Measuring Wavelength

[frank_1257]

Just wondering if anyone here knows of an easy way to measure the wavelength of a laser. I have an idea in mind, I was just wondering if you have an idea! Maybe something easier than my idea...

You can get a very crude diffraction spectrometer on ebay for under $40
DIFFRACTION GRATING SPECTROMETER SPECTROSCOPE

Item number: 330272609920
ok now heres how I do it for $99 to several thousand you can get a box that is called a monochromator it has a tiny little vertical entrance slit on a sealed box. Inside the box there are 2 mirrors and a geared movable diffraction grating on the outside of the box is a micrometer dial. The gratings come made for many spectrums of resolution. The best for us guys is the 1200Gr/mm 500nm blazed one. These are essentially a simple hologram. This monochromator can be tested by allowing a visible light source lets say a 632.8nm he-ne laser into the first entrance slit through a piece of scotch tape to diffuse the laser light, stronger lasers would require reflected, not direct laser light into the box entrance. Now you you turn the micrometer and the dial readout directly corresponds to the wavelength you are testing for, when and if the monochromator is correctly calibrated you come up on 632.8 nm actually reads mm the light hitting the movable diffraction grating is reflected directly out of the monochromators secondary exit slit. These slits are interchangable and the narrower they are the higher the wavelength resolution you can obtain. Now heres how the IR wavelength determination is done a small photodetector, a pin photodiode is mounted in a cap over the exit slit and hooked to an amp meter with a current source or a diode resistance checker function of the meter. As you hit the wavelength emitted by lets say an ir 808nm laser diode the needle jumps to a peak then you simply read off the micrometer and that gives you the actual wavelength to 0.1 nm. If this seems too crude a good burleigh brand used wavelength meter is going to cost about $5000 or more! Using an internet search of Google or Ebay for: Jobin Yvon or Jarrell Ash or other monochromators will give pdf pictures of these. Mine is a Jarell Ash Monochromator 18.

Happy spectroscopy determining to you!

A decent used unit might cost $300-500 or if lucky $99 many monochromators setup for UV or other spectrums so read CAREFULLY before buying! Many are not manually readable and require a computer and hang on externally attachable photomutiplier tube.
Many of these with the right blazing of diffraction grating can be converted to home use with foil tape flat black spray paint and a vertical razor cut to create a exit slit. If it has a stepper motor and no manual control it will be difficult or impossible to use. People like Jobin Yvon make tiny little compact but still expensive plastic units that will cost you up to a grand or so. I have heard rumor that for a few thousand usb photospectrometers can be had but have not really seen any. Just A good laser power meter new costs $2000 plus Yipes!


So study first then buy or you will be sorry. The cheap diffraction spectrometers are sometimes accurate to 5nm. Who knows a really industrious person might be able to build a small meter with a commonly available diffraction grating.

[frank_1257]

The MonoSpec 18 Monochromator/Spectrograph is the ultimate in high quality compact instruments. Only 6.5 x 6.5 x 5 inches, it features much greater user flexibility than any instrument on the market today. The MonoSpec 18's 90° optical configuration lends itself to easy adaptability in OEM system design.

Because its kinematic grating is easily interchanged, the MonoSpec 18 has a wavelength range that extends from 190 nm - 40µm. There are many gratings available to suit a variety of requirements for resolution and dispersion. Plus ... scattered light is at a minimum due to the Crossed Czerny-Turner optical design, which also virtually eliminates re-entry spectra.

By a simple change in the exit flange, the MonoSpec 18 is converted from a monochromator to a spectrograph. The MonoSpec 18 Model 82-479 Spectrograph is configured to provide an expanded focal plane at the exit port when the spectrograph flanges are in place. This unique feature allows the user to interface the MonoSpec 18 with a variety of multielement detectors including CCD, or photodiode systems.

Monochromators are passive optical devices that can be used to present one wavelength of light at a time. They include an optical configuration of lenses and mirrors, a separating element (commonly a diffraction grating), and an optomechanical means for selecting the wavelength of light displayed.

Top of Page

Popular Ruled Diffraction Gratings

Groves/mm

Blaze Wavelength

Useful Spectral Range

Reciprocal Linear Dispersion nm/mm

2400

260 nm

185 nm-550 nm

2.2

1800

250 nm

180 nm-550 nm

3.3

1200

300 nm

180 nm-550 µm

3.3

1200

500 nm

350 nm-1.2 µm

6.6

600

500 mm

400 nm-1.2 µm

6.6

600

1.0 µm

700 nm-2.0 µm

13.2

300

300 mm

180 nm-750 nm

25.6

300

2.0 µm

180 nm-3.6 µm

37.8

150

4.0 µm

7.0 µm-21.0 µm

75.4

100

6.5 µm

21.0 µm-40.0 µm

128.0

50

10.0 µm

7.0 µm-21.0 µm

108.0

30

30.0 µm

21.0 µm-40.0 µm

180.0

Top of Page

MonoSpec 18 Systems & Accessories

82-477

MonoSpec 18 Monochromator 156 mm focal length, f/3.8. Crossed Czerny-Turner with entrance and exit slits 90° apart. With digital micrometer drive calibrated for a 1200 g/mm grating. Requires one grating and two slits.

82-479

MonoSpec 18 Spectrograph. Spectrograph is equipped with a coupling flange for allowing attachment of OMA (EG&G/PAR) or OSMA (Princeton Instruments) array detector. Requires one grating and one slit.

Accessories

00-6279

Exit Focus Tube for monochromator without slit.

00-6260 Coupling Flange allowing attachment of OMA (EG&G/PAR) or OSMA (Princeton Instruments) array detector. 00-4420 MonoSpec 18 Operator's Manual 00-6845 Grating Mount (Alignment bracket/holder).

Top of Page

Ruled and Holographic Gratings

28 mm x 46 mm ruled area on a glass blank 32.0 x 50.0 x 6.4 mm
The following grating assemblies include mounting to the alignment bracket/holder

11-115 Ruled grating, 2400 g/mm, 250 nm blaze 11-120 Ruled grating, 1800 g/mm, 250 nm blaze 11-125 Ruled grating, 1200 g/mm, 300 nm blaze 11-130 Ruled grating, 1200 g/mm, 500 nm blaze 11-135 Ruled grating, 600 g/mm, 500 nm blaze 11-140 Ruled grating, 600 g/mm, 1.0 µ blaze 11-145 Ruled grating, 300 g/mm, 300 nm blazev 11-150 Ruled grating, 300 g/mm, 2.0 µ blaze 11-155 Ruled grating, 150 g/mm, 4.0 µ blaze 11-160 Ruled grating, 100 g/mm, 6.5 µ blaze 11-165 Ruled grating, 50 g/mm, 10.0 µ blaze 11-170 Ruled grating, 30 g/mm, 30.0 µ blaze 11-220 Holographic grating, 1200 g/mm, 200-800 range 11-230 Holographic grating, 600 g/mm, 200-800 range

The following gratings require an 11-098 alignment bracket/holder

985411420 Ruled grating, 1800 g/mm, 400 nm blaze 985411422 Ruled grating, 1800 g/mm, 500 nm blaze 985411917 Ruled grating, 1200 g/mm, 240 nm blaze 985411920 Ruled grating, 1200 g/mm, 300 nm blaze 985411924 Ruled grating, 1200 g/mm, 600 nm blaze 985411926 Ruled grating, 1200 g/mm, 700 nm blaze 985412917 Ruled grating, 600 g/mm, 240 nm blaze 985412918 Ruled grating, 600 g/mm, 300 nm blaze 985412920 Ruled grating, 600 g/mm, 400 nm blaze 985412926 Ruled grating, 600 g/mm, 700 nm blaze 985412937 Ruled grating, 600 g/mm, 2.5 µ blaze 985413922 Ruled grating, 300 g/mm, 500 nm blaze 985413930 Ruled grating, 300 g/mm, 1.0 µ blaze 985413938 Ruled grating, 300 g/mm, 3.5 µ blaze 985414921 Ruled grating, 150 g/mm, 450 nm blaze 985414942 Ruled grating, 150 g/mm, 5.0 µ blaze 985415424 Ruled grating, 100 g/mm, 600 nm blaze 985415444 Ruled grating, 100 g/mm, 6.0 µ blaze 985417457 Ruled grating, 40 g/mm, 22.5 µ blaze

Many additional options and accessories are available for the MonoSpec 18. Please contact the factory or your representative for more information.

Specifications

Focal Length:

156 mm

Aperture:

f/3.8

Resolution:

0.6 nm with
1200 g/mm grating

Reciprocal Linear Dispersion:

4.5 nm/mm with
1200 g/mm grating

Stray Light:

0.0015%

MonoSpec 18 Monochromator / Spectrograph







Overview
MonoSpec 50
MonoSpec 27
MonoSpec 25
MonoSpec 18
MonoSpec 10
LambdaSCAN
Accessories
Detectors
Gratings

Top of Page Home Contact Us

[drlava]

I should have just asked, Do you want to borrow my manual monochromator ? 1 +/- .5 nm resolution

Steve

Ditto on the manual monochromator. These can be had for cheap/free from universities throwing out their old spectrophotometers.

[joephie]

i have problematic and need help for solution

i used spectrometer spex 750M of jobinyvon. apparently i moved out the grating, when i put back and try to calibrate the grating the value wont be stable, it just kept adjusting... for example, when calibrating using mercury(Hg) in 5460 point, the delta lambda value always different on 3 times meassuring, the delta lambda 0.00, 0.80, and then 1.10

what could have happened? how would i fix this

[rajaphysics]

hi joephie,
in our lab we are also using spex 750m spectrometer, we are planning to change the system from MS-DOS to windows(labview) operated. I am facing interfacing problems using GPIB.
if U have the labview drivers and programs for control of this spectrometer can U please kindly send them .
thank U very much