2. Fill in the gaps:

1. A laser is technically…rather than…as suggested by the acronym.

2. … is frequently used in the field, meaning “to produce laser light.”

3. A beam … has an instantaneous amplitude and phase which … with respect to time and position.

4. Because … device of this sort operating at microwave and radio frequencies are referred to as “masers” rather than … or “radio lasers.”

5. Most so-called “single wavelength” lasers actually produce … in several modes having …, often not in a single polarization.

6. The gain medium is a material with properties that allow it ….

7. The energy is typically supplied as ….

8. … may be provided by a flash lamp or perhaps another laser.

3. Match parts of the notions:

1. Laser beams can be focused …

2. Most “single wavelength” lasers actually produce radiation in several modes …

3. The gain medium is a material with properties that …

4. A beam produced by a thermal or other incoherent light source …

5. A laser which produces light by itself …

6. The energy is typically supplied as …

1. has an instantaneous amplitude and phase which vary randomly.

2. is technically an optical oscillator rather than an optical amplifier.

3. to very tiny spots, achieving a very high irradiance.

4. having slightly different frequencies, often not in a single polarization allow it to amplify light by stimulated emission as light at a different wavelength

5. an electrical current or

4. Say what is true and what is false:

1. The energy is supplied as an electrical current or as light at the some wavelength.

2. Most lasers do not contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.

3. Water is a material with properties that allow laser to amplify light by stimulated emission.

4. There are some lasers which are not single spatial mode and their light beam diverge as much as required by the diffraction limit

5. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated our relatively large distance along the beam.

Optical instruments

Single lenses have a variety of applications including photographic lenses, corrective lenses, and magnifying glasses while single mirrors are used in parabolic reflectors and rear-view mirrors. Combining a number of mirrors, prisms, and lenses produces compound optical instruments which have practical uses. For example, a periscope is simply two plane mirrors aligned to allow for viewing around obstructions. The most famous compound optical instruments in science are the microscope and the telescope which were both invented by the Dutch in the late 16th century.

Microscopes were first developed with just two lenses: an objective lens and an eyepiece. The objective lens is essentially a magnifying glass and was designed with a very small focal length while the eyepiece generally has a longer focal length. This has the effect of producing magnified images of close objects. Generally, an additional source of illumination is used since magnified images are dimmer due to the conservation of energy and the spreading of light rays over a larger surface area. Modern microscopes, known as compound microscopes have many lenses in them (typically four) to optimize the functionality and enhance image stability. A slightly different variety of microscope, the comparison microscope, looks at side-by-side images to produce a stereoscopic binocular view that appears three dimensional when used by humans.

The first telescopes, called refracting telescopes were also developed with a single objective and eyepiece lens. In contrast to the microscope, the objective lens of the telescope was designed with a large focal length to avoid optical aberrations. The objective focuses an image of a distant object at its focal point which is adjusted to be at the focal point of an eyepiece of a much smaller focal length. The main goal of a telescope is not necessarily magnification, but rather collection of light which is determined by the physical size of the objective lens. Thus, telescopes are normally indicated by the diameters of their objectives rather than by the magnification which can be changed by switching eyepieces. Because the magnification of a telescope is equal to the focal length of the objective divided by the focal length of the eyepiece, smaller focal-length eyepieces cause greater magnification.

Since crafting large lenses is much more difficult than crafting large mirrors, most modern telescopes are reflecting telescopes, that is, telescopes that use a primary mirror rather than an objective lens. The same general optical considerations apply to reflecting telescopes that applied to refracting telescopes, namely, the larger the primary mirror, the more light collected, and the magnification is still equal to the focal length of the primary mirror divided by the focal length of the eyepiece. Professional telescopes generally do not have eyepieces and instead place an instrument (often a charge-coupled device) at the focal point instead.