Terahertz Sum-Frequency Excitation of a Raman-Active Phonon
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-09-22 |
| Journal | Physical Review Letters |
| Authors | Sebastian F. Maehrlein, Alexander Paarmann, Martin Wolf, Tobias Kampfrath |
| Institutions | Freie UniversitÀt Berlin, Fritz Haber Institute of the Max Planck Society |
| Citations | 91 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: THz Sum-Frequency Excitation in Diamond
Section titled âTechnical Documentation & Analysis: THz Sum-Frequency Excitation in DiamondâThis document analyzes the research paper âTerahertz sum-frequency excitation of a Raman-active phononâ and outlines how 6CCVDâs advanced CVD diamond materials and customization capabilities can support and extend this pioneering work in ultrafast coherent phonon control.
Executive Summary
Section titled âExecutive Summaryâ- Breakthrough Mechanism: Experimental demonstration of Terahertz Sum-Frequency Excitation (THz SFE), the up-conversion counterpart to Stimulated Raman Scattering (SRS), for driving coherent lattice vibrations.
- Material Validation: High-purity, CVD-grown Single Crystal Diamond (SCD) (100) was successfully used as the benchmark material due to its high-frequency, infrared-forbidden F2g phonon mode ($\approx 40$ THz).
- Coherent Control Achieved: Coherent motion of the Raman-active phonon was driven by a THz pulse centered at half the phonon frequency (20 THz), confirming the two-photon absorption (2PA) mechanism.
- Phase Sensitivity: The Carrier-Envelope Phase (CEP) of the THz pump pulse was directly imprinted onto the phase of the lattice vibration, enabling direct phase controlâa critical feature for quantum processing and light storage applications.
- Reduced Parasitics: Utilizing low-energy THz photons (80-160 meV) effectively suppresses parasitic electronic excitations, which are common when using high-energy optical laser pulses.
- Application Potential: This technique opens new avenues for highly selective energy deposition in Raman-active modes, extending vibrational spectroscopy to infrared-forbidden modes, and enabling CEP-sensitive light storage at room temperature.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results and material characterization:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sample Material | Type IIa SCD (100) | N/A | High-purity, CVD grown diamond |
| Sample Thickness | 200 | ”m | Used for THz SFE experiment |
| Electronic Band Gap | 5.5 | eV | Insulator property of diamond |
| Target Phonon Frequency ($\Omega/2\pi$) | $\approx 40$ | THz | Zone-center optical F2g-mode |
| Excitation Frequency ($\omega_{0}$) | 20 (or $0.5\Omega$) | THz | Center frequency of THz pump pulse for SFE |
| Coherent Phonon Frequency | $39.95 \pm 0.01$ | THz | Measured via transient birefringence signal |
| Phonon Damping Constant ($\Gamma$) | $0.283$ | ps-1 | Lifetime of the coherent phonon oscillation |
| THz Photon Energy Range | 80 - 160 | meV | Low energy range, suppressing electronic excitation |
| IR Pump Pulse Duration | 40 | fs | Used for THz generation via DFM |
| IR Pump Pulse Repetition Rate | 1 | kHz | Laser system parameter |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material selection and advanced ultrafast spectroscopy techniques:
- Material Selection: A high-purity, CVD-grown Single Crystal Diamond (SCD) wafer (Type IIa, (100) orientation, 200 ”m thickness) was chosen for its high-frequency, infrared-inactive Raman mode (F2g).
- THz Pulse Generation: Intense, phase-locked THz pump pulses were generated via difference-frequency mixing (DFM) of two phase-correlated infrared pulses (800 nm, 40 fs) in a 1 mm thick GaSe crystal.
- Sum-Frequency Excitation (SFE): The THz pump pulse spectrum was centered at 20 THz, enabling the two-photon absorption (2PA) process where the sum frequency (40 THz) is resonant with the target F2g phonon mode.
- Phonon Monitoring: The coherent lattice vibration dynamics were monitored using a time-delayed, ultrashort optical probe pulse (7 fs duration, 750 nm center wavelength) that measured the transient birefringence (THz Kerr effect).
- Phase Control Demonstration: The Carrier-Envelope Phase (CEP) of the THz pump pulse was systematically tuned, resulting in a $2\Delta\phi_{0}$ phase shift in the resulting coherent phonon oscillation, confirming direct phase control.
- Symmetry Validation: The coherent phonon signal was shown to vanish when the sample was rotated by 45°, confirming consistency with the Raman-tensor symmetry of the diamond crystal.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe success of this research hinges on the quality and purity of the diamond material. 6CCVD is uniquely positioned to supply and customize the required CVD diamond substrates for replication, scaling, and extension of this groundbreaking THz SFE research.
Applicable Materials for Ultrafast Coherent Control
Section titled âApplicable Materials for Ultrafast Coherent Controlâ| Research Requirement | 6CCVD Solution | Technical Advantage |
|---|---|---|
| High-Purity Substrate | Optical Grade Single Crystal Diamond (SCD) | CVD-grown Type IIa diamond with extremely low nitrogen content, ensuring minimal absorption and high transparency across the THz and optical probe spectrum (5.5 eV band gap). |
| Specific Orientation | SCD (100) and (111) Wafers | We provide precise crystallographic orientation control, essential for maximizing or minimizing the Raman tensor coupling based on the experimental geometry (as demonstrated by the 45° rotation test). |
| Thickness Control | Custom SCD Thickness (0.1 ”m to 500 ”m) | The paper used 200 ”m. 6CCVD offers precise thickness control, crucial for optimizing pump/probe velocity mismatch and minimizing dispersion in future high-power THz experiments. |
| Doping/Conductivity | Boron-Doped Diamond (BDD) | For future experiments requiring electrical gating or integrated THz waveguides, 6CCVD supplies BDD films with tunable conductivity, enabling integrated device architectures. |
Customization Potential for Advanced THz Research
Section titled âCustomization Potential for Advanced THz ResearchâTo move this research from fundamental demonstration toward integrated applications (e.g., light storage or quantum processing), customization is essential:
- Large Area Scaling: 6CCVD offers Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, allowing for scaling of THz SFE experiments to larger samples or arrays, which is critical for industrial or high-throughput applications.
- Surface Quality: We provide ultra-low roughness polishing (Ra < 1 nm for SCD). Maintaining pristine surface quality is vital for minimizing scattering losses and ensuring accurate transient birefringence measurements.
- Integrated Metalization: If future experiments require electrical contacts for applying bias fields or integrating THz antennas, 6CCVD offers in-house custom metalization using materials such as Au, Pt, Pd, Ti, W, and Cu, patterned to client specifications.
- Precision Fabrication: We offer laser cutting and shaping services to produce custom dimensions or complex geometries required for specialized THz optics or waveguide integration, beyond standard wafer sizes.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of CVD diamond for high-end optical and electronic applications. We can assist researchers in similar Ultrafast Coherent Phonon Control projects by:
- Consulting on optimal SCD orientation and purity grade to maximize Raman coupling efficiency.
- Providing material specifications necessary for high-power THz pulse handling and thermal management.
- Developing custom metalization schemes for integrated THz device prototypes.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
In stimulated Raman scattering, two incident optical waves induce a force oscillating at the difference of the two light frequencies. This process has enabled important applications such as the excitation and coherent control of phonons and magnons by femtosecond laser pulses. Here, we experimentally and theoretically demonstrate the so far neglected up-conversion counterpart of this process: THz sum-frequency excitation of a Raman-active phonon mode, which is tantamount to two-photon absorption by an optical transition between two adjacent vibrational levels. Coherent control of an optical lattice vibration of diamond is achieved by an intense terahertz pulse whose spectrum is centered at half the phonon frequency of 40 THz. Remarkably, the carrier- envelope phase of the THz pulse is directly transferred into the phase of the lattice vibration. New prospects in general infrared spectroscopy, action spectroscopy, and lattice trajectory control in the electronic ground state emerge.