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OXP-17 Absorption and Emission

  Topics:
Lambert-Beer Law
Absorbance
Fluorescence
Phosphorescence
Absorption / Emission Spectra

Albert Einstein
1879 - 1955

 


A quantum optical description of absorption and emission as a phenomenon of interaction of light with matter is given by Albert Einstein in 1917. He distinguished between the three processes of absorption, spontaneous emission and stimulated emission (whereby the latter builds the theoretical basis for laser operation). Einstein’s derivations are precise and they give a comprehensive formulation of the processes. Nevertheless, for most investigations of absorption and emission the stimulated emission can be neglected and a description based on the laws of Johann Lambert and August Beer is sufficient.
Most colour impressions are generated by absorption. White light is filtered by coloured materials absorbing a certain region of the spectrum and transmitting the remaining light which exhibits a specific colour. In Lamberts law the absorption is a function of the thickness of the absorbing layer, in Beers law it is a function of the concentration of the absorbing species. Some absorption processes are follwed by light emission, so called fluorescence or in some cases phosphorescence.
The laws which are related to absorption and emission are discussed and investigated in this experiment. With an absorbing sample the Lambert-Beer law is verified by measuring the transmitted light with a photodiode. Light sources of different colours are used to excite fluorescent samples. The absorption and emission of light is visualized spectrally using an optical grating.




 

Examples of Investigation and Measurement


Lambert Beer Law
In a first measurement the influence of absorbing material on the intensity of transmitted light is investigated. Parameters like thickness of the sample or the wavelength of the light source are varied and the transmission is detected by a photodiode.

Absorption spectrum
With a white light source and an optical grating the spectral distribution of the absorption profile is visualized and can be observed.

Fluorescence spectrum
Slight changes in the set-up allow the excitation of fluorescing samples with LEDs of different wavelengths. The spectra of absorption and fluorescence are investigated by means of an optical grating.

Phosphorescence
A phosphorescing sample is tested for its wavelength sensitivity. With a photo detector the phosphorescence decay is measured as a function of time.
 


 

 

 

 

OXP-17   Required Equipment


1  
 


02.0500
 

 


Profile rail OCM 650, 500 mm

The high precision optical rails are made out of special anodized aluminum. The rails are the base for various modules attached to carriers.
 




 

1

02.1022

Carrier OCM 650, 20 mm with screen holder

This module can mount optical screens. Through the attached carrier, the screen holder can be placed onto the optical rail. The carrier 20 mm and the holder are made out of special anodized aluminum.

2

02.1024

Carrier OCM 650, 20 mm with attached plate holder

Using a spring loaded blade 50 x 50 mm, plates like filters or gratings can be fixed onto this module. The carrier allows the direct attachment to the optical rail. The carrier 20 mm and the holder are made out of special anodized aluminum.
 

1

02.1602

 

Screen with scale

Experimental results like colour spectra and interference patterns can be visualized on these screens. Horizontal or vertical scales allow calibrations and quantitative measurements; a screen with an aperture is used for observing back-reflected rays. The screens are made out of anodized aluminum plates with one side painted white and can be fixed onto screen holders (02.1022, 02.1608).
 

1
3

02.2126
02.2132

Mounting plate OCM 650 for click 25, including carrier 20 mm
Mounting plate OCM 650 for click 30, including carrier 20 mm

Mounting plates are used to hold optical mounts. A characteristic feature of the mounting plates is the “click” mechanism of the inserts based on spring loaded spheres. Snapping in the groove of the inserted click mount, the optical element is kept in an exact position. On the other hand, the system allows a quick and easy change of the mounted inserts.
The mounting plates are made out of special anodized aluminum. Mounted onto the carrier 20 mm, the mounting plates can be placed onto an optical rail.
 

1

02.6106

4 axis adjustment holder KH650, theta, phi, X and Y, including carrier 20 mm

This adjustment holder mounts a Diode Laser or an LED lamp. Using the fine pitch adjustment screws, the optical axis can be aligned within the range of 3 mm. For fine alignment of the angle of the light beam, two additional pitch adjustment screws are attached onto the back of the holder. The holder and the carrier 20 mm are made out of special anodized aluminum and can be placed onto an optical rail.
 

1 04.0060
04.0062

Plano convex lens f=40 mm, mounted in click 30 mount
Plano convex lens f=60 mm, mounted in click 30 mount

different glass lenses are mounted onto a special anodized aluminum click mount 30 mm by two threaded mounting rings to be used in connection with a mounting plate (02.2132).
 

2 04.0104

Phosphorescing sample in click 25 mount

With this element, the wavelength sensitivity as well as the time dependent decay of a phosphorescing sample can be investigated. A sample of phosphorescing material is mounted onto a special anodized aluminum click mount 25 mm by two threaded mounting rings to be used in connection with a mounting plate (02.2126).
Dia: 20 mm
 

1 04.0194

Set of 3 fluorescent filters

Fluorescence emission is demonstrated through the use of these three filters, effective at different spectral regions. The acrylic filter plates can be fixed onto a plate holder (02.1024).
Dim:
50 mm x 50 mm x 3 mm
 



1 04.0702

Optical grating, 600 lines / mm

This optical grating copy mounted between two glass plates is used for generating a spectrum of the investigated light.
The frame has a size of 50 mm x 50 mm x 2,5 mm and the grating window is 35 mm x 24 mm large.
 

1
1
05.0032
05.0036
05.0038

 

LED red in housing
LED green in housing
LED blue in housing

As universal and easy-to-change light sources, LED lamps are used in optical experiments. The LEDs are mounted onto a 40 mm x 25 mm diameter housing tube made out of special anodized aluminum. For the alignment, the lamps can be fixed onto a four axis adjustment holder mounted onto a carrier. For their operation, the active LDD-05 power supply (07.0206) is required which controls the output power. For the lamps 1 W (white LED: 3W), high brightness LEDs are used.
 

1 07.0010

BNC – Banana adapter connection leads 2x4 mm plugs

This BNC cable is used to connect a photodetector (07.0101) to a digital multimeter (19.0400).
Total length: 1 m
 

1 07.0102

PIN Si Photodetector BPX 61 complete with housing

Using a BNC cable, the photodetector can be connected to a measuring device. Mounted onto a special anodized aluminum click 25 head, the photodetector is to be used in connection with a mounting plate (02.2126).
 

1 07.0206

LDD-05 active power supply

The universal LDD-05 active power supply is used for all laser and LED light sources. It recognizes which source is connected and sets the parameters for it automatically. The unit is equipped with a main switch, a regulation knob for adjusting the laser or LED power and a safety lock. The provided USB bus interface allows control through a personal computer or laptop and qualifies this unit as multimedia source.
The housing is made out of shock-proof plastic with an aluminum front and rear panel.

Voltage: 230 VAC / 50 Hz
Case dimensions: 200 mm x 160 mm x 62 mm.
 




1 09.2720

Absorption unit

This unit consists of a blue colored acrylic cuboid with the size of 60 mm x 40 mm x 20 mm held by a spacer which is mounted onto a carrier 65 mm. By changing the orientation of the cuboid, different absorption lengths can be realized. Using different light sources, the absorption of the unit as a function of the wavelength can be investigated.
The metal parts are made out of special anodized aluminum.
 

1 19.0400

Digital multimeter 3 ˝ digits

he digital multimeter is used for relative intensity measurements of light beams. It has to be connected to a photodetector via banana adapter connection leads.

Specifications:

Display LCD, 3 ˝ digits  
AC voltage ranges 2 / 20 / 200 / 750 V
Frequency range 40 - 400 Hz
DC voltage ranges 0,2 / 2 / 20 / 200 / 1000 V
AC current ranges 2 / 20 / 200 mA / 20 A
Frequency range 40 - 400 Hz
DC current ranges 0,2 / 2 / 20 / 200 mA / 20 A
Resistance ranges 0,2 / 2 / 20k / 0,2 / 2 / 20 MΩ.







 


 


 




 

 

Experiments

OXP-01 Refraction of Light

OXP-02 Prisms

OXP-03 Lenses

OXP-04 Reflection & Transmission

OXP-05 Beam Bending

OXP-06 Refractometer

OXP-07 Diffraction of Light

OXP-08 Optical Gratings

OXP-09 Spectral Analysis

OXP-10 Interference

OXP-11 Interferometer

OXP-12 Holography

OXP-13 Polarisation

OXP-14 Double Refraction

OXP-15 Colour Mixing

OXP-16 Optical Filters

OXP-17 Absorption & Emission

OXP-18 Image Projection

OXP-19 Camera

OXP-20 LED & Laser Diode

 

Kits

Basic Kit

Complete Kit

Advanced Kit