Experiments In Physical Optics

M. Francon, N. Krauzman, J.P. Mathieu, M. May

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781000143935
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

Experiments in physical optics for undergraduate and graduate classes. Provides the theoretical basis of each experiment and describes the apparatus required and necessary adjustments. Most of the experiments require only lenses, prisms, mirrors, and polarizers, and can be projected on a lecture screen or viewed by television.

1 Sources of Continuous and Line Spectra

DOI: 10.1201/9781003062349-1

1.1 LIGHT SOURCES

1.1.1 Carbon arc

The types of carbon arcs suitable for experiments in optics have a vertical carbon rod of 0.5 cm diameter and a horizontal one of 0.7 cm diameter (fig. 1.1). This latter must be connected to the positive terminal of the D.C. source; its crater C serves as the source in the H direction. It radiates approximately as a black body at a temperature of 3,500 °C and consequently its emission spectrum is continuous. Its brightness is more than 10⁸ nits. The arc is lighted by bringing the two carbon rods into contact and then separating them immediately by a distance of about one centimeter. The crater C must not be masked by the negative carbon rod in the horizontal direction.

Figure 1.1

The voltage applied to the arc is of the order of 45 volts; the current, normally 4 to 5 amps, may be increased for a short duration in order to increase the light intensity. The arc has a characteristic V =f(I) with a negative slope. It is therefore essential, to obtain a stable arc that a D.C. voltage of 110 or 220 volts be applied and a rheostat with a maximum resistance of 20 Ω (110 V) or of 50 Ω (220 V) be connected in series with the arc.

If one wants to examine the radiation from the flame F of the arc, one should observe in a direction normal to the plane of the figure (1.1); or a carbon arc with vertical carbon rods (fig. 1.2) should be employed. In this case, the arc can be worked on alternating current.

Figure 1.2

1.1.2 Arcs between metallic electrodes

1 Replacing the two carbon rods in figure 1.2 by iron rods of diameter 0.4 cm approximately and using a current of 2.5 to 3 A, we obtain a flame emitting a line spectrum; the spectrum consists of a large number of lines in the visible and the ultraviolet regions continuing up to 0.2 μ. These lines given in various tables (^*) are used as secondary standards for the measurement of wave-lengths.

* Atlas of Fabry and Buisson; Atlas of Vatican.

2 The arc between copper rods gives a spectrum which is also rich in lines.

3 The arc between tungsten electrodes, contained in a bulb filled with an inert gas, provides a source of very small dimensions (pointolite lamp), one of the electrodes being spherical in form; the brightness is of the order of 10⁷ nits.

1.1.3 Incandescent lamps

1.1 Lamps with tungsten filaments in an atmosphere of inert gas are well known. Their brightness is of the order of 10⁷ nits. The form given to the coiled filament is often unsuitable for experimental purposes. However, it is possible to obtain filaments in which the axis of the helix is a straight line.

1.2 Lamps with tungsten ribbon have a better geometrical shape. They work under a voltage of 6 to 10 V and with a current of 10 to 20 A. They are worked on mains with the help of a transformer.

1.3 Tube lamps with tungsten filament and with quartz envelope, working directly on the mains, have a low brightness but produce radiations of wavelengths up to about 1.3 μ. These are very suitable for use in near infra-red.

1.1.4 Gas discharge

1 Lamps containing sodium vapour produce a light which is sufficiently monochromatic for many purposes (line D₁ λ₁ = 5896 Å, line D₂, λ₂ = = 5890 Å). Sodium being a solid at ordinary temperature and its vapour pressure being very small, the lamp contains argon which enables the discharge to pass between the electrodes and gives a small amount of pink light. The metal evaporates as the temperature rises due to the discharge and the yellow light of sodium starts appearing. After a few minutes this is the only light which remains visible.

2 The lamps containing other metals (K, Rb, Cs, Zn, Cd, Hg) function in an analogous manner.

All the preceeding lamps work on 110 V or 220 V through an auto-transformer supplied especially with the lamp. When the steady state is reached, the voltage across the terminals is of the order of 20 V and the current is of the order of 1 A.

3 Lamps containing mercury vapour which attain a pressure of ten atmospheres and have a quartz envelope, yield an intense source of radiations in the visible and the near ultra-violet. The principal lines are

λ(Å) 3022 3130 3655 4047 4358 5461 5780

They do not contain any rare gas. One of the electrodes E (fig. 1.3) is cold; the other E′ is adjacent to an auxiliary electrode e put in series with a resistance R of 20,000 Ω contained in the lamp which works on 110 V or 220 V across a special inductance S. When the lamp is switched on, a discharge passes between E′ and e and energizes the lamp; then, the current passes between E and E′ on account of the high value of R. After a few minutes, the brightness reaches a value of the order of 10⁷ nits.

Figure 1.3

4 These lamps can be furnished with a glass envelope which suppresses ultra-violet.

5 On the other hand, they may have glass envelopes which are opaque to visible light and transparent to ultra-violet.

6 Mercury lamps in which the pressure rises to 200 atmospheres and which have to be cooled by circulating water, have a brightness approaching 10⁹ nits; their spectrum is almost continuous.

High voltage (thousands or ten thousands of volts) discharge in an atmosphere of gas at low pressure (of the order of 10⁻³ atm.) yields two sources of secondary interest.

7 The hydrogen tube (Geissler tube) whose emission contains in particular the lines of the Balmer series.

8 The mercury tube with an envelope of quartz or of a special glass emits, under these conditions, very little radiation in the visible spectrum, but principally the resonance line (λ = 2537 Å).

1.1.5 Lasers

There exist in the market diverse models of lasers with He-Ne, which yield a parallel beam of coherent, monochromatic radiation λ = 6328 Å, carrying a flux of 5 to 50 mW according to the model. The weakest model suffices for the experiments described here.

In the usual experiments, it is sometimes necessary to ...

Table of contents

• Cover Page
• Half Title Page
• Title Page
• Copyright Page
• Preface Page
• Contents Page
• 1 Sources of Continuous and Line Spectra
• 2 Interference Phenomena with Non-localized Fringes
• 3 Interference Phenomena with Localized Fringes
• 4 Michelson Interferometer
• 5 Temporal Coherence and Spatial Coherence
• 6 Multiple Beam Interference Produced by Semi-reflecting Plates
• 7 Applications of Interferometry
• 8 Diffraction at a Finite Distance (Fresnel)
• 9 Diffraction at Infinity (Fraunhofer)
• 10 Reflection, Refraction, Dispersion
• 11 Polarization by Reflection
• 12 Polarization by Double Refraction
• 13 Polarizers Based on Double Refraction
• 14 Interference in Polarized Light
• 15 Study of Polarized Vibrations
• 16 Artificial Birefringence
• 17 Rotatory Polarization
• 18 Dichroism
• 19 Properties of Electromagnetic Radiations
• 20 Thermal Radiation
• 21 Absorption and Emission of Radiations by Atoms and Molecules
• 22 Luminescence
• Appendices
• Index