Method and apparatus for detecting and avoiding multiple-pulse states in ultra-short-pulse laser
In a detection method for undesired double- or multiple-pulse states in an ultra-short-pulse laser system operated in the soliton regime and intended for generating femtosecond or picosecond pulses, comprising an amplifying laser medium for producing a laser emission, a laser resonator having at least one resonator mirror and a pump source, a first signal μ proportional to the pulse power P(t) or pulse energy averaged over the resonator cycle is measured for the laser emission. A second signal ν proportional to the square of the pulse power P(t), averaged over the resonator cycle, is measured for the laser emission, and the occurrence of a double- or multiple-pulse state is detected on the basis of a comparison of the measured signals μ and ν.
1. Detection method for undesired double- or multiple-pulse states (DP/MP) in an ultra-short-pulse laser system for generating femtosecond or picosecond pulses, comprising at least
an amplifying laser medium for producing a laser emission,
a laser resonator having at least one resonator mirror and
a pump source, in particular a laser diode source, for pumping the laser medium,
the ultra-short-pulse laser system being operated in the soliton regime and a first signal μ proportional to the pulse power P(t) or pulse energy averaged over the resonator cycle being measured for the laser emission,
wherein
a second signal ν proportional to the square of the pulse power P(t), averaged over the resonator cycle, is measured for the laser emission and the occurrence of an undesired double- or multiple-pulse state (DP/MP) is detected on the basis of a comparison of the measured signals μ and ν which are independent in the range of resonator cycle times.
2. Detection method according to claim 1 , wherein the first signal μ is measured by means of one-photon absorption.
3. Detection method according to claim 1 , wherein the second signal ν is measured by means of two-photon or multiphoton absorption.
4. Detection method according to claim 1 , wherein the second signal ν is measured using frequency multiplication, in particular frequency doubling or tripling.
5. Detection method according to claim 1 , wherein a ratio of |μ−ν|≦1 indicates a single-pulse state (SP), the two signals μ and ν in a state with defined single-pulse characteristic being calibrated so that they substantially correspond.
6. Detection method according to claim 1 , wherein a ratio of von |μ−ν|≧1.5 indicates a double- or multiple-pulse state (DP/MP), the two signals μ and ν in a state with defined single-pulse characteristic being calibrated so that they substantially correspond.
7. Method for avoiding double- or multiple-pulse states (DP/MP) and optimising the laser operating point (AP) by a detection method according to claim 1 ,
placing of the ultra-short-pulse laser system in the double- or multiple-pulse state (DP/MP),
reduction of the operating current for the pump source for deriving the dependency of the signals μ and ν on the operating current,
determination of the operating current value for the transition from the double- or multiple-pulse state (DP/MP) to the single-pulse state (SP).
8. Method according to claim 7 , wherein an increase to an operating current end value is effected after the reduction of the operating current.
9. Measuring apparatus for detecting double- or multiple-pulse states (DP/MP) in an ultra-short-pulse laser system which can be operated in the soliton regime and is intended for generating femtosecond or picosecond pulses; comprising at least one laser detector, this first laser detector being formed and arranged so that a signal proportional to the pulse power P(t) or pulse energy averaged over the resonator cycle can be measured for one or more pulses,
a second laser detector, this second laser detector being formed and arranged so that a signal proportional to the square of the pulse power P(t), averaged over the resonator cycle, can be measured for one or more pulses, and an evaluation component for detecting the occurrence of a double- or multiple-pulse state (DP/MP) on the basis of a comparison of the measured signals of first and second laser detector.
10. Measuring apparatus according to claim 9 , wherein the first laser detector is a photodiode operated in the one-photon absorption regime.
11. Measuring apparatus according to claim 9 , wherein the second laser detector is a photodiode operated in the two-photon or multiphoton absorption regime.
12. Measuring apparatus according to claim 10 , wherein the first and second laser detectors are in the form of different operating states of a photodiode.
13. Measuring apparatus according to claim 9 , wherein the second laser detector is an LED or a photoresistor with two-photon or multiphoton effect or has InP for 2-photon absorption in transmission.
14. Measuring apparatus according to claim 9 , wherein the second laser detector has at least one BBO, LBO, PPLN or KTP crystal for frequency multiplication.
15. Ultra-short-pulse laser system for generating femtosecond or picosecond pulses, comprising at least
an amplifying laser medium for producing a laser emission,
a laser resonator having at least one resonator mirror,
a pump source, in particular a laser diode source, for pumping the laser medium and
a measuring apparatus according to claim 10 .