Download two-slit interference,one photon at a time

Two-slit interference,one photon at a time
一、目的：encounter Wave-Particle Duality with photons
二、理論：refer to modern physics or optics physics
三、方法：Decreasing the light output of a given incandescent bulb shifts the
spectrum toward the longer, red wavelengths. So,by turning down the bulb
intensity and placing a very narrow band green filter in front of the bulb, the
passed photon will drop dramatically.Use this obvious phenomenon to create a
source of single photons.
四、儀器
1.U-channel (Optical Light Path: 1 meter)
Including:
a. photomultiplier tube
b.preamplifier-Discriminator
c.interference Filter:
d.three double slit,one single slit,all slit widths: 0.09 mm,double slit
separations: 0.35, 0.40, 0.45 mm
e. 670 ± 20 nm,1.0 mW laser
f. flashlight bulb ,housed in a black plastic tube with a green interference filter
(546 nm) at the output end. A schematic is shown below.
※The photodiode is mounted on the outside of the shutter so that it is in the
light path when the shutter is closed, and when the shutter is opened to let the
light pass to the photomultiplier.
2. cricket：turns signals emerging from the photomultiplier into audible
individual clicks
3. electronic counter
4. voltmeter
五、實驗：
1. Two-Slit Interference: (by laser)
Recreate Young's two-slit measurement of the wavelength of laser light,and compare
and contrast with single-slit interference.You can see obviously the interference
pattern by eyes or in data. At the far end of the U-channel is a moveable single slit,
the detector slit. It is attached to a translational stage actuated by a micrometer.Move
the detector slit across the interference pattern in front of the photodiode to make
quantitative measurements of the light intensity arrival rate as a function of position.
P.S. the photodiode detector is connected with a current-to-voltage converter
2. Two-Slit Interference, One Photon at a Time: (by filtrated bulb light)
The channel is opened, the laser turned off and the bulb lifted into place. The bulb
intensity is set to about half of maximum. Because of the green filter, the number of
photon passing through the channel is too rare to be detected by the photodiode.So
we use the much sensitive photon detector , the photomultiplier tube (PMT).In other
words, the PMT is so sensitive that any ordinary light will burn it!!So never let the
PMT work when the channel is opened or the laser is on , OR YOU WON’
T PASS
IMMEDIATELY!!
a. The photomultiplier's high voltage supply and pulse-height discriminator level are
both controlled and monitored from the front panel. Connect discriminator to the
cricket and redo the exp.part 1, hear the clicks
b. Connect discriminator to a electronic counter .Before redo the exp.part 1 ,
optimizing the electronic countor unit first.
˙Optimization：With the discriminator level fixed, counting for dark current
(photomultiplier shutter closed) and counting for green photons as a function of
photomultiplier voltage. Interpret these graphs leads to an optimal bias voltage.
˙Redo the exp.part 1.
※ photomultiplier is rated at 5% efficiency, the actual photon arrival rate is 20
times greater
3. A Dramatic Demonstration Of The “Essential Quantum Paradox”
The slit-blocker is set to permit light passing through only one slit, through both
slits, or through only the other slit. Respectively, count the photon rate as a function
of position, empirically, -1 minimum, the central maximum, and the +1 minimum
of the interference pattern.