Undergraduate Optics Research Articles

Chiral media and optical rotatory dispersion by means of a simple polarimetric experiment for undergraduate students

A simple experiment taking into account media with natural optical activity and their characterization by means of Mueller polarimetry is proposed for undergraduate Optics and Photonics laboratories. The objectives are, first, to review how to characterize dielectric and homogeneous media with natural optical activity by means of a Mueller matrix, taking into account the variation of these characteristics with wavelength, and combining concepts such as polarimetry, natural optical activity, and rotatory dispersion. Secondly, a complete and simple experiment is proposed to characterize a chiral medium by means of its Mueller matrix for different wavelengths. This experiment can be performed by undergraduate students in a standard optics laboratory. As a particular example of a chiral medium, a quartz crystal is used. The experimental results are compared with those published for crystalline quartz to validate the experiment.

The Identification of Criteria for a Lab Report Scoring Checklist to Assess Practical Skills Indirectly in an Undergraduate Optics Course

Practical skills are essential skills in physics courses, especially in the laboratory setting. Therefore, these skills must be appropriately assessed to ensure undergraduates' readiness in the working environment with adequate skills. This paper aims to identify the criteria for a scoring checklist to assess practical skills indirectly in an undergraduate optics course. This study employed a Developmental Research Type 1 design using qualitative and quantitative methods. A scoring checklist is constructed using the ADDIE instructional model of five main phases: (1) Analysis, (2) Design, (3) Development, (4) Implementation, and (5) Evaluation. In this paper, the researcher describes the first three phases of producing the lab report scoring checklist to assess practical skills indirectly among undergraduates in an optics course. In conclusion, a set of 47 criteria to assess practical skills indirectly among undergraduates in an optics course has been identified and is ready for the next stages of analysis. The process of identifying suitable criteria can be replicated where applicable to another course to identify or generate criteria that fit the study context.

Femtosecond excitation of two-photon absorption in ruby

We report two-photon absorption in ruby in an experiment simple enough to reproduce in an undergraduate optics course. The high peak power of a femtosecond (fs) pulse from an unamplified titanium:sapphire laser is sufficient to drive a two-photon transition to ruby’s broad absorption bands, with subsequent emission at 694 nm from the metastable state. This experiment uses pulses with tens of nanojoules rather than the tens or hundreds of millijoules required for nanosecond experiments, and can be performed with trivial instrumentation – eliminating photomultiplier tubes in favor of simple, inexpensive photodiodes with no amplification or signal processing. A two-photon measurement provides excellent educational value for undergraduate students and expands the repertoire of pedagogical optics experiments in an interesting direction.

Hooke’s law experiment using an electronic speckle pattern interferometry

This paper presents an approach based on a laser interferometer set-up to perform an experimental study of Hooke’s law for the case of the bending of a cantilever beam. We used weights and a pulley to deform the beam laterally and measured displacement with an electronic speckle pattern interferometer (ESPI). The ESPI set-up was built using items commonly found in an undergraduate optics laboratory and the software used for the measurement as presented in this paper is available for anyone to use. This represents an attempt at content development with an ESPI; development of various types of content with ESPIs can broaden the horizons of higher education and enhance classroom environments.

Microscope projection photolithography based on liquid crystal microdisplay

We developed a microdisplay-based microscope projection photolithography (MDMPP) technique in which a liquid crystal (LC) microdisplay is used as a reconfigurable photomask for a microscope projector. The LC microdisplay provides a significant advantage in terms of cost and speed since patterns can be generated through software instead of redesigning and fabricating glass photomasks. The constructed MDMPP system could produce line patterns as narrow as 2.4 µm, smaller than that specified by the diffraction limit, with the aid of a 4× objective lens. The achievement of a linewidth smaller than the theoretical limit may be ascribed to a combination of overexposure and the underetching effect, in addition to the good optical performance of the system. In a diffraction experiment performed with fabricated slits, the application of the MDMPP technique helped provide various patterns of the slits, demonstrating the potential usefulness of the MDMPP system in undergraduate optics courses. We expect that MDMPP can contribute to the field of physics education and various areas of research, such as chemistry and biology, in the future.

Promoting optical fibre sensor technology with educational experimental setup

This work shows the production steps of two optical fibre sensing setups which were specially designed for the activities of the 2018 Photonics Lab Open Day realized at the Federal University of Technology—Paraná in Brazil as a celebration of the first International Day of Light (16 May). The systems are based on the sensing properties of fibre Bragg gratings, a well-established photonic sensing technology but not covered in regular undergraduate Optics courses. The demonstrations of optical fibre sensing properties by means of funny scientific activities intended to stimulate high school and college students’ interest in science, seeking greater engagement of these students in the research projects developed at the University. Fibre Bragg ability of detecting mechanical vibration and temperature changes was used to measure the temperature of the attendee’s breath and vibrations produced during a short walk. Demonstrations were realized in a contest where students were challenged to walk smoothly over a flat surface instrumented with vibration sensors, as well as to blow into a tube containing the temperature sensor. Steps of the sensing systems implementation are provided in detail including aspects concerning to the choice of the apparatus design and the installation of the sensors.

Simple undergraduate experiment for synthesizing and analyzing non-uniformly polarized beams by means of a Fresnel biprism

A simple scheme to synthesize non-uniform patterns of polarization across the transverse section of a beam is proposed with the standard materials in an undergraduate optics laboratory. The experiment is based on the superposition of two orthogonally polarized fields obtained by using a Fresnel biprism and dichroic polarizers. Although no interference pattern appears in the superposition area, a non-uniformly totally polarized field is synthesized. Analytic expressions for the Jones vector and Stokes parameters of the output beam are calculated and, in the process, students can cement their knowledge about the representation of polarized light with these formalisms. The experimental polarization pattern is either obtained from intensity measurements with a CCD camera or measured directly with a commercial polarimeter modified with a pinhole. This experiment will help students discover an easy way to vary the state of polarization across the transverse section of a light field.

Measuring the spatial resolution of an optical system in an undergraduate optics laboratory

Two methods of quantifying the spatial resolution of a camera are described, performed, and compared, with the objective of designing an imaging-system experiment for students in an undergraduate optics laboratory. With the goal of characterizing the resolution of a typical digital single-lens reflex (DSLR) camera, we motivate, introduce, and show agreement between traditional test-target contrast measurements and the technique of using Fourier analysis to obtain the modulation transfer function (MTF). The advantages and drawbacks of each method are compared. Finally, we explore the rich optical physics at work in the camera system by calculating the MTF as a function of wavelength and f-number. For example, we find that the Canon 40D demonstrates better spatial resolution at short wavelengths, in accordance with scalar diffraction theory, but is not diffraction-limited, being significantly affected by spherical aberration. The experiment and data analysis routines described here can be built and written in an undergraduate optics lab setting.

Using flatbed scanners in the undergraduate optics laboratory—An example of frugal science

We describe the use of a low-cost commercial flatbed scanner in the undergraduate teaching laboratory to image large (∼25 cm) interference and diffraction patterns in two dimensions. Such scanners usually have an 8-bit linear photosensor array that can scan large areas (∼28 cm × 22 cm) at very high spatial resolutions (≥100 Megapixels), which makes them versatile large-format imaging devices. We describe how the scanner can be used to image interference and diffraction from rectangular single-slit, double-slit, and circular apertures. The experiments are very simple to setup and require no specialized components besides a small laser and a flatbed scanner. Due to the presence of Automatic Gain Control in the scanner, which we were not able to override, we were unable to get an excellent fit to the data. Interestingly, we found that the less-than-ideal data were actually pedagogically superior as it forced the students to think about the process of data acquisition in much greater detail instead of simply performing the experiment mechanically.

Experimental method to characterize the retardance function of optical variable retarders

In this work, we present an experimental method to characterize variable optical retarders, which can have linear or non-linear behavior of the retardance variation. A theoretical analysis of such is presented using a combination of Stokes vectors and Mueller matrixes for three different optical retarders. A straightforward method for phase unwrapping, or reconstructing the original phase from the measured retardance, is proposed that yields high-accuracy results. This work can be used in an undergraduate optics lab to help students understand the concepts of retardance and its control and also how variable retardance devices work.

Reflection of a polarized light cone

We introduce a visually appealing experimental demonstration of Fresnel reflection. In this simple optical experiment, a polarized light beam travels through a high numerical-aperture microscope objective, reflects off a glass slide, and travels back through the same objective lens. The return beam is sampled with a polarizing beam splitter and produces a surprising geometric pattern on an observation screen. Understanding the origin of this pattern requires careful attention to geometry and an understanding of the Fresnel coefficients for S and P polarized light. We demonstrate that in addition to a relatively simple experimental implementation, the shape of the observed pattern can be computed both analytically and by using optical modeling software. The experience of working through complex mathematical computations and demonstrating their agreement with a surprising experimental observation makes this a highly educational experiment for undergraduate optics or advanced-lab courses. It also provides a straightforward yet non-trivial system for teaching students how to use optical modeling software.

Measurement of sub-natural linewidth AC Stark shifts in cold atoms: An experiment for an advanced undergraduate laboratory

We measure sub-MHz AC Stark shifts, also known as light shifts, in an undergraduate laboratory setting using Raman pump-probe spectroscopy to observe sub-natural linewidth spectral features in the transmission spectrum of a weak probe beam passing through a sample of cold 85Rb atoms confined in a magneto-optical trap. To make this observation a pair of inexpensive fast photodiodes and acousto-optic modulators is needed, in addition to equipment commonly found in advanced undergraduate optics labs with laser cooling and atom trapping setups. A theoretical description of light shifts accessible to junior and senior-level physics majors is provided.

Bringing science policy into the optics classroom: Solid state lighting and United States lighting standards

The challenges associated with the development of innovative energy efficient technology require a new generation of skilled and creative scientists and engineers. Moreover, it is vital that they possess the ability to communicate their expertise to the general public and to serve as advisors and participants in the development of science policy. This paper describes a curriculum for a course in optics that investigates the physical principles and policy aspects of solid state lighting. Recent legislation places stringent efficiency and reliability requirements on lighting, promoting the development of new commercial lighting options. The physics of solid state lighting fits naturally into the undergraduate optics curriculum, and the policy aspects provide students with an engaging connection between science and society.

Accurate measurements of refractive indices for dielectrics in an undergraduate optics laboratory for science and engineering students

Based on our novel method recently published in the Am. J. Phys. 77 337–43 (2009) for finding precise values of the indices of refraction for dielectrics from measurements of the polarized light reflected by the surface, in this paper we propose an improved technique for finding Brewster angles with a better precision, of 0.001°, using the same relative inexpensive optical equipment provided by the PASCO Scientific company and a simpler setup. The goal is to implement our procedure in a 3 h optics laboratory for undergraduate students using two different laser–dielectric systems. As compared to our previous work, now we eliminate the random fluctuations of the experimental time-dependent reflectance by controlling the irradiation time on the dielectric surface (and thus avoiding the overheating of the surface) and by using lasers which are stable during the data acquisition process. Also, in the present experiment, we use a computer-based filtering procedure of the experimental reflectance during the data acquisition process for increasing the precision of the measurements at any angle of incidence.

A simple, inexpensive photoelastic modulator

A block of birefringent gelatin acts as a variable retarder when driven harmonically by a speaker coil and can be used to vary the polarization of a laser beam sinusoidally. We model this effect with Mueller matrices and show that the gelatin behaves much like a commercial photoelastic modulator and is suitable for a variety of polarimetry experiments in an advanced undergraduate optics course.

Constructing and using a low cost speckle pattern interferometer for analysis of musical instruments.

Following the design of Moore [Am. J. Phys. 72, 1380 (2004)], a speckle-pattern interferometer for use in exploring the mode shapes of vibrating structures, especially musical instruments, has been constructed. The interferometer was built primarily by undergraduates with mostly common optical elements found in any undergraduate optics laboratory. The interferometer uses a FireWire (IEEE 1394) camera, which has a built-in frame-grabbing capability, eliminating the need for expensive frame-grabbing hardware. The interferometer has been used to study vibrating structures such as snare drum heads, mandolins, and a tennis racket. The interferometer has also been used to study the the vibrational properties of a cured carbon fiber disk. The design and implementation of an affordable speckle-pattern interferometer along with a brief overview of some of the results of research projects conducted with undergraduate students will be presented.

Colour mixing based on daylight

Colour science is based on the sensation of monochromatic light. In contrast to that, surface colours are caused by reflection of wide sections of the daylight spectrum. Non-spectral colours like magenta and purple appear homologous to colours with spectral hue, if the approach of mixing monochromatic light is abandoned. It is shown that a large region of the colour space can be covered by mixing three primary colours derived from lossless spectral decomposition of daylight. These primaries are specified by hue, saturation and luminosity. Duality of additive and subtractive mixing is formulated quantitatively. Experimental demonstrations of calculated results are suggested. This paper is intended for undergraduate optics courses, and advanced interdisciplinary seminars on arts and physics.

Development of a variable spectral-width, wavelength-tunable light source using a superluminescent diode with optical feedback

We have constructed a variable spectral-width, wavelength-tunable light source using a non-fiber-coupled broadband superluminescent diode device with an optical feedback mechanism. As lasing occurs, a strong output light which is linearly polarized and monochromatic is obtained. The spectral width varies with the injection current and the optical feedback ratio. By incorporating a dispersing prism into the feedback branch, a wavelength-tunable, external-cavity-feedback laser source is achieved. The result is a convenient, inexpensive apparatus suitable for experiments in undergraduate optics courses.

Phase-shift interferometry with a digital photocamera

A phase-shift interferometry experiment is proposed, working on a Twyman–Green optical configuration with additional polarization components. A guideline is provided to modern phase-shift interferometry, using concepts and laboratory equipment at the level of undergraduate optics courses.

Fourier spectroscopy of ultrashort laser pulses

We describe a Fourier-transform spectrometer appropriate for use in an undergraduate optics laboratory. The modular design, which uses off-the-shelf equipment, is suitable for determining the spectra of ultrashort pulsed and continuous light sources. The spectrometer does not require equal step sizes for the motion of the mirror. An algorithm interpolates the phase of both a reference and an unknown light beam at equal intervals before performing the Fourier transform. The interferometer scan and the phase and spectral analysis are performed in a few seconds, making the apparatus a useful tool for teaching concepts of temporal coherence and Fourier spectroscopy.