Re: laser beam balances bead

[brian whatcott <inet@INTELLISYS.NET>]

At 13:59 6/13/99 +0930, Scott Johnston wrote:
> Hi all,
> I'm trying to find out some details on an experiment I recall from quite a
> few years back in which a very small bead of glass(?) was balanced
> vertically on the focused beam of a high powered laser.
> Can anyone tell me some basic stats like: the power and wavelength of the
> laser,and the mass of the bead used? Either that or a reference to a
> website which has the info or a magazine link.

Petter Hagberg's page at Chalmers Tech University has a straight forward
exposition on optical levitation and optical tweezers.

 http://fy.chalmers.se/f3a/tweezers/tweezers2.html

On the topic of levitation, I should mention that references abound
on the web to magnetic levitation at 16 Tesla - water drops and
frogs (!)
Electrostatic levitation is a well-established experimental mode
(oil-drops). Ultrasonic levitation has been demonstrated.


> Also, while I'm at it, am I correct in saying that the dark adapted eye
> responds to around five visible light photons per second striking a given
> receptor cell?
> Many thanks in advance.
> Scott.


I seem to recall that though the eye has demonstrated unit quantal
sensitivity, its efficiency is possibly not so high as 20%.
 I have in mind a figure like <5%
brian whatcott <inet@intellisys.net>
Altus OK