Lecture #6 High pressure and temperature phononics & SASER

Transcription

1 Lecture #6 High pressure and temperature phononics & SASER Dr. Ari Salmi

2 High temperature and pressure phononics Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi

3 Phononics at high temperatures and pressures Why are we interested in high pressures and temperatures? Pressures and temperatures inside the Earth Phase transitions Liquid metals Soft phononics

4 Soft phonons Liu et al., NPG Asia Materials 2016 High pressures phonon instability Phonon frequencies become imaginary lattice slipping This could maybe be studied in the future

5 Phononics at high temperatures and pressures Which one is more important for solid state physics? Gibbs free energy (= potential energy of thermodynamics) As a function of pressure 150 GPa = 3 ev As a function of temperature 1000 K = 90 mev Decremps et al., Ultrasonics

6 Phononics at high temperatures and pressures How does one generate high pressures? Diamond anvil Decremps et al., Ultrasonics

7 Phononics at high temperatures and pressures How does one do nanoacoustic measurements in high pressures? Diamond just happens to be transparent

8 Phononics at high temperatures and pressures Single waveforms as a function of pressure

9 Phononics at high temperatures and pressures Change the position of the probe Imaging of the wavefronts propagating in the material

10 Phononics at high temperatures and pressures Anisotropic measurements Calculated time-of-arrival of different phononic modes

11 Phononics at high temperatures and pressures Anisotropic measurements Measure the arriving nanoacoustic wavefronts on the surface full elasticity tensor (silicon)

12 Phononics at high temperatures and pressures Also elastic tensor as a function of pressure

13 Phononics at high temperatures and pressures From such a speed of sound measurement one can determine other parameters Density as a function of temperature

14 Phononics at high temperatures and pressures Determination of melting point as a function of pressure One can detect the transition from the measured anisotropy ellipsoid

15 Phononics at high temperatures and pressures Determination of melting point as a function of pressure

16 Liquid gallium Phase transition detected at high pressures Ayrinhac et al., J. Phys: Cond. Matt

17 SASER Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi

18 LASER Light amplification by stimulated emission

19 LASER Light amplification by stimulated emission Energy of the pump is absorbed and excites atoms E.g. a powerful white flash or another laser Population inversion Stimulated emission happens

20 Towards a SASER (phonon laser) So, one needs Something to excite that would then generate phonons by stimulated emission A way to generate this population inversion A way to trap the phonons so that stimulated inversion can happen

21 Towards a SASER (phonon laser) First steps towards a SASER Right after invention of LASER in the 1960 s Tucker, PRL 1961 Microwave pumped ruby rod Maybe amplification, but has not been verified

22 Towards a SASER (phonon laser) Vahala et al., Nature Physics 2009 Single trapped ion acted as a phonon laser Not really a phononic laser because it is very hard to use and the phonons cannot really be coupled to anything

23 A way to excite something Quantum cascade A superlattice y6psahxifzokhxaycweqjrwibw&url=http%3a%2f%2fasumbe.eas.asu.edu%2fformermembers%2fwolfg ang%2fthesis%2fsect41.html&bvm=bv ,d.bgs&psig=afqjcng8gitbnknqezg03wghf13r30ympq &ust=

24 A way to excite something Quantum cascade An electronic miniband forms There is a conduction band at which the wavefunction is continuous amongst the wells Bloch wave Tunneling between the wells

25 A way to excite something Quantum cascade Physics advances by accident Kini et al., JAP 2005 Generated phonons with a laser pulse and measured the phonon assisted tunneling as a function of angle and bias voltage

26 Stark effect Splitting of spectral lines with electric field

27 A way to excite something Quantum cascade Bias voltage into superlattice tilted energy wells Tilting dependent on the voltage Wannier-Stark ladder of states

28 A way to excite something Quantum cascade Theoretical prediction of increase (decrease) in the detected current as a function of bias voltage

29 A way to generate a population inversion Practical measurement as a function of angle Discrepancy at 0 degrees (direct transmission into SL)!

30 A way to generate stimulated emission The current causes a cascade of phonons Maryam et al., Nature Communications

31 A way to trap the energy into the cavity Acoustic Bragg mirror At a suitable frequency (wavelength SL constant) the reflectance is close to 100%

32 The SASER phonon laser Maryam et al., Nature Communications 2013 Combine these into a phononic laser f = 325 GHz

33 The SASER phonon laser Short phononic pulses with pulsed bias voltage

34 Future realizations of SASER Han et al., PRL 2015 MD simulation + theory based prediction of a new phononic laser system Thermally excited phonons in a cavity

35 Future realizations of SASER Kosevich, Physics-Uspekhi 2008 Defects in a lattice cause localized resonances which prevent transmission at certain frequency bands

36 Future realizations of SASER One can use pump-probe to excite the phononic modes in the cavity For both long and shear sasing

37 Future realizations of SASER How does one generate sasing from this? Apply strain to the cavity resonance changes excitation of coherent phonons until the strain is turned off Phononic Q-switching!

38 Why are we interested in SASERs? Super high resolution acoustic imaging with narrowband, higher power acoustic sources Intense THz electromagnetic wave generation by SASER

39 Take-home Matemaattis-luonnontieteellinen tiedekunta / Henkilön nimi / Esityksen nimi

40 Take-home High pressure phononics can give insight into phase transitions in materials SASER can be used to generate high fluences of phonons at a narrow frequency band