In‐Source High‐Resolution Spectroscopy Using an Integrated Tunable Raman Laser
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-11-23 |
| Journal | Laser & Photonics Review |
| Authors | E. Granados, Georgios Stoikos, Cyril Bernerd, K. Chrysalidis, Daniel T. Echarri |
| Institutions | European Organization for Nuclear Research |
| Citations | 6 |
| Analysis | Full AI Review Included |
Integrated Diamond Raman Laser for High-Resolution Spectroscopy
Section titled “Integrated Diamond Raman Laser for High-Resolution Spectroscopy”Executive Summary
Section titled “Executive Summary”This research demonstrates the successful integration of a tunable diamond Raman laser into a high-resolution in-source spectroscopy setup, validating diamond’s critical role in advanced quantum and nuclear physics applications.
- Integrated Platform: A monolithic Fabry-Perot diamond resonator (7 x 2 x 2 mm³) was used to generate a spectrally-bright Stokes pulse, circumventing the need for complex external cavity stabilization.
- Spectral Squeezing: The diamond resonator acted as a spectral funnel, reducing the multi-mode pump linewidth from 7 GHz down to 280 MHz for the Stokes output, yielding a 25x linewidth reduction factor.
- High Efficiency: Achieved a high power conversion efficiency of 40% from the 409.3 nm pump to the 433.9 nm Stokes pulse.
- Tunability and Stability: Continuous, fine frequency tuning of the Stokes laser was achieved exclusively via high-precision temperature control of the bulk diamond, demonstrating a tuning slope of -3.2 GHz/°C and frequency accuracy better than 30 MHz.
- High Purity: The integrated laser demonstrated high spectral purity, achieving a side-mode suppression ratio greater than 25 dB at 2 GHz from the center Stokes frequency.
- Application Validation: The system achieved a combined resolution of 0.51 GHz for the high-selectivity ionization spectroscopy of ${}^{152}\text{Sm}$, paving the way for integrated laser sources in Doppler-reduced spectroscopy.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental results of the integrated diamond Raman laser system:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Dimensions | 7 x 2 x 2 | mm³ | Cuboid crystal, (100) axis propagation |
| Pump Wavelength ($\lambda_{p}$) | 409.3 | nm | Input Ti:Sapphire laser |
| Stokes Wavelength ($\lambda_{s}$) | 433.9 | nm | Output, tuned for ${}^{152}\text{Sm}$ transition |
| Pump Linewidth ($\Delta\nu_{p}$) | 7 | GHz | Multi-mode input spectrum |
| Stokes Linewidth ($\Delta\nu_{s}$) | 280 | MHz | Minimum output linewidth (near center FSR) |
| FSR (Free Spectral Range) | $\approx 8$ | GHz | At 433.9 nm |
| Max Pump Power | 1 | W | Input average power |
| Max Stokes Power | 400 | mW | Output average power |
| Conversion Efficiency | 40 | % | Pump to Stokes |
| Resonator Reflectivity ($R_{1}, R_{2}$) | 18 | % | Un-coated Fresnel reflectivity |
| Temperature Tuning Slope | -3.2 | GHz/°C | Measured tuning rate (60-70 °C range) |
| Temperature Stability | < 10 | mK | Required for stable tuning |
| Frequency Accuracy (Estimated) | < 30 | MHz | Based on temperature stability |
| Spectral Purity (RIN) | > 25 | dB | Side-mode suppression at 2 GHz |
| Final Spectroscopy Resolution | 0.51 | GHz | FWHM, non-saturated transition |
Key Methodologies
Section titled “Key Methodologies”The experiment relied on precise material engineering and controlled optical pumping within a specialized spectroscopy environment:
- Diamond Material Selection: A high-quality synthetic, cuboid Single Crystal Diamond (SCD) was selected for its superior thermal and thermo-optic properties, crucial for stable temperature tuning.
- Resonator Fabrication: The diamond crystal (7 x 2 x 2 mm³) was plane-cut parallel to the (100) axis. The resonator edges were polished to a parallelism better than 0.5 µm mm⁻¹.
- Resonator Configuration: The monolithic Fabry-Perot resonator utilized the 18% Fresnel reflectivity of the un-coated diamond surfaces to guarantee efficient Raman operation.
- Pumping and Focusing: The diamond was pumped by a 7 GHz linewidth, 1 W, 10 kHz repetition rate Ti:Sapphire laser (409.3 nm). The pump beam was focused and re-focused (two-pass geometry) within the diamond to maximize conversion efficiency.
- Thermal Tuning: The diamond was mounted on a copper substrate controlled by a high-precision temperature controller (stability < 10 mK) to achieve continuous, fine tuning of the Stokes wavelength.
- Spectroscopy Environment: Experiments were conducted in a Doppler-reduced geometry using the PI-LIST (Perpendicularly Illuminated Laser Ion Source and Trap) device at CERN, minimizing Doppler broadening effects for high-resolution measurement of ${}^{152}\text{Sm}$.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the high-purity, precision-engineered diamond materials required to replicate and advance this high-resolution spectroscopy research.
Applicable Materials
Section titled “Applicable Materials”To achieve the high spectral purity and thermal stability demonstrated in this paper, the highest quality diamond is essential.
- Optical Grade Single Crystal Diamond (SCD): Required for the monolithic Fabry-Perot resonator. 6CCVD provides high-purity SCD with extremely low nitrogen content, minimizing absorption and maximizing the quality factor (Q-factor) necessary for efficient Stimulated Raman Scattering (SRS) and spectral squeezing.
Customization Potential
Section titled “Customization Potential”The research highlights the need for precise dimensions, superior polishing, and the potential for tailored optical coatings to optimize performance.
| Research Requirement | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Custom Dimensions | Plates/wafers up to 125mm (PCD) and custom SCD plates. | We can supply the exact 7 x 2 x 2 mm³ SCD cuboid used, or scale dimensions for higher power handling or alternative resonator designs. |
| Precision Polishing | Ra < 1 nm (SCD) standard capability. | We guarantee the sub-nanometer surface roughness and high parallelism (< 0.5 µm mm⁻¹) necessary to maintain the high Q-factor and Fourier-limited pulse characteristics. |
| Optical Coatings | Internal metalization (Au, Pt, Ti, etc.) and capability for custom dielectric coatings (upon request). | While the paper used un-coated diamond, the authors noted that tailored spectral coatings (high transmission at higher Stokes orders) are needed to minimize cascading. 6CCVD can work with your team to implement custom dielectric coatings for spectral management. |
| Substrate Thickness | SCD thickness from 0.1 µm up to 500 µm, and substrates up to 10 mm. | We provide the necessary thickness control for precise Free Spectral Range (FSR) engineering in monolithic resonators. |
Engineering Support
Section titled “Engineering Support”The success of this integrated Raman laser hinges on optimizing the diamond material for both optical performance (SRS gain, spectral purity) and thermal management (precise frequency tuning).
- SRS Optimization: 6CCVD’s in-house PhD team specializes in MPCVD diamond growth and processing, offering consultation on material selection to maximize SRS gain and minimize residual intensity noise (RIN) for similar High-Resolution Spectroscopy and Quantum Technology projects.
- Thermal Management: We assist engineers in selecting diamond grades and geometries that ensure predictable and stable thermo-optic tuning, critical for achieving MHz-class frequency accuracy as demonstrated in this work.
- Global Supply Chain: We offer reliable global shipping (DDU default, DDP available), ensuring prompt delivery of high-specification diamond components worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Tunable single‐frequency lasers are the most prominent tool for high‐resolution spectroscopy, allowing for the study and exploitation of the electronic structure of atoms. A significant milestone relies on the demonstration of integrated laser technology for performing such a task. The device presented here is composed of a compact Fabry-Perot monolithic resonator capable of producing tunable and Fourier‐limited nanosecond pulses with a MHz‐class frequency stability without active cavity stabilization elements. It also has the remarkable capability of exploiting the Raman effect to funnel efficiently the broad spectrum of an input laser to a spectrally‐bright Stokes pulse at hard‐to‐access wavelength ranges. The targeted atom for the demonstrations is 152 Sm, released as an atomic vapor in a hot cavity environment. Here, the Stokes field is tuned to a wavelength of 433.9 nm, while a crossed‐beams spectroscopy setup is used to minimize the Doppler broadened spectral features of the atoms. With this work, the suitability of integrated diamond Raman lasers as a high‐resolution in‐source spectroscopy tool is demonstrated, enabling many applications in atomic and nuclear physics. The integrated form‐factor and inherent simplicity makes such a laser an interesting prospect for quantum‐technology based sensing systems and related applications.