Fluorescence of a laser vs its pulse duration

C_and_LasersIn summary, the fluorescence lifetime can be longer than the pulse of a pulsed laser due to the process of stimulated emission, which allows for energy to be stored in the gain medium before lasing. This allows for the creation of a population inversion, necessary for lasing to occur. The pulse is short because of stimulated emission, which quickly depletes the upper state, while fluorescence (spontaneous emission) occurs more slowly and randomly.
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When working with a pulsed laser (nitrogen),
How can the fluorescence lifetime be longer than the pulse of the laser?

Thanks for any explanations
 
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The upper-state lifetime is always longer than the pulse in pulsed lasers. This allows you to store energy in the gain medium prior to lasing. In a laser you must be able to create a population inversion, where a photon interaction (of the correct type) is more likely to stimulate emission than be absorbed. i.e. more energy available in upper to lower state transition than vice-versa. This requires some "storage time" in the upper state.

The pulse is short because of stimulated emission. The large quantity of photons cause the upper-state to be depleted quickly during lasing. Prior to that the fluorescence (spontaneous emission) happens more slowly at more random times.

https://eng.libretexts.org/Bookshel...on,_Spontaneous_Emission,_Stimulated_Emission
 
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1. What is the relationship between fluorescence and the pulse duration of a laser?

The pulse duration of a laser refers to the length of time the laser beam is emitted. Fluorescence is the emission of light from a substance when it is excited by a higher energy source, such as a laser. The shorter the pulse duration of the laser, the more intense the excitation of the substance and the greater the fluorescence produced.

2. How does the pulse duration affect the intensity of fluorescence?

The shorter the pulse duration of the laser, the higher the intensity of fluorescence. This is because a shorter pulse duration means a higher peak power, which leads to a more intense excitation of the substance and thus a greater fluorescence signal.

3. Can the pulse duration of a laser affect the color of fluorescence emitted?

Yes, the pulse duration can affect the color of fluorescence emitted. This is because different substances have different fluorescence spectra, or ranges of colors they emit when excited. A shorter pulse duration can lead to the excitation of a wider range of fluorescence spectra, resulting in a broader range of colors being emitted.

4. Is there an optimal pulse duration for producing fluorescence?

The optimal pulse duration for producing fluorescence depends on the substance being excited and the desired intensity and color of fluorescence. In general, shorter pulse durations tend to produce higher intensities of fluorescence, but there may be trade-offs in terms of color and potential damage to the substance being excited.

5. Can fluorescence be produced without using a laser?

Yes, fluorescence can be produced without using a laser. Other sources of high energy, such as UV lamps or electron beams, can also excite substances to emit fluorescence. However, lasers are often preferred due to their ability to produce intense and specific excitation of substances, leading to more precise and controlled fluorescence signals.

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