The driving force has been military applications including pumping Nd-doped solid-state lasers. Wavelength: The wavelength at which laser diodes operate is dictated by the size of the bandgap since the light arises from the recombination of electrons and holes in a PN junction. The bandgap may be tuned in size by two main processes: i Altering the composition of the host material. Other physical effects such as the application of pressure may also change the bandgap but they tend to produce too small an effect to be useful [7].
The output wavelength of diode lasers varies from diode to diode because of small differences in fabrication and the wavelength changes with temperature. The variation in output wavelength leads to increased cost because only diode lasers in a small wavelength range are usable. The change in wavelength resulting from temperature variation requires that the diodes must be temperature controlled. Operational lifetime: The operational lifetime of laser diodes or arrays is much larger than that of conventional arc or filament lamps.
A typical laser diode array can operate without significant degradation for more than The performance of a diode laser degrades exponentially with time. Initially, the failure rate is low, but it increases exponentially with the operating time. Failure mechanisms of laser diodes are divided into two main classes: 1. User induced damage such as mechanical, thermal or electrical shock or electrostatic discharge.
Intrinsic damage, which results from three main sources: i degradation of laser mirrors or facets because of high current densities or current spikes. This will increase internal losses and lead to catastrophic failure. Such defects are common in AlGaAs laser diodes because of the oxidation and migration of the aluminum. At present efficient aluminum-free laser diodes replace the aluminum-containing lasers. Temperature: Since the diode laser is a narrow bandwidth pumping source, it pumps only the useful absorption bands relevant to laser action, reducing the thermal load in the crystal.
This thermal load results from the quantum gap between the pump and the leasing photons. Thermal effects such as thermal lensing, thermally induced birefringence, and thermal damage to the lasing to the crystal are reduced significantly. Fine-tuning the temperature of the laser diode causes a change in wavelength.
This feature is used to tune the laser diode into coincidence with the absorption bands of rare-earth ions. Normally the lasers will be cooled down since this gives a longer lifetime for the laser diode. It is usual to specify the room temperature wavelength of the laser diode some 5 nm longer than the rare earth absorption feature that will be pumped. The influence of temperature on the wavelength of the laser diode causes problems of packaging the DPSS laser.
Pulsed laser diodes suffer from a transient thermal wavelength shift. Since the current is pulsed through the laser diode, the temperature is never in equilibrium and a transient wavelength shift occurs. The wavelength increases during the optical pulse. Shifts of this magnitude are larger than the absorption linewidth of many solid-state laser materials.
Account has to be taken of this effect when predicting the efficiency of pulsed DPSS lasers. The diode lasers are normally cooled by a thermoelectric cooler for low power systems, and by liquid cooling for high powers.
Cooling can stabilize the diode laser frequency. Beam quality: Although the beam quality of a laser diode or diode array is not good, the use of coupling optics makes it possible to obtain a good TEM00 beam mode from a DPSS laser. The coupling optics circularize the output beam emanating from the laser diode array or bar, and then couple the beam into the solid-state laser crystal either by direct coupling or an optical fiber [12].
The cylindrical fast axis collimating lens can reduce the beam divergence of diode laser stacks to a value of lens than 10 mrad.
The solid-state laser can be pumped longitudinally or transversely. This subject is technologically well established and will be discussed in the next section. The laser crystal host can be in the form of a crystal, waveguide or optical fiber [7].
Since the absorption length of the diode laser beam focused inside the solid-state laser crystal is short, the pump mode volume is smaller than the laser cavity mode volume and one expects a good spatial beam quality. The laser cavity itself is short and therefore the output power of the DPSS laser is a single longitudinal mode. The best transverse mode quality is obtained from single stripe devices.
Single laser diodes may provide up to mW in a single transverse mode. To date, the most extensively used pumping geometry is longitudinal pumping. The output from the diode laser is collimated and beam-shaped to achieve a circular profile before being focused down to form a pump spot on the laser rod. This technique allows good matching between the lasing spot size of the solid-state laser cavity and the pump spot size in the gain medium.
This spatial overlap between pump and lasing modes, known as mode matching, is critical to the efficiency of the diode pumping process. Frequently, DPSS lasers are pumped by laser diode arrays in order to achieve high output powers. As has been noted, the simplest way to increase the output power from a single laser diode is to increase the width of the emitting region either by fabricating a number of laser diode stripes in close proximity so that there is a series of emitting regions or by enlarging the width of the electrically pumped region.
The output of arrays lies in the region of mW to 3 W cw output at present. True arrays of laser diode stripes tend to be partially coherent and may exhibit the two-lobe structure in the far-field characteristic of the phase changes due to the evanescent coupling between adjacent stripes. This feature appears less obvious as the output power and number of stripes increase due to reduced coherence across the array.
The broad stripe arrays are multi-transverse mode devices and the beam quality depends on how hard they are driven [7]. Laser Diodes. Laser Diode Mounts. Liquid Crystal Noise Eater. Power and Energy Meters. Aspheric Lens Adapters. Lab Safety. Precision Windows. Please Wait. Laserstrahlung dieser Klasse verursacht auch Brand- oder Explosionsgefahr. Please Give Us Your Feedback. First Name. Last Name Submit Anonymously:. Contact Me:. Prefer to Request a Quote?
Request Quote. Enter Comments Below:. Submit Feedback:. Click for a new code. I am interested to a laser for Raman spectroscopy and microscopy. The critical factors to be considered are the low linewidth, wavelength variation with temperature and beam quality. Can you give me more information about these properties?
Thank you for contacting Thorlabs. Please note that these are not specs and are not guaranteed and they are dependent on laser drive current and the temperature setpoint combination.
We also have not determined the temperature tuning coefficient, but it is essential to the proper operation of this DPSS laser to be mounted on to a temperature-controlled mount anyway, especially if wavelength-stability is required. The laser emits a single mode TEM00 beam with a divergence of 12 mrad typical.
The laser can, in principle, be used for Raman spectroscopy, depending on your other components and your requirements for spatial and spectral resolution. Unfortunately, we do not spec stability for component laser diodes as this spec is dependent on the drive electronics, mounting, and temperature control of the diode.
I am looking to scan a molecular iodine transition. Three questions. Since this is a DPSS laser, thermal tuning does not have an impact on the final nm wavelength. These lasers are sensitive to temperature and can only operate optimally within a small range of C. I noticed the beam divergences for most of your other laser diodes are in degrees and around 10 in terms of order of magnitude; however, for the DJ and DJ, the beam divergence is listed at about 12 mrad, which is much smaller of course.
Is this supposed to be the case or is that a measurement in degrees. I would like to know so I know whether I will need to colliminate the light or not. Thank you. Hello, thank you for contacting Thorlabs. The low beam divergence spec is correct -- this is an artifact of the DPSS design of the laser. The divergence is typically around 12 mrad could be as high as 15 mrad from that point on.
So collimation may not be necessary, depending on your application and requirements. We have also seen very low divergences less than 5 mrad as well. Given that the divergences can be very low, placing a short focal length lens can result in the beam being focused to a spot. Is it possible to only buy the 9. Would it work with high powers? Thanks a lot. I have reached out to you directly to discuss the possibility of offering this. Hi, I am also interested in the spectrum of DJ diode lasers and the coherence length.
Could you please send me the same information you sent to jxxu posted Thank you! Note: the article keyword search field and some other of the site's functionality would require Javascript, which however is turned off in your browser. Find more supplier details at the end of this encyclopedia article , or go to our. Using our ad package , you can display your logo and further below your product description.
Virtually all optically pumped lasers fall into one of two categories:. This article treats the latter category, for which the term all-solid-state lasers is also used. These are either bulk lasers , using some kind of laser crystal or bulk piece of glass , or fiber lasers although the term DPSSL is less common for fiber lasers.
There are different types of laser diodes which can be used for diode pumping, and very much differ in terms of optical power :. In most cases, the pump diodes are operated continuously.
This applies to all continuous-wave and mode-locked lasers , and also to many Q-switched lasers. However, quasi-continuous-wave operation with higher peak power for limited time intervals e. Some pump diodes are explicitly optimized for such an operation mode. Depending on the type of laser diode, different kinds of pump optics are used. It is also possible to use fiber-coupled diode lasers , which make it possible to separate the actual laser head from another package containing the pump diodes, so that the laser head can become very compact.
In the early years of diode pumping, the output powers achievable were very limited — smaller than those of lamp-pumped lasers. In the meantime, however, high-power diode bars and diode stacks have become very powerful, and the highest output powers are now usually achieved with diode pumping. The main disadvantage of diode pumping as compared with lamp pumping is the significantly higher cost per watt of pump power.
This is severe for high powers, and particularly for generating high-energy pulses where a rather high pump power is required for limited time. For this reason, lamp pumping is still used in cases where high powers and particularly high pulse energies are needed. For example, lamp-pumped Q-switched Nd: YAG lasers are still widely used for laser marking , and will not soon be replaced with diode-pumped lasers.
For some applications, even joule-level pulse energies and many tens of kilowatts of pump power are required, while low repetition rates e. Laser diodes are electrically less robust than discharge lamps. They may e. In conjunction with properly designed electronics, however, this should not happen. Problems can also arise from optical feedback. Diode-pumped solid-state lasers have a very wide range of applications.
Indeed, they are used in all of the areas mentioned in the article on laser applications. Among them:. Here you can submit questions and comments. The author will decide on acceptance based on certain criteria.
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