My shopping cart
  • The lasers - see laser diode, are a particular type of light sources or, more generally, of electromagnetic waves sources; they basically consist of an active material, an exciting system of the active material and a mirrors system, which reflect the radiation emitted by the active material.

    The active material contains atoms or molecules that, excited by a light beam or an electrical field or a chemical reaction, are able to cumulate, for relatively long time, a great part of the absorbed energy, in the levels of energy higher than the starting level (population inversion). When part of the active materialis de-energized, it re-emits the stored energy in form of electromagnetic radiation, then this latter invests others, still excited, parts of the active material,inducing their de-energization with an avalanche effect (stimulated emission). If the active material is placed between two mirrors, the emitted radiation can travel several times within the still excited material , fostering the further de-energization of the active material and the amplification of the emission radiation.

    This simplified description is already contained in the word “laser”, which is an acronym to indicate the amplification of the stimulated emission (Light Amplification by Stimulating Emission of Radiation).

    One of the two mirrors can transmit a small percentage (1-2%) of the radiation which hits it.

    This radiation is the laser beam emerging from the partially reflecting mirror (Fig.32).

    Fig. 32

    The two mirrors can be both flat, or one flat and the other concave, or both concave. The choice of the mirror geometry and their distance, together with the shape of the active medium, affect the divergence of the laser beam.

    If, within the space between the mirrors, an optical switch prevents that the radiation crosses several times the active material, provided that the energy cannot be significantly emitted by spontaneousemission, then energy continues to be accumulated during the excitement. When the switch is opened (Q-switch) all the stored energy is emitted in very short time.

    By means appropriate choice of the optics and of the active material, you can obtain pulses of duration of ps (10ˉ s ) or fs ( 10ˉs ).

    Letting pass the radiation through appropriate crystals, it is possible to generate radiations with wavelengths submultiples of the fundamental one and, with reference to the frequency of the electromagnetic wave, we can speak of higher harmonic generation.

    For example, a Nd.YAG laser emits radiation at a wavelength of 1.064 µm (near infrared). The second harmonic has a wavelength of 0.532 µm (green), the third harmonic 0,355 µm (Near ultraviolet) and the fourth harmonic 0.266 µm (ultraviolet).

    Since the laser are related to the amplification of stimulated emission, they are radiation sources withcharacteristic very different from the common sources (like incandescent lamps, arc lamps, black body, sun, etc..); the laser sources include various types that emit not visible radiation.

    The main characteristics of the laser beams are:
    • Monocromacity and consequently they offer the possibility to observe interference phenomena;
    • High energy density that means that small amount of energy are transported by small area section of the beam;
    • Low divergence that allows focusing on very small images with very high energy density; a beam with a total divergence of 1 mrad is focusedby a 17 mm focal length lens on a disk of 17 µm of diameter.
    • High power of the very short laser pulses. For example if a beam that in a pulse of duration of 1ns (10-9 s) transports 1mJ of duration, it has apower of 1 Mw (106 watt).


    When a laser beam impinges on a diffusing surface (as a wall), the collected energy by the eye pupil can be enough to destroy part of the retina. These are irreversible damages, that, if accumulated over time, can involve very extended regions. The damage can be very serious (i.e. able to produce blindness) in the case of reflected beams.

    The amount of energy that forms the image is proportional to the area of the eye pupil. Hence it is convenient that the lab where we are working with a laser, is strongly illuminated in order to reduce the pupil diameter.

    The human eye is transparent to several wavelengths, included those that can be absorbedbut not viewed. The typical example is the Neodimio/YAG whose 1064 µm emission wavelength is not visible. The eye cannot view such radiation but it can be damaged by it.

    The UV lasers beams (e.g. produced by excimer laser) cannot reach the retina because they are absorbed by the crystalline, but they can damage the crystalline, the conjunctive and the cornea itself. The CO2 laser emit radiation at 10.6 µm: they are not visible and do not penetrate the eye, but they can damage any other superficial human tissue, constituted for more than 70% by water, that strongly absorbs such wavelength.

    When the laser radiation impinges on the retina, one of the effects is the thermaleffect, directly proportional to the total energy. Since pulsed radiation can have veryhigh power, ionization phenomena can occur and very short pulses, even if at low energy, are able to produce serious damages.

    Also see our Laser Diode product line

    Back to top