I have some laser diodes. I want to know how to measure the wavelength of laser diodes ranging from visible to near infrared? (300 nm to 1100 nm)
What type of instrument/meter do I need to use? spectrometer, spectrophotometer, wavelength meter, reflectometer, oscilloscope or what and how?
You want a wavelength meter if you have one or otherwise a spectrometer. In more detail:
A wavelength meter uses an interferometer to measure wavelength. It can measure wavelengths very accurately.
A spectrometer measures a spectrum, that is intensity vs wavelength. The wavelength at the peak intensity is what you are looking for.
A spectrophotometer is used to measure the transmission spectrum of some material. This is not what you want.
A reflectometer measures reflectivity. Again, not what you want.
Oscilloscopes measure electrical voltage vs time. Again, not what you want.
