Single-frequency Lasers | previous | next | feedback |
You can buy single-frequency lasers from:
- NP Photonics: narrow-linewidth fiber lasers and ASE sources, suitable for fiber-optic sensing
- Onefive: offering broadband tunable narrow-linewidth laser sources for OEM and R&D applications
Ask RP Photonics on any advice in the context of single-frequency lasers, e.g. on design issues or noise characterization.
Definition: lasers emitting radiation in a single resonator mode
A single-frequency laser (also sometimes called a single-wavelength laser) is a laser which operates on a single resonator mode, so that it emits quasi-monochromatic radiation with a very small linewidth and low phase noise (see also: narrow-linewidth lasers). Because any mode distribution noise is eliminated, single-frequency lasers also have the potential to have very low intensity noise. In nearly all cases, the excited mode is a Gaussian mode, so that the output is diffraction-limited.
Types of Single-frequency Lasers
Details of the physics of single-frequency operation are discussed in the corresponding article; in the following the present article discusses the most important types of single-frequency lasers, which differ very much in terms of output power, linewidth, wavelength, complexity and price:
- Some low-power laser diodes, in particular index-guided ones, usually emit on a single mode. Stable single-mode operation is often achieved with distributed feedback lasers (DFB lasers) or distributed Bragg reflector lasers (DBR lasers). Typical linewidths are in the megahertz region (→ Schawlow-Townes linewidth, linewidth enhancement factor). Significantly smaller linewidths are possible e.g. by extending the resonator with a single-mode fiber containing a narrow-bandwidth fiber Bragg grating, or with external cavity diode lasers.
- Special kinds of fiber lasers allow for single-frequency operation. Some of those are based on unidirectional ring laser designs, others have linear resonators and very short (highly doped) fibers. In any case, at least one fiber Bragg grating is usually used. Linear fiber lasers are sometimes realized as distributed feedback lasers. Very narrow linewidths of a few kilohertz can be achieved (particularly with devices having somewhat longer resonators), whereas output powers vary between a few milliwatts and several watts – in combination with a single-frequency fiber amplifier even more.
- Diode-pumped solid-state bulk lasers can be forced to operate on a single mode; this is often achieved with unidirectional ring laser designs, often with an intracavity filter, and sometimes with the twisted-mode technique. Output powers can reach the multi-watt level, and the linewidth can be as low as a few kilohertz.
- Vertical cavity surface-emitting lasers (VCSELs) have very short monolithic laser resonators, thus huge cavity mode spacings, and easily emit a few milliwatts on a single mode. The linewidth is at least a few megahertz, but the tuning range (without mode hops) can be very large.
- A helium-neon laser can easily be single-frequency, if its laser resonator is made short enough (order of 20 cm), because the gain bandwidth is rather small.
Most single-frequency lasers operate continuously, but there are also Q-switched single-frequency lasers, which do not exhibit mode beating and thus exhibit very clean pulse shapes and low noise.
Methods for Higher Output Powers
For higher output powers, master oscillator power amplifier configurations are often used. An alternative with potentially lower laser noise is to use injection locking of a high-power laser with a single-frequency low-power seed laser.
Applications
Typical applications of single-frequency lasers occur in the areas of optical metrology (e.g. with fiber-optic sensors) and interferometry, optical data recording, high resolution spectroscopy (e.g. LIDAR), and optical fiber communications. Single-frequency sources are also attractive because they allow to drive resonant enhancement cavities e.g. for nonlinear applications, and for coherent beam combining. The latter technique is currently used to develop laser systems with very high output powers and good beam quality. Finally, single-frequency lasers are often preferred in cases where very small intensity noise is required.
Bibliography
| [1] | M. Fleming and A. Mooradian, "Spectral characteristics of external-cavity controlled semiconductor lasers", IEEE J. Quantum Electron. 17 (1), 44 (1981) |
| [2] | K. Kobayashi and I. Mito, "Single frequency and tunable laser diodes", J. Lightwave Technol. 6 (11), 1623 (1988) |
| [3] | J. J. Zayhowski and A. Mooradian, "Single-frequency microchip Nd lasers", Opt. Lett. 14 (1), 24 (1989) |
| [4] | J. J. Zayhowski, "Limits imposed by spatial hole burning on the single-mode operation of standing-wave laser cavities", Opt. Lett. 15 (8), 431 (1990) |
| [5] | R. Paschotta et al., "Single-frequency ytterbium-doped fiber laser stabilized by spatial hole burning", Opt. Lett. 22 (1), 40 (1997) |
| [6] | K. I. Martin et al., "Stable, high-power, single-frequency generation at 532 nm from a diode-bar-pumped Nd:YAG ring laser with an intracavity LBO frequency doubler", Appl. Opt. 36 (18), 4149 (1997) |
| [7] | Y. Takushima et al., "Polarization-stable and single-frequency fiber lasers", J. Lightwave Technol. 16 (4), 661 (1998) |
| [8] | A. Liem et al., "100-W single-frequency master-oscillator fiber power amplifier", Opt. Lett. 28 (17), 1537 (2003) |
| [9] | K. H. Ylä-Jarkko and A. B. Grudinin, "Performance limitations of high-power DFB fiber lasers", IEEE Photon. Technol. Lett. 15 (2), 191 (2003) |
| [10] | A. Polynkin et al., "Single-frequency fiber ring laser with 1 W output power at 1.5 μm", Opt. Express 13 (8), 3179 (2005) |
See also: single-frequency operation, single-mode operation, mode hopping, linewidth, narrow-linewidth lasers, distributed Bragg reflector lasers, laser diodes, fiber lasers, injection locking, twisted-mode technique, stabilization of lasers, fiber-optic sensors
