Spontaneous Parametric Downconversion - Revision history

Aplstudent at 22:23, 8 November 2021

2021-11-08T22:23:51Z

Aplstudent: /* Single Photon Fields and g2 */

2015-09-06T20:01:25Z

‎Single Photon Fields and g2

Aplstudent: /* Single Photon Interference and the Polarization Interferometer */

2015-09-06T19:43:05Z

‎Single Photon Interference and the Polarization Interferometer

Aplstudent: /* Single Photon Interference and the Polarization Interferometer */

2015-09-06T19:42:11Z

‎Single Photon Interference and the Polarization Interferometer

Aplstudent: /* Single Photon Interference and the Polarization Interferometer */

2015-09-06T19:36:01Z

‎Single Photon Interference and the Polarization Interferometer

Aplstudent: /* Single Photon Interference and the Polarization Interferometer */

2015-09-06T19:35:06Z

‎Single Photon Interference and the Polarization Interferometer

Wikiuser: /* Physics Background */

2015-08-28T19:25:37Z

‎Physics Background

Wikiuser: /* Overview */

2015-07-20T20:45:47Z

‎Overview

Wikiuser: /* Quantum Eraser */

2015-06-14T23:04:14Z

‎Quantum Eraser

Wikiuser: /* Quantum Eraser */

2015-06-14T22:49:39Z

‎Quantum Eraser

← Older revision		Revision as of 22:23, 8 November 2021
Line 111:		Line 111:

	Sadly were not able to get past this part since we had too many complications and so we are now just going to talk theory rather than what we have done experimentally. Here is where we would have placed a polarized into the idler leg and if the system would work properly we would be able to see the photon counts on the B and B'sensors to fluctuate and then this wold show that at certain polarizations of the A sensor the B and B' sensors would be minimum showing the fact that even when the photons are not in contact they are still able to communicate and thus they are constantly entangled, expressly showing the theory of quantum entanglement.		Sadly were not able to get past this part since we had too many complications and so we are now just going to talk theory rather than what we have done experimentally. Here is where we would have placed a polarized into the idler leg and if the system would work properly we would be able to see the photon counts on the B and B'sensors to fluctuate and then this wold show that at certain polarizations of the A sensor the B and B' sensors would be minimum showing the fact that even when the photons are not in contact they are still able to communicate and thus they are constantly entangled, expressly showing the theory of quantum entanglement.
		+
		+	[[SRS Photon Counter]]

	= External Resources =		= External Resources =

← Older revision		Revision as of 20:01, 6 September 2015
Line 28:		Line 28:

	[[File:G2info.png\|x350px\|thumb\|center\|Left: Summary of g2 values as a ratio of electric field intensities in a two-detector scheme. (See Beck for relevant details). Right: Summary of g2 values relevant for this experiment]]		[[File:G2info.png\|x350px\|thumb\|center\|Left: Summary of g2 values as a ratio of electric field intensities in a two-detector scheme. (See Beck for relevant details). Right: Summary of g2 values relevant for this experiment]]
		+
		+	<p> Because the downconverted photons are produced at (approximately) the same time, and the distance along the path of each photon is equal, the photons generated in the SPDC process will reach the detector at the same time. Therefor, it is useful to count the number of coincidences at the detectors to tell when down conversion happens. The detectors have a 'temporal resolution' of a few nanoseconds. If the photons arrive at detectors A & B within this window, the FPGA designates this event as a coincidence and shows up in labview as an AB count. The speed of light is ~1 foot per nanosecond, so if a coincidence is counted then the arriving photons were spatially separated by less than a few feet. </p>
		+
		+	<p> The single photon state can be determined by adding a beam splitting cube in the path of the signal beam and a third detector placed perpendicular. In the classical view of electromagnetic fields described by Maxwell, the excitations of the field propagate like waves. If this were the case, the excitation along the signal beam would split into two at the PBS and arrive at detectors B AND B' at the same time. </p>
		+
		+	<p> A more accurate view of nature describes the excitations with wavelike and particle like properties. When considering a photon traveling down path B', the photon will choose one discrete direction at the beam splitting cube and arrive at detector B OR B'. </p>
		+
		+	<p> The second order temporal coherence parameter measures the amount of bunching of the photons. Bunching describes photons that arrive grouped together. If we consider a photon that arrives at B, if the photons are bunched the probability of a photon arriving at B' within a very short time window increases. (i.e. they arrive in bunches, so if one arrives then another is probably going to arrive right after that.) If we ignore what is happening at detector A, we see these photons are bunched and the parameter that measures this, G2 is greater than 1 </p>
		+
		+	<p> If we consider the relationship between the coincidences AB & AB', the photons arrive antibunched. We are now detecting the SPDC photon pairs, so the photon in the signal path that corresponds to the photon in the idler path goes to EITHER B OR B'. (The process of using detector A to signal events in the other path is known as heralding, because it is like the photon at detector A is saying, “hear ye, hear ye. A SPDC process occurred and my fellow is in one of the other detectors) Therefor, if an detection happens at AB, it is more likely that the next arrival at AB' will be separated in time. The parameter that measures bunching (G2), is less than one, indicating an antibunched single photon state. </p>

	Measurement of photon counts over time at an array of photodetectors can be analyzed for their degree of correlation. Positive, zero, and anti-correlations at the detectors all play a very important role in claiming the nature of the electric field present in the chosen experiment. The constraints on g2 being 0 < g2 ≤ 1 for a quantum mechanical field and g2 ≥ 1 for a classical electric field are determined by analyzing the ratios for the 2-detector and 3-detector schemes for our chosen experiments. To understand this in the context of the experiment, please see the results section.		Measurement of photon counts over time at an array of photodetectors can be analyzed for their degree of correlation. Positive, zero, and anti-correlations at the detectors all play a very important role in claiming the nature of the electric field present in the chosen experiment. The constraints on g2 being 0 < g2 ≤ 1 for a quantum mechanical field and g2 ≥ 1 for a classical electric field are determined by analyzing the ratios for the 2-detector and 3-detector schemes for our chosen experiments. To understand this in the context of the experiment, please see the results section.

@@ Line 32: / Line 32: @@
 == Single Photon Interference and the Polarization Interferometer ==
-Polarization interferometer info and help:
+How to align to polarization interferometer:
 <p> The B collection lens was displaced 4 mm to the right, coupled to the alignment laser and aligned through two irises set to the level of the BBO crystal. (mainly for the vertical alignment, the irises were placed on the center of the track about 1 & 2 feet from the BBO, so the beam was slightly displaced to the right on the irises.)  The tilt of the the BBO was kept constant for the rest of the polarization interferometer.  The B lens was then moved to the center of the track and an iris was placed such that the beam passed through the center. </p>

@@ Line 34: / Line 34: @@
 Polarization interferometer info and help:
-The B collection lens was displaced 4 mm to the right, coupled to the alignment laser and aligned through two irises set to the level of the BBO crystal. (mainly for the vertical alignment, the irises were placed on the center of the track about 1 & 2 feet from the BBO, so the beam was slightly displaced to the right on the irises.)  The tilt of the the BBO was kept constant for the rest of the polarization interferometer.  The B lens was then moved to the center of the track and an iris was placed such that the beam passed through the center.
+<p> The B collection lens was displaced 4 mm to the right, coupled to the alignment laser and aligned through two irises set to the level of the BBO crystal. (mainly for the vertical alignment, the irises were placed on the center of the track about 1 & 2 feet from the BBO, so the beam was slightly displaced to the right on the irises.)  The tilt of the the BBO was kept constant for the rest of the polarization interferometer.  The B lens was then moved to the center of the track and an iris was placed such that the beam passed through the center. </p>
-The Beam Displacement Prism (BDP) closer to the collection lens was added to the center of the track.  This is the BDP with the picomotor on the horizontal tilt.  The BDP transmits one polarization and displaces the other about 4 mm to the right (not to the left like the illustration on the BDP suggests), so the position of the BDP was moved so the beam entered the left half of the calcite.  The horizontal and vertical tilt were adjusted to set the surface of the BDP orthogonal to the beam by aligning the back-scattered radiation from the BDP through the center of the iris.  The  process of adjusting the position of the BDP and aligning the back-scattered radiation was iterated until the beams passed the through the calcite without hitting the mount on the front or back of the BDP.  A mount was constructed to keep the red part of the picomotor fixed in place.
+<p> The Beam Displacement Prism (BDP) closer to the collection lens was added to the center of the track.  This is the BDP with the picomotor on the horizontal tilt.  The BDP transmits one polarization and displaces the other about 4 mm to the right (not to the left like the illustration on the BDP suggests), so the position of the BDP was moved so the beam entered the left half of the calcite.  The horizontal and vertical tilt were adjusted to set the surface of the BDP orthogonal to the beam by aligning the back-scattered radiation from the BDP through the center of the iris.  The  process of adjusting the position of the BDP and aligning the back-scattered radiation was iterated until the beams passed the through the calcite without hitting the mount on the front or back of the BDP.  A mount was constructed to keep the red part of the picomotor fixed in place. </p>
-The displaced beam (the one on the right) was pointed towards the center of the BBO crystal by adjusting the position of the collection lens orthogonal to the optical axis to pass through the center of two irises placed one and two feet from the BBO.  The BDP was checked to make sure the beam passed through without clipping the edges.
+<p> The displaced beam (the one on the right) was pointed towards the center of the BBO crystal by adjusting the position of the collection lens orthogonal to the optical axis to pass through the center of two irises placed one and two feet from the BBO.  The BDP was checked to make sure the beam passed through without clipping the edges. </p>
-A Polarizing Beam Splitting cube (PBS) was placed perpendicular between collection lens B and the third iris.  The green sticker was oriented toward detector B.  One of the beams emerging from the BDP appeared much lighter due to the PBS decreasing the intensity of one of the beams.  A half wave plate set to 22.5° was added between the iris and the BDP to rotate the polarization 45°.  The half wave plate was placed perpendicular to the alignment beam.
+<p> A Polarizing Beam Splitting cube (PBS) was placed perpendicular between collection lens B and the third iris.  The green sticker was oriented toward detector B.  One of the beams emerging from the BDP appeared much lighter due to the PBS decreasing the intensity of one of the beams.  A half wave plate set to 22.5° was added between the iris and the BDP to rotate the polarization 45°.  The half wave plate was placed perpendicular to the alignment beam. </p>
-A half wave plate rotated 45°  was placed perpendicular to the beams behind the BDP to change  the polarization of each beam by 90°.  This was done so the path length difference would be approximately equal when the beams converge in the second BDP.
+<p> A half wave plate rotated 45°  was placed perpendicular to the beams behind the BDP to change  the polarization of each beam by 90°.  This was done so the path length difference would be approximately equal when the beams converge in the second BDP. </p>
-A BDP  placed in a kinematic mount was added behind the second half wave plate to make the beams converge.  The beams passed through the BDP with minimal clipping on both sides and aligned parallel to the other BDP by making the back-scattered radiation pass through the center of the iris closest to the collection lens.  A third half wave plate was added after the BDP and set to 22.5° to rotate the polarization another 45°,  so the beam entering and exiting the polarizer would  shifted a total of 180°.
+<p> A BDP  placed in a kinematic mount was added behind the second half wave plate to make the beams converge.  The beams passed through the BDP with minimal clipping on both sides and aligned parallel to the other BDP by making the back-scattered radiation pass through the center of the iris closest to the collection lens.  A third half wave plate was added after the BDP and set to 22.5° to rotate the polarization another 45°,  so the beam entering and exiting the polarizer would  shifted a total of 180°. </p>
-An interference pattern was observed with the alignment laser by placing  a horizontal polarizer and screen between the BBO & half wave plate.  The horizontal tilt of the BDP closest to the collection lens was adjusted with a picomotor to observe interference on the screen.  The size of the fringes were comparable to the spot size of the beam, so it was difficult to observe the interference unless the tilt was varied.  The picomotor was used to make a darker spot on the screen and the contrast was maximized by slightly changing the angle (on the order of a few degrees) of each half wave plate such that the intensity on the dark fringe was minimized.
+<p> An interference pattern was observed with the alignment laser by placing  a horizontal polarizer and screen between the BBO & half wave plate.  The horizontal tilt of the BDP closest to the collection lens was adjusted with a picomotor to observe interference on the screen.  The size of the fringes were comparable to the spot size of the beam, so it was difficult to observe the interference unless the tilt was varied.  The picomotor was used to make a darker spot on the screen and the contrast was maximized by slightly changing the angle (on the order of a few degrees) of each half wave plate such that the intensity on the dark fringe was minimized. </p>
-The alignment laser was disconnected from B and connected to B'.  The B' detector was translated parallel to the signal beam to make the alignment laser go through the iris between the PBS and polarizing interferometer.  The horizontal and vertical tilt of the collection lens were adjusted to make the alignment laser go through the interferometer.  This process was iterated until the beam passed through the center of all three irises.
+<p> The alignment laser was disconnected from B and connected to B'.  The B' detector was translated parallel to the signal beam to make the alignment laser go through the iris between the PBS and polarizing interferometer.  The horizontal and vertical tilt of the collection lens were adjusted to make the alignment laser go through the interferometer.  This process was iterated until the beam passed through the center of all three irises. </p>
-With the lights out, FPGA, violet laser, SPCM, and labview running, the horizontal tilt of the BDP closer to the collection lenses was slowly adjusted with a picomotor.  Interference was not observed, so the angle of the 45 degree half wave plate (with respect to the signal beam) was adjusted to make sure it was perpendicular to the signal beam, and the orientation angle of the BDP closer to the BBO was varied by a degree at a time, scanning over the horizontal range each time.  When interference was observed, the BDP closer to the collection lens was rotated to 355°, while the BDP closer to the BBO was near 2°.
+<p> With the lights out, FPGA, violet laser, SPCM, and labview running, the horizontal tilt of the BDP closer to the collection lenses was slowly adjusted with a picomotor.  Interference was not observed, so the angle of the 45 degree half wave plate (with respect to the signal beam) was adjusted to make sure it was perpendicular to the signal beam, and the orientation angle of the BDP closer to the BBO was varied by a degree at a time, scanning over the horizontal range each time.  When interference was observed, the BDP closer to the collection lens was rotated to 355°, while the BDP closer to the BBO was near 2°. </p>
 == Double Slit and the Quantum Eraser ==

@@ Line 34: / Line 34: @@
 Polarization interferometer info and help:
-     The B collection lens was displaced 4 mm to the right, coupled to the alignment laser and aligned through two irises set to the level of the BBO crystal. (mainly for the vertical alignment, the irises were placed on the center of the track about 1 & 2 feet from the BBO, so the beam was slightly displaced to the right on the irises.)  The tilt of the the BBO was kept constant for the rest of the polarization interferometer.  The B lens was then moved to the center of the track and an iris was placed such that the beam passed through the center.
+The B collection lens was displaced 4 mm to the right, coupled to the alignment laser and aligned through two irises set to the level of the BBO crystal. (mainly for the vertical alignment, the irises were placed on the center of the track about 1 & 2 feet from the BBO, so the beam was slightly displaced to the right on the irises.)  The tilt of the the BBO was kept constant for the rest of the polarization interferometer.  The B lens was then moved to the center of the track and an iris was placed such that the beam passed through the center.
-     The Beam Displacement Prism (BDP) closer to the collection lens was added to the center of the track.  This is the BDP with the picomotor on the horizontal tilt.  The BDP transmits one polarization and displaces the other about 4 mm to the right (not to the left like the illustration on the BDP suggests), so the position of the BDP was moved so the beam entered the left half of the calcite.  The horizontal and vertical tilt were adjusted to set the surface of the BDP orthogonal to the beam by aligning the back-scattered radiation from the BDP through the center of the iris.  The  process of adjusting the position of the BDP and aligning the back-scattered radiation was iterated until the beams passed the through the calcite without hitting the mount on the front or back of the BDP.  A mount was constructed to keep the red part of the picomotor fixed in place.
+The Beam Displacement Prism (BDP) closer to the collection lens was added to the center of the track.  This is the BDP with the picomotor on the horizontal tilt.  The BDP transmits one polarization and displaces the other about 4 mm to the right (not to the left like the illustration on the BDP suggests), so the position of the BDP was moved so the beam entered the left half of the calcite.  The horizontal and vertical tilt were adjusted to set the surface of the BDP orthogonal to the beam by aligning the back-scattered radiation from the BDP through the center of the iris.  The  process of adjusting the position of the BDP and aligning the back-scattered radiation was iterated until the beams passed the through the calcite without hitting the mount on the front or back of the BDP.  A mount was constructed to keep the red part of the picomotor fixed in place.
-     The displaced beam (the one on the right) was pointed towards the center of the BBO crystal by adjusting the position of the collection lens orthogonal to the optical axis to pass through the center of two irises placed one and two feet from the BBO.  The BDP was checked to make sure the beam passed through without clipping the edges.
+The displaced beam (the one on the right) was pointed towards the center of the BBO crystal by adjusting the position of the collection lens orthogonal to the optical axis to pass through the center of two irises placed one and two feet from the BBO.  The BDP was checked to make sure the beam passed through without clipping the edges.
-     A Polarizing Beam Splitting cube (PBS) was placed perpendicular between collection lens B and the third iris.  The green sticker was oriented toward detector B.  One of the beams emerging from the BDP appeared much lighter due to the PBS decreasing the intensity of one of the beams.  A half wave plate set to 22.5° was added between the iris and the BDP to rotate the polarization 45°.  The half wave plate was placed perpendicular to the alignment beam.
+A Polarizing Beam Splitting cube (PBS) was placed perpendicular between collection lens B and the third iris.  The green sticker was oriented toward detector B.  One of the beams emerging from the BDP appeared much lighter due to the PBS decreasing the intensity of one of the beams.  A half wave plate set to 22.5° was added between the iris and the BDP to rotate the polarization 45°.  The half wave plate was placed perpendicular to the alignment beam.
-     A half wave plate rotated 45°  was placed perpendicular to the beams behind the BDP to change  the polarization of each beam by 90°.  This was done so the path length difference would be approximately equal when the beams converge in the second BDP.
+A half wave plate rotated 45°  was placed perpendicular to the beams behind the BDP to change  the polarization of each beam by 90°.  This was done so the path length difference would be approximately equal when the beams converge in the second BDP.
-     A BDP  placed in a kinematic mount was added behind the second half wave plate to make the beams converge.  The beams passed through the BDP with minimal clipping on both sides and aligned parallel to the other BDP by making the back-scattered radiation pass through the center of the iris closest to the collection lens.  A third half wave plate was added after the BDP and set to 22.5° to rotate the polarization another 45°,  so the beam entering and exiting the polarizer would  shifted a total of 180°.
+A BDP  placed in a kinematic mount was added behind the second half wave plate to make the beams converge.  The beams passed through the BDP with minimal clipping on both sides and aligned parallel to the other BDP by making the back-scattered radiation pass through the center of the iris closest to the collection lens.  A third half wave plate was added after the BDP and set to 22.5° to rotate the polarization another 45°,  so the beam entering and exiting the polarizer would  shifted a total of 180°.
-     An interference pattern was observed with the alignment laser by placing  a horizontal polarizer and screen between the BBO & half wave plate.  The horizontal tilt of the BDP closest to the collection lens was adjusted with a picomotor to observe interference on the screen.  The size of the fringes were comparable to the spot size of the beam, so it was difficult to observe the interference unless the tilt was varied.  The picomotor was used to make a darker spot on the screen and the contrast was maximized by slightly changing the angle (on the order of a few degrees) of each half wave plate such that the intensity on the dark fringe was minimized.
+An interference pattern was observed with the alignment laser by placing  a horizontal polarizer and screen between the BBO & half wave plate.  The horizontal tilt of the BDP closest to the collection lens was adjusted with a picomotor to observe interference on the screen.  The size of the fringes were comparable to the spot size of the beam, so it was difficult to observe the interference unless the tilt was varied.  The picomotor was used to make a darker spot on the screen and the contrast was maximized by slightly changing the angle (on the order of a few degrees) of each half wave plate such that the intensity on the dark fringe was minimized.
-     The alignment laser was disconnected from B and connected to B'.  The B' detector was translated parallel to the signal beam to make the alignment laser go through the iris between the PBS and polarizing interferometer.  The horizontal and vertical tilt of the collection lens were adjusted to make the alignment laser go through the interferometer.  This process was iterated until the beam passed through the center of all three irises.
+The alignment laser was disconnected from B and connected to B'.  The B' detector was translated parallel to the signal beam to make the alignment laser go through the iris between the PBS and polarizing interferometer.  The horizontal and vertical tilt of the collection lens were adjusted to make the alignment laser go through the interferometer.  This process was iterated until the beam passed through the center of all three irises.
-     With the lights out, FPGA, violet laser, SPCM, and labview running, the horizontal tilt of the BDP closer to the collection lenses was slowly adjusted with a picomotor.  Interference was not observed, so the angle of the 45 degree half wave plate (with respect to the signal beam) was adjusted to make sure it was perpendicular to the signal beam, and the orientation angle of the BDP closer to the BBO was varied by a degree at a time, scanning over the horizontal range each time.  When interference was observed, the BDP closer to the collection lens was rotated to 355°, while the BDP closer to the BBO was near 2°.
+With the lights out, FPGA, violet laser, SPCM, and labview running, the horizontal tilt of the BDP closer to the collection lenses was slowly adjusted with a picomotor.  Interference was not observed, so the angle of the 45 degree half wave plate (with respect to the signal beam) was adjusted to make sure it was perpendicular to the signal beam, and the orientation angle of the BDP closer to the BBO was varied by a degree at a time, scanning over the horizontal range each time.  When interference was observed, the BDP closer to the collection lens was rotated to 355°, while the BDP closer to the BBO was near 2°.
 == Double Slit and the Quantum Eraser ==

← Older revision		Revision as of 19:25, 28 August 2015
Line 30:		Line 30:

	Measurement of photon counts over time at an array of photodetectors can be analyzed for their degree of correlation. Positive, zero, and anti-correlations at the detectors all play a very important role in claiming the nature of the electric field present in the chosen experiment. The constraints on g2 being 0 < g2 ≤ 1 for a quantum mechanical field and g2 ≥ 1 for a classical electric field are determined by analyzing the ratios for the 2-detector and 3-detector schemes for our chosen experiments. To understand this in the context of the experiment, please see the results section.		Measurement of photon counts over time at an array of photodetectors can be analyzed for their degree of correlation. Positive, zero, and anti-correlations at the detectors all play a very important role in claiming the nature of the electric field present in the chosen experiment. The constraints on g2 being 0 < g2 ≤ 1 for a quantum mechanical field and g2 ≥ 1 for a classical electric field are determined by analyzing the ratios for the 2-detector and 3-detector schemes for our chosen experiments. To understand this in the context of the experiment, please see the results section.
		+
		+	== Single Photon Interference and the Polarization Interferometer ==
		+	Polarization interferometer info and help:

	== Double Slit and the Quantum Eraser ==		== Double Slit and the Quantum Eraser ==

← Older revision		Revision as of 20:45, 20 July 2015
Line 8:		Line 8:
	== Overview ==		== Overview ==

−	Spontaneous parametric downconversion (SPDC) is a non-linear optical process that takes place with the assistance of specially-engineered optical crystals. These optical crystals are designed with specific index of refraction properties along given crystalline axis. When light of a specific frequency is incident upon the lattice, it will ~~experience preferential absorption and re-emission as~~ a ~~result of this design~~. This will result in an overall "splitting" of one incident light beam into two beams, a "signal" and an "idler" beam, at some well-defined angle with respect to the optical input axis (serving as the zero). The quanta of light will experience a downconversion but within this the momentum and energy of the beam is conserved in the signal and idler beams. See figure 1 for an illustration, below for a simplified explanation, and the WikiPedia article for maximum detail.[http://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion].	+	Spontaneous parametric downconversion (SPDC) is a non-linear optical process that takes place with the assistance of specially-engineered optical crystals. These optical crystals are designed with specific index of refraction properties along given crystalline axis. When light of a specific frequency is incident upon the lattice, it will undergo a parametric downconversion process. This will result in an overall "splitting" of one incident light beam into two beams, a "signal" and an "idler" beam, at some well-defined angle with respect to the optical input axis (serving as the zero). The quanta of light will experience a downconversion but within this the momentum and energy of the beam is conserved in the signal and idler beams. See figure 1 for an illustration, below for a simplified explanation, and the WikiPedia article for maximum detail.[http://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion].

@@ Line 81: / Line 81: @@
 === Quantum Eraser ===
-Here is where we actually set up the experiment to determine certain characteristics of light, namely the concept of entanglement. We started by placing the interferometer into the signal leg of the system that we had already had in place. We followed the procedure lined up in the Beck book but we still found it to be an incredibly difficult task to align the interferometer correctly. We broke the whole procedure down and found that both the B and B' sensors should be placed on translation stages for easier access. It takes a very large amount of patient in order to setup and odds are since this is on such a small scale that you will have to repeat the procedure many times in order to see any sort of intrference pattern by altering one of the Beam Displacing Prisms (BDP) and watching the spot get brighter and dimmer as the angle changes. Once properly aligned the alignment laser can be taken out of the setup and then the actual laser diode can be turned on (after lights out procedure) and then you can view the interference pattern that was visually seen now by the photon counts. they should gradually fluctuate such as what is shown below. If properly aligned the B and B' counts should be symmetrical but some issues arose and the interferometer was not competely aligned.
+Here is where we actually set up the experiment to determine certain characteristics of light, namely the concept of entanglement. We started by placing the interferometer into the signal leg of the system that we had already had in place. We followed the procedure lined up in the Beck book but we still found it to be an incredibly difficult task to align the interferometer correctly. We broke the whole procedure down and found that both the B and B' sensors should be placed on translation stages for easier access. It takes a very large amount of patient in order to setup and odds are since this is on such a small scale that you will have to repeat the procedure many times in order to see any sort of intrference pattern by altering one of the Beam Displacing Prisms (BDPs) and watching the spot get brighter and dimmer as the angle changes. Once properly aligned the alignment laser can be taken out of the setup and then the actual laser diode can be turned on (after lights out procedure) and then you can view the interference pattern that was visually seen now by the photon counts. they should gradually fluctuate such as what is shown below. If properly aligned the B and B' counts should be symmetrical but some issues arose and the interferometer was not competely aligned.
 [[File:Bcounts.jpg|x350px|thumb|center|alt=B detector counts.|]]
 [[File:B'counts.jpg|x350px|thumb|center|alt=B' detector counts.|]]
 = External Resources =