ECDL is an external cavity diode laser, where we give a frequency dependent feedback to a laser diode to reduce its linewidth. Linewidths of the order of 10 MHz and less can be achieved by such a configuration. Can the same thing be done using an LED instead of a laser diode? Of course LED has a much larger linewidth than a laser diode, but can such a frequency selective feedback allow me to create such a laser? ( I thought of getting some expert opinions before attempting it in lab, because making an ECDL is a complicated process)
Are LED and laser diode same? Yes and NO. Yes, because both are made of semiconductor material. No, because one is ordinary light while other is laser light created by stimulated emission. You cannot reduce the LED line-width or control its emission wavelength with the external grating feedback as it is done for ECDL. The main reason is that operation of LED is little different from the laser diode. Unlike laser diode, there is no internal cavity in the LED for the light amplification to take place.
Yes ofcourse. However, at he same time because of the lack of an internal cavity, we will not have internal modes trying to compete with external modes of the cavity and hence single mode region of operation should be much higher. I can always amplify using the external cavity instead of the internal one and that. The only problem that I can see is the reflectivity of the back panel of an LED, if it can be high enough for sustaining a cavity with a grating!!
To achieve lasing you need a low loss gain medium and mirrors. The mesa of an LED might provide (in combination with your external mirror) the necessary feedback, but you will not be able to get enough gain to overcome your losses (intrinsic, mirrors, etc.). The heterostructure design of an LED does not provide wave guiding and the current density in an LED is typically to low for stimulated emission. Good luck!
What about stimulated emission ? A laser is not just a cavity it must also possess strong population inversion and this is realised in semiconductors by using carrier and photon confinement (in general Quantm wells but not only), now a LED is based on spontaneous emission (no threshold current). So it seems quite difficult for a LED even with very selective cavity to attail laser threshold.
it is possible in terms of amplifying the signal and reducing the linewidth but there is one significant problem would arise which is the feedback signal from the light being bounced back from the mirror to the source can cause fluctuations in the output intensity and make it unstable beam pattern.
Just some extra thoughts....
An ECDL works by using a frequency-selective element, such as a diffraction grating, to provide optical feedback to a laser diode, thereby narrowing its linewidth. This is possible because laser diodes are capable of producing coherent light, which means the light waves are in phase and have a definite relationship to each other.
LEDs, on the other hand, produce incoherent light. The light waves emitted by an LED are not in phase and do not have a definite relationship to each other. This is a fundamental difference between LEDs and laser diodes, and it is the reason why LEDs have a much broader linewidth than laser diodes.
Because of this fundamental difference, it is not possible to create an ECDL using an LED. The frequency-selective feedback mechanism of an ECDL relies on the coherence of the light produced by the laser diode. Since an LED does not produce coherent light, this mechanism cannot be used to narrow the linewidth of an LED.
In addition, LEDs typically operate in spontaneous emission mode, while laser diodes operate in stimulated emission mode. Stimulated emission is necessary for lasing to occur, and it is this process that allows the light waves to maintain phase coherence. LEDs, which operate in spontaneous emission mode, do not have this property.
In conclusion, while the idea of creating an ECDL with an LED is intriguing, it is not feasible due to the fundamental differences in the way LEDs and laser diodes produce light. The broad linewidth and incoherent light produced by LEDs make them unsuitable for the frequency-selective feedback mechanism used in an ECDL.
However, successful use of ECDLs (with laser diodes) have been used extensively, as in the following paper in a temperature-measurement application:
Article High-Repetition-Rate Combustion Thermometry with Two-Line At...
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