A1. the provided volume could be defined using 5 surfaces: elliptical air-n1 interface, tubular air-n1 interface, elliptical n1-n2 interface, tubular air-n2 interface, and elliptical air-n2 interface. the material composition is defined by defining a database of material parameters, particularly the refractive index. the INTERFACE command is necessary to define not only the material refractive index but the reflection, transmission, and absorption properties as well.
then
SYSTEM NEW
RESET
UNITS MM
MISSED 0.5
WAVELENGTH 1550 NM
SPLIT 1
MEDIA
1.4 'N1'
MEDIA
1.5 'N2'
DIA=2
L1=2
L2=2
!! Grin substrate
SURFACE
PLANE Z 0 ELLIPSE (DIA/2) (DIA/2)
OBJECT 'N1.EDGE'
INTERFACE 0 1 N1 AIR
SURFACE
TUBE Z 0 (DIA/2) (DIA/2) (L1) (DIA/2) (DIA/2) 0
OBJECT 'N1.TUBE'
INTERFACE 0 1 N1 AIR
SURFACE
PLANE Z (L1) ELLIPSE (DIA/2) (DIA/2)
OBJECT 'N1N2INTERFACE'
INTERFACE 0 1 N1 N2
SURFACE
TUBE Z (L1) (DIA/2) (DIA/2) (L1+L2) (DIA/2) (DIA/2) 0
OBJECT 'N2.TUBE'
INTERFACE 0 1 N2 AIR
SURFACE
PLANE Z (L1+L2) ELLIPSE (DIA/2)
OBJECT 'N2.EDGE'
INTERFACE 0 1 N2 AIR
!! DETECTOR
SURFACE
PLANE Z (L1+L2+1) 0 ELLIPSE 2@((DIA)/2)
OBJECT 'DETECTOR'
!!SOURCE
WINDOW Y Z
PLOT FACETS OVERLAY
EMITTING DISK Z 0 -(DIA/2) (DIA/2) 100 5 5
!!SOURCE DIR 0 0 1
FLUX TOTAL 100
TRACE PLOT
CONSIDER ONLY DETECTOR
WINDOW X Y
!!SPOTS POS
!!PLOT FACETS OVERLAY
!!STATS
$VIEW
Q2. (a script for a light pipe is provided) what is the intensity at the output of the light pipe? calculate the etendue at the entrance and end facets of the light pipe.
A1. the etendue is a pure geometric concept that does not say anything about the energy distribution of the light but determines the positional and angular extent of a bundle of light. it is important for calculating how much light can be coupled from a source to a detector theoretically. the etendue is a function of the refractive index, detector/emitter area, as well as the acceptance/exit solid angle. the light pipe exit angle could be extracted from the simulation by using the ANGLES command.
then
SYSTEM NEW
RESET
UNITS MM 'WATT'
MEDIA
1.48 'ACRYLIC'
PIXELS 101
SPLIT 1 MONTECARLO
FRESNEL AVE
SURFACE
PLANE Z 0 ELLIPSE 1 1
OBJECT 'FACE_ENTRANCE'
INTERFACE COATING BARE_SUBSTRATE AIR ACRYLIC
SURFACE
TUBE Z 0 1 1 10 2 2 0 0
OBJECT 'TUBE'
INTERFACE COATING BARE_SUBSTRATE AIR ACRYLIC
SURFACE
PLANE Z 10 ELLIPSE 2 2
OBJECT 'FACE_EXIT'
INTERFACE COATING BARE_SUBSTRATE AIR ACRYLIC
EMITTING DISK Z -0.01 1 1 500000 90 90
FLUX TOTAL 100
WINDOW Y Z
PROFILES OVERLAY
TRACE PLOT 10000
!!TRINIDAD START
PIXELS 101
WINDOW X Y
CONSIDER ONLY FACE_EXIT
!!SELECT ONLY COS[25] C
SPOTS DIR
STATS
DISPLAY
ANGLES
PICTURE
RETURN
!!TRINIDAD END
$VIEW
Q3. (this question was about a comparison of the simulation time between SPLIT and SPLIT MONTECARLO commands using the light pipe scripts previously provided) which simulation model would you use for optimization?
A1. (add $TIC command to script to get quantitative values of the simulation time) the SPLIT command would generate much more rays than the SPLIT MONTECARLO because it could generate more than one child rays with power distributions according to INTERFACE and MATERIAL settings. SPLIT MONTECARLO, on the other hand, generates only the child ray with the highest probability of occurrence and in fact conserves the number of rays created within the simulation. this being the case, it also follows that SPLIT MONTECARLO simulations are faster than normal SPLIT commands. for design and optimization of light pipes, since we are only interested in getting a homogeneous distribution of light at the output, using SPLIT MONTECARLO would be acceptable since it's faster and gives us the information we need, anyway. on the other hand for ghost analysis, for example, one should use the SPLIT command in order to study where unwanted rays could come from or arrive on your detector.
Q4. describe how you would design an hot mirror. no need to write a script.
A1. a hot mirror is a reflective filter, composed of layers of dielectric materials, which reflects IR light (around 750-1200 nm) and allows visible light to pass. as a starting point we can first define a low-pass filter with central wavelength around 750nm or so. this generates not a perfect low pass filter but some sort of a band pass filter with a bandwidth of about 200nm. since the range of visible light is larger (380-750nm) we need to increase the bandwidth to allow all visible light to pass. this can be done by adding another set of layers of dielectric material to create low pass filters centered on the wavelengths you wish to suppress. ripples in the spectrum may be smoothed out by optimizing the widths of the quarter-wave plates. furthermore, hot mirrors are extremely sensitive to the incident angle of light. in order to account for this sensitivity in the design (and minimize it as much as possible), one may use materials of higher refractive index.
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