98683 - LASERS

Learning outcomes

At the end of the course the student has acquired the basic principles of laser operation, knowledge of their optical properties and the chemical applications of the main commercially available laser sources.

Course contents

Principles of laser operation

• Stimulated emission
• Inversion of energy levels population
• Pumping processes
• Optical resonators
• The threshold condition in a real laser
• Continuous wave lasers
• Pulsed lasers
  
• Properties of laser's light
• Multi-mode and single-mode laser emission

Applications of laser light

• Uses of laser's light
• Raman spectroscopy

Commercially available lasers

The different types of laser sources and the physical or chemical phenomena which make them work.

• Atomic electronic emissions: He-Ne, Ar+ , and Nd3+ lasers
• Molecular vibronic: N2, excimer, and dye lasers
• Molecular rovibrational: CO2 and HF lasers
• Transition metals doped crystals: ruby and Ti:sapphire lasers
• Diode lasers

Instrumental techniques

• Non-linear optics for harmonics generation
• The creation of ultra short pulses
  - Q-switching
  - Mode-locking
  - Chirped pulse amplification

Laboratory laser-based experiments

• Photophysical characterization of ruby
• Laser-induced fluorescence
• Raman spectroscopy

Anonymous statistical survey

Once 2/3 of the lessons have been completed, a survey will be carried out to know students' opinions on the course, in order to make it more effective. Reference links:

• https://opinionistudenti.unibo.it  
  
• https://val.unibo.it/ (student)
• https://val.unibo.it/demo.php (survey)
• https://gestioneval.unibo.it (lecturer)

Calendar

• 18/09/2023 Ammonia-maser
• 21/09/2023 Ruby-laser
• 25/09/2023 Longitudinal modes in a plane-mirror resonator
  
• 28/09/2023 Single mode operation, directionality, brightness and irradiance, transverse EM modes in a confocal resonator cavity.
  
• 02/10/2023 Resonant optical cavity types, coherence, polarization
  
• 05/10/2023 He-Ne laser
• 09/10/2023 Time-dependent perturbation theory. Weak interaction approximation
  
• 12/10/2023 Probability of transition. Semi-classical theory of the radiation-matter interaction.
  
• 16/10/2023 Probability of transition for absorption and stimulated emission. Transition moment of electric dipole. Einstein coefficients for stimulated transition. Selection rules.
  
• 19/10/2023 Probability of transition for spontaneous emission. Homogeneous and inhomogeneous broadening.
  
• 23/10/2023 Case study: calculation of A and B Einstein's coefficients. Intensity of a light beam through the matter.
• 26/10/2023 Kind of active media. Losses and threshold for laser action.
  
• 30/10/2023 2, 3 and 4 level schemes. Copper vapour laser.
  
• 02/11/2023 Ar+, Kr+, He-Cd, N2 lasers.
• 06/11/2023 Exciplexes laser. Normal modes of vibration.
• 09/11/2023 CO2, HF, dye, Ti-Sapphyre lasers. 
• 13/11/2023 Lanthanide lasers.
• 16/11/2023 Fiber lasers. Q-switching technique.
• 20/11/2023 Mode-locking technique. 
  
• 23/11/2023 Nonlinear optics: optical rectification, SHG, THG, Kerr's effect, Pockels'effect, waves' mixing.
  
• 27/11/2023 Laser-induced fluorescence of molecular iodine.
  
• 30/11/2023 Selection rules for Raman and infrared spectroscopy.
  
• 04/12/2023 LAB-INF Laboratory: quantum mechanical calculation of vormal modes of vibration.
  
• 05/12/2023 LAB-P3 Laboratory: Vibrational Raman spectroscopy of liquid and solid samples.
  
• 06/12/2023 LAB-P3 Laboratory: Photophysical characterization of ruby, a lasing material.
• 07/12/2023 LAB-P3 Report (data analysis).
  
• 11/12/2023 LAB-P3 Laboratory: Photophysical characterization of ruby, a lasing material.
• 12/12/2023 LAB-P3 Laboratory: Disentanglement of spectral properties of vegetable oils.
  
• 13/12/2023 LAB-P3 Report (data analysis).
• 14/12/2023 LAB-P3 Question time.

Readings/Bibliography

• D.L. Andrews
  Lasers in Chemistry
  Springer, 3rd edition

• O. Svelto
  Principles of Lasers
  Plenum Press, 4th edition

• Donald A. McQuarrie & John D. Simon
  Physical Chemistry: A Molecular Approach
  University Science Book
  - Chapter 15: Lasers, Laser Spectroscopy, and Photochemistry
  - Chapter 12: Group Theory: The Exploitation of Symmetry

 

Teaching methods

Projector for transparencies and slides in the classroom.

Laser instrumentation available in the laboratory for Laser-based experiments.

• Vacuum line + Thermostat + Spectrometer Ocean-HR + DPSS laser (green 532 nm)
  LIF I2
• Spectrometer Ocean USB4000 + DPSS and diode lasers (red, 671 nm)
  Spectral features of vegetable oils
  
• Spectrophotometer + Spectrofluorometer
  Photophysical characterization of Ruby
  
• Raman spectrometer Ventana 532 nm + DPSS laser (green)
  Raman Stokes spectroscopy of liquid and solid materials
  
• Spectrofluorometer + DPSS laser (blue 473 nm)
  Raman Stokes and anti-Stokes spectroscopy of liquids

As concerns the teaching methods of this course unit, all students must attend Module 1, 2 [https://www.unibo.it/en/services-and-opportunities/health-and-assistance/health-and-safety/online-course-on-health-and-safety-in-study-and-internship-areas] online, while Module 3 on health and safety is to be attended in class or on Microsoft Teams according to the modality chosen by the teacher. Information about Module 3 attendance schedule is available on the website of your degree programme.

Assessment methods

The assessment for the LASERS module is a single oral exam at the end of the semester.

The student has to report on three topics of the educational program, including:

• principle and properties of lasers
• laser sources
• laboratory activity (the reports can be used during the examination)
  

The total duration of the exam is approximately 30 minutes.

The exam can be passed with a minimum score of 18/30.

The grade for the entire APPLIED PHYSICAL CHEMISTRY integrate course is calculated as the average of the grades obtained in the two modules (if both are at least 18/30).

 

Teaching tools

Lessons in the classroom (4 CFU) for the theory, numerical exercises in the classroom or in the laboratory (1 CFU), and laboratory activities (1 CFU) where lasers-based experiments are performed.

Lecture notes are available in electronic format on the course's institutional website:

• https://virtuale.unibo.it/course/view.php?id=47169

Students who need compensatory tools because of disabilities or specific learning disorders (SLD) can contact:

• https://site.unibo.it/studenti-con-disabilita-e-dsa/en

to agree on the adoption of the most appropriate measures.

Office hours

See the website of Assimo Maris