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OXP-16 Optical Filters

  Topics:
Absorption
Low-, High-, Band-Pass
Interference Filter
Dichroitic Filter
Neutral Density Filter
IR Filter
Lambert - Beer Law

Johann Heinrich Lambert
1728 – 1777

 


August Beer describes the absorption process as a reduction of the transmitted light by absorbers embedded in a transparent material. If one takes into consideration the spectral characteristics of these absorbers one gets the basics for a colour filter: a material with a spectral absorption profile strongly depending on the wavelength. In contrary to such absorbing broad band filters, interference filters are able to transmit light within bandwidths of only 10 nm and below. Another type of filters is able to cut off the continuous spectrum from a certain wavelength on, so called cut-off filters. One distinguishes between long-, short-, and band- pass filters, depending whether long, short or only a certain range of wavelengths are transmitted. All these filters are mainly used for filtering spectral or laser lines and separating excitation from emission light, because of their spectral selectivity. On the other hand, there are filters which dim the light over the whole visible spectrum by a certain factor, so called neutral density filters. Similar types of filters are available for the near UV and IR region.
In this experiment different kinds of filters are presented. With a set of colour filters transmission and absorption of certain spectral ranges are demonstrated. Neutral density filters are provided to dim the whole spectral range. An infrared LED and an IR filter demonstrate light filtering in the IR range.




 

Examples of Investigation and Measurement


Colour filters
The spectrum of a white light source will be dispersed by an optical grating and can be observed on a screen. In the white light beam, different colour filters will be placed and the change in the spectrum will be observed and detected by a photodiode.

Neutral density filters
Intensity reduction over the whole spectrum is achieved by neutral density filters. The overall reduction as well as dimming of a certain colour is detected by a photodiode.

Interference filters
White light, sent through a pair of coated plates, shows colourful interference stripes. Together with a colour filter a certain colour can be selected which shows a more narrow spectrum than generated by the colour filter only.


IR filters
Since the detector in use is sensitive to infrared light, a filtering experiment of IR light with special IR filters can be performed.


 

 

 

 

OXP-16   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
2

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).
 

1 04.0192

Set of eight optical filters

This set of filters comprises of one high- , one low-, one band-pass filter and one band-block filter, two neutral density filters, one IR block and one IR pass filter. The acrylic (glass in the case of the IR block filter) filter plates can be fixed onto a plate holder (02.1024).
Dim:
50 mm x 50 mm x 3 mm
 

1 04.0630

Fabry Perot, mounted in click 25 mount

A pair of parallel semi-transparent high quality mirrors in close contact act as a Fabry Perot filter. The Fabry Perot 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).
 

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
05.0030
05.0040

 

LED white in housing
LED infrared 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 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