Raman spectroscopy
In Raman spectroscopy, precise and stable laser illumination is essential: a laser excites molecular vibrations, and the scattered light reveals a unique spectral fingerprint for material identification and analysis. At Modulight, we offer a modular laser platform delivering narrow-linewidth, low-noise, stable and customizable light output for integration into Raman spectroscopy systems.
What is Raman spectroscopy?
Raman spectroscopy is a vibrational technique that uses laser light to study molecules. When the laser interacts with a sample, a small portion of the scattered light changes energy. This change, called the Raman shift, creates a molecular fingerprint that provides information about the sample’s chemical structure, bonding, and composition.
Raman spectroscopy’s key advantages include fast, sensitive, and non-invasive chemical analysis, with minimal sample preparation, nondestructive operation, and applicability to solids, liquids, and gases.
Raman Spectroscopy applications/uses/areas of use
Raman spectroscopy is a versatile, non-destructive analytical technique for identifying molecular structures, chemical composition, and material properties across a wide range of scientific and industrial fields.
Application areas:
- Chemistry & Molecular Analysis — compound identification, molecular vibration studies, real-time reaction monitoring
- Pharmaceuticals — Active pharmaceutical ingredient identification, polymorph analysis, quality control of tablets and powders, contaminant and counterfeit detection
- Biology & Life Sciences — label-free analysis of cells, tissues, and proteins; cancer diagnostics; Raman microscopy imaging
- Materials Science — characterization of polymers, composites, and coatings; defect and stress detection; phase transition analysis
- Nanotechnology & Carbon Materials — graphene and carbon nanotube characterization, diamond-like carbon films, nanomaterial synthesis monitoring
- Geology & Earth Sciences — mineral identification, fluid inclusion analysis, rock composition, planetary exploration
- Industrial & Process Monitoring — real-time process control, in-line quality assurance, raw material identification
- Forensics & Security — drug and explosive detection, ink and fiber analysis, counterfeit detection, microplastics identification
- Environmental Science — pollutant monitoring, microplastics analysis, soil and mineral composition
Role of Lasers in Raman Spectroscopy
Lasers are essential to Raman spectroscopy due to the Raman effect being inherently weak. Since only about one in 10⁶ to 10⁸ photons contributes to the Raman signal, higher laser power improves sensitivity and shortens acquisition time. As high power as possible is preferrable as long as the sample is not damaged by heating or degradation.
A laser provides the monochromatic light needed for Raman scattering. Its narrow linewidth and spectral purity enable accurate, reproducible peak positions, while wavelength drift or instability can reduce measurement accuracy.
Other laser properties also strongly influence data quality. Low intensity noise, excellent power stability, and mode-hop-free operation reduce baseline drift and spectral artifacts. For portable and industrial systems, compact size, thermal stability, and long operating lifetime are critical for robust continuous use.
In modern sequencing-by-synthesis (SBS) systems, DNA fragments are immobilized on a flow cell and amplified to form millions of clusters. During sequencing, fluorescently labeled nucleotides are incorporated one base at a time. Each incorporation event is excited by laser light, and the emitted fluorescence is captured by a high-resolution camera to determine the nucleotide sequence.
Common wavelengths used for Raman Spectroscopy
Illumination Wavelength
Selecting the optimal wavelength for Raman spectroscopy is always a trade-off between several factors: Raman scattering efficiency, fluorescence background, detector sensitivity, and the properties of the sample itself.
Shorter wavelengths generally produce stronger Raman signals because scattering efficiency increases as wavelength decreases. However, they also tend to generate more fluorescence, which can overwhelm weak Raman peaks. The extent of fluorescence strongly depends on the investigated material.
785 nm often offers the best overall balance between signal strength, reduced fluorescence and detector efficiency.
633 nm is often chosen as an intermediate option, providing higher scattering efficiency than 785 nm with lower fluorescence than 532 nm, making it useful for many semiconductors, pigments, and biological samples.
1064 nm is often preferred for highly fluorescent samples where background suppression is critical.
532 nm and other visible wavelengths are widely used for inorganic materials such as metals, as well as for resonance Raman experiments.
UV excitation is used for biomolecules including proteins, DNA, and RNA.
Modulight Solutions for Raman Spectroscopy
Monolithic grating technology
Distributed Bragg reflector (DBR) lasers enable narrow linewidth single frequency operation
- The integration of on-chip gratings provides low-system complexity
- High robustness and small size
- Exceptional wavelength stability due to small cavity length with no external components
- No drifting in cavity length!
- Easy and precise wavelength control using a thermoelectric cooler (TEC)
Single mode DBR laser
- 10s to 100s of mWs of output power
- Tunable power
- <MHz linewidth (<0.002 pm)
- TEM00 single mode emission
- Ideal for high accuracy Raman systems
- >200mW at 785 nm
Multimode DBR laser
- Watt level output power
- Tunable power
- <0.2 nm linewidth
- Multimode emission
- Ideal for handheld operation
- >1 W at 785 nm, >500mW at 680 nm
High power external cavity lasers
Vertical-external-cavity surface-emitting lasers (VECSELs), as a part of the ML6600 product family, offer several advantages for Raman spectroscopy
High power (>W) and single-mode beam (M^2 <1.1): Up to several watts with excellent beam quality enables tight focusing, stronger Raman signals, shorter acquisition times, and higher-throughput mapping or screening.
Wide power control (5–100%): Output can be optimized for each sample, maximizing signal while minimizing heating or damage.
Configurable wavelength (UV-1.8 um): Flexible wavelength configuration, including the uncommon 560–630 nm range, allows selection of wavelengths that improve Raman efficiency, enable resonance excitation, or reduce fluorescence for specific materials.
Ultra-narrow linewidth (<<1 MHz): High spectral purity supports accurate peak positions, high-resolution measurements, and excellent repeatability.
Stable long-term performance: Low noise and reliable output improve sensitivity and make the lasers well suited for both research instruments and continuous industrial operation.
ML6600 Laser Platform for Raman Spectroscopy
ML6660 for Raman spectroscopy is demonstrated with a 785 nm Distributed Bragg Reflector (DBR) laser, which uses a monolithic on-chip grating to lock the emission to a single frequency. This configuration showcases the platform’s capabilities but represents only one example of what ML6660 can deliver.
The 785 nm configuration with DBR laser technology enables exceptional wavelength stability, as the laser cavity is small, and there are no external components that can drift. The laser provides exceptionally high single-mode output powers with over 200 mW in free-space configuration and 150 mW fiber-coupled. In addition, the output power is configurable from 10 to 100% of the maximum power, with support for multiple power setpoints. This eliminates the need for external attenuation when working with delicate samples.
Modulight’s narrow-linewidth lasers are ideally suited as light sources for Raman spectroscopy, offering high spectral purity and wavelength stability. The required optical isolation is included in the system, making the laser insensitive to optical back reflections. Modulight designs all aspects of the laser – from semiconductor laser manufacturing to electronics, mechanics and software – enabling easy OEM integration as well as stand-alone use. As a vertically integrated laser manufacturer, Modulight offers a broad wavelength portfolio spanning from the UV region to beyond 3 µm.
ML6600 Laser Platform
- ML6600 platform was originally launched in 2013.
- ML6600 can host different laser technologies (diode, fiber, DPSS, VECSEL).
- Wavelength can be tailored from UV up to 3+ µm.
- Designed in accordance to IEC 60601-1:
- Safety features to support risk control measures of your medical system.
- Manufactured in ISO13485 certified fab
- ML6600 is a platform product, which enables flexible tailoring to OEM customers’ needs.
- Preventive maintenance with predictive analytics and machine learning algorithms, powered by Modulight Cloud.
- Plug and play: included calibration data
- Standard interlock interface
- PC control interface
- Preventive maintenance
- External trigger
- RS422 or Ethernet
- Integrated laser driver
- Passive or active integrated cooling
- 1-8 output channels
- Compact size & tailored mechanics
- Tailorable for wide variety of applications
- Environment & laser status
Summary
Raman spectroscopy is a widely used analytical technique used for material and life science research as well as industries such as pharmaceutical, chemical, and food and beverage. The method provides fast, sensitive and non-invasive chemical analysis.
Raman spectroscopy measures small shifts in Raman scattered light following laser illumination. During illumination most of the incident light is Raleigh scattered without a shift in wavelength. Some of the light interacts with phonons, leading to a shift in wavelength. The Raleigh scattered light is then blocked with a filter and the shifted light is analyzed with a spectrometer to determine the material characteristic phonon states.
Modulight narrow linewidth lasers are ideal Raman spectroscopy light sources with high spectral purity and wavelength stability.
Why Modulight
With more than 25 years of experience in laser development for medical and high-value applications, Modulight offers a vertically integrated supply chain from chip to system. Our engineering team collaborates directly with Raman instrumentation manufacturers to tailor laser engines meeting their exact optical, thermal, and mechanical requirements.
