Single pass scheme - simple

Transcription

1 Laser strategy

2 For the aims of the FAMU project a dedicated laser system emitting tunable nanosecond pulsed light in the mid-ir spectral region will be used to stimulate the transitions ( 1 S 0 to 3 S 1 ). The laser scheme has to be developed at side and will be based on direct difference frequency generation (DFG) in non- oxide crystals (LiInS 2 - lithium thioindate crystal, cut for type II difference frequency generation) using a fixed wavelength (1.064 μm) singlemode diode pump laser and a tunable (in the spectral range μm) narrow-linewidth (Mg 2 SiO4:Cr 4+ ) laser, pumped by a second synchronised to the first one. The pulses of the lasers are combined through a dichroic mirror and sent to the nonlinear crystal in different optical geometries (simple schemes are given on Figures 1 & 2, more detailed on Figure 3). 2

3 Single pass scheme - simple Wavelength Sync device T2 M5 M4 DC NL TOPAG Prism CaF2 Pump beams Idler beam Beam dump M1 T1 M3 M2 Spectro graph - waveplate, - polarizer, M1-M5 - mirrors, T1 andt2 - matching telescopes, - beamsplitters, DC - dichroic mirror, NL - nonlinear crystal 3

4 Double pass scheme - simple Sync device M1 2 T2 M5 M4 T1 M6 DC 1 NL DC 2 Wavelength 1 M2 Spectro graph M3 Energy - waveplate, Po - polarizer, M1-M5 - mirrors, T1 and T2 - telescopes, beamsplitters, DC1 - dichroic mirror (reflecting 1.26µm, transmitting1.06µm), DC2 - dichroic mirror (reflecting 1.06 and 1.26 µm, transmitting 6.76µm) 4

5 Single pass scheme final setup Sync device M1 Injection Seeder Oscilator M2 M3 Amplifier 1 or 2 stage Amplifier M4 T1 M7 M6 T2 Spectro graph DC TOPAG M5 NL CaF2 Prism Pump beams Idler beam BD Wavelength Pump 1 Pump 2 - waveplate, - polarizer, M1-M7 - mirrors, T1 andt2 - matching telescopes, - beamsplitters, DC - dichroic mirror, NL - nonlinear crystal 5

6 For the realization of the final laser system pumping lasers with specific paras will be needed (high energy and pointing stability, low temporal and spectral jitter, narrow linewidth). In order to obtain stable radiation at 1,064 μm we plan to use commercially available diode pumped lasers (DPSS ) that offer very good beam stability (peak to peak energy and pointing stability and relatively low temporal jitter - <0.5 ns). Nevertheless these lasers have linewidths too large for the muonic-hydrogen experiment - this requires a further decreasing of the spectral bandwidth (the linewidht) of the laser radiation which will be obtained by injection seeding. This will allow us to have a single-longitudinal mode operation at the required energies of the laser at 1,064 μm with linewidth appropriate for the experiment and also will lead to smaller spectral jitter (wavelength's jumps ). For the purpose an injection seeding laser (seeder) is planned to be purchased. There are a big number of suppliers of appropriate lasers, based either on the fibre laser technology or on solid state technology, which are suitable for our case. 6

7 For the other pumping laser (the ) there does not exist a commercial solution, so the laser will be developed in collaboration with company that has experience in the producing of solid state lasers, more precisely nanosecond lasers. The final laser system will consist of a single longitudinal mode tunable (step ~ 0.5 pm) narrow linewidth oscillator (spectral bandwidth < 2 pm), generating energy more than 3 mj at 1,262 μm, and a single-stage or two-stage amplifier that will deliver energy of the order of 35 mj. All the lasers are pumped by lasers, for the oscillator we plan to use a 100 mj DPSS laser, which will result in very good beam stability (peak to peak energy and pointing stability and relatively low temporal jitter - < 1.5 ns), as for the amplifier/amplifiers after additional estimations a flash lamp lasers could be used, which will decrease the total price of the final laser system. Here again the purpose is to have a laser at 1,262 μm with linewidth appropriate for the experiment and smaller spectral jitter (wavelength's jumps ). 7

8 The possibility to use injection seeding also for the at 1,262 μm will be considered, as recently there are lasers at 1,262 μm that can be suitable for the purpose, but as these technologies are not so mature (as for the 1,064 μm) this option needs more detailed study. An additional and very important work has to be done in the direction to obtain laser radiation from both lasers (Nd:AYG and ) with longer pulses, as the commercially available laser is generating 9-10 ns long pulse. Increasing the pulse lengths to 15 ns will favour in two aspects: = first the longer pulses will result in better phase-matching of both pumping pulses (from and lasers), thus increasing the efficiency of nonlinear process (DFG) = second will decrease the power density of both laser beams and gives us the possibility to work at power densities far from the damage threshold of the crystals. (This to great extend concerns the radiation of the lasers for which the damage threshold of the crystals is 30 MW/cm 2 or 5 times lower than for the radiation.) 8

9 The initial plan was to start the realization of the final system (following the available approved budget) according the scheme presented at Figure 4: For the first year = purchasing the oscillator of the laser and seeder for the laser, which after coupling with the laser now available at the collaborating lab at Elettra could give the possibility to work in the direction of narrowing the linewidth of the output radiation at 6,8 μm. = studying the behaviour of the linewidht of the output radiation at 6.8 μm according to the different working regimes of the two pumping laser = studying the impact of the different optical configurations at the linewidth of the output radiation at 6.8 μm For the second year = purchasing the amplifiers for both and lasers, and studying the dependence of the linewidth of the output radiation at 6,8 μm of the final laser system from the different characteristics of the both pumping lasers. 9

10 Single pass scheme initial purchase plan Sync device Injection Seeder Oscilator Amplifier 1 or 2 stage Amplifier T1 M7 M6 T2 DC NL TOPAG CaF2 Prism M5 Pump beams Idler beam BD Wavelength M1 M2 M3 M4 Spectro graph Pump 1 Pump 2 - waveplate, - polarizer, M1-M7 - mirrors, T1 andt2 - matching telescopes, - beamsplitters, DC - dichroic mirror, NL - nonlinear crystal 10

11 Estimating the possible risks that can occur and having in mind that the solution for the whole Nd:AYG system (seeder and laser) is on the shelf product while the both oscillator and amplifier with the required characteristics need R&D (research and development), which process can take up to 6 months for each laser, we decided to reorganize the work and to make the purchases as showed on Figure 5: For the first year = starting the work on research and development of the oscillator and the amplifier of the laser (which will need an additional financing of 50 ke). Which is planned to be done in the following steps: - research & development of oscillator - studying different schemes for obtaining single longitudinal mode radiation with narrow linewidth and covering the other requirements - building one-box oscillator according to the requirements - research & development on the amplifier of the laser delivering 35 mj radiation at 1,262 μm with narrow linewidth and covering the other required paras (this activity can pass also in ) - building one-box amplifier according to the requirements. 11

12 For the second year Purchasing the seeding laser and the laser system and optimizing the paras of the output radiation at μm. Studying the dependence of the linewidth of the output radiation at 6,8 μm of the final laser system from the different characteristics of the both pumping lasers ( and ) Studying the impact of the different optical configurations at the linewidth of the output radiation at 6.8 μm. Building a complete portable laser system generating infrared radiation at 6.8 μm with the required paras for the muonic-hydrogen experiment. 12

13 Single pass scheme final purchase plan Sync device Injection Seeder Oscilator Amplifier 1 or 2 stage Amplifier T1 M7 M6 T2 DC NL TOPAG M5 CaF 2 Prism Pump beams Idler beam BD Wavelength M1 M2 M3 M4 Spectro graph Pump 1 Pump 2 - waveplate, - polarizer, M1-M7 - mirrors, T1 andt2 - matching telescopes, - beamsplitters, DC - dichroic mirror, NL - nonlinear crystal 13