[題目] 兩題近物考古題

[burialberyl ()]

[領域]近代物理 雷射＆energy gap

[來源]台大近物研所考古題  98,87

[題目]

1.A niobium-titanium alloy has Tc~20度C.

(a) What is the gap energy Eg?

(b) Estimate the size of Cooper pairs by dimensional arguements.

2.是關於laser cooling的題目.

Laser cooling is a modern technique to cool atoms to extremely low temperature.

the key point is to tune the laser frequency slightly lower than the nominal

frequency of an electron transition in the atom.

(a) Derive the Doppler shift using Lorentz transformation in one dimension.

(b) From the above derivation, explain why the atom can absorb the laser light.

(c) Describe the phenomenon of spontaneous emission

(d) Explicitly show that after the spontaneous emission, the atom is cooled

    in the Lab frame

(e) What is the condition that the atom can keep

    its original energy？



[瓶頸]

第一題我完全不知道energy gap怎麼算,cooper pair是用測不準原理估計嗎？

整個很沒有頭緒！



第二題我是不會e小題

維持原本能量則光子能量/動量不變

但原子則有可能有內能變化

因此是用動量守恆來計算

討論光子頻率和原子速度的關係嗎？

不過他只佔兩分,所以我在想是不是有更關鍵的條件我沒想到～"～




感謝各位大大襄助！！




--
※ 發信站: 批踢踢實業坊(ptt.cc) 
◆ From: 114.43.214.183
推 jass970991:e小題沒有那麼難 就相等
→ jass970991:第一題我在想如果是導體的話EG就可以直接寫0或是數量級
→ jass970991:純粹是我的淺見....我現在也在準備近物QQ
→ burialberyl:嗯相等是指什麼相等？這提示半導體 所以Eg大概是1eV
→ burialberyl:囉
→ burialberyl:發現打錯字XD          題是
推 ayaga3540:他這邊Eg的意思是指"Cooper pair"的束縛能，而非能帶能
→ ayaga3540:非能帶能隙
→ burialberyl:!!原來我徹底搞錯了！感謝樓上！所以是3.5Tc囉？要算
→ burialberyl:這3.5好像有點麻煩┴┴︵╰（‵□′）╯︵┴┴