Tunable Lasers
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Definition: lasers the output wavelengths of which can be tuned
Alternative term: wavelength-tunable lasers
More specific term: wavelength-swept lasers
Category: 
DOI: 10.61835/e7x Cite the article: BibTex plain textHTML Link to this page LinkedIn
A tunable laser (alternative spelling: tuneable laser) is a laser the emission wavelength of which can be tuned (i.e. adjusted) (→ wavelength tuning). That tuning is usually possible during operation, i.e., it does not only mean that a certain wavelength can be permanently set in the factory. Very wide tuning ranges (hundreds of nanometers) are achieved in some cases, while in other cases tuning is possible only over a fraction of a nanometer. Lasers are sometimes called wavelength agile or frequency agile when the tuning can be done with high speed.
Tunable lasers are usually operating in a continuous fashion with a small emission bandwidth, although some Q-switched and mode-locked lasers can also be wavelength-tuned.
The tuning characteristics can be of substantially different kinds:
- There are single-frequency lasers, where the emission linewidth is very narrow, corresponding to a very well defined wavelength. Some of these lasers can be continuously tuned only over a small range of optical frequencies, while others can be tuned over a frequency range which is much larger than the free spectral range of the laser resonator. Only with relatively sophisticated technology, one can achieve tuning over a large range without mode hopping, i.e., a discontinuous evolution of the optical frequency.
- Other lasers operate on multiple resonator modes simultaneously, so that their optical spectrum exhibits several or even many spectral lines. In such cases, wavelength tuning usually just means that the envelope of the optical spectrum can be shifted, but with no control of the individual line frequencies.
There are certain lasers which are optimized such that the output wavelength can be periodically and rapidly swept through a substantial range. They are called wavelength-swept lasers and discussed in a separate encyclopedia article. Some of those lasers are not suitable for arbitrary tuning, but only for the mentioned periodic mode.
Note that there are also other kinds of wavelength-tunable light sources such as optical parametric oscillators and sources based on supercontinuum generation. The latter are much more limited in terms of radiance and particularly spectral radiance, but can cover a very wide spectral range.
Widely Tunable Lasers
Some types of lasers offer particularly broad wavelength tuning ranges:
- A few solid-state bulk lasers (see Figure 1), in particular titanium–sapphire lasers and Cr:ZnSe and Cr:ZnS lasers allow tuning over hundreds of nanometers in the near- and mid-infrared spectral region. (In general, transition-metal doped laser gain media offer larger tuning ranges than rare-earth-doped laser gain media, since the electrons involved in such media interact more strongly with the host lattice; see the article on vibronic lasers.) Output powers can be hundreds of milliwatts or even multiple watts.
- Dye lasers also allow for broadband tunability. Different dyes can cover very broad wavelength ranges, e.g. throughout the visible region. There are narrow-linewidth dye laser systems (continuous-wave or pulsed) for use in laser spectroscopy, and also mode-locked dye lasers generating femtosecond pulses.
- Some free electron lasers can cover enormously broad wavelength ranges, and often in extreme spectral regions.
Other types of lasers offer tuning ranges spanning a few nanometers to some tens of nanometers:
- Rare-earth-doped fiber lasers, e.g. based on erbium, can often be tuned over tens of nanometers, sometimes even more than 100 nm. Often, they can cover one or two telecom wavelength bands, e.g. the C and L band. Most Raman fiber lasers also have the potential for wideband tuning.
- Some rare-earth-doped laser crystals, often doped with ytterbium, also allow for substantial tuning ranges of bulk lasers. Examples are tungstates, vanadates, Yb:BOYS, and Yb:CALGO.
- Color center lasers rely on broadband gain from certain lattice defects in a crystal, which can be generated e.g. with gamma irradiation. They are not widely used, however.
- Most laser diodes can be tuned over a few nanometers by varying the junction temperature, but some special types such as external-cavity diode lasers and distributed Bragg reflector lasers can be tuned over 40 nm and more with additional means such as an intracavity diffraction grating.
- Quantum cascade lasers are also broadly tunable mid-infrared laser sources.
Some fine tuning, often continuously without mode hops, is possible for other lasers:
- Some compact solid-state bulk lasers such as nonplanar ring oscillators (NPROs, MISERs) allow continuous tuning within their free spectral range of several gigahertz. Tuning may be accomplished by applying stress to the laser crystal via a piezo, or by varying the crystal temperature.
- Similar fine tuning is possible with some single-frequency laser diodes, e.g. by varying the drive current.
For wideband tuning in various spectral regions, optical parametric oscillators (OPOs) can be used. These are actually not lasers, but OPO sources are nevertheless sometimes included with the term tunable laser sources.
Applications of Tunable Lasers
Wavelength-tunable laser sources have many applications, some examples of which are:
- In optical fiber communications with wavelength division multiplexing, a tunable diode laser can serve as a spare in the case that one of the fixed-wavelength lasers for the particular channels fails. Even though the cost for a tunable laser is higher, its use can be economical as a single spare laser can work on any transmission channel where it is needed. As the cost of a tunable lasers may not be much higher than for non-tunable ones, tunable lasers are sometimes even used throughout. There are C-band-tunable versions and others for other telecom bands like the S, L, U, E or O band.
- In laser absorption spectroscopy, a wavelength-tunable laser with narrow optical bandwidth can be used for recording absorption spectra with very high frequency resolution. In a LIDAR system, a laser may be tuned to a wavelength which is specific to a certain substance to be monitored.
- Various methods of laser cooling require a laser wavelength to be adjusted very precisely at or near some atomic resonance.
- Tuning to atomic resonances is also used in laser isotope separation. The laser is then tuned to a particular isotope to ionize these atoms and subsequently deflect them with an electric field.
- A tunable laser can be used for device characterization, e.g. of photonic integrated circuits.
- In optical frequency metrology, it is often necessary to stabilize the wavelength of a laser to a certain reference standard (e.g. a multipass gas cell or an optical reference cavity). This can be accomplished e.g. with an electronic feedback system, which automatically adjusts the laser wavelength.
- Some interferometers and fiber-optic sensors profit from a wavelength-tunable laser source, e.g. if this makes it possible to remove an ambiguity or to avoid mechanical scanning of an optical path length.
More to Learn
Encyclopedia articles:
- wavelength tuning
- wavelength-swept lasers
- wavelength-tunable light sources
- titanium–sapphire lasers
- vibronic lasers
Blog articles:
- The Photonics Spotlight 2008-10-03: “Wavelength-Tunable Lasers: Does the Tuner Degrade the Power Efficiency?”
Bibliography
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| [2] | C. V. Shank, “Physics of dye lasers”, Rev. Mod. Phys. 47, 649 (1975); https://doi.org/10.1103/RevModPhys.47.649 |
| [3] | J. R. Taylor, “Tunable solid state lasers”, J. Mod. Opt. 32 (12), 1450 (1985); https://doi.org/10.1080/716099684 |
| [4] | K. Kobayashi and I. Mito, “Single frequency and tunable laser diodes”, IEEE J. Lightwave Technol. 6 (11), 1623 (1988); https://doi.org/10.1109/50.9978 |
| [5] | P. F. Moulton, “Tunable solid-state lasers”, Proc. IEEE 80 (3), 348 (1992); https://doi.org/10.1109/5.135352 |
| [6] | E. Gulevich et al., “Current state and prospects for tunable titanium–sapphire lasers”, Proc. SPIE 2095, 102 (1994); https://doi.org/10.1117/12.183081 |
| [7] | C. Hönninger et al., “Efficient and tunable diode-pumped femtosecond Yb:glass lasers”, Opt. Lett. 23 (2), 126 (1998); https://doi.org/10.1364/OL.23.000126 |
| [8] | C. J. Chang-Hasnain, “Tunable VCSEL”, J. Sel. Top. Quantum Electron. 6 (6), 978 (2000); https://doi.org/10.1109/2944.902146 |
| [9] | C. Petridis et al., “Mode-hop-free tuning over 80 GHz of an extended cavity diode laser without antireflection coating”, Rev. Sci. Instrum. 72 (10), 3812 (2001); https://doi.org/10.1063/1.1405783 |
| [10] | L. A. Coldren et al., “Tunable semiconductor lasers: a tutorial”, J. Lightwave Technol. 22 (1), 193 (2004); https://doi.org/10.1109/JLT.2003.822207 |
| [11] | M. C. Y. Huang et al., “A nanoelectromechanical tunable laser”, Nature Photon. 2, 180 (2008); https://doi.org/10.1038/nphoton.2008.3 |
| [12] | F. Mollenauer, J. C. White, and C. R. Pollack, Tunable Lasers, Springer, Berlin (1993) |
| [13] | F. J. Duarte, Tunable Lasers Handbook, Academic Press, New York (1995) |
| [14] | M. C. Amann and J. Buus, Tunable Laser Diodes, Artech House Publishers, Norwood, MA (1998) |
(Suggest additional literature!)
Suppliers
The RP Photonics Buyer's Guide contains 100 suppliers for tunable lasers. Among them:
Sacher Lasertechnik
Sacher Lasertechnik offers scientific tunable diode lasers based on Littman/Metcalf or Littrow configurations. There are also high-power versions containing broad area lasers or tapered amplifiers.
The industrial Micron laser is a mode-hop free tunable external cavity laser for emission of up to 300 mW. Versions with emission wavelengths between 638 nm and 1700 nm are available.
HÜBNER Photonics
HÜBNER Photonics offer tunable lasers from 450 nm up to the MIR based on OPO technology in the Cobolt Odin Series and C-WAVE. Our C-WAVE tunable lasers are widely tunable continuous wave (cw), single frequency laser light sources based on optical parametric oscillator (OPO) technology. They are tunable from 450 nm to 3500 nm with powers up to 1 W.
The Cobolt Odin is a wavelength selectable laser which is tunable over up to 50 nm and operating at 10 kHz.
Lumibird
The Q-scan from Lumibird is a high resolution tunable nanosecond dye laser ranging from 200 nm to 4.5 µm. Dye cells are "plug & play" and nonlinear crystals are controlled via integrated look-up tables for quick and easy scans.
NKT Photonics
The SuperK CHROMATUNE is the World’s broadest tunable laser. It gives you an unmatched, gap-free tuning range from 400–1000 nm. SuperK CHROMATUNE is a fiber laser that ensures excellent reliability and a lifetime of thousands of hours. It requires no maintenance or service, no alignment or adjustments. It is easy to use and lets you focus on your work.
ID Photonics
Introducing our CoBrite tunable narrow linewidth laser ecosystem for 1515 nm to 1625 nm. Designed with simplicity and versatility in mind, CoBrite offers multiple chassis options and laser variants, making it an essential tool for researchers in the lab and on the production floor. With tunability options in the C-band, L-band, or C+L band, from a single source or in configurations of more than 100 ports, there's a CoBrite configuration to suit virtually every application. We keep expanding the CoBrite ecosystem to address new applications and market requirements when they arise.
O-E Land
Our tunable pulsed fiber laser is a turn-key solution with tunable wavelengths in the 1-, 1.3-, 1.5-, 1.7- and 2-μm spectral region with moderate output power. Pulse durations can be between a few picoseconds to milliseconds. The center wavelength is controlled with a a user-friendly computer interface through the USB port.
Our tunable CW laser sources can perform continuous scanning over up to 100 nm tuning range at various center wavelengths from 780 to 3000 nm. Both manual and electrical tuning versions are available.
EKSPLA
For researchers demanding wide tuning range, high conversion efficiency and narrow linewidth, EKSPLA tunable wavelength lasers are an excellent choice. All models feature hands-free wavelength tuning, valuable optical components protection system as well as wide range of accessories and extension units.
EKSPLA's long-term experience and close cooperation with scientific institutions made it possible to create a wide range of models, offering probably the widest tuning range: from 193 nm to 16000 nm. Versions offering near transform limited linewidth as well as operating at kilohertz repetition rates are available.
APE
The tunable picosecond laser source picoEmerald emits ultrashort pulses with a duration of 2 ps (other durations possible). A wavelength scan / sweep function for fast spectra acquisition over certain specific wavelengths is included. Key features:
- wavelength 1 IR beam 1032 nm
- wavelength 2 tunable 700 – 990 nm
- wavelength 3 tunable 1080 – 1950 nm
- temporal and spatial overlap of the output wavelengths
- integrated time-delay between the wavelengths
- common output port for all beams
- fully automated wavelength tuning
- EOM optionally integrated
Leukos
By combining the LEUKOS supercontinuum source Rock with the widely tunable filter BEBOP, you obtain a light source which can be tuned from the near UV to the infrared.
Radiantis
All Radiantis lasers are broadly tunable lasers, specially designed for the scientific community. Femtosecond and picosecond pulses as well as continuous-wave (CW) temporal regimes are offered with automatic tuning across the UV, visible and IR.
Stuttgart Instruments
The Stuttgart Instruments Alpha is an ultrafast and fully wavelength-tunable frequency conversion system in an ultra-compact and completely passively stable system based on revolutionary parametric oscillator design which guarantees outstanding stability, reproducibility and shot-noise limited performance.
The revolutionary design of Stuttgart Instruments Alpha, characterized by outstanding low noise and passive long-term stability, is based on the fiber-feedback optical parametric oscillator (FFOPO) technology and results in outstanding performance and high flexibility at the same time.
The Alpha covers a gap-free rapid tunable spectral range from 700 nm to 20 µm wavelengths, while maintaining high output power up to the Watt-level with femto- or picosecond pulses at several MHz pulse repetition rates. It provides multiple simultaneously tunable outputs with a selectable bandwidth from a few to 100 cm-1. Shot-noise limited performance above 300 kHz, passive spectral stability (< 0.02% rms) and wavelength-independent stable beam pointing (< 30 µrad) enable excellent sensitivity. In addition, each Alpha is equipped with a user-friendly ethernet and Wi-Fi interface and a matching graphical user interface (GUI) as well as easy to access API interfaces for e.g. LabView, Python, C++.
Typically, the Alpha is pumped by an ultra-low-noise Primus pump laser, which provides more than 8 W average output power at 1040 nm wavelength and 450 fs pulse duration at 42 MHz repetition rate. In addition, the Alpha can be operated with other pump lasers around 1 µm wavelength and enough power.
Due to our modular platform, the Alpha can be adapted and optimized for various applications and is particularly suited for spectroscopic applications requiring a robust and reliable tunable radiation with low noise.
Spectra Quest Lab
Spectra Quest Lab offers tunable lasers providing mode-hop-free tuning over nearly the entire tunable range wider than 100 nm while suppressing ASE noise (SMSR > 80dB) and delivering high PM fiber output power at any wavelength model. Available from 880 nm to 1680 nm.
The high precision model λ-Master is suitable for laboratory use and has a data acquisition function that is synchronized with wavelength tuning.
The high scan rate model: λ-Rapid achieves scan rates of up to 600 nm/s, making it suitable for frequency domain measurements such as OFDR. It is compact and can be installed in instruments.
λ-Lock is a manual tuning model.
All models have an analog wavelength tuning function using PZT and LD current modulation function (bandwidth: 5 MHz).
RPMC Lasers
Serving North America, RPMC Lasers offers a selection of tunable lasers including the Q-TUNE family of ns-pulsed DPSS lasers, utilizing an OPO to produce tunable wavelengths from 210 – 4500 nm. The TLS series of broadband tunable ps-pulsed supercontinuum lasers provides the only available device with simultaneous center wavelength (410-1700 nm) and bandwidth. We also provide several tunable, DFB-like laser diodes and quantum cascade lasers (QCLs) with wavelengths ranging from 11.3 µm to 14 µm, designed for use in the detection and monitoring of critical, gaseous compounds in the industrial and nuclear industries. Standard and custom options available. Let RPMC help you find the right laser today!
GWU-Lasertechnik
GWU-Lasertechnik has more than 30 years of experience in lasers and non-linear optics. We are the pioneer of commercial BBO OPO technology. Our widely tunable laser sources cover the spectral range from the deep-UV at <190 nm to the IR at >2700 nm continuously. We offer pulsed solutions for nano-, pico- and femtosecond pulses with best performance and highest reliability. Our rugged all-solid-state Laser technology does not require any consumable supplies and is thus providing most convenient usability, longest lifetime and excellent total costs of ownership. With a vast flexibility and a huge versatility, GWU’s laser products can serve the needs even for the most demanding scientific and industrial applications.
Alpes Lasers
Alpes Lasers designs and manufactures single-mode mid-IR lasers with wavelength tuning of up to 40 cm-1. We offer fast tuning over a wide range of wavelengths with our QC-ET product line, and extremely wide tuning with our QC-XT lasers.
Quantifi Photonics
Quantifi Photonics' Laser 1000 Series is a fully-compliant micro-ITLA laser with up to four channels in a compact benchtop or PXI form factor. It offers 0.01 pm resolution tunability across C or L bands, exceptional power accuracy up to 16.5 dBm, and optional dither suppression. It is a versatile and cost-effective general-purpose instrument.
DRS Daylight Solutions
DRS Daylight Solutions offers a number of wavelength-tunable quantum cascade lasers:
- The MIRcat-QT™ is a very rapidly wavelength-tunable version with up to 30,000 cm−1/s, covering wavelengths beyond 13 μm.
- The Hedgehog™ models are wavelength-tunable lasers for mid-IR spectroscopy with up to 0.5 W average power and 1 W peak power. Ultra-quiet, superior wavelength repeatability.
- The CW-MHF™ is the ultimate tool for high-resolution, mid-IR spectroscopy with high spectral resolution and phase-continuous tuning to avoid jumping over spectral lines.
- The H-Model mid-IR laser offers high-power, mid-IR OEM laser performance in a compact footprint. CW and pulsed operation are possible.
TOPTICA Photonics
TOPTICA offers various tunable diode laser systems. The combined spectral coverage is from 190 nm to 3500 nm, powers up to 4 W (TA), mode-hop-free tuning over up to 110 nm (CTL).
Light Conversion
LIGHT CONVERSION has worldwide recognition for its industrial-grade Yb-based PHAROS, CARBIDE, and FLINT femtosecond lasers.
- The PHAROS series focuses on customizability, reliability, and process-tailored output parameters, providing pulse durations down to 100 fs and pulse energies up to 4 mJ.
- The CARBIDE series features a compact industrial design with both air- and water-cooled models, the latter reaching 120 W of output power for the fundamental wavelength and 50 W for UV radiation, while sustaining excellent output stability.
- The FLINT oscillators extend the parameter range with repetition rates of up to 100 MHz.
Together, these products cover a wide range of scientific, industrial, and medical applications.
Thorlabs
Thorlabs produces a variety of tunable laser sources, including ultrafast tunable sources at a variety of wavelengths and pulse energies. For multiphoton imaging and other nonlinear processes, our SC4500 MIR supercontinuum laser, when used with bandpass filters, covers 1.3 – 4.5 mm.
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