倍频激光器,,,,光束质量

无聊瓜子 · 发表于 2007-11-26 21:10:08

为什么激光器内放了倍频晶体后,光束质量就变得不好了?这是为什么啊 ?

欢迎各位大侠前来探讨留言.

lisqun · 发表于 2008-1-14 23:06:11

KTP、SKTP、LBO、BIBO都有用的到。论数量的话，肯定是KTP了，胶合晶体的数量是惊人地。

annespring · 发表于 2008-1-14 13:44:12

原帖由 watermoon 于 2008-1-14 13:42 发表

目前应该说，还是KTP晶体用得比较多吧。。。

小功率的用KTP

watermoon · 发表于 2008-1-14 13:42:17

原帖由 zgzxb 于 2008-1-14 13:17 发表
KTP和LBO以及BBO晶体是目前比较成熟和常用的倍频晶体。腔内倍频输出光束质量变差外，还会引起输出功率不稳定等问题。这是腔内倍频不可克服的缺点。
顺便问一下：大家在做倍频是哪个晶体用的比较多啊？？？

目前应该说，还是KTP晶体用得比较多吧。。。

zgzxb · 发表于 2008-1-14 13:17:32

KTP和LBO以及BBO晶体是目前比较成熟和常用的倍频晶体。腔内倍频输出光束质量变差外，还会引起输出功率不稳定等问题。这是腔内倍频不可克服的缺点。
顺便问一下：大家在做倍频是哪个晶体用的比较多啊？？？

无聊瓜子 · 发表于 2008-1-8 18:59:59

我还在寻找答案

希望大家多多指教

[ 本帖最后由无聊瓜子于 2008-1-8 19:03 编辑 ]

lisqun · 发表于 2008-1-8 18:13:04

相当地专业！但是好象和使用的倍频晶体有很大关系。

波斯地毯 · 发表于 2008-1-3 17:06:44

顶起！

高深！！！

我是学生。

t0y · 发表于 2008-1-2 17:20:44

Principles of Nonlinear Optics (Wiley Series in Pure and Applied Optics) (Hardcover)
by Y. R. Shen (Author) "Physics would be dull and life most unfulfilling if all physical phenomena around us were linear..." (more)

Nonlinear Optics, Second Edition (Hardcover)
by Robert W. Boyd (Author) "Nonlinear optics is the study of phenomena that occur as a consequence of the modification of the optical properties of a material system by the..." (more)

Fig. 1: Spatial walk-off: the intensity distribution of a beam in an anisotropic crystal propagates in a direction which is somewhat different from that of the wave vector.

Spatial walk-off
Definition: the phenomenon that the intensity distribution of a beam in an anisotropic crystal drifts away from the direction of the wave vector

For a laser beam propagating in an isotropic medium, the transverse intensity distribution propagates along the beam axis as defined by the medium k vector.

In anisotropic (and thus birefringent双折射晶体) crystals, this is not necessarily the case: it can occur that the intensity distribution drifts away from the direction defined by the k vector, as illustrated in Fig. 1, where the gray lines indicate wavefronts and the blue color the region with optical intensity. This phenomenon, called spatial walk-of, birefringent walk-off or Poynting vector walk-off , is associated with some finite angle ρ (called walk-off angle走离角) between the Poynting vector （能流传播方向）and the k vector（波前传播方向）. The Poynting vector defines the direction of energy transport, while the k vector is normal to the wavefronts.

Spatial Walk-Off in Nonlinear Interactions

Spatial walk-off is encountered in nonlinear frequency conversion schemes based on critical phase matching in nonlinear crystals. Its consequence is that the waves interacting within a focused beam lose their spatial overlap during propagation, because those waves with extraordinary polarization experience the walk-off, while this is not the case for those with ordinary polarization. (Note that birefringent phase matching necessarily involves beams with both polarization states.)

In effect, the useful interaction length and thus the conversion efficiency can be limited, and the spatial profile of product beams may be broadened and the beam quality reduced（倍频光束质量下降）.

Unfortunately, it is no solution simply to work with more strongly focused beams, requiring a shorter interaction length, because the spatial walk-off becomes more important for smaller beam radii.（进一步聚焦，可以缩短基波与非线性晶体作用长度，但是这对于补偿走离效应无济于事） The problem gets reduced, however, for high optical intensities, which allow for good conversion within a short length.

The phenomenon of spatial walk-off is directly related to that of a finite angular phase-matching bandwidth. The equation above shows that a large walk-off angle occurs in situations with a strong angular dependence of the extraordinary refractive index. In such cases, the phase-matching conditions also strongly depend on the propagation angle, and phase matching becomes incomplete when using tightly focused beams, having a large beam divergence.

It is possible to achieve a kind of walk-off compensation [1] by using two subsequent nonlinear crystals which are oriented so that the walk-off directions are opposite to each other. There is then still walk-off within these crystals, but its overall effect can be strongly reduced.

Spatial walk-off can be avoided altogether by using a noncritical phase matching scheme. This, however, generally requires operation of the crystal at a temperature which is not by coincidence close to room temperature.

[ 本帖最后由 t0y 于 2008-1-2 17:26 编辑 ]

无聊瓜子 · 发表于 2008-1-2 13:33:47

看来啊
很多人都是没机会亲身做做实验的
没亲身体验过,当然不知道我在说什么了

各位,加油了

希望高手能帮我解答

watermoon · 发表于 2008-1-2 11:18:20

没说明白光束质量不好了是指什么不好了？
激光器的结构是怎么样的？腔内还是腔外？腔外的话是否经过聚焦？
光束质量差了是发散角变大了还是M2因子变大了？
都没说。

无聊瓜子 · 发表于 2007-12-29 22:44:28

我这个帖子技术量那么高,怎么大家都不想发表点什么意见呢?

真让我失望啊

对回帖的兄弟们表示感谢.

我会听取你们的意见,对激光器进行改进的.

多谢了

倍频激光器,,,,光束质量

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