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Single Frequency Laser
Definition of a Single Longitudinal Mode Laser
To understand single longitudinal mode, we must first know how laser light is formed inside an optical cavity. Light bounces back and forth between two mirrors (cavity mirrors), being amplified each time. Only "standing waves" that meet specific conditions can exist stably and be emitted. These stable optical wave states are called "modes." There are two types of modes:
Transverse Mode: This refers to the intensity distribution of the laser beam in its cross-section. A common example is the perfect circular Gaussian beam spot, known as the fundamental transverse mode (TEM₀₀). For details, please refer to the "Laser Transverse Mode TEM₀₀" document in the same directory.
Longitudinal Mode: This refers to the frequency distribution of the laser along its propagation direction. Each longitudinal mode corresponds to a specific frequency (or wavelength).
An ordinary laser (a multi-longitudinal mode laser) is like an entire band playing multiple notes simultaneously, resulting in a noisy and chaotic sound. In contrast, a single longitudinal mode laser is like all instruments in the band playing only one precise note in perfect unison. Its output consists of a single frequency, offering extremely high spectral purity.
A single longitudinal mode laser, also known as a single-frequency laser, is a type of laser that oscillates on only one longitudinal mode (a single frequency).
Multimode Laser Measurement | Single-Frequency Laser Measurement |
CNI offers single longitudinal mode lasers in solid-state, fiber, and semiconductor types.
Single Frequency Solid-State Laser | Single Frequency Fiber Laser | Single Frequency Diode Laser |
Key Parameters of Single Longitudinal Mode Lasers
The key parameters of a single longitudinal mode laser primarily include Side Mode Suppression Ratio (SMSR), spectral linewidth, coherence length, laser noise, beam quality, and wavelength range. The details are as follows:
(1) Side Mode Suppression Ratio (SMSR)
CNI's single longitudinal mode lasers typically feature an SMSR of >80 dB. This effectively suppresses the oscillation of other longitudinal modes within the resonator, ensuring single-frequency output. They are widely used in applications such as low-wavenumber Raman spectroscopy.
CNI 532 nm Single-Frequency Laser,
Side Mode Suppression Ratio (SMSR): >80 dB (measured over ±2 nm / 70 cm⁻¹)
(2) Spectral Linewidth
The spectral linewidth is typically sub-MHz (specifically, for CNI's single-frequency fiber lasers, it is on the order of <10 kHz, measured using the self-heterodyne method). Please consult the dedicated "Spectral Linewidth" document in this directory for further information.
633 nm Single Longitudinal Mode Laser: Linewidth 18.8 kHz (2.5 × 10⁻⁸ nm) | 1064 nm Single Longitudinal Mode Laser: Linewidth 5.6 kHz (2.1 × 10⁻⁸ nm) |
(3) Coherence Length
With a coherence length typically greater than 100 meters, the single longitudinal mode laser is well-suited for fields like long-distance interferometry and optical communications. Please consult the dedicated "Coherence Length" document in this directory for further information.
Fringe Visibility ≈ 93.5% | Distinct Interference Fringes |
(4) Laser Noise
Laser performance can be adversely affected by optical noise. Specifically, intensity noise causes output instability, and phase noise reduces coherence. The typical relative intensity noise (RIN) of CNI's single-frequency lasers is on the order of 0.01% - 0.05%. Please consult the dedicated "Laser Noise" document in this directory for further information.
1064nm@10W Single-Frequency Laser (RMS Noise <<0.012%）
532 nm @ 10 W Single-Frequency Laser (RMS Noise < 0.043%)
(5) Beam Quality
Laser beam quality encompasses parameters such as transverse intensity distribution (transverse mode), beam diameter, divergence angle, and the M² factor (beam quality factor). Measurement is typically performed with a beam quality analyzer. Please consult the dedicated "Beam Quality" document in this directory for further information.
Beam Quality Characterization of Single-Frequency Lasers
CNI's Representative Single Longitudinal Mode Lasers
CNI offers a range of highly reliable single longitudinal mode (single-frequency) lasers, engineered to deliver stable mode operation, long coherence, low noise, and superior beam quality. These lasers are ideally suited for demanding applications including interferometry, holography, Raman and Brillouin scattering, quantum optics, and semiconductor inspection.
Typical Single Longitudinal Mode (Single-Frequency) Lasers from CNI | |||||
Ultraviolet | Blue | Green | Yellow | Red | Infrared |
261、266nm 320、349nm 355、360nm | 457nm、473nm | 515、532nm 550、561nm | 577、589nm | 607、633nm 639、660nm | 785、1064nm 1342、1550nm |
For applications where laser coherence may cause issues—such as speckle in microscopy or uniform illumination in laser displays—decoherence modules are essential. Alternatively, low-coherence sources like wide-linewidth LEDs, SLDs, ASE sources, or conventional lamps (halogen tungsten, mercury-argon, etc.) can be used. CNI provides both types of solutions. For specific products, please visit:
Changchun New Industries Optoelectronics Technology Co., Ltd.
Address: No. 888 Jinhu Road, High-Tech Zone, Changchun, 130103, P.R.China
International Tel:+86-431-85603799
Email: sales@cnilaser.com
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