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OXP-09 Spectral Analysis

  Topics:
Spectrograph
Monochromator
Grating Diffraction
Continuous / Line Spectrum
Spectral Resolution

Henry Augustus Rowland
1848 – 1901

 


While Fraunhofer is considered as the inventor of gratings, Henry Rowland has to be mentioned as the developer of manufacturing techniques and the constructor of excellent ruled gratings which was his greatest contribution to science. In 1882 Rowland’s gratings were larger and more accurate than any previous ones. For a whole generation they were the base of physical, chemical and astronomical spectroscopy. Rowland himself used his gratings to prepare a map of the solar spectrum.
In spectroscopy the first spectral apparatuses were used to characterize the chemical elements according to their spectral emission lines. Since the spectral position of these lines were interesting, spectroscopes were sufficient for this task. Intensity estimations were done by the eye, a very unsuitable instrument for absolute intensity determination. Therefore spectrographs and monochromators were invented to perform quantitative measurements with a detector of known spectral response.
This experiment builds a model for a standard grating monochromator as well as a spectrograph. With a white light lamp a source for a continuous spectrum is provided. Here the spectrometer is used as a spectrograph and grating diffraction of first and higher orders as well as absorption spectroscopy can be demonstrated. Using the set-up in the monochromator mode in combination with a spectral lamp, line spectra are detected and features like spectral resolution or line profile are measured.



 

 


 

Examples of Investigation and Measurement


Grating spectrograph
On a screen line and continuous spectra of a spectral or white light lamp are observed. When inserting an absorbing sample in the beam path, the sample’s transmission spectrum can be seen. Further, distortions of higher order diffractions and their correction are discussed.

Grating monochromator
Since the spectral lines are extremely narrow compared to the resolution of the instrument, line profiles and spectral resolution are defined and influenced by the slit widths of the spectrometer.
 


 

 

 

 

OXP-09   Required Equipment


2  
 


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

02.1024

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 02.1608

Screen holder

A screen holder without a carrier is used in a spectrometer setup. In combination with a screen, the screen holder replaces the variable exit slit. The holder is made out of special anodized aluminum and can be fixed onto a carrier with a pair of steel bolts.

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
 

Plano convex lens f=40 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).
 

  04.0066

Plano convex lens f=20, mounted in click 25 mount with attached light tube

This glass lens mounted onto a click mount 25 mm attached by a light tube is used to focus the light on the detector and reduce the scattered light coevally using the light tube. The whole tube is made out of special anodized aluminum.
Length: 55 mm

  04.0126

Absorption filter

This acrylic filter absorbs the light of a specific spectral range and is used for demonstrating absorption spectra. The filter can be fixed onto a plate holder (02.1024).
Dim:
50 mm x 50 mm x 3 mm
 



  05.0030

 

LED white 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.
 

  05.0106

Spectral lamp with slit and power supply

This unit consists of a light source emitting descrete spectral lines in the visible range.The lamp in its housing is made out of special anodized aluminum fixed onto a mounting plate and can be placed onto an optical rail. The front aperture of the housing is a slit with 1 mm width, which is very helpful in spectrally resolving setups. The lamp is connected to a main switch unit with the following properties:

voltage: 230 VAC / 50 Hz
case dimensions: 200 mm x 160 mm x 62 mm
The spectral lamp provides the main lines at the following wavelengths:

Line                                 Length
red line                        at 615 nm
yellow line                    at 578 nm
green line                     at 546 nm
turquoise line                at 492 nm
blue line                       at 436 nm
purple line                    at 405 nm
 




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.
 




  09.1910

Spectrometer grating assembly with two gratings

Onto a bridge carrier, two adjustable slits are mounted. In a spectrometer setup, one forms the entry and the other the exit slit. Two optical gratings of different grating constants are provided and can be inserted between the two slits on a rotatable base which is graduated from -90 - +90° at intervals of 2°. Alternative to the exit slit, a screen with scale (02.1602) onto a screen holder (02.1608) can be mounted.
The length of the optical slits is 15 mm, the width can be opened up to 1 mm.
The two gratings of 30 mm x 30 mm area fixed on an aluminum holder have a grating constant of 200 l/mm and 600 l/mm respectively.
The metal parts are made out of special anodized aluminum.
 



  09.1920 Spectrometer mirror assembly

On a bridge carrier two high quality concave front-surface mirrors are mounted. In a spectrometer setup, they build the symmetric beam bending unit between entry slit, optical grating and exit slit of the spectrometer.

The two mirrors have the following dimensions:
Diameter: 50 mm
Focal length: 340 mm

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