Transcript Presentation - The University of Arizona College of Optical Sciences

Absolute Photon Calibration of
Zeiss Observer Z1 Microscope
Shawn Miller
Department of Optical Sciences
University of Arizona, Tucson, AZ 85721
Optics 521 Presentation
December 8, 2008
Absolute Photon Calibration
• Detectors give
relative light intensity
values.
• Must provide
reference to actual
photon numbers for
the detector’s value.
• “Standard” lamp
which has been
calibrated to national
standards.
Standard Lamp
• Tungsten ribbon
filament lamp.
– Temperature is
calibrated for several
currents.
• Stable high current
power supply.
• High wattage resistor.
• Photon emission is
given by Plank’s
curve.
Lamp Calibration Form
• Calibrated at hottest
(most central) area of
the filament.
• Calibrated in the
vertical position.
• 20% variation in lamp
emission.
– Area of filament
viewed by optical
setup is very
important.
Plank’s Curve
• Absolute temperature.
– 1/ Ta = 1/ Tb + (λ/C2)*[ln(ε(λ)) +
ln(τ(λ))]
•
•
•
•
Ta = Absolute temperature
Tb = Brightness temperature
λ = Wavelength of radiation
C2 = Plank’s second constant
= hc/Kb
• ε(λ) = Emissivity at emitting
wavelength
• τ(λ) = Transmission of pyrex
envelope.
• L(λ) = ε(λ,Ta)*τ(λ)*[2hc2/λ5]
/ (ehc/λKbTa – 1).
– Integrate over wavelength
region being observed.
Collecting the Lamp’s Light
• Φ = ∫L(λ)dλ*A*Ω.
– Φ = Flux of light.
• Watts, or ergs/second.
– ∫L(λ)dλ = Radiance.
• W/m2*Sr
– A = Area of filament.
• m2
– Ω = Solid Angle.
• Sr
Zeiss Observer Z1 Microscope
•
•
•
•
EMCCD camera.
Three objectives.
8 wavelength filters.
6 gain settings.
– Detector’s response is
different for each
setting.
A Simple Design
• Small central area of
the filament imaged
onto the focal plane
the objective lens.
• Lamp stand, two
lenses, mirror, and
stop.
Design Details
• First lens mount.
– Barrel mount.
– Axially adjustable by
threading the mount
into the lamp housing.
– About one focal length
from filament.
– Off Axis alignment is a
one time adjustment of
setscrews.
Design Details
• Mirror mount /
aperture stop.
– Adjustable kinematic
mirror mounted above
aperture at 45°
– One time adjustable
height.
– Base for aperture
slide.
– Connection to
microscope.
Design Details
• Second lens mount.
– Adjustable height.
– One time off axis
adjustment.
• Fixed in place with
epoxy.
• Microscope’s stage
acts as fine system
adjustment when
removing and
replacing system.
System Alignment
•
•
•
•
•
Set lamp height.
Adjust first lens.
Adjust mirror height.
Set mirror alignment.
Center second lens.
– Epoxy in place.
• Adjust second lens
height.
635.2 µm
31
6.2
5µ
m
Measurements
• Calculate first lens to filament distance. (z1)
– Measure width of filament spot on wall and distance to wall.
– z1 = (-Wf/Ww)*(DL1w).
• Aperture radius measured with 10x objective. (Rs)
• Distance from first lens to stop and to the second lens
measured with caliper. (DL1S, DL1L2)
Solid Angle
• 1/z1’ = 1/z1 + 1/f1.
• RL1 = Rs +
[Rs/(z1’–(DL1s))]*(DL1s).
– RL1 = Radius of light
spot on first lens.
• Ω = π RL12/z12
Area of Filament / Magnification
• Radius of the filament being imaged onto the
objective lens focal plane. (Rfo)
– Rfo = z1*(Rs/(DL1s).
• Radius of the filament image in the objective
lens focal plane. (Ro)
• m = -Ro / Rfo.
• 100x and 40x objective.
635.2 µm
31
6.2
5µ
– Wf = Wfov / m.
– Af = (Wfov / m)2.
m
• Area of the filament viewed by the microscope.
Number of Photons
• Φ = L*A*Ω*TL*Rm.
– TL = Transmission of lenses.
– Rm = Reflectivity of mirror.
• Theoretical # Photons = (Φ*t*λ) / (h*c).
– t = Exposure time.
– λ = Central wavelength.
– h = Plank’s constant.
– c = Speed of light.
• Calibration factor = #Pt / Detector reading.
References
• Kowalski, Brian. Absolute calibration of a spectrometer through the
ultraviolet. Department of Physics Thesis, 1993.
• Bickel, William. Absolute intensity calibration of a spectrometer
using a blackbody radiation source. Short paper, September 2001.
• Merchant, John. Blackbody calibration sources function as
standards. Laser focus world, April 1995.
• Stair, Ralph. Standard of Spectral Radiance for the Region of 0.25
to 2.6 microns. Journal of Research of the National Bureau of
Standards, Physics and Chemistry Vol. 64A, No.4, July-August
1960.
• G.A.W., Rutgers. “Relation between brightness, temperature, true
temperature and color temperature of tungsten. Luminance of
tungsten.”