n laser described in item 9 of the patent range, wherein the resonant cavity includes a high-power 4% ° rate diode described in item 9 of the patent range. Excited Diode Excited Concave Mirror. Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Excitation Diode Body-excited ί switch. Diode Excitation D: \ Patent \ pdl602. Ptd Page 16 4α ^ 285 6. Scope of patent application Solid-state laser, the output slope efficiency is greater than 40%. Hill p. 17 D: \ Patent \ pdl602.ptd