Intrapulse Correlated Dynamics of Self-Phase Modulation and Spontaneous Raman Scattering in Synthetic Diamond Excited and Probed by Positively Chirped Ultrashort Laser Pulses

At a Glance

Metadata	Details
Publication Date	2023-05-29
Journal	Photonics
Authors	S. I. Kudryashov, П. А. Данилов, Jiajun Chen
Institutions	P.N. Lebedev Physical Institute of the Russian Academy of Sciences
Citations	1
Analysis	Full AI Review Included

Technical Analysis and Documentation: Ultrafast Nonlinear Dynamics in Synthetic Diamond

Executive Summary

This research investigates the complex, intrapulse-correlated dynamics of Self-Phase Modulation (SPM) and Spontaneous Raman Scattering (SRS) in synthetic diamond under tight focusing conditions, providing crucial data for high-power laser processing applications.

Core Material: High-purity Type IIa synthetic diamond was used to study nonlinear optical and lattice dynamics.
Methodology: Positively chirped ultrashort laser pulses (0.3-9.5 ps) at 515 nm were tightly focused (NA = 0.25) to induce strong excitation and filamentation.
Key Achievement: Direct observation of the Raman-Kerr contribution to nonlinear polarization, establishing itself on the sub-picosecond timescale.
Critical Threshold: The filamentation onset threshold energy was precisely identified in the range of $\approx$ 210-230 nJ.
Dynamic Timescale: The study quantified the characteristic timescale ($\sim$1-2 ps) for electron-lattice thermalization, which leads to the suppression of delayed Kerr nonlinearity via anharmonic decay of optical phonons.
Application Relevance: These findings are essential for optimizing parameters for high-precision laser inscription, waveguide fabrication, and micro-optical device manufacturing in diamond.

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Material Type	Type IIa Synthetic Diamond	N/A	Cube dimensions 2 x 2 x 2 mm
Excitation Wavelength	515	nm	Second Harmonic of Yb-laser
Pulse Duration ($\tau$) Range	0.3 - 9.5	ps	Variable, positively chirped
Focusing Numerical Aperture (NA)	0.25	N/A	Tightly focused micro-objective
Focal Spot Radius (1/e intensity)	< 2	µm	Prefilamentation regime
Filamentation Threshold Energy	210 - 230	nJ	Onset of nonlinear focusing
Peak Fluence (Prefilamentation)	$\sim$ 2	J/cm²	At 200 nJ pulse energy
Peak Intensity (Prefilamentation)	$\sim$ 7	TW/cm²	At 200 nJ pulse energy
Raman Shift (Zone-Center Phonon)	$\approx$ 1340	cm^-1	Spontaneous nonresonant scattering
Electron-Lattice Thermalization Time	$\sim$ 1 - 2	ps	Timescale for phonon decay and Kerr damping

Key Methodologies

The experiment utilized advanced ultrafast laser techniques combined with high-resolution spectral analysis to probe the diamond lattice dynamics.

Material Preparation: A 2x2x2 mm Type IIa synthetic diamond cube with six polished facets was used as the sample medium.
Laser Source & Wavelength: Ultrashort laser pulses were generated at 515 nm (second harmonic of a Yb-laser) with a repetition rate of 10 kHz.
Pulse Shaping: Pulse duration was varied (0.3-9.5 ps) using partial positive chirping (incomplete compression) to control the temporal interaction dynamics.
Tight Focusing: Pulses were tightly focused within the crystal volume using a micro-objective (NA = 0.25) to achieve high peak intensities ($\sim$7 TW/cm²).
Energy Control: Pulse energy was adjusted in the range of 50-800 nJ using a thin-film transmission attenuator.
Spectral Analysis: Transmitted radiation was collected (NA = 0.2) and guided to a spectrometer (ASP-190) to measure SPM broadening and spontaneous Raman scattering spectra simultaneously.
Spatial Mapping: The sample was translated in 50 µm steps using a motorized stage after each spectrum acquisition to ensure consistent measurement conditions.

6CCVD Solutions & Capabilities

The successful replication and extension of this high-intensity nonlinear optics research require ultra-high purity, low-defect diamond materials and precision fabrication capabilities. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond solutions.

Applicable Materials for Nonlinear Optics

Research Requirement	6CCVD Material Recommendation	Technical Rationale
High Purity, Low Defect Density (Type IIa)	Optical Grade Single Crystal Diamond (SCD)	Essential for minimizing two-photon absorption and scattering losses, ensuring consistent Kerr nonlinearity and Raman response under high-intensity excitation.
Exploration of Plasma/Conductivity Effects	Boron-Doped Diamond (BDD)	For extending the research to electro-optic applications or studying plasma dynamics in conductive diamond, BDD offers tunable carrier concentration.
Large Area Scaling	Optical Grade Polycrystalline Diamond (PCD)	If the application requires scaling beyond the SCD size limit, our PCD wafers offer high thermal conductivity and optical quality up to 125 mm diameter.

Customization Potential & Fabrication Services

The tight focusing and high-intensity regimes studied demand exceptional material quality and precise dimensions. 6CCVD’s in-house capabilities directly address these needs:

Custom Dimensions and Thickness: The paper utilized a 2x2x2 mm cube. 6CCVD offers SCD plates up to 10 mm thick and custom dimensions for wafers/plates up to 125 mm (PCD), enabling scaling of experiments or integration into larger optical systems.
Ultra-Precision Polishing: The experiment requires six highly polished facets. 6CCVD guarantees Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring minimal surface scattering and optimal beam transmission under high-NA focusing.
Integrated Device Fabrication: For future work involving electrical probing or integrated optics, 6CCVD offers custom metalization services, including deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to define electrodes directly onto the diamond surface.
Global Logistics: We ensure reliable, global delivery of sensitive diamond materials via DDU (default) or DDP shipping options.

Engineering Support

This research highlights the critical interplay between optical field, electron-hole plasma, and lattice dynamics on picosecond timescales. 6CCVD’s in-house PhD team specializes in the material science of MPCVD diamond and can assist researchers in selecting the optimal material specifications (purity, orientation, doping level, and surface finish) required to replicate or extend similar ultrafast laser inscription and nonlinear optics projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In synthetic diamond plates, the intrapulse-correlated dynamics of self-phase modulation and spontaneous nonresonant Raman scattering by center-zone optical phonons were for the first time directly investigated for tightly focused (focusing numerical aperture NA = 0.25) positively chirped visible-range high-intensity laser pulses with variable durations (0.3-9.5 ps) and energies transmitted through the sample. The observed self-phase modulation broadening and modulation of the transmitted light and Stokes Raman spectra for the (sub)picosecond pulse durations indicate the considerable Raman-Kerr contribution to the nonlinear polarization. The latter appears through plasma emission of the optical phonons, which emerges on the (sub)picosecond timescale and dominates at ≈1 ps. Later, this phonon contribution is eventually suppressed in the material due to picosecond-scale electron-lattice thermalization and the related thermally enhanced symmetrical decay of optical phonons into lower-frequency acoustic ones.

Tech Support

Original Source

DOI: https://doi.org/10.3390/photonics10060626

References

2014 - Ultrafast Lasers-Reliable Tools for Advanced Materials Processing [Crossref]
2022 - 100-Layer Error-Free 5D Optical Data Storage by Ultrafast Laser Nanostructuring in Glass [Crossref]
2007 - Femtosecond Filamentation in Transparent Media [Crossref]
2011 - Anatomy of a femtosecond laser processed silica waveguide [Crossref]
2015 - In the heart of femtosecond laser induced nanogratings: From porous nanoplanes to form birefringence [Crossref]
2010 - Peculiarities of Filamentation of Sharply Focused Ultrashort Laser Pulses in Air [Crossref]
2022 - High-NA Focusing of Ultrashort Laser Pulses in Bulk of ZnSe [Crossref]
2010 - Generation of Coherent Terahertz Phonons by Sharp Focusing of a Femtosecond Laser Beam in the Bulk of Crystalline Insulators in a Regime of Plasma Formation [Crossref]