Radiant energy – Electrically neutral molecular or atomic beam devices and...
Reexamination Certificate
2002-01-29
2004-11-23
Wells, Nikita (Department: 2881)
Radiant energy
Electrically neutral molecular or atomic beam devices and...
C250S492100
Reexamination Certificate
active
06822221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for laser cooling of atoms and an apparatus therefore. More specifically, the present invention relates to a coherent light source for laser cooling atoms, and to a method for laser cooling a variety of atoms, such as silicon atoms and germanium atoms, each having a plurality of magnetic sublevels.
2. Description of the Related Art
In recent years, developments in the field of laser cooling of atoms has exhibited quantum leaps, starting with substantiation of Bose-Einstein's condensation and breakthroughs with atom lasers, nonlinear atom optics and the like.
In the laser cooling field, if it becomes possible to realize laser cooling of semiconductor atoms, such as silicon and germanium, instead of alkaline metal atoms and the like (which have been heretofore an object of laser cooling), novel developments can be expected from an engineering point of view. Hence, expansion in the possibilities of application are inestimable.
In these circumstances, there has been a strong need for provision of a technology for laser-cooling a variety of atoms, including semiconductor atoms, such as silicon and germanium.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention has been made in view of the needs involved in the prior art as described above.
An object of the present invention is to provide a method for laser cooling of atoms by which it becomes possible to laser-cool a variety of atoms, including semiconductor atoms such as silicon and germanium, and an apparatus therefor as well as a coherent light source used in the apparatus.
In order to achieve the above-described objects, a method for laser cooling atoms and an apparatus therefor as well as a coherent light source used for laser cooling atoms are implemented in accordance with a manner as described hereinafter.
Laser cooling of atoms means herein a cooling method wherein the atoms collide against (are scattered with) a laser beam to repeat absorption and spontaneous emission of light, whereby kinetic energy of the atoms is released into such spontaneous emissions of light, whereby the atoms are cooled.
Such a process for laser cooling of atoms can be classified into a stage wherein atoms are sufficiently decelerated, and a stage wherein the atoms decelerated sufficiently are cooled. In such deceleration of atoms and cooling of atoms, a scattering force function occurs, as shown in FIG.
1
.
In the following, “deceleration of atoms due to scattering force” and “cooling of atoms due to scattering force” will be described in detail.
First, cooling of atoms due to a scattering force will be described. The cooling of atoms due to a scattering force relates to so-called “Doppler cooling”. Namely, Doppler shift acts most effectively with respect to cooling of atoms, which have been decelerated to around several times wider width than natural width.
In order to effect cooling of atoms by means of spontaneous emission, it is required that an average energy of photons emitted be higher than that of photons absorbed. Namely, Doppler cooling means to realize such a situation wherein an average energy of emitted photons is higher than that of absorbed photons. A particularly effective negative detuning amount is around a natural width (half width at half maximum) of resonance.
Incidentally, since a natural width (half width at half maximum) of silicon is around 28 MHz, a laser having a linewidth of the same degree as, or lower degree than, that of the natural width, i.e., around 28 MHz is required for Doppler cooling. Furthermore, such a laser takes about 130 microseconds until it reaches 220&mgr; Kelvin which corresponds to the Doppler cooling temperature. Therefore, it is required to use a continuous wave (CW) light source.
It is to be noted that the natural width (half width at half maximum) of silicon, the Doppler cooling temperature, and the time (stop time) required for reaching 220&mgr; Kelvin corresponding to the Doppler cooling temperature are determined by the mathematical expressions shown in FIG.
2
.
Next, deceleration of atoms due to a scattering force will be described herein. In this case, a melting point of silicon is 1414° C., while a melting point of germanium is 958.5° C. The melting points of both of the materials are relatively high melting points, respectively.
A velocity of a silicon atom, which is ran off from the surface by means of electron-beam evaporation, exhibits a Boltzmann distribution centering on about 1000 m/s (meter per second). A half-value width thereof is wide, i.e., about 1500 m/s or more, so that it is about 6 GHz (gigahertz) in a resonance frequency region.
Namely, Doppler broadening (Doppler width) due to velocity broadening is about 6 GHz at melting temperature.
Accordingly, when a frequency of a single frequency coherent light source is changed with a lapse of time to effect chirped cooling in the case where the single frequency coherent light source is used, it becomes possible to decelerate atoms.
On one hand, it may be arranged to use a picosecond laser for decelerating atoms. Namely, in pulses of Fourier transform-limit, 100 picoseconds can involve a frequency zone of 10 GHz. In other words, when the picosecond laser is used, atomic beams, which are in Doppler velocity broadening, can be decelerated at the same time.
Doppler width is determined by the numerical expression shown in FIG.
3
.
The reason why laser cooling of silicon atoms is difficult resides not only in that a cooling wavelength is short, but also in that energy level in a ground state, i.e., its cooling lower level being in a ground level involves a plurality of magnetic subsidiary levels, and specifically, three magnetic subsidiary levels.
More specifically, there are three magnetic subsidiary levels as its cooling lower level being a ground level in silicon atom, so that a magnetooptic trap cannot be prepared as in case of alkaline metal atom. This is a major cause of difficulty in laser cooling of silicon atoms.
Referring to FIGS.
4
(
a
) and
4
(
b
), a detailed explanation will be further continued. In silicon atom, a magnetic quantum number m is degenerated in three magnetic subsidiary levels “m=−1”, “m=0”, and “m=+1” in energy level in a ground state, i.e., its cooling lower level (3s
2
p
2 3
P
1
, J=1) being the ground level.
In order to laser-cool silicon atoms, it is required that laser beams are emitted to the silicon atoms to excite them, whereby their energy level is elevated from their cooling lower level in their ground state to their cooling upper level (3 s3 p
2
4s
3
P
0
, J=0) being their excitation level.
As a result, the silicon atoms are excited by means of emission of laser beams, whereby they are elevated to the cooling upper level. However, such silicon atoms excited from the cooling lower level to the cooling upper level return again to the cooling lower level after expiring spontaneous emission lifetime.
In this case, silicon atoms in the cooling upper level return equivalently to three magnetic subsidiary levels “m=−1”, “m=0”, and “m=+1” with one third each of them in the case where the silicon atoms return from the cooling upper level to the cooling lower level (a solution is obtained from the simultaneous differential equations shown in FIG.
4
(
b
).).
On one hand, silicon atoms in the magnetic subsidiary level of “m=−1” being its cooling lower level in a ground state are excited to its cooling upper level when laser beams of right-handed polarized light (&sgr;+) were emitted to such silicon atoms, silicon atoms in the magnetic subsidiary level of “m=0” being its cooling lower level in a ground state are excited to its cooling upper level when laser beams of linearly polarized light (n) were emitted to such silicon atoms, and silicon atoms in the magnetic subsidiary level of “m=+1” being its cooling lower level in a ground state are excited to its cooling upper level when laser
Kumagai Hiroshi
Midorikawa Katsumi
Birch & Stewart Kolasch & Birch, LLP
Gill Erin-Michael
Riken
Wells Nikita
LandOfFree
Method for laser cooling of atoms and apparatus therefore does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for laser cooling of atoms and apparatus therefore, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for laser cooling of atoms and apparatus therefore will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3356540