Experiments with Polarized Light - Laptörténet

Halbritt, 2017. szeptember 17., 05:39-n

2017-09-17T05:39:20Z

Halbritt: /* Measurement Tasks */

2017-09-17T05:36:58Z

‎Measurement Tasks

Halbritt: /* Measurement Tasks */

2017-09-17T05:36:00Z

‎Measurement Tasks

Halbritt, 2017. szeptember 17., 05:30-n

2017-09-17T05:30:56Z

Halbritt: /* Investigation of Liquid Crystal Displays */

2017-09-17T05:02:08Z

‎Investigation of Liquid Crystal Displays

Halbritt, 2017. szeptember 17., 04:54-n

2017-09-17T04:54:48Z

Halbritt: /* Liquid Crystals */

2017-09-17T04:51:19Z

‎Liquid Crystals

Halbritt: /* Liquid Crystals */

2017-09-17T04:50:45Z

‎Liquid Crystals

Halbritt, 2017. szeptember 17., 04:47-n

2017-09-17T04:47:22Z

Halbritt, 2017. szeptember 17., 04:41-n

2017-09-17T04:41:33Z

@@ 63. sor: / 63. sor: @@
 </wlatex>
 ===Measurement Tasks===
-During the measurements a commercial 2 digit liquid crystal display is studied (Fig. 4.) such that the driving voltage is applied to all segments in parallel. The measurements are performed both by white and laser light. In the latter case '''be very careful not to look into the laser beam directly! Note, that there are also beams reflected by the polarizers or other optical elements!'''
+During the measurements a commercial 2 digit liquid crystal display is studied (Fig. 4.) such that the driving voltage is applied to all segments in parallel. The original polarizers of the display are removed, and replaced by rotatable polarizers. The measurements are performed both by white and laser light. In the latter case '''be very careful not to look into the laser beam directly! Note, that there are also beams reflected by the polarizers or other optical elements!'''
 #Assemble the optical setup with a white light source, the two polarizers, the LC cell, a lense and a screen. Project the image of the LC cell to the screen.

@@ 63. sor: / 63. sor: @@
 </wlatex>
 ===Measurement Tasks===
-During the measurements a commercial 2 digit liquid crystal display is studied (Fig. 4.) such that the driving voltage is applied to all segments in parallel. The measurements are performed both by white and laser light. In the latter '''case be very careful not to look into the laser beam bdirectly by your eyes. Note, that there are also beams reflected by the polarizers or other optical elements!'''
+During the measurements a commercial 2 digit liquid crystal display is studied (Fig. 4.) such that the driving voltage is applied to all segments in parallel. The measurements are performed both by white and laser light. In the latter case '''be very careful not to look into the laser beam directly! Note, that there are also beams reflected by the polarizers or other optical elements!'''
 #Assemble the optical setup with a white light source, the two polarizers, the LC cell, a lense and a screen. Project the image of the LC cell to the screen.

@@ 63. sor: / 63. sor: @@
 </wlatex>
 ===Measurement Tasks===
 #Assemble the optical setup with a white light source, the two polarizers, the LC cell, a lense and a screen. Project the image of the LC cell to the screen.
 #Study the image of the LC cell at crossed and parallel polarizer directions. Investigate the image as the angle between the LC cell and the polarizer is rotated, such that the analyzer is always perpendicular/parallel to the polarizer. Discuss the observations!

←Régebbi változat		A lap 2017. szeptember 17., 05:30-kori változata
62. sor:		62. sor:

	</wlatex>		</wlatex>
		+	===Measurement Tasks===
		+	#Assemble the optical setup with a white light source, the two polarizers, the LC cell, a lense and a screen. Project the image of the LC cell to the screen.
		+	#Study the image of the LC cell at crossed and parallel polarizer directions. Investigate the image as the angle between the LC cell and the polarizer is rotated, such that the analyzer is always perpendicular/parallel to the polarizer. Discuss the observations!
		+	#Repeat the previous task by gradually increasing the voltage on the LC cell. Always apply an a.c. voltage with ~100Hz frequency from a function generator, a d.c. voltage could destroy the cell. The voltage amplitude should not exceed 7V.
		+	#To quantify the above experiments repeat them with a laser as the light source and a light sensor. (In this case the lense should be excluded.)
		+	#Study the transmitted light intensity at zero driving voltage as a function of the angle between the LC cell and the polarizer. (In all cases keep the perpendicular/parallel orientation between the polarizer and the analyzer)
		+	#Set the TN mode, and study the optical transmission as a function of the driving voltage amplitude. Determine the electro-optical switching slope.
		+	#Set the polarizers such, that the vertical axis of the LC cell is in 45<sup>o</sup> angle with respect to the polarizer. The analyzer should be perpendicular/parallel to the polarizer. Study the transmission as a function of driving amplitude, and try to understand the observations!

@@ 36. sor: / 36. sor: @@
 {|  cellpadding="5" cellspacing="5" align="center"
-| align="center"|[[Fájl:LC_cell.jpg|közép|400px]]
+| align="center"|[[Fájl:LC_cell.jpg|közép|500px]]
 |-
-| align="center" style="width: 900px;"|Fig. 2. ''90<sup>o<sup> TN LC cell''
+| align="center" style="width: 900px;"|Fig. 2. ''90<sup>o</sup> TN LC cell''
 |}

@@ 24. sor: / 24. sor: @@
 {|  cellpadding="5" cellspacing="5" align="center"
-| align="center"|[[Fájl:LC_cell_structure.jpg|közép|700px]]
+| align="center"|[[Fájl:LC_cell_structure.jpg|közép|400px]]
 |-
 | align="center" style="width: 900px;"|Fig. 1. ''LC cell structure''
@@ 34. sor: / 34. sor: @@
 parallel to the transmission axis of the polarizer. An incident unpolarized light is converted
 into a linearly polarized light by the front polarizer.
 When a linearly polarized light traverses through a 90<sup>o</sup> TN cell, its polarization
@@ 48. sor: / 54. sor: @@
 $V_{90}$ are the applied voltages enabling output light signal reaches up to 10% and 90% of its
 maximum light intensity, respectively.
 </wlatex>

@@ 22. sor: / 22. sor: @@
 (optical anisotropy) is defined as the difference between the extraordinary and the ordinary
 indices of refraction $\Delta n=n_e - n_o$.
 ===90<sup>o</sup> Twisted Nematic LC Cell===

@@ 24. sor: / 24. sor: @@
 ===90<sup>o</sup> Twisted Nematic LC Cell===
-In the 90o twisted nematic (TN) cell shown in Fig. 8, the LC director of the back
+In the 90<sup>o</sup> twisted nematic (TN) cell shown in Fig. 2, the LC director of the back
-surface is twisted 90o with respect to the front surface. The front local director is set
+surface is twisted 90<sup>o</sup> with respect to the front surface. The front local director is set
 parallel to the transmission axis of the polarizer. An incident unpolarized light is converted
 into a linearly polarized light by the front polarizer.
-When a linearly polarized light traverses through a 90o TN cell, its polarization
+When a linearly polarized light traverses through a 90<sup>o</sup> TN cell, its polarization
-follows the twist of the LC directors (polarized light sees ne only) so that the output beam
+follows the twist of the LC directors (polarized light sees $n_e$ only) so that the output beam
-remains linearly polarized except for that its polarization axis is rotated by 90o (it’s called
+remains linearly polarized except for that its polarization axis is rotated by 90<sup>o</sup> (it’s called
-the polarizing rotary effect by ne; similarly we can also find polarizing rotary effect by no).
+the polarizing rotary effect by $n_e$; similarly we can also find polarizing rotary effect by $n_o$).
-Thus, for a normally black (NB) mode using a 90o TN cell, the analyzer’s (a second
+Thus, for a normally black (NB) mode using a 90<sup>o</sup> TN cell, the analyzer’s (a second
 polarizer) transmission axis is set to be parallel to the polarizer’s transmission axis, as
-shown in Fig. 9. However, when the applied voltage V across the LC cell exceeds a critical
+shown in Fig. 3. However, when the applied voltage V across the LC cell exceeds a critical
-value Vc, the director of LC molecules tends to align along the direction of applied external
+value $V_c$, the director of LC molecules tends to align along the direction of applied external
 electrical field which is in the direction of the propagation of light. Hence, the polarization
 guiding effect of the LC cell is gradually diminishing and the light leaks through the
-analyzer. Its electro-optical switching slope γ is defined as (V90–V10)/V10, where V10 and
+analyzer. Its electro-optical switching slope $\gamma$ is defined as $(V_{90}–V_{10})/V_{10}$, where $V_{10}$ and
-V90 are the applied voltages enabling output light signal reaches up to 10% and 90% of its
+$V_{90}$ are the applied voltages enabling output light signal reaches up to 10% and 90% of its
 maximum light intensity, respectively.
 </wlatex>