one week in the lab: i hate ir

By snake at 2:40 pm on February 21, 2006 | No comments

星期六早上, 11点起(备注: 这不是我的常规起床时间). 早饭中饭做一顿了, 出门, 我kao, 冷啊. 不过想想今年冬天还真不像冬天, 一月份每次去跑步都不用戴帽子, 也该是时候冷上一阵子了.

进实验室的第一件事: 打开激光. 先给这35k的光纤激光器来个特写: 一个长方形盒子, 前面面板上两个数字显示, 一个显示光纤温度(不同的温度对应于不同的光纤折射率, 从而对应于不同的波长输出), 一个显示输出功率. 每个配一个旋钮可以调节. 几个按钮, 具体作用不明. 一个钥匙, 一旋后, 1120nm的激光就从一根光纤中出来, 导入其他的光学器件. 激光器启动以后, 需要等上半个小时, 让输出光的偏振方向稳定下来. 一般光学实验, 偏振方向都取在平行于光学桌面.

这台激光是整个实验室第三危险的设备, 同时也是最危险的光学设备(第一第二都是高压设备). 它的最大输出达到1瓦, 打在皮肤上不会有太大问题, 但如果聚焦后射入眼睛就有一定危险了, 所以激光实验第一条, 你应该了解所有光束的大概位置, 包括各种散射光. 更加危险的是: 这是不可见的激光. 1120nm在红外波段, 人眼看不到, 所以当这台激光器开启时, 进入实验室必须佩戴防护眼镜. 比较搞笑的是, 经常有人看着实验室门口的红灯(说明有激光开启)亮着, 门上大标语贴着非请勿入, 仍然一如反顾的冲进去… 我曾经建议在门口贴骷髅头…

进入正题, 激光倍频. 最常用的方法就是非线性晶体倍频. 当一束固定频率的光照射在原子上, 可以把原子中的电子想象成一个用弹簧和原子核相连的带电小球(Lorentz模型), 光(电磁波)的电场以一定的频率变化, 从而激发电子也以同样的频率振动. 对于某些特殊的晶体, 这个连接电子和原子核的弹簧并不是个很好的弹簧, 电子的振动还包含有两倍, 三倍于光频率的振动. Maxwell电磁波理论告诉我们, 带电粒子的简谐振动将激发同样频率的电磁波. 这样, 我们就得到了倍频光. 这种办法的缺点是转换率很低, 基本在10^-5, 也就是说1W的光射入, 只有10微瓦的倍频光出来. 一种解决方法就是将非线性晶体放入一个谐振腔里, 谐振腔的腔内强度能够达到10倍甚至100倍于入射光, 从而产生比较强的倍频光.

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one week in the lab: beginning

By snake at 8:48 am on | 1 Comment

上上周一去签美国签证, 再次体会了美国签证真是件体力活, 早晨6点爬起来往多伦多赶, 上了Go Bus后昏昏沉沉, 费了很大力气回想上一次起来后天还是黑的是什么时候的事了. 嗯, 去年一年好像就两回, 一次去跑半程马拉松, 还有一次, 也是去签证. 在使馆里干坐了两个小时, 叫了名后和签证官白话了两句, 瘾都还没过足, 就被check了. nnd, 因为会是一周后, check一般要2-3周, 所以去不成了.

老板临走之前假惺惺的来安慰我, 说下次还有机会. 然后话锋一转, 说正好乘这段时间好好把倍频腔搭起来, 希望能在他回来后看到绿光. 我kao, 想想真是郁闷啊, 本来可以在阳光灿烂的新墨西哥州晒上一周的太阳, 现在去不成了也不算坏, 老板不在也能轻松一周, 没想到竟然还要完成倍频腔…

先来点背景介绍了. 我们正在搭一个离子陷阱希望能束缚镁离子, 计划用镁离子的两个超精细能级作为量子比特的|0>和|1>, 从而试图做量子计算. 为了从实验上对这个二能级的量子系统进行控制, 我们将用激光来激发镁离子的能级. 镁离子只有一个价电子, 所以能级跟氢原子差不多, 基态是S_1/2, 两个稍高的激发态是P_1/2和P_3/2. 基态和激发态之间的能级间隔对应于280nm的激光. 具体细节我先略过, 反正最后发现我们需要3束激光, 波长都在280nm附近. 实验室里有一台拍卖来的染料激光器, 输出在绿光(560nm)附近, 波长可调, 功率接近1瓦(理论值), 我玩过一阵子, 拼死拼活才搞到280毫瓦:-(; 同时实验室里有一台激光倍频的仪器, 还没动过, 看说明书好像蛮高级, 打光进去, 调调几个旋钮, 倍频光就出来了. 这样我们就有一束280nm激光了, 还要两束. 嘿嘿, 记得我刚来时候听老板介绍到这里, 一直疑惑不解为啥不就买三套得了. 原因很简单, 没钱. 染料激光器一套大概100k, 还特别难侍侯, 老坏. 我们现有的那台有个部件就出了问题, 寄出去修, 昨天我凑巧瞟了一眼帐单, holy shit, 维修公司收费245美元一小时… 我立马在脑海中演算245美元*8小时*5天*4周除以我的月收入, 由于对自己心算能力的信心不足又按计算器算了一遍, 然后瞅着跳出来的数字小发了一阵子呆.

跑题了, 另外那台倍频的仪器大概50k. 老板再有钱也没能力买上三套. 还有两束激光怎么半呢? 老板不知道从哪里搞到的小道消息, 听说一个丹麦的公司生产接近1120nm的激光, 于是搞了两套回来, 合计70k. 然后花接近30k一年雇一个研究生, 来搭倍频腔, 先倍一次到绿光, 然后再倍一次到紫外. 和我同实验室的Jason花了去年一年的时间, 搭了两个; 剩下两个就轮到我了.

前不久看blog, 逛到这个.

觉得很有趣, 于是东施效颦一下, 也来一个我自己的”one week in the lab”. 一来自己blog的自来水太多, 没什么内容; 二来, 嗯, 还是引上面链接里的几段话, 他说的比我好多了:

The bigger problem, though, is that most of the people posting regularly about research stuff are theorists, while I’m an experimental atomic physicist. The business of experimental atomic physics, at least in my experience, involves a whole lot of thinking “Where’s the goddamn socket wrench, anyway?”, and not so much the Deep Thoughts about Big Questions in physics. Not on a daily basis, anyway.

Theoretical work, at least from my outsider’s perspective, provides many more opportunities for thinking about big picture issues. Particularly in the less computational areas of theory (people doing complicated molecular modelling spend a lot of time thinking “Why won’t this goddamn thing compile, anyway?” Some of them give research talks that are like that…)– A field like string theory or quantum information theory appears to be nothing but Deep Thoughts (though that might be an illusion caused by the fact that I don’t understand about 80% of what they say).

As I tell my students when they prepare to give talks, the big picture stuff is a lot more interesting than the nuts-and-bolts daily grind of an experiment. But, as I said, I do feel guilty sometimes about not posting more about my own research.

记得当时看完很想和作者握手, 嘿嘿, 不知道其他人是怎么样, 反正我在实验室里, 至少1/5的时间是用来找Alan Key或者是Ball Driver的… 当然, 我还不知道能不能在一周内把绿光搞出来, 尽力而为了.

要做的第一件事情…

找到孙燕姿的那首绿光的mp3, 带到学校, 边做实验边听.

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30k 9-10/15

By snake at 7:17 pm on February 20, 2006 | No comments

Feb. 9th: 3x 800m fast run with 1.5min REC, 1600 jogging, 3x 800m fast run with 1.5min REC.

Feb. 16th: supposed to run a test half-marathon 21k, but the weather was too bad and after 3k i am totally wet. i don’t want to get sick so i came back.

Feb. 17th: basketball, 1.5 hour

need to buy new shoes now:
Nike Pegasus 2005 or Asics GT-2110

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clutch shot #31

By snake at 7:09 pm on | No comments

David West sank the game-winning jumper as time expired, lifting the Hornets to a dramatic 97-96 victory over the Washington Wizards, who wasted a huge effort by Gilbert Arenas. (Oklahoma City, February 13th, 2006)

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clutch shot #30

By snake at 7:07 pm on | No comments

Pau Gasol made a spinning floater in the lane as the final buzzer sounded to lift the Memphis Grizzlies to a thrilling 81-79 triumph over the stunned Golden State Warriors. (Oakland, February 13th, 2006)

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February 17th

By snake at 9:32 am on February 17, 2006 | 1 Comment

我们亲爱的Jordan同学今天43岁了.

“If I had to pick the best player in the game, he certainly is up there right now in the way that he approaches the game. . . . Anybody can go out and take a lot of shots and end up with 81 points, but if you lose, who cares? He was in a great rhythm and went out and played well. So you have to commend him for that. [But] if I were on the other side, there would be no way I would have been able to be in that game without six fouls.”

– A certain Michael Jordan, reacting publicly to Kobe Bryant’s 81-point game for the first time at a New York press conference for his Jordan All-American Classic for high schoolers.

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clutch shot #29

By snake at 11:11 am on February 12, 2006 | No comments

Joe Johnson scored 29 points, including a go-ahead runner with 7.6 seconds remaining as the Hawks posted a 99-98 victory over the Detroit Pistons, who have lost consecutive games for the first time this season. (Atlanta, Tuesday, February 7th, 2006)

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clutch shot #28

By snake at 11:07 am on | No comments

Mehmet Okur had 15 points, including a go-ahead 3-pointer with seven-tenths of a second left, as the Utah Jazz posted a thrilling 109-107 overtime victory over the slumping Bulls, who have dropped the first four games on a seven-game road trip. (Slat Lake City, Monday, Februray 6th, 2006)

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30k 8/15

By snake at 7:05 pm on February 4, 2006 | No comments

Feb. 1st: Tempo, 3k 4:40min/km pace x2 with 5min REC @waterfront

Feb. 2nd: Group trainning, 8min tempo x3 with 2.5min REC @waterfront

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clutch shot #27

By snake at 10:37 pm on February 3, 2006 | No comments

Joe Johnson scored 23 points, including an off-balance jumper with seven-tenths of a second remaining, as the Hawks posted their third straight win, a 96-94 triumph over the Orlando Magic.

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