Perhaps you could explain to Mr Pratheep, who asked the question, how you actually conduct the experiment, assuming you know this. Since he asked the question, I think that he deserves to get details of your method. Simply saying "Use a spectrometer" and adding no further details is a little like intellectual strutting. How do you 'use' a spectrometer? How do you translate the results on the spectrometer into a measurement of emulsion depth? What did you use it for? An emulsion depth measurement, or some other displacement? What was the error? Were these errors taken into consideration? Were they random errors? Was there any statistical analysis at all at Digilens? Did Digilens publish results? Do you have a reference? Do you have a theoretical basis, or any calculations? Perhaps you could point Mr Pratheep to someone at Digilens to discuss their results? I think Mr Pratheep needs a little more than intellectual posing for the fan base.
Whatever you did, or did not do at, Digilens, without details of method and/or a reference and/or some theory, the 'spectrometer method' seems of no value to Mr Pratheep. It also depends on the application; for most applications, emulsion depth to an error of 10% or even more is acceptable and that may be the reason for the Digilens result, assuming there was one. Since the rms (Did you take account of the rms at Digilens?) is usually below this, a certain inaccuracy is acceptible.However, for different applications, an rms of 10% may be disastrous. For example, an rms of 10% in a high speed communication channel with an FBG would lower the bandwidth, perhaps considerably