Terahertz Electromagnetic Wave Detection - Revision history

Shizhuo: /* LN-based THz pulse generation */

2025-04-29T15:10:25Z

LN-based THz pulse generation

← Older revision		Revision as of 23:10, 29 April 2025
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	'''Phase Match Condition'''		'''Phase Match Condition'''

	We assume that an electromagnetic wave goes in the direction with an angle <math>\epsilon</math> between z axis. The electric field is given as:		The susceptibility of LN-generated THz wave is basically <math>d_{33}</math>. Now we introduce the theory of the THz generation. We assume that an electromagnetic wave goes in the direction with an angle <math>\epsilon</math> between z axis. The electric field is given as:

	<math>E(t)=\int E(\omega) e^{i\omega t-ikz\cdot\cos\epsilon-ikx\cdot\sin\epsilon} d\omega=\int E(\omega) e^{i\omega t-i\varphi} d\omega</math>		<math>E(t)=\int E(\omega) e^{i\omega t-ikz\cdot\cos\epsilon-ikx\cdot\sin\epsilon} d\omega=\int E(\omega) e^{i\omega t-i\varphi} d\omega</math>

Shizhuo: /* Results with the thermopile sensor */

2025-04-29T15:08:44Z

Results with the thermopile sensor

← Older revision		Revision as of 23:08, 29 April 2025
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	2. After positioning black polyplastics correctly, the heat effect would result in a heat effect of about 1 mW.		2. After positioning black polyplastics correctly, the heat effect would result in a heat effect of about 1 mW.

	However, the strong heat effect and the scattered light hindered the optimisation, because these signals are also position-dependent. It took an unexpectedly long time to solve it. Though it is still challenging, we believe that Terahertz wave may be detected in another way.		However, the strong heat effect and the scattered light hindered the optimisation, because these signals are also position-dependent. Thus, they satisfied parts of the criteria and were so confusing that it took an unexpectedly long time to solve it. We tried to block them but we haven't made it so far. Though it is still challenging, we believe that Terahertz wave may be detected in another way.

	==Conclusion & Discussion==		==Conclusion & Discussion==

Shizhuo: /* Conclusion & Discussion */

2025-04-29T15:04:41Z

Conclusion & Discussion

← Older revision		Revision as of 23:04, 29 April 2025
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	3. Thermopile sensor was reported to detect the terahertz wave. However, the scattered light and heated housing temporarily prevent us to realise a terahertz wave detection in LN-based terahertz generation system.		3. Thermopile sensor was reported to detect the terahertz wave. However, the scattered light and heated housing temporarily prevent us to realise a terahertz wave detection in LN-based terahertz generation system.

	4. The EO sampling system is promising in THz spectroscopy with a good SNR of 30 dB.		4. The EO sampling system also has promising potential in THz spectroscopy with a good SNR of 30 dB. Time-resolved THz spectroscopy is also a significant detection system in condensed matter research.

	5. Though we didn't detect the terahertz wave within the time of the course, we believe our criteria are solid. Thus, we will keep trying to finish the thermopile sensor part after the course.		5. Though we didn't detect the terahertz wave within the time of the course, we believe our criteria are solid. Thus, we will keep trying to finish the thermopile sensor part after the course.

Shizhuo: /* Conclusion & Discussion */

2025-04-29T15:03:19Z

Conclusion & Discussion

← Older revision		Revision as of 23:03, 29 April 2025
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	2. We demonstrated that the SNR is approximately 30 dB given a maximum electric field of Terahertz wave ranging from 0.2 kV/cm to 3 kV/cm.		2. We demonstrated that the SNR is approximately 30 dB given a maximum electric field of Terahertz wave ranging from 0.2 kV/cm to 3 kV/cm.

	3.		3. Thermopile sensor was reported to detect the terahertz wave. However, the scattered light and heated housing temporarily prevent us to realise a terahertz wave detection in LN-based terahertz generation system.

			4. The EO sampling system is promising in THz spectroscopy with a good SNR of 30 dB.

			5. Though we didn't detect the terahertz wave within the time of the course, we believe our criteria are solid. Thus, we will keep trying to finish the thermopile sensor part after the course.

	==Source for Codes==		==Source for Codes==

Shizhuo: /* Results with the thermopile sensor */

2025-04-29T14:59:16Z

Results with the thermopile sensor

← Older revision		Revision as of 22:59, 29 April 2025
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	===Results with the thermopile sensor===		===Results with the thermopile sensor===

	In the thermopile sensor experiments, we tried to measure the Terahertz wave with thermopile sensors. As we have demonstrated that there should be Terahertz pulses, we could thereby tried to showcase the ability of thermopile sensors via further optimisation of the setup to reach a maximum generation efficiency from a series of experiments.		In the thermopile sensor experiments, we tried to measure the Terahertz wave with thermopile sensors. As we have demonstrated that there should be Terahertz pulses, we could thereby tried to showcase the ability of thermopile sensors via further optimisation of the setup to reach a maximum generation efficiency from a series of experiments. Not only could this show that we detected the Terahertz wave, but also could help us determine the resolution of this method.

	Since the thermopile sensor can also detect the NIR and the second harmonic generation laser (515 nm) from LN crystal, we should put a filter to block the light with other wavelengths. Here, we chose the black polyplastics which was recommended as a high transmission rate material for THz wave.[6] Though silicon plate is a widely used filter that blocks NIR and visible light in Terahertz generation experiments, we didn't use it in this experiment. It can hardly fully block the intense input pulses, which could be a server problem in our experiment. The signals of NIR and Terahertz wave could mix up when the unoptimised Terahertz wave signal could be sufficiently small (<0.1 mW). Also, since the refractive index of silicon in terahertz range is about 3.4 [7], almost half of the terahertz wave would be reflected according to the Fresnel equations.		Since the thermopile sensor can also detect the NIR and the second harmonic generation laser (515 nm) from LN crystal, we should put a filter to block the light with other wavelengths. Here, we chose the black polyplastics which was recommended as a high transmission rate material for THz wave.[6] Though silicon plate is a widely used filter that blocks NIR and visible light in Terahertz generation experiments, we didn't use it in this experiment. It can hardly fully block the intense input pulses, which could be a server problem in our experiment. The signals of NIR and Terahertz wave could mix up when the unoptimised Terahertz wave signal could be sufficiently small (<0.1 mW). Also, since the refractive index of silicon in terahertz range is about 3.4 [7], almost half of the terahertz wave would be reflected according to the Fresnel equations.
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	2. After positioning black polyplastics correctly, the heat effect would result in a heat effect of about 1 mW.		2. After positioning black polyplastics correctly, the heat effect would result in a heat effect of about 1 mW.

	However, the strong heat effect and the scattered light hindered the optimisation, because these signals are also position-dependent.		However, the strong heat effect and the scattered light hindered the optimisation, because these signals are also position-dependent. It took an unexpectedly long time to solve it. Though it is still challenging, we believe that Terahertz wave may be detected in another way.

	==Conclusion & Discussion==		==Conclusion & Discussion==

Shizhuo: /* Reference */

2025-04-29T14:56:19Z

Reference

← Older revision		Revision as of 22:56, 29 April 2025
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	[7] Herrmann, Michael, et al. "Terahertz imaging of silicon wafers." Journal of Applied Physics 91.3 (2002): 1247-1250.		[7] Herrmann, Michael, et al. "Terahertz imaging of silicon wafers." Journal of Applied Physics 91.3 (2002): 1247-1250.

			[8] Fülöp, J. A., et al. "Design of high-energy terahertz sources based on optical rectification." Optics express 18.12 (2010): 12311-12327.

Shizhuo: /* LN-based THz pulse generation */

2025-04-29T14:55:56Z

LN-based THz pulse generation

← Older revision		Revision as of 22:55, 29 April 2025
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	'''Optimisation of the system'''		'''Optimisation of the system'''

	The parameters of the system shall be well optimised. Here, ~~we propose~~ 3 rules in the optimisation.		The parameters of the system shall be well optimised. Here, there are 3 rules in the optimisation [8].

	1. All wavelengths of the beam should focus on one spot in the crystal, so the lens shall image the grating in the crystal.		1. All wavelengths of the beam should focus on one spot in the crystal, so the lens shall image the grating in the crystal.

Shizhuo: /* LN-based THz pulse generation */

2025-04-29T14:54:06Z

LN-based THz pulse generation

← Older revision		Revision as of 22:54, 29 April 2025
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	<math>		<math>
			\tan\gamma=-\frac{n_0\Theta}{g}\sin\theta_d
			</math>

	\tan\gamma=-\frac{\Theta~~}{g~~}\~~sin~~\theta_d		<math>
			\tan\gamma=-\frac{1}{n_0\Theta}\tan\theta_d
			</math>

	\~~tan~~\~~gamma~~=-\frac{1}{\~~Theta~~}\~~tan\theta_d~~		By solving these 2 equations, we can give the optimised parameters: angular magnification of the telescope <math>\Theta\approx0.53</math> and diffraction angle <math>\theta_d\approx59.4^\text{o}</math>. Here, a defined factor <math>g=\frac{n_g}{p n_0\lambda_0}</math>, where <math>n_g</math>, <math>n_0</math>, <math>p</math>, and <math>\lambda_0</math> are respectively group and phase refractive indices, groove density, and central wavelength of the laser.


	</math>

	===Electro-Optical Sampling===		===Electro-Optical Sampling===

Shizhuo: /* LN-based THz pulse generation */

2025-04-29T14:49:04Z

LN-based THz pulse generation

← Older revision		Revision as of 22:49, 29 April 2025
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	<math>		<math>

	\tan\gamma		\tan\gamma=-\frac{\Theta}{g}\sin\theta_d

			\tan\gamma=-\frac{1}{\Theta}\tan\theta_d


	</math>		</math>

Shizhuo: /* LN-based THz pulse generation */

2025-04-29T14:47:48Z

LN-based THz pulse generation

← Older revision		Revision as of 22:47, 29 April 2025
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	where a rotation of <math>\gamma</math> in <math>x-z</math> plane is imposed. The term <math>e^{i\frac{\Omega}{v_g\cos\gamma}z-i\frac{\Omega}{v_\text{THz}}z}</math> represents the phase mismatch.		where a rotation of <math>\gamma</math> in <math>x-z</math> plane is imposed. The term <math>e^{i\frac{\Omega}{v_g\cos\gamma}z-i\frac{\Omega}{v_\text{THz}}z}</math> represents the phase mismatch.

	~~‘’‘Optimisation~~ of the ~~system’‘’~~		'''Optimisation of the system'''

	The parameters of the system shall be well optimised. Here, we propose 3 rules in the optimisation.		The parameters of the system shall be well optimised. Here, we propose 3 rules in the optimisation.
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	3. The tilt pulse front <math>\gamma\approx 63.4^\text{o}</math>.		3. The tilt pulse front <math>\gamma\approx 63.4^\text{o}</math>.

	Hence, the rules ~~gives~~ 2 equations.		Hence, the rules give 2 equations.

	<math>		<math>

			\tan\gamma

	</math>		</math>