Laser system and method for controlling the laser pulse shape
A laser system for medical treatment is disclosed which comprises a pump, wherein the laser system is adapted to be operated in pulsed operation so that at least one laser pulse of a temporally limited pulse duration (T p ) is generated. The generated laser pulse irradiates some part of the human or animal body so that a two-dimensional laser spot S is located on the top layer of the irradiated part of the human or animal body. The pump power of the pump of the laser system is modulated in such a way that the cumulative energy E S (T p /2) which is delivered by said laser pulse to said laser spot S during the first half of the pulse duration is less than 45% of the energy E S (T p ) which is delivered by said laser pulse to said laser spot S during the entire pulse duration T p .
1. A Laser system for medical treatment, comprising:
a pump,
wherein the laser system is adapted to be operated in pulsed operation so that at least one laser pulse of a temporally limited pulse duration (T p ) is generated,
wherein said laser pulse irradiates some part of a human or animal body so that a two-dimensional laser spot (S) is located on a top layer of an irradiated part of the human or animal body; and
wherein a pump power of the pump is modulated in such a way that a cumulative energy (E S (T p /2)) which is delivered by said laser pulse to said laser spot (S) during a first half of the temporally limited pulse duration is less than 45% of an energy (E S (T p )) which is delivered by said laser pulse to said laser spot (S) during an entire of the temporally limited pulse duration (T p ),
wherein said laser pulse comprises a plurality of micro-pulses, wherein in between two micro-pulses of the laser pulse there is a temporal region of the laser pulse where a pulse intensity is smaller than 1/10 th of a maximal pulse intensity for the two micro-pulses, and
wherein a time duration of the temporal region of the laser pulse where the pulse intensity is smaller than 1/10 th of the maximal pulse intensity for the neighboring two micro-pulses lies between 0.1 microseconds and 2 milliseconds.
2. The Laser system according to claim 1 , wherein the cumulative energy (E S (T p /2)) which is delivered by said laser pulse to said laser spot (S) during the first half of the pulse duration is less than 35% of the energy(E S (T p )) which is delivered by said laser pulse to said laser spot (S) during the entire temporally limited pulse duration (T p ).
3. The Laser system according to claim 2 , wherein the cumulative energy (E S (T p /2)) which is delivered by said laser pulse to said laser spot (S) during the first half of the pulse duration is less than 25% of the energy (E S (T p )) which is delivered by said laser pulse to said laser spot (S) during the entire temporally limited pulse duration (T p ).
4. The Laser system according to claim 1 , wherein the cumulative energy which is delivered by said laser pulse to said laser spot during the last quarter of the pulse, i.e. during the time span ¾ T p <t<T p , is more than 50% of the energy which is delivered by said laser pulse to said laser spot during the entire pulse duration.
5. The Laser system according to claim 1 , wherein, for times (T) in the interval [T p /20, T p /2], it holds for the cumulative pulse energy (E S (T)) which is delivered by said laser pulse to said laser spot (S), until time (T)
E
S
(
T
)
<
0.5
·
T
·
E
S
(
T
p
)
T
p
,
wherein E S (T P ) is the energy which is delivered by said laser pulse to said laser spot during the entire temporally limited pulse duration (T p ), wherein the laser pulse starts at t=0.
6. The Laser system according to claim 1 , wherein, for all times (T) in an interval [T p /20, T p /4], it holds
E
S
(
T
)
<
0.25
·
T
·
E
S
(
T
p
)
T
p
.
7. The Laser system according to claim 6 , wherein, for all times (T) in an interval [T p /20, T p /2], it holds
E
S
(
T
)
<
0.25
·
T
·
E
S
(
T
p
)
T
p
.
8. The Laser system according to claim 1 , wherein the temporally limited pulse duration (T p ) is in a range between 0.020 milliseconds inclusive and 500 milliseconds inclusive.
9. The Laser system according to claim 1 , wherein the laser system further comprises water sprayer.
10. The Laser system according to claim 1 , wherein the laser system comprises a Pulse Width Modulation (PWM) power supply.
11. The Laser system according to claim 1 , wherein the pumping current which is input into the pump reaches a level which is at least 10% above the threshold pumping current density (I thresh ) within a time period that is shorter than 0.50×T p , wherein the threshold pumping current density (I thresh ) is the minimal pumping current density so that the laser reaches the lasing threshold when pumped with a constant pumping current density.
12. The Laser system according to claim 1 , wherein the laser system is used for one of the following medical treatments: ablation of tissue; treatment of vascular lesions; and hair removal.