Tóm tắt: Xây dựng hệ nghiên cứu tính chất quang của nguyên tử Rubi.

MINISTRY OF EDUCATION AND TRAINING
VINH UNIVERSITY
----------

NGUYEN VAN AI

ESTABLISHMENT OF THE SYSTEM TO
INVESTIGATE OPTICAL PROPERTIES
OF THE ATOMIC RUBIDIUM
Specialization: OPTICS
Code: 9440110

ABSTRACT OF DOCTORAL THESIS IN PHYSIC

NGHỆ AN, 2022


The work is accomplished at Vinh University

Adviser:

Reviewer 1:

Prof. Dr. Nguyen Huy Bang

………………………………………
……………………………………...

Reviewer 2:

………………………………………

……………………………………...

Reviewer 3:

………………………………………
……………………………………...

The thesis was defended before the doctoral admission board of
Vinh University at ….....h…....., …...., …...., 2022

The thesis can be found at:
- Nguyen Thuc Hao Information – Library Centre, Vinh University
- Viet Nam National Library


1
PREFACE
1. Reason to choice the investigation subject
Spectroscopy is a scientific field that was born a long ago and is associated with important
milestones in the history of physic development. The development of modern methods and
spectrophotometers has gradually elucidated the microstructure of atoms/molecules to the superfine level.
Design and construction of modern experimental systems to study ultra-high-resolution spectral structures
and study atomic optical properties are topics that are always of interest to domestic and international
scientists.
Currently, high-resolution spectroscopy techniques such as saturation absorption spectroscopy
(SAS) [1]–[4], combined excitation spectroscopy [3], [4] and polarization spectroscopy techniques are
available [4] is used to determine the hyperfine transition of atoms/molecules. Thereby, helping us to
understand the atomic structure with high precision, so that we can easily manipulate and control them and
serve as the basis for the formation of new theories. Such as laser cooling and trapping of atoms [5]–[9] or
create new materials with special properties such as Electromagnetically Induced Transparency (EIT) [10]–

[20] . This material is formed by the quantum interference between the displacement probability amplitudes
of the quantum states inside the atom under the simultaneous action of the laser fields.
Typical optical properties of EIT materials include: transparency at resonant frequency, giant Kerr
nonlinearity [10], [13], [15], [21]–[26], dispersion rate is extremely large, so the group velocity of the
photon is extremely small [27]–[32]. In particular, we can control the aforementioned intrinsic properties
of atoms external laser. With these outstanding properties, EIT materials are expected to create many
important applications. For example, using EIT materials for light storage [33]–[38], optical bistabilization
and optical switching [39]–[43] (a fundamental element for modern optical information processors) will
have a sensitivity several million times higher than using traditional Kerr nonlinear materials. Furthermore,
since the Kerr nonlinear coefficient of EIT materials can be controlled in both magnitude and sign, we can
control the optical bistable and all-optical switching characteristics, in other words, the application of This
will create active optical switches.
The basic model for creating EIT materials is based on the association between the three hyperfine
states of the atom and two laser fields (in which one laser acts as a driver), so the basic configuration of
EIT are atomic systems with three energy levels (lambda, V, and ladder configuration). Under the action
of the pump laser beam, the medium becomes transparent with the laser beam detecting at a certain
frequency domain (called the transparent window or the EIT window). Although three-energy EIT materials
have been widely applied to modern photonic devices [40], [44], this material has only a narrow transparent
spectral domain, so the active domain of these devices is limited confined to a small frequency domain.
Therefore, finding a solution to increase the number of transparent windows of EIT materials has been of
interest in scientists today. One of the solutions proposed by many scientists is to use atomic systems with
close hyperfine states [26], [43], [45], [46], such as alkali metal atom. At that time, a laser field can


2
simultaneously link many hyperfine transitions close together, so it is possible to create many transparent
windows.
Besides the EIT effect, ultra-high-resolution spectroscopy can make it easier to observe the
Macaluso-Corbino effect (also known as the optical-magneto effect). This effect was first discovered by
scientist Faraday when shining light through a solid medium and a liquid crystal medium [47], [48]. Then

two scientists Macaluso-Corbino observed the rotational effect of the plane of polarization of the light beam
travelling through the atomic gas medium and showed that the rotation angle depends on the frequency and
intensity of the laser beam [49], [49]. 50]. Recently, the optical-magneto effect has also received a lot of
research attention [51]–[54] because it has many useful applications such as light modulation,
supersensitive magnetometer [55]–[57] ], etc
In foreign countries, there have recently been some experimental studies on the effect of multiwindow EIT/EIA transparency. For example, in 2014 Kang Ying and colleagues observed seven EIT
windows in a V-configured Rubi atom when two laser beams pumped and probed in the same direction
[45]. In 2015, Dipankar Bhattacharyya and colleagues observed five velocity-selectively induced
absorption (EIA) peaks, in the six-energy lambda configuration of the Rubi atom [58]. Then, Bo-Xun Wang
and co-workers integrated a Mach-Zehnder interferometer to observe the group refractive index of the
atomic Rubidium vapour medium [26]. In 2017, Khairul Islam and colleagues observed six EIA absorption
peaks, in the V-shaped five-level atomic system of the Rb atom [59]. The experimental observations in the
above works are in good agreement with the theoretical model. However, the obtained spectral signals are
not really clear and other investigations have not been exploited.
In the country, besides the successes in theoretical research on the EIT effect and related
applications, our group has also successfully built an experimental system to observe the electromagnetic
induced transparent spectrum of atomic gas Rb at room temperature [23], [60]. The advantage of this
experimental system is that the EIT spectrum and EIT dispersion spectrum have been observed with three
perfect transparent windows (transparency is close to 100%). However, this experimental system also has
the disadvantage that the installation is spread out and not flexible, the stability is not high, so some EIT
spectral lines have not been observed and it is difficult to perform related experiments requiring high
sensitivity. as high as Kerr nonlinearity and optical bistable.
Therefore, the design and construction of a high-resolution spectral experimental system with
compact size, high stability, and low cost, which integrates research into many atomic optical properties
and related applications is becoming a challenge. wishes of research groups in the country and around the
world. With the desire to build such an experimental system, we chose the topic “Establishment of the
system to investigate optical properties of the atomic Rubidium” as our doctoral thesis.
In this experimental system, we use the Rubi atom for the following reasons: The First is the energy
level structure of the Rubi atom have transition frequencies consistent with those of the lasers diode is
widely used in the market; The second is the Rb atom of the alkali metal group has one electron in the

outermost shell, so it has a simple energy level structure and a relatively close frequency gap between the


3
energy levels. Therefore, just using a laser beam can easily link many neighbouring displacements; the
Third is the Ruby atom is easily converted to a gas at room temperature, thus making it easy to model.
2. Research objectives
Design and build a high-resolution spectral experimental system, with compact size, high stability,
and low cost, integrating various ultra-high-resolution spectroscopy measurements. From there, use the
experimental system to study the optical properties of the atomic gas Rubidium.
3. Research content
To achieve the set objectives, the content of the thesis focuses on the following issues:
+ Learn about related experimental systems at home and abroad, and understand the advantages
and disadvantages of existing experimental systems. From there, it is proposed to design and build a
versatile experimental system that can investigate many optical properties of the Rubidium vapour medium
based on the EIT effect.
+ Develop a procedure for performing spectral measurements of the Rubi atom.
+ Orientation to develop experimental systems for research-related applications.
4. Research Methodology
- Theory
We rely on the principles of high-resolution spectrometry such as absorption and dispersion
spectroscopy, velocity-selective optical pump spectroscopy, electromagnetic induced transparency
spectroscopy, etc. At the same time, based on the principles of measuring effects related such as group
refractive index, Kerr nonlinear coefficient, optical bistable, etc
Based on semi-classical theory and density matrix formalism to build theoretical models to simulate
research results.
- Experiment
+ Develop the existing experimental system, build an experimental system that can perform many
measurements to study the optical properties of the Rubidium vapour medium.
+ From the data obtained from the measurements, we use data processing software to come up with

an experimental path, thereby analyzing the change in the optical properties of the Rubidium vapour
medium according to the controlled laser parameters.
5. Thesis structure
In addition to the introduction and conclusion, the thesis has three chapters presented as follows:
Chapter I. Principles of high-resolution spectroscopy
In this chapter, we present the principles of high-resolution spectroscopy as a basis for building an
experimental system to study atomic optical properties. Here, we also present the principle of investigating


4
some applications of the electromagnetic induction transparency effect, to guide the construction of a
comprehensive experimental system within the framework of the thesis.
Chapter II. Building an experimental system to study optical properties of the atomic
Rubidium vapour medium
In this chapter, on the basis of some experimental systems on atomic spectrum published in recent
years, through analyzing the advantages and disadvantages of the existing experimental systems. We build
a multifunctional, compact, highly sensitive and stable experimental system that can investigate optical
properties. Based on the existing equipment in the laboratory, design and build an experimental system for
atomic spectroscopy including saturated absorption spectroscopy, saturation dispersion, velocity-selective
optical pump spectroscopy, etc…
Chapter III. Study of the optical properties of atomic gases
In this chapter, we carry out spectral measurements to study the optical properties of the medium
based on the built experimental system. Simultaneously, survey the application measurement models of
optical properties of the Rubidium vapour medium. Thereby, giving parameters and diagram of
measurement principle, as well as additional necessary equipment to develop the built experimental system.

CHAPTER I
PRINCIPLES OF HIGH RESPONSIBILITY spectroscopy
In this chapter, we present the principles of high-resolution spectroscopy such as saturated
absorption spectroscopy and dispersion spectroscopy, velocity-selective optical pump spectroscopy,

electromagnetically induced transparent spectroscopy, group refractive index and nonlinearity Kerr as well
as related effects such as optical stability and all-optical switching. The contents presented in this chapter
are the theoretical basis for building an integrated experimental system to research the optical properties of
atomics, which is present in chapter 2.
1.1. Principle of saturated absorption spectroscopy and dispersion saturated spectroscopy
1.2. Principle of velocity-selective optical pump spectroscopy
The velocity-selective optical pump spectroscopy system uses two laser beams propagating in opposite
directions as shown in Figure 1.6. The first low-intensity laser beam is called the detector laser (DL1). The
frequency of the detector laser is locked at a value close to the resonant shift frequency of the spectral
region to be investigated.

DL2

DL1

Figure 1.1 Schematic diagram of the velocity-selective optical pump spectroscopy.


5

Hình 1.2 velocity selective optical pump spectroscopy of

85

Rb

When the pump laser sweeps through these 6 frequency values, the groups of atoms will
respectively switch to the saturation state, so the absorption coefficient for the probe beam decreases. This
leads to 6 times when the beam intensity increases, so the received signal will be 6 peaks as shown in Figure
1.8. For the 85Rb atom, the window spacing from left to right is 63.40 MHz, respectively; 63.40 MHz;

57.24 MHz; 63.40 MHz; 120.64 MHz.
1.3. Principle of electromagnetic induced transparent spectroscopy
1.4. The Macaluso-Corbino Effect
1.5. Some applications of the EIT medium
1.5.1. Measure the speed of the group of light
1.5.2. Kerr Nonlinear
1.5.3. Optical bistability
1.6. Ruby (Rubidium) atom

Chapter II
BUILDING THE EXPERIMENT SYSTEM
INVESTIGATION OPTICAL PROPERTIES OF THE ATOMIC VAPOUR

In this chapter, we review some experimental systems that measure spectral atoms in the world and
analyze the advantages and disadvantages of the systems. On that basis, we designed and built a compact
experimental system, integrating many different spectral measurements. Which ensures flexibility and ease
of switching between different measurements. The integrated system also need to ensure accuracy and stability
in the measurements.
2.1. Some experimental systems measure spectral atoms in the world


6
2.1.1. The experimental system of Thorlab measures saturated absorption spectroscopy
2.1.2. Experimental system of Teachspin
2.1.3. EIT Experimental system pump-probe V-shaped configuration in the same direction
2.1.4. Experimental system for measuring refractive index of light group
2. 1.5. EIT experiment at Vinh University
2.2. Building a versatile experimental system
2.2.1. General principles
On the basis of analyzing the advantages and disadvantages of the above atomic spectrometer

experimental systems, we design and build an experimental system that can integrate many spectral
measurements. The integrated test system must ensure the following requirements:
+ The path of the light beams is short, minimizing the noise of the Rubidium vapour medium.
+ Multi-function, it could be flexibly switched between measurements.
+ Compact, easy to move.
The experimental system consists of three main parts with a block diagram as shown in Figure 2.13:


Optical parts:
The first part is an optical system consisting of optical devices placed on a table with dimensions

of 45 cm x 60 cm.


Control part: consists of three control modules. Module 1 controls the DL1 laser source of
Teachspin, module 2 controls the DL2 laser source of Moglabs and module 3 controls the
temperature of Thorlabs.

OPTICAL

CONTROL

DISPLAY

Figure 2.1 Block diagram of the compact system.



The parts of Display and storage: The signals received on the three Photodetectors are connected
to a Tektronix electronic oscilloscope. Here the data is recorded with images and digital data.

The layout diagram of optical components on an optical tabletop is shown in Figure 2.14. Here, the position
of the optical devices is arranged so that flexibility can be made between different spectral measurements.


7

Rb

Figure 2.2 Diagram of the arrangement of optical devices on the optical surface of the experiment system investigation
optical properties. M1 – M7: Mirror; S1 – S3: beam shutter; ND1 – ND3: neutral density filter; BS1 – BS6: beam
splitter; FPI: Fabry-Pérot Interferometer ; MZI: Mach-Zehnder Interferometer; P1 – P2: Polarizer; PD1 – PD3 :
Photodetector; DL: Laser diode ; IS: optical isolator .

The system can be used to observe absorption spectroscopy, dispersion spectroscopy, saturated
absorption spectroscopy, saturation dispersion spectroscopy, absorption spectroscopy and dispersion
spectroscopy in the presence of the EIT effect in case both beams are present at the same time. pump in the
same direction and in the opposite direction, the change of light beam polarization when passing through the
atomic gas medium.
2.2.2. Optical parts

Figure 2.3 Arrangement of the devices on the optical surface of the experimental system.
2.2.3. Control unit
2.2.4. Display Parts
2.3. Schematic diagram of spectroscopy measurements


8
2.3.1. Optical diagram to observe absorption and dispersion spectroscopy

Figure 2.4 Optical diagram to observe absorption spectroscopy.

Figure 2.5 Optical diagram to observe dispersion spectroscopy.

2.3.2. Optical diagram observe the saturated absorption and dispersion spectroscopy


9

Figure 2.6 Optical diagram observe the saturated absorption spectroscopy

Figure 2.7 Optical diagram observe the saturated dispersion spectroscopy

2.3.3. Optical diagram observe EIT configuration probe-pump counter-propagating


10

Figure 2.8 Optical diagram observe EIT configuration probe-pump counter-propagating

2.3.4. Optical diagram observe EIT configuration probe-pump co-propagating

Hình 2.9 Optical diagram observe EIT configuration probe-pump co-propagating.

2.3.5. Optical diagram of the EIT observation configuration two pump beam


11

Hình 2.10 Optical diagram observe EIT configuration two pump beam.

2.3.6. Optical diagram to observe the Macaluso-Corbino effect
Chapter III
RESEARCH OF OPTICAL CHARACTERISTICS OF ELECTRIC GAS
In this chapter, we perform atomic spectrometric measurements of Rb with the experimental system
built in chapter 2. Detailed presentation of spectrometric procedures, processing of spectral data and
building of theoretical models to explain the results obtained. At the same time, there is a comparative
evaluation with results from published experimental systems. On the basis of spectral measurement results,
we also propose some development directions of the experimental system to be implemented in the near
future.
3.1. Investigation of absorption and dispersion spectra
3.1.1. Measurement process
Optical diagrams used to investigate the absorption and dispersion spectra are shown in Figure 2.33
and Figure 2.34. When performing absorption and dispersion spectroscopy of the medium, we use the DL1
laser system of TeachSpin. Since the frequency of the laser head depends on the stability of the power
supply parameters, the laser source must be turned on for at least 30 minutes before proceeding with further
operations.
Step 1: Turn on the laser source, increase the current for the laser generator to 2.4 mA (Teachspin's
diode laser emission threshold), and observe the laser beam with the CCD camera, if the laser signal is
bright-dark according, the laser is on work. In the case that the laser beam intensity does not change,
showing that the laser resonator chamber has not satisfied the resonance conditions for laser activate, we


12
need to adjust the rotation angle of the diffraction mirror, find the position to get the maximum resonance
signal (for the laser system we have assembled stably, this process usually does not need to be repeated).
Step 2: Increase the current supply to the DL1 up to 5.26 mA, then the wavelength of the laser will
go to about 780.24 nm, using the CCD camera to observe the fluorescence emission spectrum of the Rubi
atom. Adjust the frequency of the DL1 laser so that the signal displayed on the CCD camera screen is a
continuous flashing light line.
Step 3: When the fluorescence spectrum of the medium corresponding to the wavelength of 780.2

4 nm is observed, adjust the laser beam entering the Fabry- Pérot interferometer so that the received spectral
signal appears the signal interference fringe biggest brand. Adjust the frequency sweep of the laser to a
value of 10 GHz.
Step 4: Adjust the arms of the interferometer so that the beams of the two interference arms after
exiting BS4 coincide, so that the optical path difference is less than 0.5 cm as we argued in Section 1.1.
Step 5: Adjust the intensity of the laser beam. For the detector laser beam, we have to adjust the
laser beam intensity to be less than the saturation intensity Isat = 2 mW/cm2, in this setup we always control
the detector laser beam below 0.1 mW /cm2 to avoid the self-focusing effect of the beam.
Step 6: Connect Photodetector with digital oscilloscope. In this system the Photodetector is set to
a mode with an impedance ranging from 100 K to 1 M depending on the intensity of the detector laser
beam signal.
3.1.2. Absorption and dispersion spectroscopy
3.2. Investigation of saturated absorption and dispersion spectroscopy
3.2.1. Measurement procedure
3.2.2. Saturated absorption spectroscopy and saturated dispersion spectroscopy

Figure 3.1 Saturated absorption spectroscopy (a) and saturated dispersion spectroscopy (b).

The results of the saturated dispersion spectroscopy measurements of the atoms of
87

85

Rb and

Rb are shown in Figure 3.2. We see on the dispersion line, at the position of the saturated absorption

spectral lines, appear normal dispersion domains. Dispersion domains often appear in the
background of anomalous dispersion lines. The slope of the dispersion line at the location of the
hyperfine shifts increases, so that the refractive index of the medium is enhanced.

13
3.3. Investigation of EIT spectroscopy and EIT dispersion spectroscopy configuration pump-probe
counter-propagating
3.3.1. Procedure measure EIT spectroscopy and EIT dispersion spectroscopy
3.3.2. EIT spectroscopy and EIT dispersion spectroscopy, configuration probe-pump counterpropagating

Figure 3.2 Absorption and dispersion spectroscopy of

85

Rb atom in the presence of EIT effect in case the probe beam

2

intensity is equal to 0.07 mW/cm , the associated laser beam intensity is 3 mW /cm2 (a), the dispersion spectroscopy
of the atomic gas 85Rb when reducing the associated laser frequency, all dispersion domains shift to the left by 68
MHz (b).

The EIT spectrum and EIT dispersion are obtained as shown in Figure 3.7. The measurement results
show that the absorption coefficient and refractive index of the medium depend on the intensity and
frequency of the pump laser. We can obtain up to 6 normal dispersion domains in the anomalous dispersion
domain. The measured results are consistent with the previous measurement results.

3.4. Investigation of EIT spectroscopy and dispersion of EIT configuration pump-probe copropagating
3.4.1. Measurement process
3.4.2. The EIT spectroscopy and dispersion of EIT configuration pump-probe co-propagating.

14
Figure 3.3 Absorption ( 1 ) and dispersion ( 2 ) spectra of the 85Rb atom in the presence of the EIT effect.

We see that, on the Doppler line, there are 7 EIT windows, of which three have the largest intensity
corresponding to the shift from right to right of 5S1/2 (F=3) → 5P3/2 (F'=4) of the group of atoms bonded to
5S1/2 (F=3)→5P3/2 (F'=2); 5S1/2 (F=3)→5P3/2 (F'=4) of the group of atoms bonded to 5S1/2 (F=3)→5P3/2 (F'=3)
and 5S1 /2 (F=3)→5P3/2 (F'=3) of the group of atoms bonded to 5S1/2 (F=3)→5P3/2 (F'=2).
3.5. Velocity selective optical pump Spectroscopy
3.5.1. Measurement process
3.5.2. Velocity selective optical pump spectroscopy
In the case of the pump laser beam in the opposite direction of the detector laser, the obtained
spectral image is as shown in Figure 3.9. Here, in case the laser beam is pumped against the detector laser
beam, the number of spectral lines obtained is 6. The distance between the spectral lines is 63.41,
respectively. 1.12 MHz; 63.42 1.12 MHz; 57.36 1.12 MHz; 63.39 1.12 MHz; 120.6 0  1.12 MHz.

Figure 3 .4 Velocity-selective optical pump spectroscopy configuration probe-pump counter-propagating of 85Rb.

Comparing the experimental results with the theoretical model as presented in Section 1.2, we find
that the positions of the spectral lines are consistent with the given theoretical model. The spectral line
intensity corresponding to the fourth and fifth largest shifts due to the superposition enhances the
electromagnetic transparency of the two groups of atoms B, C and A, C.
3.6. Investigation EIT spectroscopy configuring two pump beams in opposite directions
3.6.1. Measurement process
3.6.2. EIT spectroscopy of two pump beams in the same direction and opposite direction as the
detector beam
In this experiment, we measure the absorption spectroscopy in the presence of the EIT effect using
two pump laser beams. These two beams separate from the DL2 laser, which propagate in opposite
directions. Fixed frequency of DL2 at offset = 100 MHz relative to shift F = 3  F= 2 to red region.
Adjust the intensity of the two laser beams to the value of 2 mW/cm2, the received signal is shown in Figure
3.10. Figure 3.10a shows that the detector laser beam signal has a Gaussian shape, there are 13 EIT windows

15
on the Doppler expansion line corresponding to a shift of 52 S1/2 (F = 3) → 52 P3/2 (F' = 2, 3, 4) of six groups
of atoms moving thermally with different velocities.

Figure 3. 5 EIT spectroscopy of 13 windows on the Doppler line of the 85Rb atom. a) experiment, b) theory .

To explain the experimental results, we use a four-energy-level model, V-configuration. The
number of transitions is determined according to the energy level diagram as shown in Figure 3.11, we
consider two cases:
In the first case, pump-probe co-propagating, the pump beam is associated with three displacements
|1|2, |1|3 and |1  |4 corresponding to three groups of atoms A, B, C. Due to the effect Doppler,
the probe beam will have three resonance frequency values for each group of atoms. However, there is one
frequency value of the probe beam that resonates with all three groups of atoms, so we get seven detector
beam frequencies that resonate with all three groups of atoms.
Group A:

 pA1 = 12 - c2 = c,

(3.3)

 pA2 = 13 - c2 = 13 - 12 + c,

(3.4)

 pA3 = 14 - c2 = 14 - 12 + c.

(3.5)

 pB1 = 12 - c3 = 12 - 13 + c,

(3.6)

Group B:

 pB2 = 13 - c 3 = c,

(3.7)

 pB3 = 14 - c3 = 14 - 13 + c.

(3.8)

 Cp1 = 12 - c4 = 12 - 14 + c,

(3.9)

Group C:


16
 Cp2 = 13 - c4 = 13 - 14 + c,
 Cp3 = 14 - c4 = c.

(3.10)
(3.11)

The second case, pump-probe counter-propagating, the pump beam is associated with three
displacements |1|2, |1|3 and |1|4 corresponding to three groups of atoms D, E, H. Due to the

effect Doppler, the detector beam will have three resonance frequency values for each group of atoms.
However, there are three overlapping frequency values of the three groups of atoms, so we get only 6
frequencies of probe beam that resonate with all three groups of atoms.
Group D:

 pD1 = 12 + c2 = 212 - c,

(3.12)

 pD2 = 13 + c2 = 13 + 12- c,

(3.13)

 pD3 = 14 + c2 = 14 + 12 - c.

(3.14)

 pE1 = 12 + c3 = 12 + 13 - c,

(3.15)

Group E:

 pE2 = 13 + c3 = 213 - c,

(3.16)

 pE3 = 14 + c3 = 14 + 13 - c.

(3.17)

 pH1 = 12 + c4 = 12 + 14 - c,

(3.18)

 pH2 = 13 + c4 = 13 + 14 - c,

(3.19)

Group H:

 pH3 = 14 + c4 = 214 - c.

(3.20)

Therefore, we obtain 13 EIT windows when changing the probe laser frequency as the results in
Figure 3.10b (see Appendix B). The experimental results obtained are the positions of the EIT windows
corresponding to the displacements as shown in Table 3.1 (see details in the thesis).
3.7. Investigation of electromagnetic induced absorption (EIA) spectroscopy in pump-reverse
detector configuration
3.7.2. EIA spectrum in reverse pump-detector configuration
The obtained results of EIA spectral signal as shown in Figure 3.12.


17

Figure 3. 6 Absorption spectrum in the presence of EIA effect corresponding to the 52S1/2 (F = 1) 52P3/2 (F = 0, 1,
2) shift of the 87Rb atomic.

We see that on the absorption background five EIA peaks appear, the model explaining the

formation of EIA peaks is shown as shown in Figure 3.13.
During frequency shift the laser beam injects an amount of 169.9 0  1.12 MHz, the received beam
spectral signal shows that when increasing the pump laser beam frequency to 169.90 1.12 MHz, the
resonance absorption peaks are shifted to the right by the same amount and equal to 169.90 1.12 MHz.
The image of the detector laser beam spectrum when changing the pump laser frequency is shown in Figure
3.1.2b.
The absorption coefficient of the medium depends on the frequency of the detector laser and the
pump laser. When the pump laser is locked at frequency c near displacement 52 S1/2 (F = 2) 52 P3/2 (F =
2), the absorption coefficient of the enhanced medium at five frequencies p1 , p2 , p3 , p4 , p5 as given
in expressions (3.26) to (3.30).
3.8. Investigation of the Macaluso-Corbino effect
3.8.1. Measurement process
3.8.2. Macaluso-Corbino Effect (MC)
The experimental results show that, when there is no magnetic field and fix the polarizer P1, if we
change the polarization direction of the polarizer P2, the intensity of the spectral signal changes, but the
shape of the spectrum signal is unchanged. This shows that the polarization direction of the beam as it
passes through the medium is independent of frequency (Figure 3.15a).


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(a)

Probe response [arb. units]

B=0

300
00

85

87

Rb
F=2

Rb
F=3

85

Rb
F=2

-300
87

Rb
F=1

(b)

B = 48 G

300
87

Rb
F=2

85

Probe response [arb. units]

(c)

87

Rb
F=2

85

Rb
F=3

85

Rb
F=3

Rb
F=2
87

Rb
F=1

p (GHz)

p (GHz)

300

B = 48 G
B=0

85

Rb
F=2

Rb
F=2

(d)

-300

87

85

Rb
F=3

B = 48 G
B=0

85

Rb

F=2
87

Rb
F=1

87

Rb
F=1

p (GHz)

- 300

p (GHz)

Figure 3.15. The results investigating experimentally the Macaluso - Corbino effect: (a) B = 0; (b) B = 48 Gauss; (c,
d) the comparison in the presence of a magnetic field and when magnetic field is zero.

When current intensity reaches I = 1.5A, the magnitude of the magnetic induction B = 48 Gauss,
we obtained spectral signal corresponding to frequencies near transition D2: 52S1/2(F = 3) 52P3/2(F = 2,
3, 4); 52S1/2(F = 2)  52P3/2(F = 1, 2, 3) of the atom 85Rb and 52S1/2 (F = 2)  52P3/2 (F = 1, 2, 3); 52S1/2 (F
= 1)  52P3/2 (F = 0, 1, 2) of the atom 87Rb has variable shape and intensity (Figure 5b, c, d). Figure 5b
shows that when the polarizer is placed at an angle of 300, the spectral signals obtained at the resonance
shifts change more than when the polarizer is placed at -300. This shows that when the frequency of the
laser beam approaches the resonance transitions, the polarization direction of the light beam rotates in a
negative direction. Therefore, when a magnetic field is present, the spectral signals obtained at the resonant
transitions change more. The variation of the spectral signal in resonance transitions compared to the case
in the absence of a magnetic field for both rotational angles 300 and -300 is shown in Figures 5c and 5d.

Figure 5d shows that when the magnetic field is present, the spectral signal obtained at transition 52S1/2(F
= 3) 52P3/2(F = 2, 3, 4) of the atom 85Rb is smaller than without magnetic field, whereas at transition
52S1/2(F = 2)  52P3/2(F = 1, 2, 3) of the atom 85Rb the spectral signal obtained was greater than without
magnetic field. This proves that the polarization rotation angle at transition 52S1/2(F = 3) 52P3/2(F = 2, 3,
4) is greater than 600 while the polarization rotation angle at transition 52S1/2(F = 2)  52P3/2(F = 1, 2, 3)
is less than 600.


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Probe response [arb. units]

Theory

2

4

p (GHz)

6

8

Figure 3.16. The dependence of the rotation angle of the polarization plane on the external magnetic field strength,
the top purple line is the theoretical simulation line, the lower lines correspond to the experimental lines of the other
magnetic values. when considering  = 600.

By varying the different magnetic field values, the measurements of the polarization plane rotation angle
at resonant frequencies. We found that as the magnetic field increased, the polarization plane rotation angle
increased at near-resonant frequencies. Based on the theoretical model and simulation [15], we find that the

simulation results agree with the experimental results obtained with the same gas atom Rb (Figure 3.16).
3.9. Investigation Optical switching
3.9.1. Theoretical model
Consider the V + Ξ double configuration four-level atomic system as shown in Figure 1.1 5 a.
Accordingly, the system consists of a ground state |1 and three excited states |2 , |3 , |4  respectively with
energy levels |5S 1/2 , F = 1 , |5P 3/2 , F = 2 , |5P 1/2 , F = 2 , |5D 5/2 , F = 1  as depicted in Figure 1.15 b.
The probe beam has a weak intensity with frequency p and Rabi frequency p acting on the transistions
|1|2, |1|3 and |2|4 are excited by laser coupling (frequency c) and signal lasser (frequency s)
with Rabi frequency c and s , respectively .
Here, the probe field (solid line) is a continuous wave that has been converted by the signal field. In Figure
1.1 6 a, the signal field strength is Ω s (τ) = Ω s0 {1 − 0.5tanh [0.4(τ − 20)] + 0.5tanh[0.4(τ−45)] − 0.5tanh[0.4]
(τ−70)] + 0.5tanh[0.4(τ−95)]} with period 50/21 . In Figure 1.1 6 b, the strength of the signal field is Ωs (τ) =
Ωs0 {1 − 0.5tanh[0.2(τ−40)] + 0.5tanh[0.2(τ−90)] − 0.5tanh[0.2 (τ−140)] + 0.5tanh[0.2(τ−190)]} with a period
of approximately 100/21. In both cases, the amplitude of the signal field is normalized by the peak value
Ωs0 = 9 21. From Figure 3.16a shows that the period of the probe beam and the period of the signal beam
are the same. Furthermore, the probe beam is switched in ON or OFF mode when the signal beam switches
the signal from OFF or ON respectively. On the other hand, the probe pulse oscillation will be suppressed
when the signal pulse width is large (Figure 3.26b).


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Figure 3. 26 (a) V + Ξ double configuration atomic diagram, (b) energy level diagram of atom 87 Rb.

Figure 3. 27 Continuous probe beam signal change as the signal field transitions with periods of 50/21 (a) and
100/21 (b). With the parameters Ω p0 = 0.01 21 , Ω s0 = Ω c = 9 21 , p = 0, c = 0, s = 0; time τ is in units of 21 -1 .

3.9.2. Experimental model
3.10. Investigation of negative refractive index in the atomic medium
3.10.1. Theoretical model

The principle of measuring the negative refractive index of the EIT medium is similar to that of the
dispersion measurement of the EIT effect presented in Section 2.3.1. Here, we build a theoretical model to
create a negative refractive index in the medium of Rubi atom gas based on the EIT effect. From there, it
is possible to find the necessary parameters for the investigation by negative refractive index experiment.
We consider a Three-level lambda-type atomic system as shown in Figure 3.19.

Figure 3.7 Three-level lambda-type atomic system is excited by the probe and coupling fields.


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We can determine the refractive index of the medium as follows:

n    r  D  r  D  .

(3.47)

We apply the calculation results to the 87Rb atom with the states 5S 1/2 (F = 1), 5P 1/2 (F = 2) and 5S 1/2 (F =
2), respectively energy levels 1 , 2 and 3 . Atomic density and other parameters are N = 10 27 atoms/m3
, m = 1.44 1027 kg, d 21 = 1.2 1029 Cm, m 31 = 7.26 1023 Am2 , 21 = 23 = 6 MHz, 0 = 8.85 1012 Fm1
, 0 = 4 107 NA2 and k B = 1.38 1023 J/K.

The amplitude of the negative refractive index changes when the intensity of the pump laser is
adjusted. For example, We fix the probe frequency detuning at p = 2 MHz which corresponds to the
negative index region in figure 3.21, and study the influence of the coupling laser intensity on the negative
refractive index. The graphs of relative permitivity anh relative permeability, and the refractive index versus
the coupling Rabi frequency when p = 2 MHz, c = 0 MHz, and T = 300 K are shown in figure 3.22. From
figure we can see that both relative permittivity (dashed line) and relative permeability (solid line) varies
from 0 to 100 MHz. It is beacause for given frequency of the probe beam, a change in coupling laser
intensity can lead to transition between electromagnetically induced transparency (EIT) and
electromagnetically induced absorption (EIA) [54], which changes the corresponding disperion properties.

In this case, we also find the medium shows negative reflective index when 38 MHz < c < 78 MHz
3.10.2. Experimental model
3.11. Some extended studies of the integrated experimental system
3.11.1 . Measure the speed of the group of light
propose a intuitive light group velocity measurement scheme which is relying on the propagation
pulse deviation of two lasers with different emission frequencies, one passing through the sample chamber
and the other as a reference pulse.
Optical diagram of light group velocity measurement based on the comparison of optical path
difference of two light pulses arranged as Figure 3.17. In this optical scheme, We add two more electro-


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optical modulators (AOM - Acousto-optic modulator) for generating pulses (nanosecond size) for the
detector laser and the reference laser.

Figure 3. 8 Installation diagram of light group velocity measurement system .
3. 11.2. Observe Kerr nonlinear coefficient
The layout of the Kerr nonlinear measurement experiment is shown as shown in Figure 3.18. The
construction system is similar to the group velocity measurement system. We just added an electro-optical
modulator (EOM - Electro-Optic Modulator ) to modulate the intensity of the detector and reference laser
beams.

Figure 3.9 Installation diagram of nonlinear Kerr measurement.

3.11.3. Additional equipment and components required to develop the experimental system
The optical switching system is developed based on the integrated experimental system presented
in Chapter II . Therefore, the equipment used for the optical switching system is similar to that described
in section 2.2. The LD3 laser is a Moglabs laser as described in section 2.2. In addition, the system also
needs to add the following devices:
a. Electro-Optical Modulator (EOM)

b. Optical Acoustic Modulator (AOM)


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GENERAL CONCLUSION
1. We have successfully designed and built experiment system, which integrating the following techniques:
+ Measure the absorption spectroscopy and saturated absorption spectroscopy.
+ Measurement of dispersion spectroscopy and saturated dispersion spectroscopy.
+ Measure EIT absorption and dispersion spectroscopy with three configurations (probe-pump counter
propagating, probe-pump co-propagating, and two pump beams).
+ Measure the EIA absorption spectrum in case the probe-pump counter-propagating..
2. Compact optical benchtop construction (45 cm x 60 cm), easy switching between measurement
configurations by opening and closing the block beam and rotating the Mirrors. This allows us to save more costs than
the case of building on many spread test systems, the design of the flexible system helps us to save time on installation
and surveying difficult experiments.
3. We have built a theoretical model to explain the measured results on the experimental system and the
procedure of the measurements, helping users (especially at universities).
4. Some new research results when applying the experiment system and research model.
+ Observing the 85Rb atomic spectrum by velocity-selective optical pump spectroscopy, we obtained 6
spectral lines corresponding to the 52S1/2 ( F = 3) → 52P3/2 ( F' = 2, 3, 4) of three groups of atoms interacting with the
pump laser. The obtained results show that the positions of the spectral lines are consistent with the theoretical model
we have built.
+ Observe the EIT spectrum to obtain 6 EIT windows in the case of the probe-pump counter-propagating, 7
EIT windows in the case of the probe-pump co-propagating, and 13 EIT windows in the case of the advent of both
pump beams. The number of obtained windows is more than the number of windows of the first EIT observation
system built at Vinh University (3 windows). Here, we have also built a theoretical model explaining the formation
of windows as well as changing the parameters to control the position and intensity of the spectral lines and observe
the dispersion spectrum in the presence of the effect EIT.
+ The Macaluso- Corbino effect is observed, opening up the potential to study the phenomenon of opticalmagneto switching experimentally in the near future.
+ On the basis of the components and equipment of the experimental system and the layout design of optical

components in the experimental system, we have also proposed to build an experimental system for measuring the
speed of light group, measuring refractive index. Kerr power and optical switching.
+ Successfully built a theoretical model to study the refractive index of the Rubidium vapour medium and
discovered that a negative refractive index can be created in the Rubidium vapour medium when advent EIT effect,
thereby providing an experimental model for further research. experiment in the future.