# How Do You Calculate the Output Power of a Laser After Multiple Adjustments?

• stunner5000pt
In summary, a laser with a power of 15.6 dBm is attenuated by a 10 dB neutral density filter before being captured by a photodiode. The signal is then stepped down by 15 dB and amplified by 20.2 dB. To calculate the output signal power from the amplifier, we use the formula G [dB] = 10 log (Pout/Pin) with a total gain of -4.8 dB.
stunner5000pt

## Homework Statement

A laser produces 15.6 dBm of power. The light is propogated through a 10dB neutral density filter that attenuates the signal so that it can be detected by a photodiode without saturation. The optical signal is steppeddown by 15dB when captured by teh photodiode and converted to an electric signal. This signal is later amplified by 20.2 dB by an inverting amplifier. What is the output signal power from teh amplifier in mW?

## Homework Equations

$$G [dB] = 10 \log_{10} \left(\frac{P_{out}}{P_{in}}\right)$$
where P is the power

$$G [dBm] = 10 \log_{10} (P[mW])$$

## The Attempt at a Solution

15.6 is in dBm while the others are in dB. How do we convert from dBm to dB??

Since G represents the gain or loss
then the total gain by the signal is -10 - 15 + 20.2 = -4.8

Thus we would use hte first equation
with G = -4.8 , Pin = 15.6 dBm and calculate Pout

would that be correct??

The power of a laser is usually stated in units of watts, or more likely milliwatts. Even 15.6 mW will be a reasonably powerful laser.

See bottom of this webpage:

http://www.lumalaser.com/laser-power_recommendations.htm"

Last edited by a moderator:

Yes, your approach is correct. To convert from dBm to dB, you can use the formula dB = dBm - 30, since 1 mW = 0 dBm. So in this case, the input power in dB would be 15.6 - 30 = -14.4 dB. Then using the first equation with G = -4.8 dB, you can calculate the output power in dB and convert it back to mW using the second equation. This will give you the output signal power from the amplifier in mW.

## 1. What is the cause of gain/loss of a laser power?

The gain/loss of a laser power can be caused by a variety of factors, such as changes in the laser's environment, aging of the laser components, or improper alignment of the laser beam.

## 2. How does temperature affect laser power gain/loss?

Temperature can have a significant effect on laser power gain/loss. High temperatures can cause the laser's components to expand, leading to misalignment and decreased laser power. Low temperatures can also affect the laser's performance, especially if the laser relies on a gaseous medium.

## 3. Can dust or debris affect laser power gain/loss?

Yes, dust and debris can affect the gain/loss of laser power. If the laser's components or optics become dirty, it can result in decreased laser power due to light scattering or absorption. Regular cleaning and maintenance can help prevent this issue.

## 4. How can I measure the gain/loss of laser power?

The gain/loss of laser power can be measured using a power meter specifically designed for laser measurements. These meters can accurately measure the laser's power output and provide valuable information about any changes in power over time.

## 5. Can gain/loss of laser power be fixed?

In some cases, the gain/loss of laser power can be fixed by identifying and addressing the underlying cause. This may involve cleaning the laser components, realigning the laser beam, or replacing aging parts. In other cases, the issue may be more complex and require professional maintenance or repairs.

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