专业英语作业

2021年1月25日发(作者：报到)

通信与信息工程学院

专业英语结课作业

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2017
年
12
月
23
日







通信与信息工程学院

二〇一七年














Passage B

Liquid

Lasers,the Free-electron
Laser and the X-ray Laser

Liquid lasers

Liquid
Lasers
If
gases
and
solids
can
sustain
laser
action,
why
not
liquids?
Indeed
liquids
can
be
the
active
media
in
lasers,
and
there’s
a
large
and
important
family of liquid lasers based on organic dyes. The dyes, which are actually solids at
room temperature, are dissolved in a liquid (generally an organic compound, such as
alcohol) to form a solution.
液体激光器如果气体和固体能维持激光作用，
为什么液
体不能 呢？的确，
液体可以在激光工作介质，
并有一个大的和重要的家庭基于有
机液体激光器

C
染料。这些染料在室温下实际上是固体，它们被溶解在液体中
（通常是有 机化合物，如酒精）形成溶液。







What makes the dye laser special is the nature of its transitions. In almost all
other
lasers,
the
laser
transition
is
between
two
states
at
fixed
energy
levels,
which
means
that
the
laser
emission
is
in
a
fixed,
very
narrow,
well-defined
band
of
wavelengths. Even in carbon dioxide lasers and other types with a family of closely
spaced
energy
levels,
there
are
discrete
transitions
at
distinct
wavelengths.
Organic
dyes, in contrast, have energy levels so closely spaced that to all intents and purposes
they form a continuum. This large number of levels exists because of the complexity
of the dye molecules, and as a result, electronic transitions in the dye can produce a
broad range of wavelengths, most of them visible.
染料激光器之所以特别， 是因为它的过渡性质。在几乎所有其他激光器中，
激光在固定能级的两种状态之间发生跃迁，这意味着激 光发射

在一个固定的、
非常窄的、
定义良好的波段中。
即使在二氧 化碳激光器和其他具有紧密间隔能级
的类型中，在不同的波中也存在着离散的跃迁。

长度。相比之下，有机染料的
能级如此密集，
以致于它们都形成了连续统。
由于染料的 复杂性，
这一数量级存
在。

分子，因此，染料中的电子跃迁能产生宽范围的波长，大部分波长可见。

It’s possible to devise an optical system that will select a single wavelength in the
laser’s
range. Moreover, these optics can be adjusted to
tune t
he output wavelength
continuously
across
the
range
of
wavelengths
possible
for
that
particular
dye.
Most
dyes
are
tunable
across
at
best
10
percent
of
the
visible
region,
but
it’s
possible
to
arrange several dyes in sequence so as to be able to tune the output wavelength across
the entire visible spectrum.
有可能设计出一种能在激光范围内选择单个波长 的光学系统。
此外，
这些光
学元件可以被调整以连续调整输出波长。

可能的波长为特定的染料。大多数染
料在可见光区域的
10%
处是可调谐的，但也可 以按顺序排列几种染料以便调谐
T
。

他在整个可见光谱上输出波长。

What makes a commercial dye laser worth its price tag of $$5,000 to $$50,000 is
the fact
that it can be tuned precisely
—

often with
just a twist of a dial
—
to
emit
a
smaller
range
of
wavelengths
than
any
other
source,
and
that
within
this
range,
the
light is much more intense. This can make a dye laser invaluable for experiments in
such areas as chemistry and atomic physics.
是什么使一个商业染料激光价值
5000
美元至< br>50000
美元的事实是，它可以
精确地调整
-
往往只是一个扭曲的拨 号发出更小的波长范围比任何。

在这个范围
内，
光线要强烈得多。
这可以使染料激光器在化学和原子物理等领域的实验中发
挥重要作用。

Incidentally, one of the strangest lasers ever built was a dye laser. It doesn’t even
emit a beam, but rather a halo. Z. G . Horvath, of the Central Research Institute for
Physics in Budapest, Hungary, and two colleagues at the Lebedev Physics Institute in
Moscow
built
a
disk-shaped
laser
that
emits
light
along
all
360
degrees
of
its
circumference. In this device, the circumference is coated with a partially reflecting
film,
producing
a
disk- shaped
laser
cavity.
At
the
heart
of
this
weird
laser
is
a
dye
that’s pumped by another laser. Horvath believes it should be possible to extend his
technique
to
make
a
spherical
laser
—
one
that
will
emit
laser
light
from
the
entire
surface of a ball-
shaped device. But it’s unclear if either a disk or a spherical laser will
ever find applications outside the laboratory.
顺便说一句，
有史以来最奇怪的激光器之一是染料激光器。
它甚至不发出光