# Calculate % Excitation of Sample X w/ Laser Pulsed Source

• sciphys1
In summary, a new forum user is seeking help with a problem involving a sample in gas phase with a known absorption coefficient. They want to calculate the energy needed to excite a certain percentage of the sample using a pulsed laser source, and are unsure of how to use absorption cross section calculations to determine the necessary energy or power. They are seeking assistance from more experienced members.
sciphys1
Hi Everyone,

I am new to this forums. I am not sure where to post but general discussion is a good place. I am trying to figure out a problem:

I have a sample X in gas phase. Say it has an absorption coefficient of 9.895e-18 cm2 molecule-1 @ 532nm. I have a laser pulsed source (say 50 Hz) giving me 532nm light. How does one calculate what energy one needs to excite 5% or any percentage of the sample? The measured power of the pulsed laser is related to the energy by:

E=power/rep.rate

and one can use this to calculate the number of photons N,by

E=Nhc/lambda where lambda is the wavelength (in the example above it is 532nm).

we can also calculate the fluence by measuring the spot size as we focus the laser beam into the sample. I can't figure out how people choose the energy/power from absorption cross section calculations? I am a novice, so need a little help please. Thank you.

sciphys1

## 1. What is the purpose of calculating % excitation of a sample with a laser pulsed source?

The purpose of calculating % excitation is to determine the efficiency of the laser in exciting the sample and producing a measurable signal. This information can be used to optimize experimental conditions and improve the accuracy of results.

## 2. How is % excitation calculated?

% excitation is typically calculated by comparing the intensity of the signal produced by the excited sample to the maximum possible signal that could be generated. This is often represented as a percentage of the maximum signal, with 100% indicating perfect excitation.

## 3. What factors can affect the % excitation of a sample with a laser pulsed source?

The % excitation can be affected by various factors such as the laser power, wavelength, pulse duration, and the properties of the sample itself (e.g. absorption and scattering coefficients). Additionally, experimental conditions such as the angle of incidence and sample positioning can also impact the % excitation.

## 4. How can the % excitation be optimized for a specific sample?

To optimize the % excitation for a specific sample, the laser parameters and experimental conditions can be adjusted to find the ideal combination that maximizes the signal output. This may involve changing the laser power, wavelength, or adjusting the sample's position and orientation.

## 5. What are the limitations of using % excitation to evaluate a sample's response to a laser pulsed source?

While % excitation can provide valuable information about the efficiency of the laser in exciting a sample, it does not take into account other factors that can affect the overall signal, such as the sensitivity of the detection system and the background noise. Therefore, it should be used in conjunction with other methods of analysis to fully understand the sample's response to the laser.

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