Lasers are divided into continuous lasers and pulsed lasers. Pulsed laser refers to a laser that has a single laser pulse width of less than 0.25 seconds and works only once per interval. It has a large output power and is suitable for laser marking, cutting, and distance measurement. Common pulsed lasers include yttrium aluminum garnet (YAG) lasers, ruby ​​lasers, and neodymium glass lasers in solid-state lasers, as well as nitrogen molecular lasers and excimer lasers. Q-switching and mode locking are the two most commonly used techniques for obtaining pulsed lasers. This article first introduces the classification of pulsed lasers and the laser level of pulsed lasers. Secondly, it describes the relationship between energy parameters of pulsed lasers and energy conversion. Finally, we introduce the commonly used pulsed lasers.
Classification of pulsed lasers1, short pulse laser
2, long pulse laser
Pulse Laser LevelFirst level: Under normal operating conditions, no harmful light radiation is generated.
Second level: The radiation range is in the visible spectrum, and its AEL value is equivalent to the value of 0.25 seconds exposure in the radiation of the first stage product. This product requires additional warning signs for safety testing.
The third level: divided into 3a and 3b. Level 3a does not cause damage to the naked eye for people who have a normal avoidance response to strong light, but it can cause damage to the human eye when viewed using a lens instrument. Class 3b products include radiation in the 200nm to 1000000nm range, which can cause unexpected injury if the naked eye is in direct view. Its management and control are stricter than the second level.
Level 4: The AEL is above the third level and not only causes direct damage to the human eye but also in other situations. Not only to the eyes, but it may also hurt the skin and even cause a fire. This kind of product must be strictly managed and controlled.
Pulsed lasers emit discontinuous laser light, which is generally emitted at high repetition rate pulse intervals. The emitted energy is measured in joules (J) in units of work, that is, how many joules are performed per pulse.
The energy emitted by a continuous laser is measured in Watts (W), which is how many joules are performed per second, indicating how much work is done per unit of time.
Watt and Joule relationship: 1W=1J/sec.
For a pulsed laser, the pulse emission energy is 1 Joule/shot, the pulse frequency is 50Hz, and then the laser is emitted 50 times per second. The average power for doing work per second is 50X1 Joules = 50 Joules, so the average power is converted It is 50 watts.
An example illustrates the calculation of the peak power. A green laser pulse laser has a pulse energy of 0.14mJ/time, a pulse width of 20ns and a pulse frequency of 100kHz.
The average power is: 0.14mJX100k=14J/s=14W, ie, the average power is 14W;
The peak power is the ratio of pulse energy to pulse width, ie
Peak power: 0.14mJ/20ns = 7000W = 7kW, peak power 7 kW.
To know whether the pulsed laser damage threshold of the lens is within the limit, it is necessary to calculate the peak power of the pulsed laser and calculate the average power of the pulsed laser.
For example, the laser damage threshold of a ZnSe lens is 500 MW/cm2. In a pulsed laser, the pulse laser has a pulse energy of 10 J/cm2, a pulse width of 10 ns, and a frequency of 50 kHz.
First, calculate the average power: 10J/cm2X50kHz=0.5MW/cm2
Second, calculate the peak power again: 10J/cm2/10ns=1000MW/cm2
From the perspective of the average power of the pulsed laser, the lens can withstand undamaged, but from the peak power of the pulsed laser, it is greater than the laser damage threshold of the lens. Therefore, a comprehensive judgment, the ZnSe lens should not be used for this pulsed laser.
If conditional, pulsed laser lenses should be tested for laser damage thresholds for average power and peak power, respectively.
Ave.Power: Average Power
Pulseenergy: pulse energy
PulseWidth: pulse width
PeakPower: Peak Power
Rep.Rate: Pulse frequency
Ps: picoseconds, 10-12S
Ns: nanoseconds, 10-9S
M: trillion, 106
J: Joule
W: tile
1. YAG lasers in solid-state lasers
2. Ruby lasers and sapphire lasers
3, neodymium glass laser
4, nitrogen molecular lasers, excimer lasers and so on.
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