Influence of phonon harmonicity on spectrally pure resonant Stokes fields

At a Glance

Metadata	Details
Publication Date	2022-08-03
Journal	Physical review. A/Physical review, A
Authors	Georgios Stoikos, E. Granados
Analysis	Full AI Review Included

Technical Documentation & Analysis: Monolithic Diamond Raman Resonators

Reference Paper: Stoikos, G., & Granados, E. (2022). The influence of phonon harmonicity on spectrally pure resonant Stokes fields. arXiv:2204.11255v1.

Executive Summary

This research validates the use of monolithic MPCVD diamond resonators for achieving ultra-stable, spectrally pure light sources, directly addressing critical challenges in integrated quantum technology and high-resolution spectroscopy.

Ultra-Stable Emission: Demonstration of Fourier-limited Stokes nanosecond pulses with a stabilized center frequency deviation of less than < 4 MHz over 16 hours, confirming diamond’s superior thermal stability.
Novel Measurement Method: Introduction of the “resonant Stokes field” method for accurately measuring the temperature-dependent index of refraction and thermo-optic coefficient (TOC) in diamond.
Material Validation: Confirms diamond’s suitability for high-power optical applications due to its giant Raman gain, ultra-wide transparency, and unsurpassed thermal conductivity (1800 W/m/K at 300 K).
Quantified Thermal Parameters: Measured the average frequency-temperature tuning slope ($\partial \nu_s / \partial T$) at approximately -2.3 GHz/K, providing essential data for temperature-sensitive device design.
TOC Calculation: Calculated the thermo-optic coefficient at room temperature (300 K) to be approximately $3.5 \times 10^{-6}$ K^-1, crucial for modeling thermal drift in integrated photonic devices.
6CCVD Relevance: The successful replication and scaling of this work requires high-purity, custom-dimensioned, and ultra-polished Single Crystal Diamond (SCD) substrates, a core offering of 6CCVD.

Technical Specifications

The following hard data points were extracted from the experimental results and material properties cited in the research.

Parameter	Value	Unit	Context
RMS Frequency Deviation	< 4	MHz	Stabilized Stokes center frequency (over 16 hours)
Stokes Linewidth (FWHM)	100 ± 20	MHz	Measured at 573 nm
Frequency-Temperature Tuning Slope ($\partial \nu_s / \partial T$)	-2.3	GHz/K	Average slope within a FSR
Raman Phonon Line Temperature Dependence ($\partial \nu_R / \partial T$)	+0.23	GHz/K	Between 300 K and 400 K
Thermo-Optic Coefficient (TOC)	$\approx 3.5 \times 10^{-6}$	K^-1	Calculated at 300 K
Diamond Crystal Dimensions	$7 \times 2 \times 2$	mm³	Monolithic FP Resonator
End-Face Parallelism Requirement	< 0.5	µm/mm	Required for FP resonator stability
Pump Wavelength	532	nm	Frequency-doubled Nd:YAG
Thermal Conductivity (Diamond)	1800	W/m/K	At 300 K (Cited material property)

Key Methodologies

The experiment utilized a monolithic Fabry-Pérot (FP) diamond resonator to measure the temperature dependency of the Stokes resonant frequency, enabling accurate calculation of the thermo-optic coefficient.

Material Selection & Preparation: A synthetic diamond cuboid crystal ($7 \times 2 \times 2$ mm³) was used. The crystal was plane-cut for beam propagation along the (110) axis to maximize SRS efficiency.
Resonator Fabrication: The end-faces were re-polished to achieve a parallelism better than 0.5 µm/mm. The intrinsic Fresnel reflectivity ($R_{1}, R_{2} \approx 18%$) of the uncoated surfaces was sufficient for efficient Raman operation.
Pumping Source: The resonator was pumped by a frequency-doubled Q-switched Nd:YAG laser (532 nm) generating 10 ns pulses at a 100 Hz repetition rate, focused to a waist of 50 ± 5 µm.
Temperature Stabilization: The diamond crystal was mounted in a high-precision oven, achieving temperature stability with a standard deviation of less than < 10 mK.
Measurement Technique: The Stokes resonant frequency was actively stabilized using temperature control. The “resonant Stokes field” method involved scanning the temperature setting of the oven in 10 mK increments while measuring the resulting Stokes wavelength shift with high accuracy.
Data Extraction: The measured frequency-temperature tuning slope was fitted to a theoretical model incorporating thermal expansion and phonon harmonicity to extract the temperature-dependent index of refraction and Grüneisen parameter.

6CCVD Solutions & Capabilities

The successful execution and future scaling of this research—particularly in integrated quantum photonics—rely on ultra-high quality, precisely engineered diamond substrates. 6CCVD is uniquely positioned to supply the required materials and fabrication services.

Research Requirement	6CCVD Solution & Capability	Value Proposition
Material Purity & Stability	Optical Grade Single Crystal Diamond (SCD)	Provides the necessary low-birefringence and high thermal conductivity (up to 2000 W/m/K) required for ultra-stable, single-frequency Raman lasing and minimal thermal lensing effects.
Custom Dimensions & Orientation	Precision SCD Substrates	We supply custom SCD plates up to 500 µm thick and substrates up to 10 mm, precisely cut to specific crystallographic orientations (e.g., (110) or (100)) to optimize Stimulated Raman Scattering (SRS) gain.
High-Finesse Resonator Fabrication	Ultra-Low Roughness Polishing (Ra < 1 nm)	Our advanced polishing capabilities ensure end-face parallelism and surface quality far exceeding the < 0.5 µm/mm requirement, critical for achieving high-finesse Fabry-Pérot resonators.
Integrated Photonic Device Scaling	Large Area PCD Wafers (Up to 125mm)	For scaling integrated quantum systems beyond the lab bench, 6CCVD offers inch-size Polycrystalline Diamond (PCD) wafers up to 125mm in diameter, enabling high-throughput device manufacturing.
Advanced Device Integration	Custom Metalization Services	Although the paper used uncoated surfaces, we offer in-house metalization (Au, Pt, Pd, Ti, W, Cu) for creating integrated electrodes, heaters, or high-reflectivity mirror coatings necessary for active temperature tuning and device packaging.
Engineering Support	In-House PhD Team Consultation	6CCVD’s material scientists specialize in optimizing diamond properties for complex applications like Stimulated Raman Scattering (SRS) and temperature-sensitive integrated photonics. We assist clients in selecting the optimal material grade and geometry.

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

View Original Abstract

Thanks to their highly coherent emission and compact form factor, single axial mode diamond Raman lasers have been identified as a valuable asset for applications including integrated quantum technology, high resolution spectroscopy or coherent optical communications. While the fundamental emission linewidth of these lasers can be Fourier limited, their thermo-optic characteristics lead to drifts in their carrier frequency, posing important challenges for applications requiring ultra-stable emission. We propose here a method for measuring accurately the temperature-dependent index of refraction of diamond by employing standing Stokes waves produced in a monolithic Fabry-Perot (FP) diamond Raman resonator. Our approach takes into account the influence of the temperature on the first-order phonon line and the average lattice phonon frequency under intense stimulated Raman scattering (SRS) conditions. We further utilize this model to calculate the temperature-dependent thermo-optic coefficient and the Gruneisen parameter of diamond in the visible spectral range. The theory is accompanied by the demonstration of tunable Fourier-limited Stokes nanosecond pulses with a stabilized center frequency deviation of less than <4 MHz.

Tech Support

Original Source

DOI: https://doi.org/10.1103/physreva.106.023504