Galileo's Sky

最近在 S&T 注意到有一家新的 solar telescope (太陽望遠鏡)製造商冒出來,
Lunt Solar Systems, Andy Lunt 是 David Lunt (Funder of Coronado, Coronado 的創始人)的兒子,
使用的是和 Coronado 一樣的 etalon 干涉儀技術, 近期季將推出產品, LS60T/Ha 望遠鏡一支現在預購價不到 USD$900!!, Coronado (現在是 Meade 的子公司)祭出大幅降價正面迎戰, SM90T15 降了將近一半 (USD$9950 -> USD$4999)!!! SM60T 也降到破 2000 USD, 可見在沒有競爭的時代利潤有多好!!!!!!....
真是心動啊!!



以下摘錄 Wiki 有關 etalon (Fabry-Pérot interferometer) 的說明:

基本上就是利用兩個反射面和光在兩個反射行經的路徑所造成的相位差形成干涉現象(高中物理有教喔!),  而選取所需要波長的光線. 這就是濾波器了!

In optics, a Fabry-Pérot interferometer or etalon is typically made of a transparent plate with two reflecting surfaces, or two parallel highly reflecting mirrors. (Technically the former is an etalon and the latter is an interferometer, but the terminology is often used inconsistently.) Its transmission spectrum as a function of wavelength exhibits peaks of large transmission corresponding to resonances of the etalon. It is named after Charles Fabry and Alfred Perot.^[1] "Etalon" is from the French étalon, meaning "measuring gauge" or "standard".^[2]

The resonance effect of the Fabry-Pérot interferometer is identical to that used in a dichroic filter. That is, dichroic filters are very thin sequential arrays of Fabry-Pérot interferometers, and are therefore characterised and designed using the same mathematics.

Etalons are widely used in telecommunications, lasers and spectroscopy to control and measure the wavelengths of light. Recent advances in fabrication technique allow the creation of very precise tunable Fabry-Pérot interferometers.

The varying transmission function of an etalon is caused by interference between the multiple reflections of light between the two reflecting surfaces. Constructive interference occurs if the transmitted beams are in phase, and this corresponds to a high-transmission peak of the etalon. If the transmitted beams are out-of-phase, destructive interference occurs and this corresponds to a transmission minimum. Whether the multiply-reflected beams are in-phase or not depends on the wavelength (λ) of the light (in vacuum), the angle the light travels through the etalon (θ), the thickness of the etalon (l) and the refractive index of the material between the reflecting surfaces (n).