Design And Construction Of Axial Slow Flow Cw Co2 Laser
السلام عليكم ورحمة الله وبركاته
سوف نعرض في هذا الموضوع مشروع بعنوان:
DESIGN AND CONSTRUCTION OF AXIAL SLOW FLOW CW CO2 LASER
(تصميم وبناء منظومة ليزر CO2 طولي بطيء الجريان المستمر)
وهذه الرسالة مقدمة الى:
معهد الليزر للدراسات العليا / جامعة بغداد
كجزء من متطلبات نيل شهادة الماجستير في علوم الليزر/ هندسة الليزر
من قبل :
المهندسة زينب قاسم محمد الشيخلي
في هذا البحث سيتم بحث كيفية تصميم هذا النوع من ليزر ثنائي اوكسيد الكاربون حيث تكلمت الباحثة وناقشت الاتي:
يمثل هذا البحث تصميم نظري وعملي وبناء منظومة ليزر ثنائي أو كسيد الكاربون الطولي بطي الجريان المستمر المتعدد المسارات المستخدم في التطبيقات الصناعية حيث يمثل نموذج جديد يختلف عن التصاميم السابقة.
التصميم الميكانيكية و البصرية والكهربائية ومنظومة التبريد لهذا الليزر تم عرضها بشكل تفصيلي و القياسات النظرية المتمثلة اعتماد كل من 1) القدرة الخارجة على طول أنبوب التفريغ الكهربائي وقطر ه. 2) فولتية التفريغ الكهربائي على طول أنبوب التفريغ الكهربائي والضغط داخل الأنبوب.3)سرعة جريان الماء داخل الأنبوب على قطر الأنبوب الخاص بالتبريد .تم عرضها أيضا.
تم تصميم بناء وتشغيل منظومة ليزر ثنائي أو كسيد الكار بون ذات المسار الواحد و ذات المسارين (أحادية الأنبوب وثنائي الأنبوب )باستخدام أقطاب مختلفة الأشكال حيث تم تسجيل أعلى قدرة خارجة بقيمة (37-25.5) W لنمط TEM01 عند طول موجي 10.6 μm بالتعاقب. أعلى كفاءة للمنظومة كانت 16,2% عند ضغط 16ملي بار وتيار تفريغ 40ملي امبير .
وأخيراً,تمت مقارنة النتائج النظرية والعملية والتي أعطيت نتائج جيدة بالنسبة لمنظومة أحادية الأنبوب بينما لوحظ بعض الانحراف عن المطلوب في منظومة الثنائية الأنبوب.
وهذا البحث يتضمن الفصول الاتية:
Chapter one:Introduction
Introduction.
Thesis contents
Types of CO2 Lasers
Historical Background
Lasing Transition in CO2 Laser
Energy Transfer in the Discharge
Glow Discharge in CO2 Laser
Normal Density of Current at Cathode
Normal Anode Current Density
Self –Sustained Glow Discharge
Output Stabilization by the Opto –Voltaic Effect
Effect of E/N Parameter
Parameter Affecting the CW Gain in CO2 System
Current
Gas Kinetic Temperature
Helium Molecule
Tube Diameter
Gas Composition
Efficiency
Optical Material for CO2 Laser
Optical Cavity Types
Resonator
(High Power System( Folding
Cooling of CO2 Laser
Diffusion-Cooled CO2 Laser
Connective-Cooled CO2 Laser
Output Power Design Equation
Chapter two:Co2 laser system
Introduction
Mechanical Design
Optics
Gas and Vacuum System
Cooling System
Laser Discharge tube
The CO2 Laser Power Supply
CO2 Laser System Configuration
Chapter three:Results and disscusion
Introduction
Effect of the Pressure on the Discharge Voltage
Effect of the Pressure and Flow Gas on the Output Power
Effect of the Current on the Power Output
Effect of the Input Power on the Output Power
Efficiency of the System
Conclusion
Proposal for Future Work
Reference
وسيتم عرض كل فصل على حدة ساقوم بتقسيم كل فصل الى اجزاء لتسهيل قراته
انتظرونا
مشاركة: Design And Construction Of Axial Slow Flow Cw Co2 Laser
chapter one
[SIZE="4"]i1.1 Introduction
Carbon Dioxide (CO 2) laser is the gas discharge device .It operates by electric excitation of an active medium that is a mixture of helium, nitrogen, and carbon dioxide .The excited CO2 has many energy levels it can drops to, allowing emission on groups of lines around (9.6) and (10.6) µm..
All CO2 lasers are rated in Watts or kilowatts. The distinguishing characteristic of the CO2 lasing process that make these sustained power levels possible is its relatively high efficiency at least compared to most other common gas lasers. The typical electrical power into optical power out efficiency of a CO2 laser may be any, where from 10 to 30 percent [1].
Unlike the other lasers producing visible or near IR light, the output of a CO2 laser is medium IR radiation at 10.6µm .At this wavelength, normal glass and plastic are opaque, and water completely absorbs the energy in the beam .The 10.6 µm energy is ideal for cutting, engraving, welding, heat treating and other industrial processing of many types of materials including:
****ls, ceramics, plastics ,wood ,paper ,cardboard fabric ,composites.
The CO2 laser represents the classic heat ray of science fiction .The basic construction of CO2 laser is a gas filled tube between a pair of mirrors excited by an electrical discharge. ****l coated mirrors (e.g. solid molybdenum, gold or copper coated glass) may be used for the high reflector (totally reflecting mirror). Germanium or zinc selenide which have very low losses at 10.6µm are often used, but must be cooled to minimize losses for high power.
There are many different types of design for CO2 laser divided into different groups but the basic principles are the same.
We can summarized the properties of these lasers as fallow:
1
i1. High output power. Commercial CO2 Lasers produce more than 10kW continuously.
i2.Output spectrum is in the infrared (IR) spectrum.
i3. Very high efficiency (up to 30%).
i4.Can operate both continuously or pulsed.
i5.Average output power is 50 [W/m] for slow flow of gas, and up to few hundreds [W/m] for fast gas flow.
i6.Very simple to operate, and the gasses are non-toxic.
i1.2 Thesis Contents
In this thesis, the basic theory of CO2 laser and the parameters that effects on its reviewed in this chapter. Chapter two represents the basic design aspects for slow flow CO2 laser. The details of the laser system design and construction are described in chapter three. Results, discussion, conclusion and suggestions for further works will be present in chapter four.
i1.3 Types of CO2 Lasers:
There are many types of CO2 lasers, all based on the same physical principles. The difference between them is in their structure, excitation mechanism, and the output power radiation. CO2 laser can be separated into six categories[2] :
i1. Flowing CO2 gas lasers
a.The Slow Flow CO2 Laser.
b.Fast Flow CW CO2 Laser.
i1.Fast Axial Flow.
i2. Fast Transverse Flow.
i2. Sealed-off CO2 Laser.
i3. The Gas Dynamic Laser.
In these lasers a fresh gas mixture is flowing continuously through the laser tube while lasing lasts. Flowing gas is used when the maximum power is needed out of the CO2 laser. The gas flows along the tube and is released out into the atmosphere (since it is non-poisonous)
These lasers are very simple, and the requirements from the gas purity are small. Hundreds of watts can be achieved at the output of these lasers. There are two different types of flowing gas CO 2 laser slow flow and fast flow [3].
The slow flow of CO2 laser reliable, robust, easy to operate, and are produced by the industry in many versions with powers ranging from tens of watts to a kilowatt . Figure .1.1 shows a typical setup of a conventional diffusion cooled (slow flow type) CW CO2 laser.
http://www.iraqup.com/uploads/3j2nV-ByV331015.JPG
Figure (1.1) Schematic Drawing of Slow Flow CW CO2 Laser [3].i
In these systems, the heat generated by the electrical discharge is removed by heat conduction through a water jacket surrounding the laser discharge tube .In order to continuously refresh the mixture, the gas is slowly pumped through the tube. Laser out put power can be done only by increasing the tube length [4]. i
For a fast flow system, mass transfer or the flowing gas removes the heat produced by the electric discharge. The output power is largely dependent on the mass flow rate (amount of the laser gas medium flow rate per second )of the gas, which can be as high as 120 to 150 W of output power for each gram per second of mass flow .The fast flow system can be divided into two major types as the fast-axial –flow and transverse –flow system .
Summary of CO2 lasers according to groups:
•Gas laser.
•Emit in the infrared (IR) spectrum (λ = 9-11 [μm]).
•Electrical excitation.
•Four level laser
•Continuous wave, although pulsed operation is possible. [/SIZE]
مشاركة: Design And Construction Of Axial Slow Flow Cw Co2 Laser
chapter one
1.4i Historical Background
It was some time after discovery of gas laser that special properties of the mixture of gases used in the CO2 laser were recognized .Patel et al [5].(Patel 1964 )observed laser action in pure CO2 at 10.6μm .using a 5-m laser he obtained outputs of 1 mW CW with DC excitation and 10 mW peak with 1 μse excitation pulses [6].This report was rapidly followed by the observation of laser action in a CO2-N2 mixture (Patel 1964)[7].In this case a stream of N2 was passed through high frequency discharge and the active nitrogen so formed was mixed with CO2 in an interaction region between the mirrors of a Fabry-Perot resonator; an output of over 1mW was observed with a 20-cm long interaction region .i
Further work by Patel (1965)[8] led to the direct excitation of the gas within the laser resonator and the attainment of 12 watts from a 2-m tube containing a mixture of CO2 and air. He observed oscillation on R branch lines as well as P branch lines and noted that the flow rate of the mixture effected the gain .Moeller and Rigden (1965) [9]reported 10Wm-1 from a sealed tube containing a CO2-He mixture and also mentioned,with no details ,that a flowing mixture of CO2,N2 and He gave good results ,but the simultaneous report by Patel (1965) gave a detailed account of a water–cooled tube using a flowing CO2-N2-He mixture which produced over 50 Wm-1 [10].i
Pulse energies of 1.1mj were reported in the first study of a Q-switched CO2 laser (Kovacs et al 1966)[11].i
The year1969 marked attuning point in the development of high –power CW and pulsed CO2 laser .By 1969 a 750 –f t long CW CO2 laser based on the design of Patel et al (1965) had been built and operated at a power output of 8.8 kW (Horrigan et al., 1969)[12]. Subsequently, the development of electric discharge convection and gas dynamic laser has been resulted in the generation of CW laser powers in excess of 100 kW.i
The same year also saw the development of lasers based on convective cooling (Lavaini et al., 1969; Deutsch et al., 1969;Cool and Shirley ,1969)[13] and a report was published describing the operation of a compact closed system CW laser using rapid transverse gas flow capable of generating output powers of 1kw (Tiffany et al., 1969)[14]. i
Late in 1969 ,Bealieu (1969)[15] reported that CO2 laser emission could be obtained at atmospheric pressure and above by exciting the gas transversely so that the discharge passed perpendicular to the optical axis .i
The extraordinary in powers obtained from CO2 lasers in the 10 years, 10-15 kW CW CO2 can be purchased (Locke and Hella, 1974)[16].i
Al-aobaidi A.R M., in 1981[17] discussed the design and construction of CO2 CW laser and its application in the detection of the absorption line in some gases using opt.-acoustic technique. The designed laser has been operated with TEM00 mode with an output power of 27 W, and gas mixture ratio of CO2: N2: He /12:14.3:73.7% respectively .He used a grating to tune the laser emission for the required lines. i
Noory Z.T.,(1989)[18]described the design and construction of continuous waves fast flow CO2 laser system ,the total electric discharge consist of two equal parts 112cm with DC of 15kVand 600mA power supply output power was 30 W at pressure 60mbar and gas flow rate of 240l/min.
Al-Yaseen U. A.,(2001)[19] constructed a CW CO2 laser system .The laser cavity of different lengths 50,60,70and 80cm.The maximum output power was 60 W at flow rate 150 l/min .i
Kazim Kh. N.,(2002)[20]constructed a CW CO2 laser system of different lengths60, 70 cm with internal diameter of 2cm.The maximum output power and efficiency obtained of 83 Wand 8.5% respectively at resonator length 204 cm..i
1.5i Lasing Transition in CO2 Laser:
Lasing transitions in CO2 laser occur when the molecule is going from higher energy level of the asymmetric mode into one of the following modes see figure 1.2.i
1. The transitions to the symmetric stretching mode correspond to the wavelength of 10.6 [µm].i2. The transitions to the bending mode correspond to the wavelength of 9.6 [µm].i
Fig. 1.2 : Energy Level Diagram of CO2 Laser [22 ].i
Each of the vibrational energy level is subdivided into many rotational levels. Transitions canoccur between vibrational energy levels with different rotational levels, so there are many lasing lines around the main vibration transitions [20].i
The carbon dioxide molecule is liner asymmetric triatomic molecule. The molecule has three normal modes of vibration and the three atoms are situated on a straight line with the Carbon atom in the middle. i
In figure 1.3 the three vibration modes of CO2 molecule are illustrated: i
i1.Symmetric stretch mode (υ1). i
i2.Bending mode (υ2). i
i3.Asymmetric stretch mode (υ3). i
Vibration levels are designated by three numbers representing the number of vibration quanta in each mode associated with the particular level and written in the form (υ1,υ2,υ3 ). The molecule can simultaneously vibrate in more than one mode and can have more than one quantum of vibration energy in each mode [21].i
Electric discharge is created in the laser tube. The energy of the accelerated electrons is transferred by collisions to the Nitrogen molecules and to the CO2 molecules. .i
Nitrogen molecules help in the process of the excitation of the CO2 molecules. The first vibrations energy level of the Nitrogen molecule is very similar to the asymmetric stretching mode of the CO2 molecule (see figure 1.4), so energy can be easily transferred from the excited Nitrogen molecules to the CO2 molecules [22]..i
Figure 1.3: Oscillation Modes of CO2 Molecule [22]..i
The (00˚1) upper laser level of CO2 at 2349.3cm-1 lines 18.6 cm-1 above the υ =1 level of N2 .The (10º0) and (02º0) lower laser levels for the 10.4µm and 9.4µm bands of CO2 lie at 1388.3 and 1285.5 cm-1 , respectively .These two levels are in Fermi resonance and vibration levels belonging to different vibrations have nearly the same energy .The mixed states denoted as (100,020) lying at 1388.3 and 1285.5 cm-1 respectively .The (01º0) bending mod of CO2 lies at 667.3cm-1 For exhibit laser action ,(00º1)(100,02º0) near 9.4µm,consist of an R-J is the rotational quantum number .iThe IR transitions between various levels are governed by the selection rules [24]. .i
ΔV= ±1
ΔJ= ±1
Where, J is the rotational quantum number.i
V is the vibration quantum number.i
مشاركة: Design And Construction Of Axial Slow Flow Cw Co2 Laser
بارك الله فيك ماجستير هندسة ليزر على هذه السلسلة الرائعة من المواضيع المتعلقة بالليزر وموضوع ليرز ثاني اكسيد الكربون من الليزرات التي لها تطبيقات عديدة جدا
اشكرك على هذا الشرح الوفي والواضح والسلس وان شاء الله سيفيد كل من يدرس مقرر الليزر
تحياتي
مشاركة: Design And Construction Of Axial Slow Flow Cw Co2 Laser
توضيح واستفسار
نلاحظ من الشكل الذي يوضح مستويات الطاقة التي تنتج الليزر في ثاني اكسيد الكربون ان هناك 3 انتقالات تعطي 3 اطوال موجية لليزر. وهذا يعود للحركة الاهتزازية لذرتي الاكسجين بالنسبة لذرة الكربون حيث يكون هناك 3 انماط اهتزازية هي الموضحة في الشكل
http://www.iraqup.com/uploads/im6L0-j3YE6932.JPG
كيف يمكن الحصول على ليزر بطول 10.6 µm فقط
ما فائدة النيتروجن المخلوط مع ثاني اكسيد الكربون
تحياتي
مشاركة: Design And Construction Of Axial Slow Flow Cw Co2 Laser
السلام عليكم ورحمة الله وبركاته
حياك الله
شكرا دكتور على المرور
حلو مرورك والسؤال احلى
اقتباس:
كيف يمكن الحصول على ليزر بطول 10.6 µm فقط
اهتزاز الذرة ضمن مستوياتها يتحكم بنوع الليزر والطول الموجي المنتج فمثلا الانتقالات الاهتزازية والدورانية تؤدي الى تكوين ليزر ضمن مدى تحت الحمراء (IR) او قريب هذا المدى (near IR). كما موضحة في الشكل المذكور فلذرة (Co2) ثلاث حركات اهتزازية كما لها ايضا انتقالات دورانية.اي انتقالته هي اندماج لهذين الانتقالين.
اما الانتقالات الاهتزازية لوحدها فتنتج طول موجي مرئي ( visible).
اقتباس:
ما فائدة النيتروجن المخلوط مع ثاني اكسيد الكربون
ان اول ليزر ثنائي اوكسيد الكاربون اكتشف في عام 1964 بواسطة عالم اسمه بتل لم يكن يستعمل النتروجين فقط غاز ثنائي اوكسيد الكاربون ولكن كانت الطاقة الناتجة قليلة جدا وكذلك كفائة الليزرحيث كانت الطاقة بحدود (1 ملي واط), فائدة النتروجين يستعمل كعامل مساعد مع الهليوم ولكل وضيفته,حيث يستعمل النتروجين في عملية التهيج ونقل الطاقة الى جزيئات ثنائي اوكسيد الكاربون حيث ان النتروجين لا يوجد له عزم كافي ليهبط الى المستوى الاوطىء لعدم وجود محصلة عزم كهربائية لتهبط لذلك تبقى في حالة رنين وتهبط الى مستويات قريبة من مستويات Co2 وبذلك سوف يحصل انتقال رنين من النتروجين الى ثنائي اوكسيد الكاربون مما يؤدي الى انتقال الطاقة.
وهناك اضافة اخرى وهو غاز الهليوم وهذا الغاز لا يشارك في عملية التهيج او في عملية التفريغ (discharge)وانما يستعمل من اجل عملية التبريد حيث انه يحاول نقل الحرارة الناتجة بسبب التفريغ (discharge) الى جدران الانبوب الحاوي.
وطبعا تختلف نسبة استخدام كل منهما كما انه باختلاف النسب سنجد اختلاف بعض عناصر ومميزات الليزر الناتج.
وسوف توضح في بقية البحث ان شاء الله
Co2+He+N2---------------->Co2
التوضيح فائدة كل منهما تاتي ان شاء الله
انتظرونا
سلامي
مشاركة: Design And Construction Of Axial Slow Flow Cw Co2 Laser
chapter one
1.6:i
Energy Transfer in the Discharge:i
The most commonly observed laser transition in the CO2 molecule, barring the use of any frequency tuning mechanisms, are from the CO2 asymmetric stretch transitions, from the (00*1) to the (100*0)(10.6) micron and (02*0) (9.6) micron states, using the notation (v1v2*v3), where v1 refers to the symmetric stretch quantum number, v2 refers to the asymmetric stretch quantum number and v3 refers to the asymmetric stretch quantum number. There are literally dozens of other lasing transition. Which employing an interactivity grating .In a CO2 laser, depending on instantaneous gain medium and resonator conditions can easily choose.:i
Any single possible laser line can be forced through the use of an interactive grating. Rotational structure, having energies clustered very close to one another, may exist at any time. Nonradiative decay to short-lived lower lying states followed by Nonradiative decay to the ground state follows .N2 is added to the laser gas to more efficiently transfer energy from electron impact to the CO2 upper vibrations laser level. The glow discharge is a very effective mechanism for vibration excitation of nitrogen. Since N2 is ahomonuclear molecule, dipole radiate de-excited is forbidden. This allows for long-lived vibration states, which makes excited N2 molecules more readily available for collision excitation of CO2.:i
De-excitation is only accomplished collisionally with the wall or other gas constituents, the most beneficial of which is the CO2 molecule .The N2 (v=2) state is only 18cm-1 (2.2E-3 eV) from the upper laser level of the CO2 molecule .This makes resonant energy transfer between N2 and CO2 more likely.This energy is much smaller than the average kinetic energy of the molecules in the surrounding glow ,so vibration energy can easily be supplied to the CO2 molecules .:i
Energy transfer occurs from vibration levels up to v=4 in N2,because the ensuing anharmonicity of these states ,due to bond stretching ,is still well blow the average molecular kinetic energy .CO is isoelectronic with N2 and also has vibration levels easily excited in the glow discharge [24].:i
Thermal poisoning can occur, which is build up of lower lasing level populations in CO2.This results in a reduction in laser output power due to a clogging of the path from the upper lasing level to the ground state, where the CO2 upper lasing level is most efficiently populated through collisions with N2 these lower levels are cooled by the addition of He to the gas mix helium energy levels are much higher than the molecular energies of N2and CO2, above 20 eV.:i
For typical electron energies in the glow discharge of 1 to 3 eV, the discharge is not significantly affected by the addition of He other than to raise the electron temperature of the discharge [25].:i
Since the first ionization level of the He is higher than that of the other gas components, high energy impacts (higher “voltage”) is required to make it apart of the glow conducting path. Only a small amount of energy is lost from the discharge due to inelastic collisions with He and subsequent collisions with the walls. Thermal conductivity in gases is independent of pressure and since thermal conductivity of the He is roughly six times that of CO2 and N2, He makes an efficient transporter of waste heat to the walls of the discharge tube. The efficiency of heat transfer resulting from the addition of He to the mixture allows for higher discharge current before radiation saturation [23].:i
CO may also be added to the laser mix to improve efficiency, but it dose not transfer vibration energy as efficiently as N2, due to a difference between the CO v=1 level and the CO2 upper lasing level of 170 cm-1 . CO also has a dipole moment which creates a radiative decay channel to depopulate the electron impact excited CO, thus making CO less available for the job of CO2 excitation. CO is also a component in the dissociation equilibrium of CO2, so when using added CO with CO oxidation catalysis, larger concentrations of CO effect the CO2 concentration not always in a predictable manner. :i With these drawbacks, CO still adds to more efficient CO2 vibration excitation than electron impact alone. H2O can be added as a heat transfer enhance but is less efficient at cooling than He. H2O, in small concentrations, also has the beneficial side effect of homogeneous catalytic recombination of the dissociated CO2 products, CO and O.H2O in a larger concentration overwhelms the beneficial catalytic effects and effectively depopulates the upper lasing levels of CO2 .:i
Xe may also be added to a laser gas mix to effectively cool the electron temperature of the discharge for a given current, thereby reducing the amount of electron impact dissociation of CO2. The prohibitive cost of laboratory grade Xe prevented this investigator from utilizing it [25].:i